Translation Series No.1211

FISHERIES RESEARCH BOARD OF CANADA
Translation Series No. 1211
Contributions to the biology and study of the stock
of the Atlantic salmon (Salmo salar L.)
in the Baltic Sea
By . Fritz
• 4e. re
• • '
OEriginal title .Beitraege 2ùr Biologie und. Bestandkundé '
- dee'AtlantisChen LaChses: (Salmi salarL) in der
.0stsee.
•From . :
Berichte der deutschen wissenschaftlichen Kommission
d. Meeresforschung, 18(3/4): 223-379, 1966.
Translated by the Translation. Bureaù
. ,
. • Foreign Languages Division'
:Department of the Secretary of State Of Canada -
Fisheries Research Board of Canada
- Biological
Station ..-
St. John's, fld'
r .
• 1969 ,:
.

•
•
TRANSLATED FROM — TRADUCTION DE
CANADA
INTO — EN
German Ehglish -
REFERENCE IN ENGL ISH RÉFÉRENCE EN ANGLAIS
Reports of the .German Scientific Commission for Oceanography
PUBL ISH ER — ÉDIT EUR
Verlag Paul Paxey
PLACE OF PUBLICATION
.LIEU DE PUBLICATION
Hambilrg
DEPARTMENT OF THE SECRETARY OF STATE
TRANSLATION BUREAU
FOREIGN LANGUAGES
DIVISION
AUTHOR — AUTEUR
REQUE,FING DEPARTMENT. Fisheries
MIN ISTERE-CLIENT
DATE OF REQUEST
DATE DE LA DEMANDE No . , 19 68
ZucevY etold
. S05-20 0-10.6 (REV. 2/4s8) '
Fritz Thurow
TIT.LE IN ECNGLISH TITRE ANGLAIS •
YEAR
AN N ÉE
DATE OF PUBLICATION
DATE DE PUBLICATION
VOLUME
ISSUE NO.
• NUMÉRO
1966 XVIII 3/4
SECRÉTARIAT D'ÉTAT
BUREAU DES TRADUCTIONS
PAGE,NUMBERS IN ORIGINAL
NUMEROS DES PAGES DANS
L'ORIGINAL.
223 - 379
NUMBER OF TYPED PAGES
, HOMBRE DE PAG,ES
DACTYLOGRAPHIEES
237
TRANSLATION BUREAU NO. 5660
NOTRE DOSSIER NO
1K 1'1,1 ■
DIVISION DES LANGUES
ÉTRANGÈRES
Contributions to the Biology and Study of the Stock of. the Atlantic Salmon (Salmo salar L.)
in the Baltic Sea
Beitrgge zur Biologie und Bestandskunde des Atlantischen Lachses
betseC
(Salmo saler L.) in der
R5F5RENCE IN FOREIGN I,ANGUAGE (NAME OF BOOK OR PUBLICATION) IN FULL. TRANSLITERATE FOREIGN CHA,RACTERS.
REFERENCE EN LANGUE ETRANGERE (NOM DU LIVRE OU PUBLICATION), AU COMPLET.TRANSCRIRE EN CARACTERES PHONÉTIQUES.
Berichte der deutschen wissenschaftlichen Kommission der MeeresforschUng
BRANCH OR DIVISION
DIRECTION OU-DIVISION Office of the Editor TRANSLATOR (INITIALS) p , p B.
TRADUCTEUR (INITIALES)
PERSON FEQUESTINGDr . A. W. May, y St. John's, Nfld.
DEMANDE PAR
YOUR NUMBER
VQT Ft E DOSSIER N°
769-18-14
DATE COMPLETED
ACHEVE LE
Fehr. 22, 1969
•

sos-2cto—lo-31
DEPARTMENTOFTHESECRETARYOFSTATE
TRANSLATION BUREAU
FOREIGN LANGUAGES DIVISION
CANADA
SECRÉTARIAT D'ÉTAT
BUREAU DES TRADUCTIONS
I. Introduction
3
2. The salmon fishery in the Baltic Sea
2.1. The historic development 10
2.2. The fishing technique • • . .. .. 15
2.2.1. River fishery *16
2.2.2. Shore fishery 16
2.2.3. Pelagic salmon fishery. 17
2.2.3.1. Vessels 17
*2.2.3.2. Fishing gear 11
13 f
DIVISION DES LANGUES ÉTRANGÈRES
VOURNO. DEPARTMENT . oivisioN/smANcH CITY
VOTRE N ° MINISTRE DIVISION/DIRECTION VILLE
769-18-14 Fisheries Office of the Editor ' Ottawa
OUR NO. LANGUAGE TRANSLATOR(MITIALS) DATE
NOTREN ° LANGUE TRADUCTEUR(INITIALES)
5660 'German P.F.B. February 22, 19 6 9
Reprint from Vol. XVIII (1966), Heft 3/4, PP. 223-379
Reports of the German Scientific Commission for Oceanography
CONTRIBUTIONS TO THE BIOLOGY AND
STUDY OF THE STOCK OF THE
ATLANTIC SALMON ( Salmo salar L.)
IN THE BALTIb SEA
By Fritz Thurow
Federal Research Institution for Fishery
Institute for Shore- and Inland-Fishery
Cont.ents

2.3. The extent of the pelagic salmon fishery
2.3.1. The fishing grounds
2.3.2. The fishing season
2.3.3. The yield of the stock
24
24
25
26
2.3.3.1. Fishing effort
2.3.3.2. Catch per unit effort
2.3.4. The yields of the salmon fishery
2.3.5. The composition of the catch in the pelagic
27
28
52
fishery
•3. The sexual maturation of the Baltic Sea salmon in the ocean . .
57
60
3.1. The sexual composition of the exploited stock 62
3.2. The condition of the gonads 64
3.2.1. The ovary 66
3.2.2. The maturing of the oocytes
3.2.3. Comparative discussion of the findings about the
7 0
sexual maturation
3.3. The fertility of the salmon
77
84
4. The migrations of the Baltid Sea salmon 87
4.1. The sections of the periodic migration 89
4.1.1. The smolt migration 89
4.1.2. The feeding migration 90
4.1.3. The spawning Migration 95
4.2. Small-scale movements 101
5. Age and growth of the salmon in the main basin of the Baltic Sea 113
5.1. On the terminology of the analyses of age and growth . . . 113
5.1.1. The relation between total length and. fork length . 114
5.1.2. The gutted weight 11 6
5.2. Material and method 118
5.2.1. The arrangement of the scales 119
- 5.2.2. The significance of the sclerite rings for age
determination ............ . . . . . .120
5.3. The age composition of the German catches
5.3.1. The results of the age analyses of January
127
catches
5.3.1.1. The brood year t s sets
5.5.1.2. The sea year classes
5.3.1.3. The salmon with spawning marks
5.3.2. Seasonal .changes in age composition
5.3.3. The age composition of the exploited stock in the
127
128
138
143
149
main basin of the Baltic Sea
5.4. The growth relations
5.4.1. Results of the investigations •
5.4.2. Discussion of the findings
5-4.2.1. The rate of growth •
5.4.2.2. The growth of the smelt of the year 1959.•
5.4.2.3. The effect of the size of smolt on the
1 54
161
161
166
166
168
• growth in the sea
6. The food of the Baltic Sea salmon
173
175
2

• 6.1. Previous investigations 175
6.1.1. The nutrition of the juvenile stages 175
6.1.2. The food in the main basin of the Baltic Sea 177
6.2. Amount and kind of food according to my investigations
1957 -6 4 180
6.3. Differences in the composition of the food 182
6.3.1. Seasonal variation 183
6.3.2. Differences on the fishing grounds 186
6.3.3. Differences depending on the kind of fishing gear . 187
6.3.4. Differences depending on sex 188
6.3.5. Differences in food related to the size or the
salmon 189
6.4. The relation between the behaviour of the prey and the
composition of the food of the salmon 190
6.5. The food consumption of the salmon 191
7. Attempt at a quantitative analysis of the stock in the main
basin of the Baltic Sea 194
7.1. The characterization of the stock 195
7.2. Losses in the exploited stock 197
7.2.1. Total mortality 198
7.2.2. Wasting through fishing and natural mortality . . . 203
7.2.2.1. Results of tagging 203
7.2.2.2. Determination with the aid of the fishing
intensity 205
7.3. Losses in the recruitment phase 211
7.3.1. The natural enemies 211
7.3.2. The mortality un til the beginning of exploitation, . 213
7.4. Models for the stock of salmon in the Baltic Sea 215
Summary 221
References 223
Appendix 230
Introduction
The genUs Salmo belongs together with the genus Oncorhynchus
to the subfamily Salmonininae (Family Salmonidae, Suborder Salmonoidè4
Order Clupeiformes) (L.S.Berg 1958). The Atlantic salmon,'Salmo-salar
occurs in the northern part of the . Altantic Ocean. The distribution reaches
from Cape Cod to the Duero River (Spain) in the south and,from West Green-
land to the Kara River (east of Novaya Zemlya) in the north (G. W. Nikolski .
1957).
1 •
The lifè cycle runs'a very uniform course everyWhere in the .
'entire area of distribution. After a period of ,feeding in the beal:the
.

• maturing salmon seek out the rivers in which they were spawned, in order
to spawn. The females make two- .:10 three-meter long depressions in the
. gravel and shingle bottom in which they deposit their eggs and colter them
afterwards. The duration of the egg development is dependent on the tem-
perature and amounts on an average to about 180 days. After spending from
one to five years in the rivers, the young salmon migrate to the sea,
where they grow very rapidly.
A large number of scientific papers have been written about the
life history of the salmon. J. Bergeron (1962) lists in his bibliography
of the Atlantic salmon for the time from 1800 to about 1960 a total of
1800 references. The scientific research of the salmon received its first
stimulus through the great economic growth of the fishery for the species
[P. 225]
of Oncorhynchus in the Pacific Ocean at about 1860. This led alsoto num-
erous investigations of the Atlantic salmon of the North American coast
of the Atlantic Ocean between 1870 and1880. In Europe a substantial in-
crease in the.scientific activities took place only after 1900 through
eXe ô1 ee Sea .
the founding of the international Council for-Geettnegraphy.
In a partial review of the literature on the Atlantic salmon
K. A. Pyefinch (1955) e‘tablished the fact that the fundamental biological
knowledge has hardly increased since the earliest times. He cites H. Boece
(1527) and P. Olauen (1545 . -1614), who already knew the life history of
the salmon in its main features.
A. Fritsch arrives at a similar result in regard to the works
of J. Johnstoni (1633) and Balbin (1679), who deacribed the life history
of the salmon of the Elbe and mentioned the period spent in the ocean. C.
Gessner (1958) Published.among other_things eready .'illustrations of the
male and female salmon (Fig. 1). It. is thus the moresurPrising that Hckel

-5-.
and Kerr very much later mention the.old male as a separate species (Salmo
hamatus Cuv.). The conception of the oceanic life of the salmon that was
developed . by.L. Roule (1929) at a time when a number of investigations of
its food had already been published, is downright grotesqùe. According to
a
Fig. 1 a. Salmon male - Fig. 1 b. Salmon female (after Gessner 1558).
a translation by H. Henking (1929) Roule. writes: "...stretched out to rest
below the branches of the thicket of the white coral, below the fields of
sponges and Pentacrinus, like the cattle below the trees of the forest
and on the meadows, they fatten themselves on the prey that surrounds them...
the darkness that envelops them would hardly bother iOthem, because their
[p- 226]
eyes are useless for the pursuit of their prey. They are surrounded by it -
on all sides...they only need to seize their easy prey all around...They
live there like cattle among their fattening fodder...."
Several questions have occupied the researcher of fo rmer times

that are still problems for us. Thus already in the nineteenth century the
threat of overtishing different waters had been pointed out. This call has
been constantly repeated until today. It must, however, be mentiohed that
such warnings were fOrmerly based more on intuition than on exact knowledge.
Very much up to date appears the demand for tagging experiments
by A. Fritsch (1893) and apparently little has changed until today, when
one reads his remark that such expensive experiments were probably possible
only in America.
A review cif the problems posed in the literature on salmon shows
that the statement by K. A. Pyef inch that the fundamental knowledge of the
biology of the salmon has increased only little up .to the present day, can
only mean that, although the older researchers actually did describe the
life cycle of the salmon in its main outlines, it required later a great .
deal of effort to provide exact proof for these statements. Even if Gessner
considered already in 1558 the parr to be the young stage of the salmon, it
remained for J. Shaw (1836, 1838) to provide the scientific proof for this
assumption through a laboratory experiment. Furthermore, it must not be
forgotten that only a few -sta.'t4en-s of the so-called life.cycle had been
described, such as the ascent of the salmon into the rivers and the spawning.
Today the river stage is well known in its sequence and one works now on
partial problems in order to understand the governing mechanisms for certain
effects. The majority of the publications until long after the turn of the
century had a purely descriptive character. Today, however, very special
questions are being studied that are supposed to contribute to the explan-
ation of the causality of the phenomena. This is the one difference that
distinguishes present day investigations from the older'ones.
A further change consiste in that besidea the individuarbeing

treated as a quality, a special population i being treated as a quantity.
This development has been pushed ahead by strong economic interests. The
two spheres of problems can no longer be separated in the present-day stage
of salmon research. When we attemPt to comprehend the'emigration of the
young salmon into the sea quantitatively, then we establish chronological
changes. The causes for such changes cari, however, only be discovered, when
it is known which hormones effect a change that causes every fish to emig
rate and, among other things, makes it resistant to . the higher salt concen-
tration in the sea.
The present paper is intended to treat problems of the biology
and the study of the stock of the salmon in the Baltic Sea. In the sense
sketched above the biology stands.here for the quality and the stock for
the quantity. The goal of the investigations is to use the results reported
on for a quantitative understanding of the stock of salmon in the Baltic
Sea.
For this end it is necessaxy to treat first the fishing technique '
and the extent of the fishery. This chapter is intended to provide three
important results for later discussions. The first task is to obtain a
measure for, the intensity of the fishery and its changes. This is to make
it possible to ascertain the effects of the fishing on the stock. The second .
task is to ascertain yearly differences in the density of the stock. This
enables us to recognize natural effects on the population density. Finally,
we shall attempt to assemble the yields of the fishery that can be considered
as a product of the intensity of the fishing and of the - amount of stock.
. [P. 221]-,
Measures for the intensity of fishing and the ameunt of stock.
(ject, r)
can only be obtained when the equipment uàed and its manner of action are
known, and when furthermore the effects of external causes on the performarme.

- 8-
(gea.r)
of the eeipment can be discovered. These questions have therefore to be
treated in detail.
It should not be assumed a priori that the salmon are distributed
uniformly in the Baltic Sea. It will therefore be attempted to enlarge our
knowledge of the migration of the Baltic salmon and to find out whether
the migration can cause distortion of oux measure for the amount of stock.
Recruitment and spawning migration cause periodic changes in the
stock. These have to be taken into account during the later analysis of
the stock. As a means of judging the effects of the spawning migration we
shall use the maturation of the oocytes. It will be attempted to use the
various degrees of the development of the oocytes for an estimation of the
proportion of the spawning migrants. In this connection other quantities
can also be used comparatively. Such aids are the determination of the age
and of the condition of the salmon. The latter is dependentpriiicipally on
the food sUpply. For this reason we shall discuss also the results of in-
vestigations into the kind and amount of food.
Finally, the age investigations are required for other reasons.
They provide in the first place the basis for a knowledge of the growth .
conditions, the chànges of which permit conclusions regarding the effects
of ecological factors. Furthermore, we require them for the determination
of the losses from the stock.
After the entire material required has been assembled, one can
try to estimate the size of the stock and establish the magnitude of the
losses that are caused during the sojourn . in the sea through natural causes,
through fishing : and through - the spawning migration.
. It can be stated already here that the present material has
been obtained from the German share only in the entire - fishery (about 15

•
-9--
per cent). Furthermore, there are complicated external effects on the
figures for the amount of the stock that cannot be eliminated entirely.
Therefore, the first result of the stock estimations is not satisfactory.
However, we are to find two criteria on hand of which it will be possible
to establish the value of the investigations and that allow to make a second,
probably better, estimate.
In recent years R. endler (1958-1964) has made salmon inves-
tigations in Germany. He has worked principally on a special statistics
of the number of fishing cruises and. of the landings at the Kiel sea-fish
market in regard to their composition according to weight categories and
concerning their amounts in different years. An earlier paper (R. Kândler
and M. Whmann 1957) concerned age determinations during the three catch
periods 1952/5 to 1954/5. However, the length7groups were not taken into
account according to their relative frequency in the catches in these in-
vestigations. Such quantitative data were required for the present work.
During the six fishing periods 1957/8 to 1962/3 I have supplied
86 cutter captains with diaries for daily entries of catch results and con-
ditioneof the environment. In this way entries for more than 7000 fishing
days could be worked out. These communications were supplemented through
the participation of scientists in 13 fishing cruises with a total of
.almost 200 days at sea. On these cruises we could also preserve the ovaries
of 70 salmon females. Food investigations were carried out at sea and in
the laboratory on 2400 salmon. From January 1958 until April 1963 samples
of scales for age determination were collected from about 7000 salmon. -
During the same period it was possible to measure and weigh more than
16,000 fish. •
These extensive investigations were supported through finâkial
•

•
•
- 10 -
contributions from the Deutsche Wissenschaftliche Kommission fer Meeres-
[P. 228]
forschung (German Scientific Commission for Oceanography [GSC0]). For
special investigations, the testing of new drift nets, and the selective
tests with fish hooks, the Federal Ministry for Nutrition, Agriculture,
and Forests made funds available.
Prof. R. Kandler, who directs the German salmon research, has
supported the present investigations not only in regard to organization,
but has also stimulated it scientifically and given directions. I should
like to thank him for numerous clarifying discussions and conversations.
Important help has been given by Dr. G. Ohlmorgen-Hple through
taking.part in 5 of the 13 cruises. The work done on board under very prim-
itive conditions and in winter, deserves high praise.
In the market analyses of the Kiel seafish market and in the
evaluation of the material.I had the help of the technical assistants Miss
U. Behrens and Miss H. v. Kistowski and also of Drs. F. Lamp and G. Rauk.
I am very grateful to the manager of the Fischverwertung Kieler Ferde, Mx.
Koschies, who showed great understanding and gave the permission for the
market research.
My appreciation and special thanks axe extended to the many
cutter captains and salmon fishermen, who provided space on board, kept
. the diaries, collected salmon stomachs ancthelped with the market inves-
tigations.
2. The salmon fishery
in the Balt , ic Sea
2.1. The historical development
B. Benecke (1881), who has carefully studied the documents on
the Teutonic Order in East- and West-Frussia, as fax as they concern the
•

•
- 11 -
fishery, mentions the granting and sale of fishing rights in the inland
waters by the Order for the first time in the 13th century. It is also
stated that at the end of the 14th century vessels sailed from Danzig to
Schonen and Bornholm for the herring fishery. There is, however, no mention
of salmon fishery in the Baltic Sea.
On March 30, 1302 the preaching monks of Elbing received the
right to fish in the Frische Haff and in the ocean with one "keitel"
(trawl-fishing) each. Pkeitel" = an unwieldy Baltic Sea fishing boat,
? still in use today, trs1.1. This is the first reference to coast fishery.
• However, it appears not to have played any role in comparison with the
inland fishery.
•
In 1409 the grand maéter of the Teutonic Order sent salmon to
the king of Hungary and to King Wenceslav of Bohemia in order to obtain
their help in a quarrel. In 1440 the salmon brings at least the tenfold
price of the pike. In 1621 it is prescribed that the salmon is not to be
given to merchants, but must be surrendered to the feudal fishmaster,
because it belongs exclusively to the feudal master. In 1641 . 220 salmon
had to be delivered through the fishmaster to the town of Elbing for the
supply of the notabllities. At that time the salmon does not eepear to
have been a fish in mass supply in East- and West-Prussia. The legend that
servants stipulated in their contraot not to receive salmon as food more
than once a week, which is current in the most divers fishing areas of the
world, certainly does not hold true here. This fish has rather stood in
high esteem until today and has alw«ys commanded a high price and has been
a food fish for kings, rather than for servants. •
Until the end of the 16th century only the fishery in inland
Waters is mentioned in the statutes. However, in 1751 N. C. Gisler reports..

•
•
- 12 -
that the salmon migrate from the rivers in northern Sweden into the
southern Baltic Sea. He derives this knowledge from the fact that al-
[p. 229]
ready in 1728 salmon caught in rivers -in northern Sweden were feund to
contain fishhooks of iron and braàs that were used, according to the Royal
Academy of Science, principally as cod hooks in Gotland, bland and in
Blekinge, but not in the Gulf of Bothnia.
The migration is, however, of no interest for us at the moment.
The remark of Gisler is actually the oldest reference to the practice of
hook-and-line fishing for salmon in the Baltic Sea. In the older works of
and Balbin (1679) (after A. Fritsch 1893) is mentioned
I. Johnston (1633)
only the rise of the salmon into the river Elbe for spawning..
B. Benecke (1881) lists the following contemgrary equipment for
the river salmon fishery: seines and salmon traps (spring traps) and for
the coast and bay fishery he mentions beach seines, set nets, as well as
salmon baskets. He writes furthermore that the salmon set lines had beer.
introduced by Pomeranian fishermen into East Prussia where they proved
very successful.
Since there hgd previously been no lino fishing along the coast
in East- and West-Prussia, it is possible that the salmon described by
Gisler concerned fish that hadcome from the Pomeranian coast.
The salmon fisherman Karl Madsen from egenwalderende, who
was born in 1881, provides information about a pelagic catch of salmon
at a distance of 10 to 15 nautical miles from shore. He had learned earlier
from older relatives that anually in Nàvember a fleet of sail Mats, 7 to
8 m long, sailed from Farther Pomerania more than 250 nautical miles to .
Liepnja ("Liebau"), in order to fish there for salmon with set lines,
200 to each boat, until Christmas. The fishermen lived during this time.
•

•
- 13 -
in LiepUva. These voyages ceased about the year 1875, because the small
vessels had sunl_s in a storm. After this the'Pomeranians fished together
with the Danish fishermen annually from October to March near Hela. Not
much later Swedish salmon fishermen crossed the Baltic Sea in their sail
boats from Schonen in order to catch salmon with driftnets along the coast
of Farther Pomerania and in the Danzig Deep.
ItES
After the foundation of the(International Board for Oceanogrphy
salmon research grew enormously. Since about 1900 many countries liberate
salmon fry that have been obtained through artificial fertilization of thé
eggs, as well as young and have carried out tagging experimenis , (Sweden
since 16°). The publications that have been stimulated by the Board now
give also the first indications of the fishing in the Baltic Sea. From
Denmark (Bornholm) and Finland (Gulf of Bothnia) we have reports on the
of salmon since 1886. Soon there appear also descriptions of the
landings
manner in which the salmon fishery was being carried out (Trybom and Wolle-
back 1904, Petersen and Otterstr8m 1904, Henking and Fischer 1905, Sandmann
1906, Trybom 1910, Henking 1913, 1916 and 1931, Nordquist 1924).
In the northern Gulf of Bothnia fishing is done mainly in the
vicinity of river moùths with setnets during spring and fall. These nets
are not anchored but are suspended from posts. In part,•several nets are .
arranged so that they work like a basket. In the Gulf of Bothnia are used
dragnets (120 x 5 m, 60 mm mesh). One also uses herring baskets for the
capture of salmon. In-Finland, where the salmon stands in second place
behind the herring in importance, one.fishes in winter with salmon nets
under the . ice. •
In the central Baltic Sea, on the southern coast,as well as
on the northern Coast, set lines played the greatest role_from fall. iill

- 14-
winter; and driftnets during 'spring. The line fishery is carried out about
20 nautical miles from shore, whereby each cutter works with 40 to 60 hooks
(Schonen) or 60 to 90 hooks (Bornholm), in later years with up to 200. In
Sweden and Denmark each setline•is- equipped With three to five hooks, in
Germany and Poland each has ene hook. The fishing with.driftnets takes place
close inshore. These nets are about 35 m long, four to eight m deep and
they have mesh widths of 60 to 90 mm (from knot to knot). Each cutter fished.
[P. 230]
with 30 to 50 hempen nets. At Bornholm and at the coast of Pomerania one
used in summer.and fall on the beach also setnets and dragnets (seines).
• • About the year 1908, which brought in many districts the motor-
ization of the sail boat, there occurred a temporary change in the structure
of the Swedish fishery at Schonen. The driftnet fishery that had hitherto
• been so important, was . replaced by the fishing with setnets. Only 11 sail
boats still sailed from Schonen with driftnets or crossed the Baltic Sea.
The importance of the line fishery declined sharply.
In the subsequent years, between the two World Wars, setline
' and driftnet fishery have consolidated their primary position, although
beach seines were still used for fishing (K. Bahr 1936).
The Swedish driftnet fishery experienced an enorMous advance
about the end of the Second World War and the subsequent years. At about
the same time Danish fishermen from Hundestedt developed the-entirely •
novel driftlinè fishery. This concerns a pelagic longline, which ié composed
of several hook sets.
To begin with, 400 to 500 hook Sets and very'long-shanked hooks
with about 20 mm - span were.being used, the number of hook sets that were-
carried by each cutter, however,.increased steadily during:the next'20 -•
yearS (Table 1).

•
1948/49 545
1949/50 730
1950/51 770
1951/52 920
1952/53 800
1953/54 950
1954/55 1000
1955/56 1200
1956/57 1220
1957/58 1370
1958/59 1500
1959/60 1580
1960/61 1700
1961/62 4743
1962/63 1722
60
80
90
100
100
110 827
110 870
110 1042
120 1055
191 1182
220 1289
237 ' 1264
287 1435
306 1249
.316 1449
12
4
3
• 14
2
6
2
3
7
155 29
191 9
197 • 11
225 9
246 9
281 9
- 15 -
At the time of writing, driftnets and driftlines are of- surpas-
sing importance for the pelagic salmon fishery in the Baltic Sea. It can,
however, be stated that the extent of net fishery has increased . steadily
ana it is at present of greater importance in the Federal Republic than
the driftline fishery.
By way of summary one can distinguish historically three dev-
elopmental periods in the salmon fishery:
(a) pure river fishing, to about the beginning of the 18th centurY,
(b) predominantly river fishing, alongside of it the increasing importance
)
of shore fishing until about 1945,
predominantly pelagic fishing with driftlines and driftnets, in addition
river and shore fishing: •
Table 1. Number of drifthooks and driftnets per vessel that
were carried by German boats in salmon fishing
(according to questioning of and to questioreires sent to salmon fishermen)
Average number Average daily Number of
.Season. of setting of . cutters
hooks nets hooks nets concerned
2.2. The technique of catching
The kind of vessel and gear employed at any•moment-dePende on
whether the fishing is carried out in the rivers, along shore or in the .
open Baltic . Sea. ' •
[P. 231]

•
- 16 a -
Fig. 2. Catching salmon with the "not" in the Indalelven
(alter Svârdson 1957).

• 2.2.1.
River fishing
- 16-
The most important fishing equipment for catching salmon in the
northern rivers of the Gulf of Bothnia is the "karsinapator". In ground
plan the device is constructed like the chamber of a basket. The four-
cornered chamber is formed of posts driven into the river bottom, which
stand at such a distance that the salmon can swim through between them.
Forthe catch one spreads a net on the upètream side of the chamber; after
this a second net is drawn through the chamber from the opposite side as
far as the first net. The salmon caught between the two nets can afterwards
be taken on board together with the gear. -
In almost all rivers of the Gulf of Bothnia and in the rivers
of southern Sweden the fishery is carried out in addition with the "not".
This is a beach seine of varying size (see Fig. 2). Besides these two Im-
portant devices . there are also in use fishtrapè that work on the principle
that a side arm of the river can be laid almost dry. In addition simple
• weirs serve to catch the ascending salmon.
besides seines.
2.2.2. Shore fishei.y
In the Soviet rivers of Latvia gill nets are also being used
The most important equipment for the shore fishery in the Gulf
of Bothniaris the trap net (etommer) in which are also caught herring.
Alomg the shores of Ingerman Land winter fishing is carried oUt with draw,.
nets underneath the ice. Of considerable importance are also the Finnish _
set mets that are frequently set in the form of a basket. Driftnets and
set lines occur also in Schonen and Blekinge; there, as well-as in Gotland
the seine also plays a certain role.'
In the Gulf of Riga the herringimskets are also.the most '.
[P. 232]

•
•e
717-
important catching device for salmon, beach seines and driftnets are being
used in all remaining coastal regions.
The vessels used in coastal fishing are mostly.open.boats.
2.2.3. Pelagic salmon fishing'
Danish, Swedish, German, and Polish fishermen are exploit4ig
the stocks of salmon in the central Baltic Sea with drift-longlines and
driftnets. •
. 2.2.3.1. Vessels
The salmon cutters have a length of 12 to 14 m and are equipped
• with engines of .f rom 50 to 350 HP. Two-way radio and echo sounders bèlong
to the standard equipment. Widely used are also radio direction finders.
Decca and radio position finders, electrical and hydraulic steering equip- .
ment have already been installed in some boats.
The fuel tanks hold from 3000 to 6000 1 diesel fuel. This cor-
responds to a cruising range of from t000 to 42000 nautical miles. A few
vessels have refrigerated fish holds, where the temperature is held near
freezing point, with a correspondingly gmaller consumption of ice. For One
voyage about 3 t of ice are required. The crew consists of the captain and
three men (mechanic, boatman, and cook). The accomodation for the captain
• is in the wheelhouse and the other crew members are housed in the bow. .
2.2.3.2. Fishing equipment
As has already been mentioned, hooks and gill nets are carried
as fishing gear. Salmon driftnets Consist> of a floating rope With floats,
norsels, leaders and net They are single-Walled gill nets, which in Ger...
, many are today made from nylon (formerly hemp 6/3). The net .(nylon 210/12,
border mesh 210/15) is about 309 meshes long and 40 to 60 _meshes deep. •
Until - recently the leader was madeof nylon 210/24, since introduction of .
ring nets (Fig. 3) a.foot rope of 1 to 2 mm diameter is, being.used. There

- 18-
are 50 norsels, 60 to 80 cm long, which are laid double from nylon 210/27
or from spun nylon 20/12. The net is adjusted at the leader at 1/3 and
.the leader is adjusted at the floating rope at 5/6 (6 meshes on 5). The
line (formerly hard-laid sisal, 7 mm diameter) consists now of laid mono-
fil propylen of 5 mm diameter. Six conical or cylindrical floats of plastic
(Plarex or foam plastic 13 x 8om) replace the formerly used cork floats.
Driftnets were formerly used only during the spring months from - .
March till May. The winter with strong windstorms was at first considered
to.be entirely unsuitable for net'fishing. The hempen nets that were pre-
• . ponderantly in use until 1960 and the "perlon nets" that were tried out •
hesitantly could hardly be used in winds of over 4 on the'Beaufort . scale,
In a stronger wind the pull on a laid line became so strong that it began
[P. 233].
to untwist and thus rolled Up the entire net. This event was much dreaded
by the fishermen, because the straightening out of the net could take selp-
eral days. They thus incurred not only the loss of catch during the stormY
night, but also on the following days.
Many fisherMen were also afraid to set out hempen nets when it
became necessary to stow them wet on deck on account of unfavourable weather
after they had been used only once or twice. Rotting then proceeded very
P. 234]'
quickly, depending on the temperature. - There remained thUs at first only "H
the possibility to extend the drift fishery into the fall months and to
begin the catch already in August and September, when line fishing does
in general nôt yet give l any results. •
The further development, the carrying out of the net fishing.
during thirwinter months from November until February:, was prevented Eie
long as hempen nets remained in use. However, the nets made of synthetic
fibres found at first no aOceptance. - During the first trials it had'been

FA
(6) .
• .4>
•• se
- 19 -
found that the net floated on the surface of the water on account of its
light weiet and the lack of absorptivity and later it aléo became tangled
in a light seaway. Through the addition of a sinker line at the bottom.the.
gear lost some of its catching ability.
Fig. 3a. Salmon driftnets with rings at the norsels.
A - attachment of the end norsels, B - foot rope, F - float, H - norsel,
R - nylon ring, S - leader ), W - swivel. ,
_ . .
• .
Fig. 3b. Salmon driftnet with simplellorselsi lettering as In Fig. 31
.
Unfortunately, I have . only few comparative figures for the cat-
ching performance of hempen and Synthetic nets. The results show 'rather •
better catches for perlon nets, but the - differences are,not statistically
significant on account of the scant material. The probàbil#Yr, tbet.pèrleli

•
nets give better results is only about 55 per cent (Table 2).
Table 2. Catching performance . of synthetic and hempen nets.
Date
Number of Number of salmon
sets per 100 nets
hemp perlon hemp perlon
Spring 195 8 380 5 345 11.31 11.59
Spring 1959 2874 474 4.66 5.90
Fall 1959 21 6 54 2.77 9.25
Szatybelko (1957) has examined the catching potential of salmon
gill nets. In his experiments he compared, among other things, the perfor-
mance of 45 fine-yarn nets (cotton) with 45 coarse-yarri nets (hemp). The
cotton nets were in part setnets and in part driftnets, both with selvedges
and a foot rope at the bottom. The mesh was 65 mm, the yarn number 135/6.
Ike hempen nets, in contrast, were made up as driftnets without a foot
rope and sinker line and they had a mesh of 85 to 90 mm and yarn numbers
of 4.8/3 and 6/3. The catching results were 0.33 salmonids per cotton net
and day compared With 0.93 per hempen net and day. The total effort las
not been given. Notwithstanding the different mesh, the average weight of
the fish was 4 kg for both nets.
If we flow come back to the goal to extend the driftnet fishing
into the winter months, we can only state that it was not possible to at-
tain this with hemp nets and nylon nets of usual manufacture . For this
reason nylon nets of a different design were employed for the first tiee
during the spring of 1959 (Thuow 1959).
In this design the net sheet is independent of the rotation of
the . line, because the norsels are fastened to rings that'Can move on the
line. Five cylindrical or conical plastic floats have been threaded on the

•
line.
- 21 -
. In order to obtain further protection against rolling up of the
net, the end norsels of each aheet can be fastened to a brass swivel in-
stead of directly to the line (Fig. 3).
The ring nets showed their superiority over the traditional geaX
already during the very first tests. Now fishing was caxried out in winds •
of up to 6 on the Beaufort scale (formerly 4). A comparison with hemp nets
is, however, no longer possible, because most of the cutters are now equipped '
exclusively with synthetic nets. At present ten cutters are employing' ring
nets. In 1960 two Danish fishermen also switched to this design. Other cutters
adopted foot ropes and floats for the nylon nets of traditional design and
obtained through this also a certain improvement. Since 1960 monofil nets
[P. 235] .
have been tested to a small Sxtent. Because the material is too stiff such
gear is hardly being used today. Recently (1963/4) synthetic nets made in
Japan have been used, made of yarn into which a heavier fibre is supposed
to have been spun.
Driftnets are set so early in the afternoon that the fleet is
on the water by sundown. Formerly they were picked up around sunrise. Sincé.the
number of nets exceSds 400, however, the taking7 up . begins around midnight.
A drift-longline (Fig. 5) is composed of a line of cotton 20/36
to 50/75, 8 to 10 fathoms long, more rarely: of braided nylon staple-fibre
(average 1.6 mm), with an attached float and the leader with hook..The leader
consists of perlon wire (o.6 mm) and. is 3.0 to 4:5 fathoms long. It is fas-
tened to a small brass swivel, which is threaded on the line and.can slide
on it between two knots about 25 cm apart."The hooks are at present mainly
typé Mustad No. 2/0 (13.5 mm between peint and shank) and to a gmaller ex-
:tent Mustad.No. 3/0 (15 mm between point and shank). The lead sinker•(- ea g)
is attached about 1 m above the hook. When the hooks are being assembled,

•
•
G
Fig. 4. End buoy for salmon fishery with
driftlines and driftnets.
G = incandescent bulb.
F - flag
N wet battery
B iron mounting
S float
L
Fig. 5. (above) salmon driftline—(below left) attachment of.
the leader on the line - b (below centre) attachment of the
hook to the leader - c (below right) float.
B - sinker-, K-- knot, L --line, S.- float,
. V - leader, W - swivel.
- 21 a -

-•22-
the free end of the line is knotted to the loop of the float of the fol-
lowing hook so that a continuous line results (the "lank") 1 . It can com-
prise'2000 hooks and is then about 35 km long. In the water the gear ex-
tends over a distance of about 15 nautical miles (27 km).
..ScowÀlerelo.AC)
The bait consiste of sprat or pieces of trigger fish about 1.5
[ P. 236],
cm wide. In the fall the fishermen prefer trigger fish, which should be
as small as possible, in the winter they prefer sprat.. However, both
species may be used simultaneously.
The setting out of the driftlines begins between 0200 and 0400
hr, so that the last hook is in the water before dawn. Between 09O0 and
1000 hr the taking up of the gear begins.
. .
In the near future Danish, Swedish, and German fishermen will
. be allowed to use 'only hooks of 'the type Mustad No. 6/0 of a new kind .
Table 3. Distribution of the' On account of a Swedish request
length of sprat used as bait.
an agreement has been reached bY the three
Length (cm) Width (cm) Number countries, which . permits the fishermen to •
1 0 .5
11.5
12.5
13.5
14.5
2.2
2.4
2.6
2.6
3.0
1
' 25
13
4
1
.
'
use only hooks with the larger span (19 mm
between point and shank). This agreement '
raised the question of selectivity of hooks
of different sizes. If we start from the
consideration that the selectivity is determined by the relation between
the size of hook and bait on the one hand and the maximum mouth opening'
of the fish on the other.hand,:then we can establish the following: the
sprat used as bait are 11 to 14:cm long, they have an average length of
12 cm and a width of 2.5 cm.' A salmOn that has been caught on a hOok baited
1 from the Dani .sh "laengde" ='length.

• with
•
Total length
(cm)
Mouth opening
percentage of
mm length
- 23-
sprat has thus a mouth opening of at least 2.5 cm between the jaws
(Tables 3, 4).
Table 4. Mouth opening in salmon
and sea trout between jaws.
According to Table 4 this ap-
plies only to salmon of over ca. 27 cm
total length. We have to reckon, however,
with the fact that only a part of the
. fish of this length take this bait, be-
15.1 1 15 9.9
16,5 1 17 10.3 • cause the selectivity is spread over a
17.1 1 16 9.4
24. 6 24 9.8 • certain range of lengths.
34.4 35 10.2
39 29 7.5 In the above statements we -
50 49 9.8
56 48 8.6 started from the fact that the selectiv-
56 • 55 9.8
56 5 8 10.4 ity is determined substantially by the
6o 55 9.2
61 59 9.7 size of the bait, as long as the shank
62 63 10.1
distance of the hook is less than the
1 Sea trout
width of the sprat. This means at the
same time that the different sizes of hooks probably have hardly any
influence on the selectivity. It will be, however, quite certain that such
an influence will be hidden by accidental changes in the catch, when the
spread of the hooks tested should be small.
The questions mentioned above could .be investigated in more
detail in 1959 to-1962. During that time.ten fishing cruises were under-
taken in order to clear up the selective effect of the different sizes of
hooks.
In the trial hooks of 10.5 and 15.0'mm Opening were tested
against those of 19 mm opening. Thtis the difference was 4.0 to , 5.5 mm,
that is, about 20 to 30 per cent. The results showed that salmon over 30
cm length took .both kinds of hooks. These fish have an average mouth opening:

- 24-
of almost 29 mm. More than 93 per cent of all fish caught were, however,
more than 60 cm long. Such salmon have a mouth opening of more than 57 mm.
This Means that a mechanically conditioned selection does not take place
in this range of lengths. If there is still some kind of selectivity at
work, it must be conditioned by sensory physiology.
LA. 237]
In contrast to this expectation the trial results showed relat-
ively small differences between the catch results for both kinds of hooks
for lengths of up to 74 cm. For lengths of over 60 cm more salmon were caught
with the large hooks than with the small ones.
Tests for significance for the catch differences between the
two kinds of hooks for the total catch, as well as for fish above 89-cm .
length showed no statistically significant differences. It thus remains
whether
to establish in case a selective effect has been presentlit has been cov-
ered up in the present case by accidental fluctuations in the catch.
2.3. The extent of the pelagic salmen fishery . .
2.3.1. The fishing grounds
It has already been mentioned that the salmon fishery has ex-.
a large extent to the open Baltic Sea only alter the Second
World War. To begih with the fishermen frequented only parts of the
southern Baltic Sea. The most important fishing ground was the Bay of Danzig
(south of 55 ° N). At that time the southern point of Gotland Deep (south .
of 56 ° N) also played already a certain role, as well as the Bornholm Basin.
In the spring months the coast of Pomerania was visited.
During the course of the years it was principally the Danish
fishermen who extended their cruiees to the more distant'fishing grounds.
At the beginning of the fishing season, in August, todayeevere Danish .
and a few German cutters sail past the Land. Islands and . visit:the Gulf
tended to

•
•
- 25-
of Bothnia. In the fall the fleet moves southwards to fish the region
between Gotska Sand8 and bsel, as well as the eastern Gotland Basin. In
the fall of some years good catches are made also near Visby and bland.
During the main period for line fishing (December to February) the
Danzig Deep, bounded by the cornerpoints Rixh8ft, Mittelbank, Memel, and
Kahlberg still remains the most important fishing ground. During this time
fishing also takes place neax Bornholm. With this the entire Baltic Sea
between about 54 ° N and 63 ° N serves as fishing ground for the driftnet and
driftline fishery. The Gulf of Finland and the region west of Bornholm
have hitherto not been fished (Fig. 6).
2.3.2. The fishing season
For biological and climatological reasons two fishing.periods
have to be distinguished during the course of the year: the summer, with
small landings, and the colder season with good yields.
Because windy and stormy weather predominates during the period
of best harvests, hitherto only driftlines• have been used exclusively.'
During spring and later also during fali, fishing with driftnets predomin-
ated. The Danish fishermen prefer this division until the time'of writing,
because the driftline fishery still plays an important role for them.
Fishing from Gotland is carried out in a similar manner. In contrast,
driftline fishing is of little importance for the Swedjàh cutters fro*
Blekinge. There driftnets are the main gear. Until 1960 the fishing aeason
for the German cutters was divided in a manner similar to that in Denmark.
After the introduction of synthetic nets one switched, however, more and
more to driftnet fishing also during the winter.months. Since then, salmon
fishery is being carried out from August to June predominantly with dxift-
'nets, line fishing, however, is being used only during the winter mdenths,

•
when stormy weather prevails.
66
65
64
63
62
61
60
59
58
57
56
55
54
15. . , . 20 25
Fig. 6. The salmon fishing grounds in the Baltic Sea.
2.3.3. The yield of the stock,
- 26 -
In Table 1 it has been shown that the salmon fishing industries
lave during the last . 15 years augmented considerably their efforts to
Lp.238]
[P. 239]

•
•
- 27-
increase the catch. Such endeavours always raise sooner or later the ques-
tion about the degree of exploitation. One attempts to learn up to which
*k>c.K •
• limits a crop can be.stressèd, how many fish can be taken without a con-
sequent impairment of future yields. For this it is necessary, to begin
with, to find yardsticks for the exploitation. In this connection we shall
here discuss the fishing effort and the population density.
2.3.3.1. Fishing effort
As fishing effort will be considered in the wide sense all
outlays for the purpose of catching fish. The number of vessels, of the
sailings for fishing, of the fishing days at sea and of the fishing gear
can express the fishing effort. A demand that has to be met by the fishing
effort is its direct relation to the exploitation of the stock, whichshall
be considered to be initially represented by the yield. We consider there-
fore that the best criterion for the fishing effort is the number of the
fishing gear set out during .a fishing season. For the determination of
these values it will be necessary to know also the number of fishing days.
Table 5. German fishing effort
in the Baltic Sea ProPer.
Number of gear x 10 6
Season Total effort
Nets Hooks expressed
as hooks,
1954/6 _ - 3.21
1955/,6 - 2.32
1956/7 0.079 4.62 4.91
1957/8 0 .108 3.57 4.44
1958/9 0.180 2.47 3.49
1959/60 0.200 3.00 4.38
1960/1 0.350 2.27 4.74
1961/2 0.400 3.32 5.57
1962/3 0.303 1.70 3.62
I was able to obtain such
values for about one-third of the total
German landings through excerpts from
logbooks and through the issue of
diaries to 10 to 20 fisherken for
daily entries. These are used is the
basis for the calculations for the
total German effort.
In Table 5 are shown the
values for the catches of driftnets
and driftlines. The two figures can',

•
.
- 28-
however, not be compared directly with each other, so that the trend of
the development of the effort is not .easily seen. Therefore, the total lan-
dings have been re-calculated as values for hooks with the aid of the diary
entries.
There is an increase in the total effort by more than one-third
since the season of 1957/8. This deyelopment was interrupted by the col d .
winter of 1963, because the German cutters could not fish from January
until March 1963.
It is our goal to obtain an expression for the exploitation of
the stock of salmon. The extent of the exploitation is, however, dependent
not only on the number of the gear employed, but also on the spatial dis- .
of the effort and of the fish. That is, it will be necessary to tribution
.
take into account besides the spatial distribution of the effort, also the
number of fish on the various fishing grounds. This value is the total ef-
fective fishing intensity. It is, however, not possible in our case to ob-
tain for this any values that are approximately correct, because it cannot
be ascertained how the entire fleet was . distributed over the fishing grounds
and what yields were obtained on the individual fishing grounds. This forces .
us to consider the effort as the measure : for the exploitation of the stock.
P. 240]
2.3.3.2. Catch per unit effort
In the above the yield of the fishery has been accepted as the
expression for the exploitation of the stock in order to make more plain
the role of the fishing effort. It can, however, easily be seèn that the
intensity of fishing is proportionaLto the exploitation only when the size •
of the stock remains constant. In contrast to this, a constant intensity
of. fishing can lead to strong depletion when the stock is very weak, whereas
it does diminish a strong stock only slightly. This shows that the intensity
•

• of
•
fishing representsavalue for the measure of the exploitation that is
necessary, but not sufficient. It has to be supplemented by statements
about the strength of the stock or about the population density. The "eap=.
cebk
leue..e per unit effort" is customarily used as such a measure. It stands in
close connection with the effort. If we put this in relation to the yield
obtained, we shall have statements that are directly comparable with etich
cate.k.
other. We call the yield per unit of the gear employed the aretliee per
unit effort. In the present case it will be given as the number of salmon
per 1000 hooks or per 100 nets.
This unit hés already been used for the determination of the
effort and in the course of this work we shall have to come back to it
frequently in order to explain phenomena or to make them clearer. For this
are extraordinarily important. The fact alonè •
ct,td,„
. that the captuTe per unit effort is to be considered as a measure for the
strength of the stock, demands a critical analysis when ascertaining these
data. To begin with, it has therefore to be examined whether the results
• of the catch are being influenced by factors that have their cause not in
the stock. In.Other words: is the capture per unit effort a value that is
composed of several factors of which the strength of the stock of salmon
is only one? •
Let us consider for a start the monthly changes in the oebliàe
per unit effort. We must expect during the course of the season a steady
reduction of the stock through fishing and other effects. As far as the
catches
strength of the. stock ié concerned, the ceptueas per unit effort should:•
diminish steadily from fall to spring.
However, the monthly. trend in Table 7 does not show such a
.course. The values of the line.fishery rather rise until December, those
. ,
in the net fishery xise in part until February, only to fall until 'June
•
reason, these statements

Mittel zg Mean
1956/57-1961/62
Mittel
1960/61-1961/62- • 9,7
cted,e s
Table 7. German ouptemee per unit effort.
(eAgorrected)
Weigh-
Season Aug. Sept. Oct. Nov. Dec. Jan. Feb. . March Apr. May June ted Simple XI - III
mean mean - •
Salmon per 1000 hooks
1954/55 (20,2) (14,6) (13,5) [ 7,9] (13,2) 14,0 13,9
1955156 • '
( 8,3) ( 8,7) 6,0 - 21,6 9,1 11,4 11,2
1956/57 1 12,3 - - 19,4 26,7 25,2 10,3 24,1 (9,3) 18,9 21,1
• 1957/58 10,8 10,5 15,9 12,0 6,3 3,1 [4,7] 11,6 9,6
• 1958159 . ( 4,6) 15,7 32,4 17,2 17,9 (12,2) (6,0) 18,1 19,1
1959/60 12,9 8,7 9,3 7,5 7,2 ( 7,3) •
• 8,8 8,0
1960/61 - 10,0 11,9 11,5 14,1 9,8 ( 5,1) [0,4] 11,6 10,5
• 1961/62 . , 8,5 12,2 21,4 18,1 15,7 ( 5,8) [6,8] 15,4 14,6
1962163 - 14,4 6,2 9,6 8,6 . - -. - [3,9] 9,0 8,01
Mittel ale Mean
1956/57-1961/62
9,9 13,1 19,5 15,9 11,2 9,6 5,1 13,9
_
Salmon per 100 nets
1955/56 ( 8 ,9) 8,5 8,7 14,0 1
1956/57 8,2 ( 7,3) 7,9 5,6 7,1 7,8
1957/58 « [ 3,01 14,2 8,6 6,5 9,0 8,6
1958/59 (20,8) 29,7 12,0 4,6 4,6 10,5 15,4
1959/60 ( 3 , 3 ) 10,6 8,3 5,0 4,4 5,9 8,0
1960/61 11,3 8,8 11,8 5,7 •( 8,4) 15,2 5,7 5,7 1,7 8,2 8,9
1961/62 8,1 10,5 11,4 (11,4) 17,4 11,9 12,6 4,5 7,1 5,1 8,6 9,7
1962/63 2,4 3,8 4,9 - - - --. - 7,4 5,7 2,5 5,7 12,0 1
13,1 10,0
' 11,6 8,6 12,9 13,6 9,2 . 5,1 4,4
9,7 ___
•
6,1 4,9 9,7
1 Values determiined•with the. aid of the mean monthly trend.
Figures' in .0 are based on the catch of 100 to 200 salmon, those in [] are based on catches of less
thgn 100 . salmon, plain figures are based on the catch of more than 200 salmon.
II-Iv
•

• to lower figures than in the fall.
•
20
10
•
x-- — x A Glowinska, J PlecAura,1961'
• — • deutsche Messung,L959
German.measurement.
31 411111
It is a well-known fact that salmon are cold-stenothermal fish.
G. Alm (1958) has pointed out that there is a critical temperature that
determines the beginning and the end of the fishing season. According to
this, salmon seek out deeper water layers when the temperature at the sur-
face exceeds 11 to 12 ° C. They return to the surface water when its tem-
perature has dropped to 11 to 12 °C. Alm, however, estaaished that this
rule holds only for such fish who are on migration for food. On the other
hand, those on spawning migrations ascend the rivers in water temperatures
of up to 17 ° C.
According to our measurements and according to Polish meas-
urements in the D4ig Deep (A. Glowinska 1961, J. Piechura 1961) the sur-
face temperature drops during October below 12 ° C and rises in June to
over 11 ° C. The course of the temperature curve in Fig. 7 coincides with
oc
oberedcher, Surface
t was.serterperatur water temperature
• monaielgonths.
Fig. 7. Temperature conditions in the Danzig Deep. ,
the increase in the captures per unit effort until Decembei HoWever,
are caught already in August, when the surface temperature is above 17 ° C
and in September also at about 14 ° C. Without doubt, at that time manY fish
[p. 242]
salmon
* still keep to the depths. On the other hand, the best catches were obtained

only in December or even in January. It is thus possible that further fish
did still rise steadily from the deeper layers of the water. With such a
fluid transition it is perhaps not correCt to speak of a critical ;tern-
core..k.es
perature. To judge by the size of the-cep-tuxes per unit effort, only about
one-half of all fish have returned to the surface in October, when a tem-
perature of about 10 ° C prevails there.
tC
Further changes in the captur -e-s per unit effort are not correl-•
ated with the course of temperature. Beginning in March (for line catches
already beginning in February), when the temperature is lowest, the yields
are already dropping again. The salmon season comes close to its end at
. the beginning of June, when the surface temperature passes 10 ° C.
As regards an explanation for the reduction in values for the
ccutclee
-cap:tee:re-8 per unit effort during February/March, we are reduced to assump-
tions. There is the possibility that temperatures of from 2 ° to 8 °C cons-
titute an optimum range for salmon. The area of its habitat lies in the
[P. 243]
summer probably under the layer of the temperature discontinuity (at a
depth of 25 to 50 m), where the temperature is 2 ° to 3 ° C. It must be as-
sumed that the fish do not dwell in still greater depths, because in the
bottom layers of tlie large basin of the Baltic Sea there is an occasional
lack of oxygen and sulfuretted hydrogen may be present. (Salmon need a
minimum of 5 mg 02/1.) If thé fish wish to escape from water that is too
cold in February/March, they will have to pass through the layer of dis-
continuity, which at that time lies at a depth of 60 to 70 m. Below this
the temperature is about 5 ° C. (A. GloWinska 1961, J. Piechura 19 6 1)
HoweVer, this question Of behaviour is at the môment not
ecdeiter,
decisive for us; because the question is in how far the eaptueee per
unit effort as expression for the stock density are infltlenced by other
32

•
•
Umfang = Cire umference
- 33 -
factors during the season. We can say with certainty that the highest
values that appear in December and January (line catches) or also in
February (net fishing) represent best the stock density. Lower values
during the fall may be attributed to the temperature conditions, because
cd.-Éke,s
the salmon return only gradually to the surface. The dropping -c-ap-tur-es ,
per unit effort in February/March do not reflect with certainty the strength
of the stock.
The question is now in what manner would it be possible to
cad,
obtain an average value for the -capture per unit effort during a season
that would represent best the density of the stock. In the first place,
the highest values of each season might be considered to be representative.
It is, however, not necessaryfor us to use exactly these statements. The
et„.teite5
decisive demand that must be made of the captures per unit effort is that
they should be directly Comparable from season to season. In regard to the
line fishery we can, for examPle, compare the December values of the years
1956 to 1958 with one another, which brought the highest :captures per unit
effort of each fishing season. The result for December 1960 can, however,
not be included in this comparison because the highest value of this season
Cm
so
ne • 745
Liirg .e = Length
. ,
.
Fig. 8. Relation between total length and circumference in
the salmon (the curve has been drawn with the aid of ,
.
group aVerages).
en1 .

was obtained in January.
- 34 -
The individual values for each month from NOvember . till January
axe based in general on the catch of more than 1000 salmon. In order to
exclude accidental changes in the catch as far as possible, it.would be
c cute-k-
suitable to calculate the represntative capture per unit effort for each
season as the arithmetical mean of these three months.
This applies, however, only to the line fishery; but we must
compare these statements also with the net catches in regard to their
value as indicators for the strength of the stock.
In theinvesegation of the selection effect of hooks it could
be shown that hooks of opening 19 mm did not have a mechanically conditioned
selective effect in comparison with those of 13.5 eening. We can therefore
Ceckes
assume that the -cupttures per unit effort by line are hardly affected by
selection. This, however, does in no case apply to the net catches. If We
select a Mesh of 80 mm, this would correspond to a periphery of 320 mm of
the fish to be taken. According to Fig. 8 such fish have a length of about
73 cm. All fish that are staller than 73 cm, Or that have a circpmference
of under 320 mm have thus the chance to slip through the meshes. Let us
._now examine in contrast to this the selective effects on the larger fish.
In Fig. 9 the circumference of the body in different regions has been en,
tered. It is found that there are indentations in the region of the eyes
• and the gill covers, by which . the salmon can be retained in a mesh of the
gill net. In addition, a part of the submaxillaries protrudes . à the end of
thé mouth opening at the height of the eyes. These extensions act in rel-
ation to the mesh of the net as a barb. One can therefore say that the-
. -body circumference in the region between the eyes*and nape is decisive for
selection. A circumference of the head of 320 mm in the region of the eyes
P. 244]

•
- 35 -
and nape corresponds to a total length of 91 to 112 cm. Furthermore,
small as we ll as large fish, who are not retained by the net on account
of the body circumference, can become entangled in the net by their teeth
and may be captured in this manner.
According to what has just been said, one cannot expect a com-
plete selection for small as well as for very large fish ., whereas for a
mesh of 80 mm the highest selection can take place for lengths of between
about 74 cm and 92 to 112 cm.
In practice there are certain differences in selection that
depend on the material of the nets. It has already been mentioned that
the heavy hempen nets are not as effective as perlon nets (Table 2). In
a net of gynthetic fibres even those fish can still become entangled whose
circumferenOe at the head is greater than the mesh sise, since some of
them can become entangled in the thin net material, or become àtuck in the
fine yarn with their teeth.
Table 8. Selectivity of salmon driftnets with an average
mesh of 78.75 mm.
1 2 3 4 5
Total Number of salmon Net catch Tripartite Value of column 4
length Hook, Net Line catch adjustment when 7.5817 100
cm
52,5 ' 6
57,5 7 0,1895 2,50
62,5 31 17 0,5484 0,4038 5,32
67,5 92 61 0,6630 0,9607 12,67
72,5 82 137 1,6707 1,9969 26,33
77,5 35 128 3,6571 2,9759 39,21
82,5 20 . 72 3,6000 5,7267 75,50
87,5 13 129 9,9231 7,1991} 94,85
92,5 , 27 218 8,0741 8,4824 0 7,5817 111,90
97,5 20 149 7,4500 7,0636 93,08
102,5 6 34 5,6667 4,8722 64,25
107,5 2 3 1,5000 2,3889 31,50
112,5 1 0,5000 6,59
341 949

Hempen nets are nowno longer used in the German salmon fishery.
For this reason we are using as basis for the present investigations the
mesh widths of the synthetic nets. The measuring of the mesh of 24 nets
on four cutters gave an average mesh width 2 of 78.75 mm (mesh opening
about 157 mm).
Ldnge
CirCUmYerence
A . eye
D insertion of dorsal fin
N .= nape -
0 = operculum
S = snout
36
• For the determination of the
selectivity of gill nets the catches
with driftlines can be used by way of
comparison. For this purpose I have
line catches of 341 fish and net catches
of 949 fish, for January 1964 from the
Danzig Deep (Table 8). If one calculates
for the groups of length the ratio of
values in the range 85 to 99 cm. If one
Fig. 9. Relation between total
length and circumference in four P uts the mean value of this range equal
salmon.
to 100, one obtains then the percentage
selectivity for the individual groups of length (Table 8, column 5).
P. 245]
the number of netted salmon to the number
of lined salmon, one obtains the highest
O. Christensen (1963) has carried out these investigations with
[p. 246 ]
the aid of Danish net catches and line catches in March 1963. The selec- • '
tivity curves for the two investigations are shown in Fig. 10. It is seen
that the German nets select larger salmon than do the Danish nets.
Only a few large fish escape from the nets, but a substantial
2 Mesh width = distance between the centre of one knot and. the Centre cf the
next; mesh . opening . length of the stretched mesh.

•
• /
100
50
Selektion Selection
/ I
/
/ •
:- 37 -
part of small salmon.can slip through the meshes. Correspondingly, the
50-per cent lengths 3 of the Danish curve are lying lover than those of
the German curve. They amount to about 68 cm or 78 cm, respectively, for
small salmon and 100 cm or 105 cm, respectively, for large salmon.
dânische Netze — - Danish nets
—deutsche Netze (78,75rnm np„rman nets
schenwene
Mésh width
0 0 100 uo cn,
. mowin g.= Total length
.. . .. .. . .
Fig. 10. Selectivity curves for salmon driftnets.
Let us return to the object of our investigation, that is,
obtain comparable data for the density of the stock. The -egelliam e per
unit effort of the driftnet fishery are, to be sure, not representative
in regard to the age composition of the stock being fished. They are,
however, comparable among themselves, if.the mesh width of the nets used
remains constant and if there are no differences in growth. They can
therefore be used as a . measure for the population density.
It can also be stated that the comparability of the
.per unit .effort by line as well as by net sis i not being influenced by the
selective effect.
•
ce-
However, the two kinds of gear differ in one substantial Point.
3 Fifty percent of all salmon.(of a certain group of lengths),.that meet
the net as Potential objects to be caught, - are retained in the net..

Number of sprat
Season Oct./Nov. Dec./Jan. Feb./March /cutter/day
8Pring, Danzig Deep
• 1956/57
1957/58
1958/59
, 1959/60
' 1960/61 937
1961/62 1 057
1962/63 519 •
453 11 681
" 1830 82 407
1 383 55 385
1 302 8 1001'
554
728
2 1 400
1 042 r
11600'
4 2001
2 1001
- 38 -
The ddftnet works entirely passively, whereas the driftline attracts the •
salmon by the.bait. Spice the fish pureue also the naturally occurring
food fish, there is competiticin between the artificial and natural offer
of food. If we assume that the population density N and the intensity of
fishing f (that is, the artificial offer of food through bait) are constant
in the years x and x + 1, whereas the natural food fish are present in the
strength p and 0.5 p, respectively. That obviously means that drift-line
catches must increase'in the year x + 1. In contrast to this, the catches
with driftnets remain the sanie in both years. In other words: if in the
year x the • catch by 1000 hooks equals the catch . by 100 nets, then the catch
. by 1000 hooks in the year x +1 is greater than the catch by . 100 nets. When
cate,h-
our investigations show such changes; then we have to reckon that.emeimae
per unit of effort by line is influenced by the ratio between the natural
[p. 247]
and artificial food offer.
Table 9. Number of hooks, which were required during
different fishing periods to equal the catch results
of 100 nets. (Calculated with the simple. Means
. of Table 7.)
1 The data were kindly supPlied by Dr. J. Elwertowski (Institute for
' Ocean FisherY, Gdynia) as. catch in kg per outter . and day. The recalculation:is
based on an average weight per sprat of 9.33 g (P.
F. Meyer-Waarden 1942), all other statements -after J. .Eawertoweki'
1959.

- 39 -
In Table 9 have been calculated the numbers of hooks that were
required in order to equal the catch per 100 nets on the basis of the cep -
-e unit of effort of sprat (dragnet) by Polinh cutters in the Danzig
Deep (Elwertowski 1959), since sprat are considered to be the most impor-
tant food fish of salmon (see Table 48).
The number of hooks required and the catches per unit of effort
of sprat in the Danzig Deep show a very good agreement for the three catching
periods 1956/7 to 1958/9. During the subsequent years a considerable decline
of the sprat catches took place. Elwertowski (1964) has pointed out that the
availability of sprat in winter depends on the temperature conditions. Eel-
atively cold water delays the time of spawning and therewith the concen-
tration of the sprat into pre-spawning and spawning swarms. It is therefore .
possible that in the years in question only the availability of these fish has
declined, whereas they were still available as food for the salmon. For the
fishing. seasons 1959/60 to 1961/2 we obtain .therefore a new ratio between
the number of the hooks required and the captures per unit àf effort,of
sprat. According to these statements it is not possible to eiclude the pos-
sibility that changes in the dênsite of the stock of sprat can effect. the
line catches of salmon in the spring.
There are only verY few comparable values available for the fall
and winter months. The compa#son betweeen the number of hooka and nets
. that are required for a certain,catch result of salmon, appears at this
time to le much more favourable for the driftlines. It suggestà itself,.
that this fact is due to the scarcity of sprat, because the sprat appear
only in spring iâ larger numbers in the upper layers.of thewater. (see
011apter 6.4w). Annual differences - cannot be demOnstrated..
It has been investigated in how far otherfactOrs than the

-4o-
stock density can affect the catches per unit effort with driftlines and
driftnets. Hitherto internal (selection) and external (temperature and
food) causes have been discussed. Now we shall investigate a further ex-
ternal factor, namely the effect of the wind.
cecÂd.!..
In Table 10 the eep-teres per unit effort with hooks in various
fishing regions4 under different wind slpeeds and wind directions have been
assembled. The figures from fishing region 5 are based mainly on catches
of from 200 to 2000 salkon, those from the other fishing regions are based
on from 20 to 300 salmon. Unreliable data are given in Q.
The best catches in all fishing regions have thus been made under
stronger winds. Before we can test the significance of the differences in
the catches, we shall have to consider that the values of columns 7 and 8
(Table 10) did not originate in a uniform system. We have started from the
ceckes
basis that the ceetutaee per unit effort should serve as a measure for the
strength of the stock. When we now investigate the effect of the wind, it
can be established at once that variations in the strength in different
years can produce perhaps far greater variations than the effect of the
wind. Effects of the food supply and of the temperature conditions have
been demonstrated above and it is not impossible that still other factors
influence the size of the capture per unit effort. •
These deviations increase the scatter of the series that also
enters as a variable into the test equation.,In order to eliminate the
effect of the strengths.of the different year classes, the deviations of
the Values in column 8 from thogeof column 7 as percentages were used as
the Iasis for the test of significance.'
4 For the fishing regions see Fig. 6.
-

. Table 10. Number of salmon per 1000 hooks in dependence on the fishing grounds
and wind directions (weighted means).
(For fishing grounds see Fig. 6.)
1 ' • 2 3 4 5 6 7 8 9
- Fishing Time of Weighted Total«
‹z 5 Beaufort >5 Beaufort
ground Season capture
Calm mean weighted
S W N E S W N E var. 5 B . mean
Simple mean
Simple mean
Signifik eu wert Value of significance f 000
fur
54 for differences. -
amone catches.. Der cent .
le
81
1,15
68
Simple mean
0.1111%
.. _ - ..
1956/57.. X • 5,0 11,1 0,0 14,6 17,6 27,4 ' 9,9 21,8 13,2
1957/58 . -X-I 11,1 21,4 . - • 14,3 15,4 . 7,8 11,5 14,6 12,5
1958/59 ' X-I 14,2 4,7 55,7 33,0 85,7 4,4 «
22,4 19,3 20,9
1959/60 • X-II . . 11,7 7,0 . 4,1 16,6 18,3 35,8 14,2 7,3 19,2 11,9
1960/61 X-XI ' 6,5 . 8,9 10,1 9,7 5,8 • 15,9 8,9 • 14,6 11,4
1961/62 X-XI 7,6 10,9 10,6 11,5 10,9 12,5 6,4 14,2 9,0 - 10,7 9,7
1962/63 VII I-X 7,9 '. - 4,1 . 14,4 5,2 8,6 7,6 12,3 5,3 - . 6,1 • 8,9 - 8,1
8,8 8,2 18,5 9,2 15,8 26,0 8,9 19,7 11,0 10,7 15,6 12,5
,
SignifiLmvwert t Value of significance f 3,02
für Fangdifferenzeni °/o for differences among catches per cent
97,5
1954/55 XI-III 15,5 12,9 14,2 19,3 15,8 13,9 15,0 3,3 14,4 15,2 14,6
1955/56 XI-V 7,2 7,0 7,6 17,7 19,7 11,2 13,4 20,1 4,9 8,9 15,7 11,2
1956/57 X-V 16,0 19,7 26,3 15,5 29,2 32,9 21,3 23,6 18,1 20,3 29,1 23,0
1957/58 X-I V 11,4 10,2 13,0 8,1 17,9 15,4 6,9 24,6 8,8 10,2 14,3 11,6
1958/59 X-IV 11,4 14,3 12,3 13,2 23,1 37,8 33,2 18,8 12,3 13,2 33,7 18,5
1959/60 X-I I I 9,0 8,7 8,0 8,5 10,8 7,6 8,7 10,1 7,2 8,7 9,9 8,9
1960/61 XI-III 12,0 19,0 10,2 8,5 11,4 11,7 19,8 10,0 8,0 11,5 13,2 12,0
1961/62 XI-IV 14,5 17,4 15,3 11,4 15,2 30,1 16,3 13,7 4,3 15,4 20,3 1 7,3
X-V 9,1 8,5 9,1 7,1 9,9 9,0 7,0 16,1 8,6 9,1 8,8 1962/63
X-IV 11,8 13,1 12,9 12,2 17,2 19,1 16,7 15,9 9,2 12,4 17,9 14,0
1956/57 X 10,2 11,0 - 12,9 8,5 21,7 26,8 21,3 4,9 10,4 24,9 11,8
I
1957/58 X-I 9,2 8,6 5,6 4,1 9,5 8,1 7,3 10,3 8,4 8,5 8,4
1958/59 XI-11 6,3 7,0 11,0 22,3 18,6 13,7 12,0 18,6 12,5
6 1959/60 X-I V 5,4 7,9 4,7 7,9 3,9 15,6 9,8 3,6 6,0 9,9 6,8 t
1960.'61 X-I 4,7 10,0 - 11,4 7,1 13,8 12,8 9,0 13,8 9,3
1961/62 XI-III 6,9 5,6 9,2 7,4 6,7 13,0 16,7 7,2 15,5 10,6
1962/63 XI-IV 6,6 11,4 4,5 . 11,3 10,4 10,6 8,3 16,2 8,5 9,8 12,1 10,5
• 7,1 8,8 .8,5 1 0, 8 12,1 12,7 13,4 12,5 9,0 9,0 14,8 10,0
_
3,53
ignifiltriztvert
für Fang di fferenzenl
t
c1 /
Value te significance t
for differences among catches per cent 99,1 NI
1 Zwisdlen deri Einheitsanen < tmd > 5 Bnuftirt..« Be twe e n the catches pér unit effort -. -2 - .and >5 Beaufort
2,63
97,1
r-n
.
-P.
Ce

- 42 -
In this manner were obtained the values of significance in Table
[P. 249]
10. Since W (t) equals 0.05 for all.fishing regions, we have here very
probably genuine differences in the catch. It is possible that they stand
in the majority of cases in relation to the wind speed. .
• The results for the net fishery (Table 11) have an entirely
different aspect. For the fishing region 5 better catche s. were recorded
for lower wind 'speeds. The probability that this concerns genuine differ-
ences in the catchis 97.6 per cent. In the other fishing regions also the
values are higher for winds under 4 on the Beaufort scale than for stronger
winds. No test for significance was made, because only few individual•
values are available for strong winds, which are based mostly on catches
of fewer than 100 salmon. The material on hand, however, gives the impres-
sion that differences in yield that are probably caused by wind can be dem-
onstrated for all fishing regions in the Baltic Sea proper.
Before the possible causes for this phenomenon are considered,
we shall first examine the relation between wind direction and yield of
catch. At winds of less than 5 on the Beaufort scale it is nôt possible
to demonstrate significant differences in line catches in relation to
wind direction. For wind speeds above 5.13eaufort only fishing region 5 can
be investigated, because there are too few values for the other regions.
The test for significance with the data of column 5 was carried out by con-
sidering the deviationà of the yields for west wind against those for east '
wind; as Well as the values for north and south winds. The•probability that
the catch differences are significant amounts to 81 per cent concerning
north wind catches, to 68 per cent in regard to east wind catches and 54
per cent for south wfnd catches. The differendes are thus not significant.
At the other fishing grounds . the , west wind catches are• greater for '

• Table 11. Number of salmon per.100 nets in dependence on fishing grounds and wind directions
(weighted means).
• (For fishing grounds see Fig. 6.)
1 2 3
Simple mean
4 5 6 7 6 9
Fishing Time of ..c. 4 Beaufort Calm ..-,..4 Beaufort • Total .
ground season capture .S W N E • var. S W N E Weighted weighted
mean mean
12,3 9,7 6,1 5,6- 6,3 10,2 1 6,3 9,3 -
.4 1961/62 VIII-XI, III-V 7,2 6,5 13,6 8,2 12,3 6,3 1,2 5,4 8,1 • 6,8 7,4
1962/63 VIII-X 2,2 4,9 5,1 3,7 4,7 3,6 4,5 5,0 3,1 5.13,8 4,3 3,9
. .
. . • - .
,
6,2 5,7 . 9,4 8,1 7,2 7,3 . 5,4 - 3,9 ' 5,0 7,4 . • 5,8 6,9 •
Simple mean
.... .. . iii-iv
. . , .
1955/56 I V-V 5,0 9,6 9,2 8,4 9,0 .. ' - 12,9 . . . - se 5,3 8,7 :
1956/57 II-V . 5,3 7,0 5,7 -7,1 8,6 ' . 5,6 .5,6 ; 2,3 7,3 ' 5,1 6,9..
1957/58 III-V - 7,4 7,3 12,0 14,7 8,1 ". 5,4 3,0 3,4 9,1 - . .4,1 . 8,9
• 1958/59 XI-V 13,3 8,8 8,2 _ 7,3 12,8 8,3 , . 3,1 2,7 . - • . 11,0. . 3,5 .10,8,
5
• 1959160 II-VI 10,9 7,6 5,6 6,0 6,2 . 6;7 - 1,8 5,3.. 7,1 . 6,5 ' 5,7 6,4
1960/61 XI-V 7,3 . 10,8 7,4 2,2 6,1 . 11,0 11,9 1,7 " 1,6 7,2 10,5 . 8,0 .
1961/62 XI-VI . 9,1 7,7 7,2 7,2 7,6"" 3,3 8,1 3,2 11,2 . 8,1 - 5,7 7,7
. • 1962/63 IIPVI 6,2 -5,7 7,6 - 4,8 . 4,3 4,1 - 5,6 4,3 2,9, . 5,8 - 3,9 5,6 .
S imp 1 e mean
Il-V 8,1 8 ,1 7,9 7,2 7,8 6,7 5,9 4,8 4,7 8,0 5,5 7,9
- Signifikanzwert t • Value of significance 5 t
fiir Fangdifferenzen 0/0 for differences among catches per cent
3,06
98,2 .
1956/57 III-IV 7,5 4,0 11,9 . 8,3 4,4 6,4 7,3 0,8
1957/58 V 4,7 4,7 4,7
1958/59 III-IV 7,3 3,6 2,8 6,9 6,1 6,1 .
6 1959/60 III-IV 3,8 3,9 5,2 3,7 6,3 6,6 3,6 3,8 4,7 4,2
1960/61 XI I-I, III-V 3,8 1,7 6,7 4,4 1,5 • 3,0 1,5 2,8
1
1961/62 I-IV 9,0 8,6 ' 6,5 125,0 20,7 12,7 5,7 7,4 19,8 7,1 18,3 -
1962/63 IX-V 4,5 '10,8 16,5 6,1 7,9 - .
2,5 10,0 5,9 9,8 4›.
te+
I-1V
6,0 4,9 6,4 31,3 10,0 7,9 10,5 4,6 4,5 7,7 5,3 7,5
•

- 44 -
winds over 5 Beaufort. However, this cannot be demonstrated for net catches
during winds of less than 4 Beaufort. For yields ut over 4 Beaufort there
are too few data.
•By
way of summary it can be said: with strong winds one obtains
better line catches but poorer net catches than with weak winds. West winds
over 5 Beaufort bring better line catches on the fishing ground 5 than
winds from north and east. •
It suggests itself to explain these results in the following
manner: with strong winds and a correspondingly rough sea the hooks are
moving up and down to a considerable extent. The salmon recognize the
[P. 251]
bait sooner than during a weak sea way. The good yields during west winds
appear only with winds of over 5 Beaufort. This suggests the assumption
that it is not the wind by itself but a current generated by the wind that
affects the yields. This explains at the saine time the smaller net catches
that are found during strong winds. The sheet of the net is no longer
tightly stretched during a heavy sea way and strong currents and thus is
less efficient than during calm weather. The - individual values of column
5 give the appearance that in the open ocean (fishing grounds 4 and 6)
the catch is better during north and east winds; in the DanZig Bay, however,
it is better with west winds.
On the basis of these findings one has to reckon with the fact
cek es •
that the strength of the wind can influence substantially the eap4ueee per
unit effort by driftnets and driftlines. At the fishing ground 5 (Table 10)
there were caught on an average during the years 1954/5 to. 1962/3 5.6 more
salmon during strong winds than.during:light winds. Weather with predom-
inantly strong winds can thus exert-a considerable influence on the yields.
•

•
- 45 -
cza-ci, es
When considering the eaptlaTee per unit effort as indicators of the stock
density it will be necessary to-take. into account the predominating
strength of the wind.
Certain differences in yield on the individual fishing grounds
have already been indicated. The statistical treatment of .the figures>in
column 8 (Table 10) shows that the differences between 14.0 (fishing ground
5) and 10.0 (fishing ground 6) are significant at 90 per cent and between
14.0 and 12.5 (fishing ground 4) at only 66 per cent. Fishing was carried
out during the entire season on the fishing grounds 5 and 6, whereas on
the fishing ground 4 fishing was carried out predominantly between October
and December. With regard to this fact, it can be seen that the fish were
probably not uniformly distributed over the entire area.
It is astonishing that these differences on different fishing
grounds can be demonstrated during a succession of years. Unfortunately,
the data for the net catches are not sufficient for the investigation of .
this problem. It can thus not be clarified unambiguously whether the dev-
iations that are connected with the fishing ground are caused by differences
[13.252]
in the population density or by differences in the behaviour of the salmon
in regard to the twe kinds of gear.
catrel.e.s
In the critical treatment of the data for the eeetAkre-e-per
unit effort it is necessary to mention the local movements as a form of
salmon migration (see 4.2.). Hitherto the answer to the question whether
eeech
a tap4uee per unit effort is to be considered as representative has been
made in relation to the number of salmon that form the basis of the
values. However, sometimes very large assemblies of salmon take place
ccotei.es
that send the enp4mees per unit effort soaring upWards tenfold. These
values are then based on .a very large number of salmon. However, they do

20
10
Number of ealmon/1000 hoOks
Mean Denmark
0-6 Mittel 1958/59-1962/63 Danemark
Mittel 1956/574961/62 Dtutschland
Mean Germany
"D et- .15-A r.1 F13 x Morale us Months
Fig. 11. Monthly means for the Danish and German cap-es
per unit effort in driftline fishing, Danish values.
(After O. Christensen 19 6 3, 19 64.)
not give the average density of the stock. In general, the effect of such
happenings on the value of the annual average is, - however, very smell,
because it is largely compensated for when forming the average value.
The evaluation of the captures per unit value will be concluded
with a comparison of the data for . different countries.
In Fig. 11 is presented the course of the monthly values of the
captures per unit effort in the Danish5 and in the German driftline fishery.
ct.tc.I.es
The two Curves show a different course. The Danish earobures. per unit effort
show the theoretically expected temperature.dependent steady rise until
February and after that a sudden slump. In contrast to this, the German
values rise quickly until December and drop slowly dûring the following
months.
33.
5 Personal - communication from O. Christensen.
„

- 47 -
If We examine once more the factors investigated hitherto that
can cause short-term fluctuations, we have to state that the effects of
temperature and the influence of selection cannot be responsible for these
differences. The two causes, food supply and wind conditions, could play
a role only if the two fleets did their main fishing during February on
different fishing grounds. To this question the monthly yields on the in-
dividual fishing grounds (Tables 12 and 13) furnish an indication.
cAtekes
The monthly values of the Danig„h 'captures per unit effort in
1962/3 on the fishing grounds 4 and 5/6 show twO clear maxima, in November
and in February (0.Christensen 1963). The difference between the two is
eight salmon on fishing ground 4, only two', however, on fishing grounds
5 and 6.-
et...tees
The German ea-pturee per unit effort show on the average not two
maxima for the fishing seasons 1957/8 to 1961/2, but the highest yields
occur on the fishing grounds 4 and 6 in January instead of December. These
differences indicate the possibility that the different monthly courses of
the Danish and German captures per unit effort by line are dependent on
the fishing grounds.
Table 12. Number of salmon per 1000 hooks on different
fishing grounds, according to Danish catches 1962/3.
(0. Christensen 1963.)
Fishing ' Months
grotind XIII IX X XI - XII I II III IV
. .. ...
- • - • • • • .
2 6 5 11. 10 9 .
3 5 6 13 15 14
4 - 5 . 9 11 . : 14 10 13 . 22 11 ..
5/6 . 9 8 16 lb • 14 18 ' 14 ' 4
5 • 8 ' 11 14 11 13 19 14 • 4
Total
There is a further difference between the Danish and German
[P. 253]
,

• ceckes
- 48 -
captuelee per unit effort that has to be pointed out (Table 14). The Danish
line catches are higher on the average and the net catches slightly lower
than the German results. It has already been said that on the German cutters
Table 13. Number of salmon per 1000
hooks on different fishing grounds
the taking up of the lines begins
according to German catches 1957/5 8
to 1961/62.
already in the forenoon; whereas
the Danish fishermen begin this in
Fishing Month general -in the afternoon. The longer
ground XI XII I II
fishing time appears thus to result
4 11,1 18,6 18,9 3,1
5 12,0 19,6 14,0 10,1 in better yields.
6 6,6 9,7 10,8 7,7
On the other hand, hempen
nets are still being used in Denmark. Furthermore, the driftnet fishery
is there carried out prepcinderantly in the spring months. In contrast, .the
eceekes
Table 14. Cmptuees per unit effort in Denmark
(0. Christensen 1963), Sweden (G. Alm 1954a,
1956- 61) and Germany.
Season
Number of salmon per 1000 hooks and 100 nets
Denmark . Germany Sweden
Hooks Nets Hooks Nets Hooks Nets
1944/45
38,2
1945/46
3 7,5
1947/48
1948/49
1949/50
1950/51
1951/52
1952/53
1953/54
1954/55
1955/56
1956/57
1957/58
1958/59
1959/60
1960/61
1961/62 •
-
•
17
20
11
14
16,5
•
• •
9
11
6
6
5,4
•
' •
' 14,0
11,2
18,9
11,2
17,9
8,4
11,6
15,5
. 8,7
6,9 .
9,0
10,1
5,8
8,2
8,8
25,1 1946/47
21,2
24,2
32,2
30,0
29,9
29,0
27,2 '
41,6
37,9
17,2
8,5
7,7
4,4
4,9
6,6
12,9
9,8
6,4
6,9
• 5,4
6,7
4,5
1962/63 11,9 5,7 9,0 5,7
Durchsdulitt = Art ■-ragc
1957/58-1962/63 1571 7,2 12,3 7,9
- - • - - • - . • -

- 49 -
German fishermen work during the entire year with synthetic nets. Since
••
the driftnet fishery gives better results in the winter months than in the
spring, the difference for this gear alào finds an explanation.
LID.254]
If we now summarize the results of the critical examination of
ctickes
the data for the captures per unit effort, we see that we found four fac-
tors than can influence in some way or other the yields of both kinds of
fishing gear: local movements.of the salmon, fishing ground, water temper-
ature, and wind condition. The significant differencesin yield on the dif-
ferent fishing grounds are astonishing and their causes cannot
be discovered unambiguously. It must be assumed that‘here two further fac7
tors play a role, namely, the different distribution of the food fish as
well as wind and current conditions. The rather rare local Movements will
be eliMinated to a large extent through forming the average values. On ac-
count of the quite uniform course of temperature in the different years,
cercites
the comparability of the captures per unit effort is preserved also in this
* regard. However, the effect of the wind cannot be neglected.
Two further factors influence in each case only the results of
one kind of fishing geax. The supply of food affects the line catches, the
selection affects the net catches. With constant mesh size and invariable
growth conditions the net catches are comparable in spiteof their selective
effects so that it will only be necessary to eliminate the effect of the
food supply.
•
ceekes
In the treatment of the effect of temperature on the eteturee
per unit effort it had been arranged to calculate the average values of
a season for the - line catches as the arithmetic mean for the months Nov',
ember till January. After . the Danish and German values and their monthly
-trend have beencompared ., it.now alipears appropriate to use the months
•

- 50 -
November to March for forming the mean value. Since sufficient data for
driftnet fishing are available only from February onwards, it will be
best to use the period February till April for the calculation of the
representative carbtiee per unit effort.
°led,
An exact correction for the cap-titre-per unit effort by line
in regard to the wind conditions could be made in the following manner.
1. All data for each of the months November to March are to be divided
into those for wind speeds above and below 5 Beaufort, and then sep-
arated according to the four wind directions.
2. It is possible to eliminate the wind effect by calculating the mean(Pf
ç'th-
the five data)for the wind directions and calm. This provides corrected
values for each month above and below 5 Beaufort.
3. A mean monthly value can be calculated from these data for the two
wind speeds.
4. The monthly trend of the melees per unit effôrt that is now available
must be corrected in regard tb the food . supply through the comparison
of net and line catches for the months February/March.
5. Finally the arithmetic mean Of the data for the months November to
March has to be calculated.
When a complicated procedure of correction as —that outlined here
Is to have any meaning, it will be necessary that the individual data menm
tioned under point 1 are based on representative catches. Each of these
statementà must have the same statistical value as the finally calcula,ted.
yearly mean value. However, for the present material this does not hold
true: The result of a correction as outlined above can . therefore be used
only with reservations. '
•
To begin with, let us inspect first the net catches, which, it

•
- 51 -
is true, have to be corrected only in regard to the wind conditions. During
the years 1955 to 1963 winds of over.4 Beaufort prevailed only on about 15
per cent of all days with net catches. For safety reasons fewer nets were
set on such days than on other days. Thus, if we neglect the results for
wind speed of over 4 Beaufort, the correction for wind speed of the net
catches has already been carried out. In order to eliminate a possible
[p. 255]
effect of the wind direction, every monthly value is formed as the simple
mean of the data for the four wind directions and calm. The mean for the
cz,tek
months February to April represents then the eapturTe per unit effort of a
season (Appendix, Table II). For 1956 and 1963 only results for April are
'available, which havelben corrected with the aid of the average monthly
trends (Table 7)..
The monthly means for the line catches can be calculated accor-
ding to the points 1 to 3 Of the above scheme. It is considered that a cor
rectiOn for food sùpply of the available data would be out of place, be-
cause the exact connection between line and net catches cannot be ascer-
tained at present.
In Table 15 have been entered the corrected net and line catches
alongside the uncorrected:mean Values according to . Table 7. A àraphic
presentation of the line catches shows that there is no correlation.iThe
correlation coefficient is r 11 0.22 ± 0 .27 6 .
According to the above discussions, we can indeed say that'the
cate.e.e..s
.-claria4zees Per unit effort by net have probably the smallest errors, we do
not know, however, whether they can be considered to be representative for
the entire season. Therefore, the data for the two kinds of gear offer
only a support. The improved values that are being added annually will
contribute to perfect Our knowledge of the extent of the stock of salmon

- 52-
ce,.,td.es
in the Baltic Sea. Later on we shall discuss the changes in the -eap-turen
per unit effort as expression for the fluctuations in the stock.
Table 15. Captures per unit effort of the German salmon
fishery as expression of the strength of the exploited
stock (percentages in parantheses).
animal
Number of salmon
Season per 1000 hooks, XI-III per 100 nets, II-IV
acc. to corrected acc. to corrected
Table 7 Table 7
1954/55 13,9 13 (85) .
' 1955/56 11 8 (52) . 14 10 (102)
' 1956/57 21,1 24,0 (157) 7,8 7,5 (77)
1957/58 9,6 10,5 (69) 8,6 9,2 (94)
1958/59 19,1 22,5 (147) 15,4 13,3 (136)
1959/60 8,0 8,4 (55) • 8,0 10,5 (107)
1960/61 10,5 10,8 (71) 8,9 . 8,5 (87)
1961/62 14,6 15,8 (103) 9,7 10,0 (102)
1962/63 8 8 (52) 12 8 (82)
Dunfischilin . = Average
56/57-61/62 15,3 = 100 9,8 = 100
2.3.4. The yields of the salmon fishery
The yields of the salmon fishery in the Baltic Sea have been
ascertained according tontitements by G. Alm (1928a, 1954a), 0 . Christensen
(19 6 1, 19 6 2, 1963), F. Chrzan - (1956b), E. lialme (pers. comm.), H. Hinking
(190 5, 1913), R. Kândler (1957, 1958-63), A. Lindroth (1950), M. Linshev
(1961), C. G. J. Petersen and A. Otterstrlim (1904), J. A. Sandmann (190e),
S. J. Sjtigren (19 6 3),.F. Trybom (1910), and from the Bulletin Statitisque.
(Vol. 1-45)(APpendix III).
In the figures for the fishery in the Baltic Sea and in part
[P. 25 6 ] -
also in those for the river fishery are'included alsothe sea trout. The
statements about their'share are incomplete. The yields of sea trout are
summarized in Table V in the Appendix according to the available data and
amounted,to about 100 to 400 t for the Baltic-Sea for
some estimates. They

Table 16. Seasonal yields of the fishery for salmon...and sea trout in the Baltic Sea properl.
Fishing • Danmark Germany Poland • Sweden Total
period t Number t ' Number t Number t Number t Number
%
'
•
1954/55 969
1955/56 644
1956/57 . 1 072
1957158 761
1958/59 1 107
1959/60 • . . 744
1960/61 1 241
1961/62 • .1 410
1962/63 1 061
•
188 900 ,
288 400
174 300
276 500
361 100
285 000
195
140
375
241
267
169
282
339
130
44 500
26 200.
93 200
49 700
62 600
36 900
55 400
86 000
32 400
191
240
225
289
170
(391)
•
40 000
58 000
" 63 000
80 000
48 000
110 000 '
328
217 .
508
185
257 •
182
321
267
(180)
82 000
40 100
108 400
35 700
54 800
31 000
75 800
(60 000)
(43 000)
•
1 378 314 300
1 871 463 800
1.320 305 200
2 133 ' 487 700
2 186 555 100
1 762 . 470 400
57/58-62/63 1 054 . 262 367 238 53 833 251 66 500 232 50 050 1 775 432 750
59,4 60,6 1;3,4 12,4 14,1 15,4 13,1 11,6 100,0 100,0
1 In these figures are included the yields of sea trout that amount to 35 to 85 per cent in
Poland. The Swedish yields have been re-calculated after the statements by Alm (1928a, 1954a)
and Segren. Figures in parantheses have beén estimated.
111'
•

•
the period from 1940 to '1962.
- 54 -
The figures for the landings for the total salmon and sea trout
fishery show considerable fluctuations for the Baltic Sea and also for the
rivers (Tables III and Iv). For the Baltic Sea they rose from 250 t to
1330 t during the 20 years from 1913 to 1932. The most astonishing phen-
omenon is, however, the sudden growth of the fishery after the Second World
War to a total of 4000 t, which finds expression also in the rivers (700 t).
The average yield for the years 1957 to 1962 amounted to 2675- t.
Of this about 275 t were caught in the rivers. The shore.fishery (Sweden,
Finland, SSSR, Poland) yielded about 600 t and the pelagic fishery 1800 t
or 440,000 fish. This corresponds to a percentage of 67 per cent of the
total yield. 'These catches were composed of 1500 to 1600 t Atlantic salmon
and 200 to 300 t sea trout.
Lp. 2581
. The pelagic fishery (Denmark, Germany, Poland,Sweden) is res-
tricted substantially to the main basin of the Baltic Sea (fishing grounds
3, 4, 5, 6), but it has been extended recently during the fall months into
the Gulf of Bothnia (fishing ground 2, Fig. 6).
Since the fishing in the ocean is carried out preponderantly
from fall to sprink, the seasonal yields are of special interest (Table 16).
They show still greater fluctuations than the figures that relate to the
calendar year. This is caused by the fact that the seasonal yields are
affected especially by the fluctuations in the stock. At the beginning of
the fishing season the salmon, which spend their second year in the Baltic
Sea, are just entering the exploited phase..They form, together with the
fish that are one year older, the main bulk of the catches. Towards the •
.end of the seaèon, in April/May of the following year, the large fish
'begin their spanning migration. This is the beginning of the rejuvenation •

Table 17. Monthly average weights of salmon, according to German landings, in kg,
gutted weight.
Season IX X XI XII . I II III IV V VI Weighted Arithm.
- mean mean
1954/55,
1956/57
1957/58
1958/59
1959/60
1960/61
1961/62
1962/63
1963/64
3,92 .4,25 4,67 4,68 4,75 . 4,63 4,33 4,38 4,47
4,87 5,79 5,88 6,68 - 5,21 5,31 5,10 4,52 5,36 5,42
4,34 4,49 4,18 3,34 4,04 4,20 4,22 ' 4,02 3,70 4,02 4,06
5,29 4,63 5,03 4,32 5,07 5,28 5,10 5,11 4,92 4,98
3,98 4,32 4,13 4,31 4,44 4,67 3,94 3,72 - 4,27 4,18
5,37 4,64 4,46 5,42 4,86 4,34 4,71 4,12 3,53 4,39 4,61
3,29 4,95 5,18 5,09 4,98 5,31 5,35 5,09 4,42 5,10 4,85.
3,55 4,05 4,13 3,90 3,62 3,85 4,14 3,87 3,89 3,84 3,91 3,88
4,39 4,63 3,63 4,05 4,04 3,57 3,35 3,87 3,95
4,93 4,38" z :..4,06 4,46 5,89 3,79 3,24 4,47 3,25 3,23 4,35 4,17
Mitrelwert = mean val .4,04 4,72 4,35 4,55 4,69 4,73 4,55 4,61 . 4,18 3,70 4,47 4,49
fiinfgliedriges Five-term
' Mittel (4,37) 4,47 4,61 4,57 4,63 4,55 4,35 (4,16)
Table 18. The monthly yields of the fishery in the main basin of the Ba3.tio Sea.
SeasOn Country :VIII IX X XI XII II III IV V VI VII Total
_
Mitte1=Mean M. 1 1,2
1955/56 bis =t0Dell 2
1961/62 Po 3
Svi 9,7
4 • '
23,3 92,8 162,8 219,6 144,0 90,4 85,5 80,1 77,5 23,4 * 0,5 1001,0
1,0 11,7 52,9 63,3 39,9 24,7 31,5 19,1 11,7 1,3 • 259,1
0,2 8,6 18,1 13,0 • 1,9 4,6 26,6 • 17,6 1,4 92,0
35,7 30,6 31,8 11,3 3,4 2,8 17,2 28,2 21,8 5,2 0,9 198,5
Ges. Mittel Tot .Mean '10,9 : 5 9,9 135,3 /56,0 314,3 200,3 - 11 9,7 138,7 153,9 1/3,6 ' 31,7 1,3 1550;6
_. .
I Schweden nur Gotland und Bleitinge: = Sweden. -only Gotland and Blekingè - ' .
1 = Denmark 2 - Germany
3 = Poland 4 = Sweden
•

- 56 -
of the stock. In the course of the summer a new crop of smolt (fish, which
emigrated from the rivers in the same year) joins the exploited stock (see
5.3.1.2.). This process is not reflected in the records of yield according
to calendar years, because two different stocks are sampled at the beginning
and at the end of the year. -
The monthly trend of the average weight points also to the
changes in the.exploited stock (Table 17). The figures increase from Sep- .
constant until March and begin - to decrease
in April. The incXease at the beginning of.the season is a consequence of .
s the growth, although here other causes may play a role. The decline of the
values that begins in April points'to the emigration Of the large salmon.
In some years there occur deviations from these average events.
The Danish share in the pelagic fishery in the Baltic Sea amounts .
to more than 60 per cent, whereas the other countries have each an 11-per •
cent to 14-per cent share in the landings. The largest landings of more
than 2000 t or more than 500,000 salmon were reached in 195 6/7, 1960/1,-
and 1961/2. The emallest yields occurred in 1957/8,and 1959/60 with. about
1350 t or 300,000 salmon.
The yeiarly trend of the landings (Table 18) shows that‘the
.fishery reaches a peak at different times in the individual countries.
Denmark and Germany have the highest yields in the winter months from Nov-
ember to January. On acCount of inclement weather, the landings in Februare
are often gmaller. This was especially pronounced during the 1962/3 season
in the German fishery, becauselthe cutters had to stay in harbour from
January until March on account of the iCe cover. When the water begins to
warm up, the yield begins tà diminish in March.
The fishery takes . a very different course in SWeden and in Poland.
tember to January, they remain

- 57 -
In February and March hardly any vessels are fishing so that the figures
for the yield show peaks about the end of the year and in spring. The
Polish statistics shows the greatest landings from November to January
and from April to May. This separation is still more pronounced for the
Swedish fishermen from Blekinge and Gotland, who carry out a pure fall
fishery and who obtain the highest yields from September to November and
from March to May.
2.3.5. The composition of the catch in the pelagic fishery
As has already been said, the sea trout are not recorded sep-
arately in the landing statistics. In order to ascertain their shaxe one
has to have recourse to market investigations.
• The results of the available analyses have been summarized in
Table 19. There are no Swedish records for the Baltic Sea proper'. When
one assumes that the percentage of the Swedish share in seà trout ià about as
high as the Danish one, one obtains for the total catch in the Baltic Sea
proper 10 per cent in 1958/9, 25 per cent for 1959/60 , 12 percent for
[p.:259]
1961/2, and 22 per cent for 1962/3 of sea trout. In the Polish catches the
share amonted in the.last few years numerically to over 80 per cent. In
the proper Baltic 'Sea alone it ameunted to 20 per cent in the season 1959/60 . •
In any case it is astonishing that up to one quarter of the yield of the
pelagic salmon fishery consists in some years of sea trout.
The'German Catches show'from January/February on an increase
in the share of sea trout,loecause at that time the fishermen work frequ
ently in the Danzig Deep. There the sea trout that originate'in the Vistula'
occur in large numbers. The total catch. of a cutter at that time can occas-
ionally conaist tô 70 per cent of this kind. Accordin'e, to the data at hand,
the share of' seà -trout is independent of whether driftlines . -or driftnets
are being used.

Table 19. The share of sea trout in
the salmonid catches in
the Baltic Sea proper.
Weightéd
Season Denm. Germ. Pol. me an
1956/57
1957/58
1958/59
' 1959/60
1960/61
1961/62
1962/63
Weighted mean
3,0
6,2 42
2,4 3,3 60 10,8
6,9 15,5 87 26,5
3,4 84
5,9 , 3,9 79 12,8
1,5 12,8 87 24,4
1 valid for January only; Danishand
Polish figures after Christensen
and Chrzan.
5 8
The cod plays the main
role as a genuine companion fish
in the salmon fishery. It is being
caught mainly with driftlines, very
rarely in nets (Table 20). The
fishermen are of the opinion that
the occurrences of salmon and cod
exclude each other and they cite
as proof that during a large catch
of cod only very few salmon are
being caught. Concerning this it
must be .said that a hook that has already been taken by a cod, can no
longer catch a salmon. Since there exists a food competition between the
two species of fish, it is possible that an effect of gear saturation may
be reached. According to the number x of the cod already hooked, we have
then a catch of salmon, not per 1000 hooks, but per 1000 x hooks. The
catches of salmon can be influenced in this way by the presence of cod.
Vice versa, the yield of cod can also be influenced by the salmon. There .
will thus become eàablished an equilibrium between the two species. A
shift will always occur when the population density of one species changes
in relation to that of the other.
[P. 260]
Effects of this kind can find expression in the ratio between
the salmon catches with lines and in nets (Table 9) because cod are hardly
cc..td.es
ever caught in driftnets. The falsification of the ceptueeQ per unit effort
of salmon can amount to a maximum cif . about± 0.5 salmon per 1000 hooks.
This possible error, however, has to be neglected, because the necessary
figures for a correction are not available,for all years.

• Table
20. Additional catch of cod in the salmon fishery,
yields and captures per unit effort.
Number Month 1957/8 1958/9 59/60 60/1 61/2 6 2/3
of cod
• Sept. 2,3
Okt. 10,2 19,7 15,0 6,2 0, 1 . 16,7
per Nov. 44,7 24,9 27,7 23,0 7,6 9,5
1000 pez. 21,0 14,7 DA 17,7 10,3 5,3
Jan. • 26,5 11,7 8,5 UA 6,0
hooks Febn 7,4 10,4 5,9 3,3 1,7
Mâm 2,6 3,0 IA 1,4
per 100 nets Apr./May 1,0 0,5 0,3 0,6 0,5 0,1
Total number
of cod . 100 000 45 000 48 000 34 000 30 000 12 000
..... . .
- 59 -
Ceeke ,",
Table 20 shows that the c-aptux-e.s per unit effort of cod and the
yields have declined considerably in recent years. The decline of the
catches has been caused, apart from changes in the stock of cod, also by
. the reduction in the intensity of line fishery. The greatest yields of
cod are Obtained in the months of November/December. Later the fish return
to the sea bottom in order to form pre-spawning aggregations . and to move
to the spawning grounds .
The other species of additional catches are quantitatively of
small importance, but they are worth noting on account of the species com-
position. In the line fishery up to 20 sea hares (Cvolonterus lumpus) of
a length of 10 to 15 cm axe caught during a voyage. Besides these there
are found occasionally trigger fish and flatfish (flounder, turbot) and, •
more rarely, mackerele In one case it is known with certainty that a
seal has been caught on a hook. Guillemots that dive for the bait and
gulls that feed on the intestines of hooked cod, are Caught frequently
on the hooks by the bill. However, they can usuallY be freed and released.
In drifnet fishing the flounder'plays the main -role as an

- 6o-
additional catch. However, hardly more than 20 fish will be caught during
one voyage. The plaice is represented in still smaller numbers. In spite
of the large mesh opening, an occasional herring or small sea hare may be
caught.
Dolphins (especially Phocaena phocaena = harbour porpoise, and
Delphinus delphus = common dolphin) are captured in every year, whereas .
the grey seal is caught more rarely. I have records for the season 1959/60
of the capture of a dolphin and a seal, and for the season 1961/2 of three
dolphins and ohe seal.. Ducks become entangled regularly in the driftnets.
3 •
The sexual maturation of the
Baltic Sea salmon in the ocean
The propagation in salmon takes place generally in such a manner
that the maturing males and females migrate from the sea into their home
streams where they spawn in late fall. In the spring the frY emerges from
the eggs that lie in the gravel at a depth of about 20 cm. After one to
five years the young transform into smolt and migrate in the spring into .
the sea. They grow up and in their turn seek but their home streams for
spawning. The so-called grilse, which are mainly males, spawn already after
the second summer in the sea.
.
Exceptions from this rule have been established early. C.
Gessner (1558) knew already that small males take part in the spawning act
without having visited the sea previously. This fact has been described
anew in 1906 by Calderwood (according to K. A.Pyefinch 1955) and G. Alm
(1943) tested it experimentally and confirmed it.
It has been known for a long time that the species of Oncorhvnchus .
and the Atlantic salmon have formed landlocked stocks (accOrding to E.
'NereSheimer 1941). Such forms exist in Japanese lakes, in North American

•
100
50
60
100 cm
Totallarle
.
20
d = '9 = ----, n ------ 997
= Total length.
Fig'. 12 .. Distribution of lengths and--gonati--1-ength-s—ef
crç Sal- e-ko
eke 1.3..êtqc, .seixtryaed., b
- 61 -
fresh-water bodies (Labrador, Maine), in Lake Ladoga and Lake Vânern.
Dahl (1914-26) found them arso in the lakes of the river Otra. These
[p . 261]
salmon live in land-locked waters that were formerly connected with the
sea. Their entire life is therefore spent in fresh water. Females and males
become mature there and migrate'into the rivers to spawn.
This knowledge showed that salmon do not absolutely require
the change of environment from fresh water to the sea and back. It came,
however, still as a Surprise when Danish fishermen succeeded in about 1925
in raising females from artificially fertilized eggs. These females matured
after four years in the fresh-water ponds and spawned three times in suc-
cession (V. O. Otterstr8m 1933). To be sure, the fish attained a length
Of only 42 cm after five years.
Anzahl Lackse = 'Number of salmon
.Recently . Swedish scientists succeeded in . repeating the ex-
periment and they have furthermore raised Atlantic salmon already to the
fourth generation in fresh water (pers. communication from B. Carlin).
However, the other extreme is also possible up to a certain
'degree. I know of four cases in which female saimon-of 1959 to 1964 with

•
- 62 -
discharging gonads were caught during the months November to February in
the Daltic Sea. Mature males are also found occasionally. Nordgaard (ac-
cording to Nereheimer 1941) also has demonstrated that salmon can mature
in the sea. Fertilization and development of the eggs, however, is not pos-
sible, because all the necessary conditions for this are lacking in the
ocean.
The development of the gonads in the rising mature salmon, the
act of spamning, the Conditions for fertilization and the embryonal dev-
elopment have in pari investigated very thoroughly. There are, however, no state-
menté about the sexual circumstances during the maritime stage.
3.1. The sexhal composition of the exploited stock
If we assume.that the newly hatched brood consists of equal
numbers of males and females, then among the migrating smolt, the females
must be in the majority, because some males always remain in the rivers.
During the 'second year in the sea, the numerical proportion among the -sexes
LP.26 2] •
continues to shift in favour of the females, because already more males
(eilse) than females have migrated to the spawning grounds. The investig-
ation of the salmon catches at sea should therefore yield more females than
males.
In this connection we shall examine the composition in regard
to length and sex of eight salmon catches of 997 fish from the-years 195 8 .
and 1959 (Fig. 12). The sexual figure 6 amounted collectiveiy to 0.391.
Thé value for the fishing ground 6 (Bornholm) was 0.438, that for the .
fishing ground 5 in contrast only . 0.371. The differenoes between the two
fishing grounds are, however, notiignificant, since the value 0.438 is
••■■■■•■•■••■■••••■•■•■■■••••••■•■••••■••■••••■••■••■■■•••••••
6 After A. BUckmann (1929). The decimal fraction that indigates the proportion
of males is called the Sexual figure.

• subject
to an error of ± o.op95.
1
30
s.20
10
CM
Gonadenlânge Length of gonads
50
6..4%
• • .
70
, . • '
. '
• • • •
• • •
• o•
• • • •
.90
6 3
110 cm Totallânge
Fig. 13. Relation between total length and gonad length of
the long gonad in the salmon, Nov./Dec. 1959.
Total length
In Fig. 12 the distribution of the lengths of both sexes shows .
two maxima that correspond substantially to sea year clasSes 7 A.1+ and A.2+..
•■•■•••••••••••••■••••••••••••••••
7 - in the second winter in the seà, A.2+ = in third winter in the sea.

- 64 -
It is found that the sexual figure for both sea year classes is very
different. It amounts to 0.446 ± 0.0195 in group A.1+ and to 0.260 ± 0.255
in group A.2+. This difference points to the fact that during the third
year in the sea at least as many males have migrated as females. The sexual
ratio can therefore not be considered as constant. Since the strength of
the year classes and with it the ratio between the two sea year classes
A.1+ and A.2+ changes annually, the sexual composition of the exploited
stock must also undergo this change. It is thus not the numerical ratio [ p. 263]
of the sexes in the total catch that deserves our special attention but
that in.the two age groups.
Since the sea year class A.2+ in the sea comprises 74 per cent
females) these must also predominate on the spawning ground. As has already
[19 . 264]
been explained, the missing males of this age class can be replaced by the
numerous emigrating younger males. This, however, does not provide the
solution for the problem of the sexual ratio on the spawning ground. When,
for example, two very weak year classes follow on an exceptionally strong
year class, then it must be taken into account that the younger males and
grilse of the two weak year classes are not present in numbers sufficient
for the females of the strong year class. Here nature has obviously taken
precautions through the mature parr; because these fish were not subject
to the strong depletion of the stock in the sea they are probably always
present in sufficient numbers in the rivers.
.
3.2. The conditions of the gonads
According to A. Backmann (1929) there are two conceptions com-
bined in the word "maturation": the process of the development from the
juvenile fish to the sexually mature one during its first period of life,'
'Which happens, only once, and the obtaining of sexual maturity (sexmsa

cycle) during the second . period of life, whih is usually repeated period-
ically.
Fig.'14. Long gonad of a female of the sea year class A.2+.
(a) full view, .(b) partial view, (c) gonadal discs.
In the female the primitive germ cells give rise to the oogonia
through mitotic divisions. The oogonia grow into oocytes of the first order.
The meiosis that follows leads through oocytes of the second. order to the

Opcytenzet
Numbep
20
I0
- 66 -
formation of mature ova. The strong growth of the female sexual products
through increase in the amount of cell content and through yolk deposition
and water uptake takes place after the diplonema stage of chromosome cor›-
jugation and before meiosis. Since this process can also be observed during .
the periodic - attainment of -spawning maturation in the second period of
life, it can be assumed that in the sexual cycle of adult fish maturation
begins with the enlargement of the oocytes.
.
The stock of salmon in the Baltic Sea is composed almost exclus-
ively of such fish that are in the first period of life and have nôt yet
spawned. The fish of the age class A.1+ have atill almost one or two years
of sojourn in the sea ahead of them and must be designated as juveniles
in the customary sense.
In the following it will be - examined whether the ovaries undergo
a change in the sea, and whether it is posàble to ascertain the probable
time of spawning already at this stage.
3.2.1. The ovary
of oocytes ,
, . . ,
,
, f
1
■
, ..• .
I ■ .
I
.. •
—■
ttesch.u. Cen %re diees
End discs .
,
Fig. 15. Size of egg in different regions of the ovary
. (means of 12 salmon, 74 to 79 cm total length).
• The ovary conditions were investigated in 68 females that were
) .
from 43 to 104 cm long. Three fish were in the first year of their star
in the Baltic Sea, 31 fdsh were in their second year and 34 fish were in
».11
20 mm
Egg- diameter
•
Enturchmesser

•
their third year.
, Recruitment oocytes
-
'maturing eggs
Fig. 16. Cross-section through a salmon ovary,
age class A.2+ (X 20).
EMurchmesser = egg diameter
mr. Number Of maturing
oocytes
Anzahl redender Oocy ten
o mittlerer Oocytendurclynesser
Mean diameter of
• oocytes
w 10 30 0
IllAnyohl rellender
Oocyten
Number of
aturing
oocytes
„ .. . . . . Ovary discs
Fig. 17. Mean diameter of occytes and number of oocytes
in different ovary regions.
200
Ovorscheiben
- 67 -

Anzaht number
5 Ttere,74-79cm(0 75,6cm)
April 1958
6 Tier. 74-79cm (0 77,1cm)
Tiere = sh
2 Tiere, 77- 79cm (.0 78,0c ini
3 lier,99-101cm (0100,3cm)
2 here,100-101 c m( 10Q cm)
5 7n.re, 91-99 cm
. 96,6cm)
3 Per., 97-99cm
(099,3cm)
Fig. 18. - Abundance distribution of salmon oocytes of
different diameters.
- 68-
The diagram of the relations between length of gonad and body
length (Fig. 13) shows that the ovaries of the salmon in the Baltic Sea
have lengths of from 5 to 31 cm, generally from 8 to 18 cm. Correlation
with 'body length'is obvious, however, the values show strong scatter.
Fig. 14 shows the long gonad of a female of the sea year class A.2+. It
[1).
can be seen plainly how the connective tissue surrounds the dorsal‘side
of the ovary. From it are loosely suspended the discs that are formed
[P. 266 ]
267]

50
r-■ 2
/ bet; 56cm = 1 fis
1 lief; 76cm
7s ere , 68-78cm (073,0cm)
1 net; 73cm
2 T ere, 86-88cm (08Z0cm
2 Tiere,43-48cm (~ 5 5 cm) = 2 f ish
Fig.
9 Tiere, 54-72cm (063,8em
5 Tiere,89- 96 c m(08Z .4cm)
3 I ■ere,8t -98cm (091,3cm)
Apri11960
6 Tiere,92 -102cm (093,0,cm)
November 1959
2 bere,82-86cm(84,0cm)
bere,90- 94cm
9Z0cm)
Oocyferedurchm
2 3 mm
diameter of oocytes
18. (continuation).
irregularly and separated from one another. The ripe eggs are later
loosened from the follicles in the disc's and fall into the body cavity.
Cutter t)r-1
Each ovary has orall a blunt end and the circumference is greatest there.
Caudally the gonad is'drawn out into a long point.
The number of discs in the longer ovary is 41 to 59, with a
mean of 47.7; in the shorter ovary the number is 31 to 52, with a mean
of 43.1. On an average the number of discs in the shorter ovary is 9.6
per cent smaller than in the longer-one. This difference is, however; not

- 70 -
expressed to the saine degree in the number of eggs. Since the shorter
gonad is generally slightly thicker than the longer one, it has on an av-
erage only 8.6 per cent fewer eggs than the longer ovary.
3.2.2. The maturing of the oocytes
According to C. F. Hickling and E. Rutenberg (1936), R. Undler
and W. Pirwitz (1957) and others, the ovary of every fish contains a gene-
eral stock of small oocytes. A part of this stock matures annually. To re-
place it, neW oocytes develop in the envelope of connective tissue. The
development until maturity takes at least two years.
We had 72 salmon ovaries for investigation at our disposal. Of
these, 30 were preserved in formaldehyde at sea in April 195 8 , 22 were
*preserved in November 1959, 20 in November 1959, and 20 in April 1960 at
[p.268 ]
sea in Gilson's solution. The oocytes of 68 ovaries were later removed from
the follicles and measured individually under a stereoscopic microscope
with the aid of an eyepiece micrometer' at magnifications of 12.5 or 32. ›
In 40 ovaries all maturing oocytes could be counted..
These investigations showed that the two groups of sizes cited
above occur in the female gonad (Fig. 15). The small oocytes have a dia-
meter of less than 0.3 mm. In the large oocytes the diameter varies be-
?
çy **" tween 0.3 and 3.4 mm. In Salvelinus fontinalis, V. slk, Vlad/kov (1956)
designated the smaller oocytes as recruitment stock and the larger oocytes.
as maturing eggs. In what follos these designations will be used also for
the two groups of sizes of oocytes in the . salmon that have been cited
above.
oocytes
A cross-section through the ovary }lows that recruitment stock
occurs scattered through the entire ovary (Fig. 16). It is, however,
especially freqUent in the connective tissue of the dorsal side of the

•
- 71 -
ovary that has already been mentioned (Fig. 14). The follicle-forming
tufts of this tissue extend deeply into the gonad. Whereas the maturing
oocytes separate easily after treatment with Gilson's solution, the re-
cruitment stock sticks very tightly in the tissue and is often invisible
and thus not amenable to quantitative treatment. Maturing oocytes are sup-
plied plentifully with yolk, whereas.the recruitment stock haà no, or hardly
any yolk. The oocytes of the recruitment stock are, however, of different .
sizes (Fig. 15). The number and the diameter of the oocytes vary greatly
in the different regions of the ovary on account of the varying size of
the discs (Fig. 17). In the discs that are situated in the region of the
greatest circumference of the"gonad, the diameter of the oocytes and their
huMberece greater than in the end discs. The number of maturing oocytes
in 12 . salmon with a total length of between 74 and 79 cm varied from 49
to 205 per disc. The weighted mean was-134.
• It will now be our task to investigate the development of the
oocytes in salmon of different length and of different age and to find an
indication of the probable time of spawning. Hitherto it has been known .
through investigations of the stock that in the spring of every year a
part of the salmori in the sea of sea year class A.2 8 and the majority of
the sea year class A.3 8 emigrate to spawn. Thus one has to take into ac-
count that at least some of these fish have reached a stage in their dev-
elOpment in April that enables theM to spawn in the following fall.
. The synopsis of the results shows that even in such salmon
that have been caught at the saine time there are considerable differences
in the diameter of the oocytes. It was not immediately possible to make .
an unambiguous distinction between salmon with Well-developed gonads,
8 A.2 = two years in the Baltic Sea, A.3 = 3 years in the Baltic Sea (cf. 5.1.).

- 72 -
which could be expected to participate in the next spawning, and those
Whith slightly developed ovaries, who would migrate to spawn only a year
later. To begin with, those fish who showed an approximately 'equal dis-
h). 269]
tribution offrequency of diameters of maturing oocytes were combined (Fig.
18). Thus a certain grouping was found in the salmon that had been caught
in November 1959. The females of the age class A.1+ (57 to 77 cm fork length)
had'a mean diameter of the oocytes of below 0.9 mm. In the females of the
age class A.2+ (82 to 97 cm forklength) it was more than 1,2 mm.
There is a possibility to test whether the indicated grouping
is correct. In this case it represents two developmental stages. The fish
who will participate in spawning in thé following year are distinguished
from those who will spend another year in the Baltic Sea by having gonads
that are better developed. It can, however, be expected that the grouping
mentioned will be much better expressed in April 1960 - that is, at about •
the beginning or shortly before the spawning migration. In order to pursue
this idea, the mean diameter of the maturing oocytes has been ascertained.
Accordingly, the frequency diagram of the mean diameter of the oocytes
shows for each catch sample two,maxima (Fig. 19), that correspondto the
groups cited. The samples of November 1959 and of April 1960 are most'suit-
able for our consideration, because in this case the same year classes
have been considered. Furthermore, they concerned only ovaries that had
been prepared in Gilson's solution. In November the mean diameter of the
oocyteads 0.59 and 1.44 mm, respectively, for both groups. The fish.that
are represented by these maxima must appear also in the sample of April
1960. In Fig. 19 We can recognize them again by the,two maxima in the
frequency distribution. They show mean diameters of the oocytes of 0.96 '
• and 1.99 mm, reSpectiVely. During the five months from November. 1959 to

5
- 73 -
April 1960 the diameter of the small oocytes increased on an average by
0.37 mm, that of the large ones by 0.55 mm.
It has still to be clarified which of the salmon represented
in the samples will emigrate next in order to spawn. We can assume that
the fish that had large oocytes. (over 1.2 mm in diameter) in April 1960
would have soon started to emigrate and would have spawned in the fall of
1960. If such fish were not to migrate in the normal manner, we should
then find salmon with still larger oocytes in the Baltic Sea in November.
That was, however, not the case. It is more difficult to resolve the ques-
tion how those fish will behave whose ovaries contain only smaller oocytes
(under 1.2 mm diameter). The large oocytes have to increase between April
'Antel= Number of salmon
Lachse
À
M
•
À•
•
April 1.960 •
ra; 4701 Affiwe' •Act
lor
.ÀUWÀ
l■ioverilber1959
April 1958
3 mm
thiftlerer0ocytexiurchmesser
Mean diameter of oocytes
Fig 19Thefreqiency distribution of the mean diameters "
of maturing oocytet)
and November, the main spawning month, from 2.0 mm to about 6.5 mm (by about
4.5 mm). From this point of view it would be possible that'also the smaller
[P. 270 ]
maturing. oocytes could grow from 1.0 mm to 6.5 mm (by 5.5 mm) on an aver-
age. If that is possible, it would be hard to understand, why there are
two groups of salmon with clearly different sizes of ovaries, and why then
[p. 271]
most salkon with smaller oocytes do not also emigrate to spawn. This latter

- 74 -
is, however, not the case, because in November fish with greater oocytes
are present. These can only have grown up from the small oocytes.df April,
in that their diameter increased frOm 0.96 to about 1.44/ that is by about
0.5 mm on an average.
In order to make still clearer the reported train of ideas, the
diameter of the oocytes will now be considered in relation to the length
of the salmon. The evaluation of the sample of November 1959 ( Fig. 20 h)
3
llocytendurdwness e; mill
r Diameter of oocytes
10 30
. _ .
.
•• .
Total length
50 70 93 rotadnytc il rn .
Fig. 20 a. Relation between total length and diameter of the maturing
oocytes, April 1958, length distribution of the age classes: A.?, 65
to 86 cm, max. 72 to 79 cm; A.3, 87 to 101 cm, max. 90 to 98 cm.
shows that it is pOssible to distinguish between recruitment stock and
maturing oocytes in salmon already during the firstyear in the Baltic Sae&
Up to a length of 76 cm the Size of the oocytes correlates with the length
of the fish. That, however, does not hold for the samples of April 1958
and April : 1960.(Figs. 20 a, c). Furthermore, it does not hold true for the
larger fish (A.2+) of all three samples.
ACcording to the findings, the process (fàf maturing during the
sojourn in the Baltic Sea can be explained in the following manner:
during the first year in the Baltic Sea recruitment stock and maturing .

- 75 -
oocytes can be demonstrated in the ovaries of salmon (Fig. 20 b, fish 43 to
54 cm long). (It is possible that the differentiation into these categories
had taken place already earlier.) Whereas the size of the recruitment oocytes
changes little during the subsequent time, the maturing oocytes show an
3
2
Oocytendurchmesser Diameter of oocytes
mm
Fork length
10 30 50 70 90
Crobelleg4grm
Fig. 20 b. Relation between fork length and diameter of maturing oocytes,
Nov. 1959,. length distribution of the sea year classes: "A.1+, 57 to 77
cm, A.24., 82 to 97 cm, A.+, 43 to 54 cm.
almost linear increase" in their diameter that is correlated with the length
of the fish (Fig. 20 h) until the second winter of their life in the Baltic
Sea. During the progress of the growth of the oocytes this correlation does
[p. 2721
no longer exist later (Figs. 20 a, c). Salmon who have a diameter of the
oocytes of more than 1.2 mm spawn already in the approaching fall4"that
is, after a stay of 2.5 years in the sea. The other fish proPagate a year .
later (Fig. 21). A Resell. (1893) gives a table of the egg maturation during
the course of a year in his_investigation of the salmon in the Elbe. The
values given for the months February to November fit excellently the curve
for the age class A.3 in Fig. 21. Fritsch, however, did not state the age
of his fish.
It becomes clear in general from the data for April (Figs. 20

- 76 -
a, c) that the age of the fish plays a.certain role in the growth of the
oocytes. Within an age class, however, the process - of ripening is depen-
dent on the length. At any rate, Fig. 20 a shows oocytes in both age classes
for which it is not possible to decide with certainty whether they will
mature already in the current year.
3
.2
Oocytundurchtnessecrnal D inmeter of odcytes
Fork length
ZO • 60 80 .100
GabellÉinge, cm '
...____. . _... ._ - _. ... .
Fig. 20 c. Relation between fork length and diameter of oocytes in April
1960, length distribution of the age classes: A.2, 63 to 80 cm, max. 66
to 75 om,A.3, 84 to 101 cm, max. 88 to 96 cm.
If we attempt to group the salmon according to their degree of
maturity with the aid of the diameter of the oocytes, we find for the fish'
investigated:
Sea year class A.+ A.1+ A.2+
Nmber of salmon investigated 3 32 33
of these in preparation for spawning in the follwing fall - 1 32

. ineftlerer Mean
OocytendurcArnesser
6
F;u0
diameter of oocytes
Range of rariatiOfl of
Vanotionsbrede ors
/run! 00cyte6durchm. diameter of
aturing ooc
the men
the oopytes
. tes
■ ocytes;
xx relit/nit Oecyten
00 Nachwuctisoocyten ecruitment
x4 inechAFrifscM9.0 e
----Rehmg.wftw ,M,i'verrem'ie4XT;'
-,--wahrsch - • - -
1 11.1 r
0-
W d V vi Vil? X XII a
LO
AO Ai
///'
r
é1 eld X k.
A'
Sea yekr classes
1.
1
1
elorare—*
A 3Heerjohreskossen
• Fig. 21. Maturing of the oocytes in the Baltic Sea salmon..
- course of maturing when attaining maturity after 3 1/2 years
in the sea
• course of maturing when attaining maturity . after 2 1/2 years
. in the sea]
3.2.3. Comparative discussion of the findings about sexual maturation
The material on whieh is based the investigation of the matur-
ation of the eggs is not very large. At any rate, the results point to
the fact that is well-known from the investigations of the stock, that
[P. 273]
some salmon of the sea year class A.2 and the majority of the individuals
of the class A.3 emigrate in the epring ofeach year in order to spawn.
According to the investigations of the fat metabolism the
amount of Let content P lays an important role.in the readiness for the
sPawning migration. L. Scheuring (1929) is of the opinion.that the tiMe
of- emigration from the sea depends not so much on the state of development
of the gonad.than on the general condition. F. R. Hayes (1949) was able

- 78 -
to show in an investigation of the chemical conditions of the salmon eggs
that fat is the most probable source of energy for the development of the
embryo. In addition, fat is being deposited in the gut mesenteries of the
yolksack-brood befors the first intake of food - .
F. Thurow (19 62) was able to demonstrate that the storage of
fat in the Baltic Sea salmon is correlated with the readiness to spawn.
The salmon of the age class A.1+ show during late fall, with
an average of 14 Per cent fat content, a value that is hardly lower than
in fish of three winterS(A.2+). In the winter most of the younger fish
suffer a considerable deterioration in condition, so that the fat content
falls to an average of 6.5 per cent. The larger and older fish are able
4.5s
to keep the food supply so favourable that only a very slight consumption
of fat takes place. Whereas the salmon of two winters lose more than 50
per cent of the fillet fat, this loss in those of three winters amounts
to only 10 per cent, so that their fat content in epring amounts to about
12 per cent. According to this there are two developmental phases during
the sojourn in the Baltic Sea. During the first phase, which ends in general
in the late fall of the second yeaT in the sea, fat is predominantly being
stored up to a content of 14 to 15 per cent. When the fish succeed to keep
the loss in condition so low that the fat content does not sink below about
12 per cent, then these salmon can take part in the spawning emigration
in the spring. In the other case they remain in the Baltic Sea, attain
again a content of 15 per cent fat until November and then survive the
winter so well that they can emigrate to spawn after a three-year stay in
the sea. When we compare these results with the findings of the investig
ations of the oocytes, we find here also the expression of the two phases
. that have been mentioned (Fig. 21)". The formation of the fat depositsi;that

- 79 -
furnish the energy fer the spawning migration and the maturing of the oo-
cyte e appear thus to proceed hand in hand.
D. R. Idler and B. Bitners have determined the energy consump-
tion of Oncorhynchus nerka during the migration from the river mouth to
thé spawning ground. They did find that a female of 2.2 kg weight requires
on an average 1.1 kcal/kg/km. The Baltic Sea salmon have to travel distances
of 700 to 1300 km from the southern Baltic Sea to their spawning grounds.
Although the travel in the Baltic Sea . certainly requires the expenditure
of less energy than in the rivers, we shall take the value of Idler and
Bitners as basis. Here it has to be taken into account that the salmon have
fat deposits not on4r in the fillets, but also in the mesentheries of the
intestines, which contain one-third to one-half as much fat as the fillet.
A aalmon of about 70 cm length has a live weight of about 3 kg and therefore
30û0
requires about(3kcal for 1000 km. Since oils, liver oils and the like have
a content Of about 900 kcal per 100 g substance (J. R. Geigy 1953), about
350 g fat will be required for 3000 kcal. This amount corresponds to a fat
content of about 12 per cent in the fillet (110 g intestinal fat, 220 g
fillet fat; fillet weight = 60 per cent of the live weight). To overcome
a migration distande - of 1000 km a fat content in the fillet of about 12
per cent is required.
The analysis of the age of the ascending salmon can undoubtedly
show best at what age the salmon emiàrate from the Baltic Sea in order to
spawn. To be sure, an unambiguous material should contain results from the
P. 275]
most important spawning rivers. For this I have three series of meaaure-
ments that have kindly put at my disposal by B. Carlin. In one case these
concern beach-dragnet catches of 715 salmon, which were caught between June
12 and September'2, 1959 in the Ingermanâlven. The second series concerns

Anzon/I Number
50
SO
100
100
100
SO
70
90
Kohx, 36 - 88 1962
Karsinopoton 621 St
Totallânge Total length
Baltic Sea ProPer
Eigenfl. Ostsee, nprtt 1962
frelb"tz 691 Driftnet
r° i'llange Total length
Lule, A6.-318.1961
Korsinopatan 1741 St
Totalbringe
Total - length
Baltic Sea proper
Eigentl. Ostsee, Jon. 196
Trelbangel 1329 St. Driftline
Gaboliaref Fork length
4ngermanOlven,12.6.- 2e 1959
Woe. (not) 715 St. Seine
raft'llenge Total 'length
Baltic Sea, proper
Eigentl, Ostsfte, April 1959
Treibnetz 575g!. Driftnet
Gabeiliinge Fork length
110 Cm Lange tength‘
Fig. 22. Series of measurements for salmon,
Baltic Sea and Swedish rivers
(the Swedish measurements were kindly put at
my disposal by B. Carlin).
- 80 -
[p. 2741

'
1741 salmon, which were.caught betWéen June 4 and August 31, 1961 in the
river Lule. A third series concerns the salmon that rose in June/aly in
the river Kalix. There are no age determinations available for these
catches. However, an estimate of the age' composition can be made when one
*compares the samples with catchesl‘rom_the Baltic Sea proper. '
Wé know from Swedish tagging experiments (B. Carlin 1959 a)
that the majority of the Swedish spawning fish of the Swedish rivers has
lived previously on the feeding grounds of the Baltic Sea proper. Driftnet
catChes from the Baltic Sea itself in April 1959.consisted of 70 per cent
salmon of the sea year class A.2; with lenehs.:of 64 to 82 cm (fork length)
and about 30 .per cent predominantly of the sea year class A.3. (Fig. 22).
•Thesé fish cannot have grown very much more until a possible immigration
into the Anegermaneven in July/AAgust. We can therefore aesume that the
length group in the séries of measurements from the Ingermanalven that
has a maximum at a length of 72 to 82 cm consists also of fish of the same -
sea year class, which has now to be designated as A.2+. These fish
amounted tcabout 66 per cent of the total catch, thatis,'4 per cent less3'
than in the catches from the Baltic . Sea proper. There is a similar/agreement
in the series of Measurements for the year 1962 in the agé class A.2 with
86 per cent (Baltic Sea) to 84 per cent (Kalix). In the year 1961 the con-
ditions are lesa unamliguous. The catches from the Baltic Sea in January
consisted to 77 per cent of salmon of the age class A.2. These fish had
grown extremely well in comparison with other years so that.the length dis-
tribution of the aàe classes A.2 and A.3 did overlap very widely. The coryroufs
responding catches of spawning âwarms in the river Lule showed the same
picture. Therefore it is not possible to separate the two age classes on
• the basis of léAgth distribution. In addition there appeared in the river
8 4f.

Laie a large number of'grilse, which are practically not being taken in
the Baltic Sea.
G. Alm investigated the age composition of spawning swarms in
the rivers Torne, Kalix, Lule, Pite, Ume,. and M8rum. The number of the
in each sample, it is true, was only 21 to 337. The age
classes A.2 and older comprised 94 per cent of the total catches. Of these
36 per cent belonged into the age class A.2.
Thé series of meaelrements,from the Swedish rivers in the years
.1959/62 indicate that the share of the age class A.2+ in the spawning
stock is at present considerably greater than the percentage of salmon that
have spent more than three years in the Baltic Sea. In supplementing these
data we qan employ investigations about the share of salmon with spawning
marks in catches from the Baltic Sea. These fish are those that had already
spawned and had then ±eturned into the Baltic Sea. The energy required for
the journey and the act of spawning is supplied by the body reserves. This
includes a degradation of substance at the scale'margin. This absorption
zone is called the spawning mark. 8Cale samples for age determination had
been taken of à total of 6914 salimmthat had been caught in the sea. Among
these were 166 fish•(2.4 Per cent) that had already sPawned. If we neglect
the grilse and consider only the spawning times of 1957 to 1961 in which
all spawning age classes were fully included, it is found that 63 per cent
of the salmon with spawning marks had spawned in the third year of their
sojourn in the sea and 37 per cent had spawned later (Table 37). In the
preceding it has been attempted to employ the series of measurements in
the rivers, the share of salmon with spawning marks, the conditions of'
the salmôn and the maturing process of the ovaries as indicators for the •
age at the time of spawning. Here we see at ance two different results:
fish analysed

•
- 83-
the series of measurements and the analysis of scales showed that the share
[p.276]
of the sea year class A.2+ in the number of spawning salmon was greater .
than the share . of all older fish. In contrast to this, the analyses of fat
and the examinations of the maturity give the impression that a amaller
percentage of the sea year class A.2+9 than the older fish does spawn.
This apparent difference becomes explicable when one reflects that both
results have a different relative basis. In the first case we start from
the spawning' stock in the rivers, in the second case we start from the
exploited stock in the Baltic Sea. Wé can establish a connection between
the two figures only through the total number of the spawning fish that
emigrate from the Baltic Sea. However, we do not know this figure.
Table 21. The percentage of spawning salmon in
the sea year classes A.2 and A.3 and older under
the assumPtion of different shares of the
migrating salmon in the total stock.
Stock in the. Baltic Sea, 1958-1963
Total A.2 A.3 and older
100.0 69.2 30.7
Spawning Spawning migrants Spawning migrants
migrants Number per cent Number per cent
Number . of A.2 of A.2
5,0 . 3,0 4,3 2,0 6,5
10,0 6,0 . 8,6 • 4,0 13,0
20,0 . 12,0 17,3 8,0 26,1
30,0 18,0 25,9 12,0 39,1
40,0 24,0 34,6 16,0 52,2'
1.1.1•■■•••••••■■•••••••■.r.+1•■•■•■■••■•••••■■■•■■■•■•■
The age determinations in Januaxyof the years 1958 to 1963 showed
on an average.69.3 per cent of salmon of the sea year class A.1+ (fish of
two winters) and 30.7 per cent older fish. In contrast to this the percentages
9 The sea year class that is designated as A.2+ at the time of spawning
(November) is identical with the class A.1+ that occurs in the sea.

- 84 -
of the corresponding sea year classes in the spawning swarms amounted to
about 60 and 40 per cent, respectively. If we now vary the number of the
salMon emigrating from the Baltic Sea and calculate with the aid of the
above figures their percentages in the sea year classes in the Baltic Sea,
we obtain the values listed in Table 21. It.is seen that, although the
number of spawning migrants of the sea year class Ai2 is always, higher than
that of the older Salmon, their Share in the sea year class A.2 of the
stock in the Baltic Sea is, however, smaller. In other words: the percenr.
tage of salmon of the sea year class A.2 that migrate is smaller than that
of the class A.3, numerically there are, however, more because the number
of the younger fish is always preponderant. After thia result there is no
* longer a dïfference .as far as the matter itself is concernedii although it
is not possible to carry out a quantitative comparison. *
One can therefore say that salmon that have a fat content of
at least . 12 per cent in the spring and a mean diameter of the oocytes of
more than 1.5 mm will probably spawn in the fall of the same year.
. 3.3. The fertility of the salmon
For the investigations of the fertility have been used in gen-
eral fish that were in the maturity stage V. With the discharging ovaries
been.
it is possible that some eggs have already/deposited. On the other hand,
it is sometimes difficult to distinguish between recruitment oocytes and
maturing oocytes during the earlier stages of maturation. Furthermore,.
V. D. Vladekov (1956) points out for Salvelinus fontinalis that more mat-
uring oocytes differentiate than there are mature eggs later. Because all
the oocytes when fully developed would not have enough room, some are
being resorbed.
B. Carlin (1951), A. Lindroth (1952) and Jokiel (1950 give
11). 277]

- 85 -
the relative amount of eggs in the salmon for practical use. The mean
values vary for different Swedish rivers from 1060 to 1400 eggs per kg
salmon, in the Vistula the valùes lie around 1400. The correlation coef-
ficient is 0.6624 for the Ulme-Xlv, 0.7512 for the river Ljusnan. B. Carlin
(1951) calculated a linear relation between number of eggs and weight of
salmon for fish weighing 2 to 14 kg.
With the aid of very careful statistical analyses, J. A. Pope,
D. H. Mill's, and W. M. Shearer (1961) have treated the fertility of the
Atlantic salmon.. The fish investigated were substantially smaller than the
Swedish salmon and had lengths of 47.5 to 95.0 cm, average 70 cm (about
3.14 kg). Pope et al. found that the changes in the number of eggs oan be
traced to 75 per cent of the different lengths of the fish and only to 7
per cent to the weight of the salmon. The changes in the condition of the
salmon during the upstream migration are reflected in considerable fluct-
uations'in weight. There.does not exist a linear relation between number
of :. eggs and weight of the salmon.
Acording to the authors cited, the relation between length and
number of eggii can be expressed best through the allometric growth formula
N = cL b , where N is the number of eggs, L the length, and c and b are con-
stants. According to . the investigations of Pope et al., b appears to be a
universal constant of the magnitude 2.3345. On the other hand, c character
izes probably the influence of the environment. Annual differences in the
values for one river were not significant, but there were significant dif-
ferences between individual rivers. The above formula can be used generally .
with an error of ± 10 Per cent. Since the fertility can vary significantly
between individual rivers,'we have to expect a priori a greater scattering
• [P. 278 1
of the individual values. for egg .counts of sample catches in the sea than

10000
5000
I_ •
N. 0,622 L 2' 3345
20 a ,60 6o ao 00 m uocyili.tin ge)'
Length
Fig. 23. Number of eggs as function of the
length in the Baltic Sea salmon.
- 86-
those of the rivers. In Fig. 23 are shown the numbers of maturing oocytes
in 40 salmon from the Baltic Sea in relation to the fork length. On the
basis of the allometric growth formula and the value b = 2.3345, the ecol-
ogical constant c was calculated as 0.662, a value that agrees well with
the results of Pope etaal. For lengths under 80 cm the values differ from
those - of the formula N = 0.662 L 2 ' 3345 that is used as basis. It has
15000
EizaN(N) Number of eggs
already been pointed out that perhaps not all the maturing oocytes develop
into mature eggs..It must therefore be assumed that the number of the mat-
uring oocytes agrees the bettèr with the final number of eggs; the higher
is the the state of maturity attained. As has been shown, one can expect
that most of the smaller (ïounger) individuals,attain maturity only a year
later than the larger (older) fish. In the fish over 80 cm long the recruit-
ment oocytes and the maturing oocytes are already very clearly differen-
tiated. It is therefore easy to understand thitt the values for the
smaller salmon do not correspond to the course of the curve that is demanded.

- 87 -
The calculation of a formula for the fertility cannot have any
special importance on account of the very large scatter of the values. It
. will be more useful to follow theppeetical usage and to state the number
of eggs per kg weight of the salmon. It is only possible to give an approx
imate figure for the present data, because no individual weights are available.
The numbers of eggs fluctuate between 700 and 1700 and are on an average
about 1200 per kg fresh weight.
4..•
The migration of
the Baltic Sea salmon
When one speaks about the migrationS of fish, one generally
•means that they Occur periodically at certain times at certain places.
This frequently concerns the formation of spawning assemblies. Tagging
has provided information about the extent and boundaries of the population
area as Well as about the general direction of the migration at certain •
. seasons. One can, however, not say what places the fish has been visiting
between release and recovery and one does not know anything about its non-
periodic changes of place.
In the Atlantic salmon likewise nothing is known *about the non»
periodic movements. After the fish have left the freshwater it is dif-
•ficult to follow their migration, eSpecially in regions of the open ocean,
where no special salmon fiehery in being carried out. One assumes that
the salmorrof northwestern Europe have their feeding grounds to the north
and west of the British Isles and between Iceland and Greenland (K. A. .
'Winch 1955). On the other hand, Huntsman (1948, after K. A.Pjeinch 1955)
says that the salmon do not leave the area of influence of their rivers.
• He considers longer wanderings to be only exceptions.

- 88-
Through the extensiveSvedish tagging activities we are better
informed about the movements of the salmon of the Baltic Sea, which form
their own stock and which are in general confined to the largely selfcon..
tained Baltic Sea. However, here also elnr knowledge has been augmented,
especially of the periodic migrations. EVen tagging is of little help in
the investigation of local movements. .
For a third kind, the extended journeys, we have only few, but
interesting data. In this connection the region of Sukkertoppen (western
Greenland) plays a special role. There five salmon have been caught that
had made long journeys. They had been tagged and released in Scotland,
Canada, and England (J. Nielsen 1961) and in western Sweden (B. Carlin
[P. 279] .
1962b). The longest jOurney had been made by a Swedish salmon from a trib-•
utary of the river Xtran, which travelled over goo° km. J. Nielsen (1961)
could demonstrate that a large part of the salmon of the Sukkertoppen dis-
trict are . not Greenlandic salmon, but must have immigrated from other aream.
Irish taggings (A. E. J. Went 1956, E. Twomey and A. 0 1 Riordan
1963) showed that the salmon remain mostly in the region of the island.
However, some fish travel as as far as the Scandinavian coast. One recap-
ture has been reported at a distance of 1750 km near Xngelholm (southern
Sweden). Corresponding results were obtained by B. Carlin (1955) with
tagging in the river Lagan (southern Sweden). Most of the fish were .caught
off the coast of southern Sweden and off the coast of southern Norway.
Three recapeires could be reported from the British Isles and two from.
northern Norway.
The salmon of the Baltic Sea are not known to leave their home
area. Only very few young salmon do wander during their first year in the
• sea as fax as the Belt. For the remainder the western boundary of their

- 89 -
area of distribution is formed by a line between Regen and Schonen accor-
ding to Swedish,Finnish,.Polish and German taggings.
4.1. The divisions of the periodic migration
• The periodic migration is determined by the life cycle of the
salmon. It takes place in three divisions, the emigration from the river,
that is connected with the transformation into the smolt stage, the search
for food in the Baltic Sea and the return to the home stream during the
spawning migration.
4.1.1. The migration of the smolt
K. A. Pyefinch (1955) calls the transformation into the smolt
stage a series of morphological and physiological changes. The most striking
external phenomenon is the change. from the "trout type" (parr) into the
"silvery fish" through deposition of guanin. The physiological process of .
the transformation into the smolt stage is not yet completeliunderstood,
although werk on the ion budget and the components of haemoglobin (H. Koch
1963), the activity of the glands (Hoar 1953, Fontaine : 1954, after7 Pyefimàh
1955) and the action of hormones (D. H. Piggins 1962) have provided partial
knowledge.
With reservations one can at present consider the process of
the transformation into the smolt stage to take place about as follows.
(various authors, according to W. S. HOar 1957).
When the parr have attained a certain size, internal changes
take place that trigger the process. There is agreement that during this
period the thyroid plays a role by causing the deposition of guanin and
'influencing processes of morphogenetic growth. D. J. Piggins (1962) suc-
ceeded in increasing the number of, young salmon capable of emigrating
(smolts) by feeding bovine thYroids. However, W. S. Hoar (1957) attributes
r

- 90 -
the initial effect to'the hypophysis, which controls not only the growth
but also the function of the thyroid. In this connection the hormone som-
atotropin appears to be of great importance,Secause it regulates growth
and in low concentrations raises the tolerance for salt. There is therefore
the possibility that the changes in the hypophysis-thyroid system result
in a mineral imbalance that can be compensated only in an environment with
a higher salt content. This means then that the smolt has not to tolerate
the higher salinity as a disturbance of its physiological state, but that
it needs it in order to remove an existing disturbance.
When the transformation into the smolt stage has.taken place,
the beginning of the emigration must be stimulated through various environ,
Mental factors. H. C. White (1939) does not consider rain or high water
levels to be decisive, but temperature increase and the amount of light
intensity. G. Alm (1934) also considers the temperature to be important.
'After they have reached the region of the river mouth, perhaps
in May/June, the smolt from the rivers of the Gulf of Bothnia remain in
a transitional area for a short while (days or weeks). A more rapid growth
begins already at this time. The fish probably eat.insects that live on
the surface of the .water (A. Lindroth 1961b). Their movements are still
non-directiOnal and do not extend fax. During the course of . summer and
fall they colonize the Gulf of Bothnia during the transition into the post-
smolt stage.
4.1.2. The feeding migrations
In Table 22 have been assembled and recalculated some results
of tagging experiments from the Indalsglv and the Lulegiv (B. Carlin 1959a,
1963) and from the Oulujoki (E. Halme 1961). The number of reports of re-
boveries has been given for the different periods and the three regions
[P. 280]

- 91 -
as percentages of thé recovery reports from all three regions (Gulf of
Bothnia, Gotland, southern Baltic Sea). In this manner it will be possible
to recognize the migrations of the. salmon.
The Indalsâlv is a Swedish river in the central region of the
Gulf of Bothnia; Luleâlv (Sweden) and Oulujoki (Finland) run into the nor-
thern part of the Gulf of Bothnia. About 50 per cent of the salmon from
the Indalelv were caught during the first year after release in the Gulf
of Bothnia, for the Oulujoki this figure was more than 90 per cent. The
differences between the two regions, are still apparent in the second and
third year after release, when a larger part of the tagged fish has mig-
rated into the other two regions. There are no fundamental seasonal dif-
ferences between the areas. The most numerous recaptures are made in the
Gulf of Bothnia during July/August on account of the spawning migrations.
During the cold season, when the Gulf of Bothnia is covered with ice,
most of the recapture reports côme from the Baltic Sea proper.
The results in Table 22 make clear the following: the salmon
of the northern zone (Gulf of Bothnia) remain for more than a year in the
Gulf of Bothnia, before a part of them move into the Baltic Sea proper.
In this they are being joined by the salmon of the Gulf of Bothnia that
are a yeax younger. The majority of these fish remain in the northern waters
only until the late summer'of the first yeax. The occupation of the Gulf
of Bothnia and of the Baltic Sea proper appears to be connected in part
with the current conditions. The Swedish as well as the Finnish salMon
move with the cuxrent along the Swedish coast of the Gulf of Bothnia to
the south. To the north of the Illandsea the water masses are being deflected
by the influence of the topography partly to the east and finally to the
north and then flow along the Finnish coast. A number of salmon that

changes annually appears to follow this current, whereas others reach the
Baltic Sea proper by way of the Ilandsea. The further course of the migration
can no longer be followed on hand of currents. Whereas the salmon frOm the
rivers Lule and Oulujoki'remain predominantly around Gotland, a very large
part of the fish from the Indalsâlv move into the soUthern Baltic Sea.
Beginning with the second year, spawning migrants can always be found during
July/August in front of the home rivers.
Nothing has been known hitherto about the sojourn in the Baltic
Sea. It appeared possible that the fish, after leaving the Gulf of Bothnia,
searched out immediately the final feeding grounds and remained there, or
that they move continuously during feeding and that they have no definite
feeding grounds. In the end an annual round through the eastern Baltic Sea
until the spawning migration had been assumed. Table 22 gives a weak hint
as regards these questions. If the salmon of the Indalsev remain during
Lp. 282]
their sojourn in the Baltic Sea proper on an average farther to the south
than the fish from.the Gulf of Bothnia, then not all can make a circuit
through the eastern Baltic Sea . or wander annually around Gotland. In other
words, a map that shows the recovered salmon within a limited period in a
definite distribution in the entire Baltic Seà proper, does not indicate
that every one of these salmon must have visited during its sojourn the
various regions of the area occupied by the population. Even if a rather
far flung migration is carried out; it is not to be assumed that those
salmon who lived in the extreme south had been previously frequently in
the far north or had moved there. This does not exclude, of course, that
individual fish do not make lengthy wanderings.
.
A feW results of my own tagging experiments support this assump-
'tion (Fig.'24 a'to c). In November 1960 15 salmon Were tagged near Bornholm,

Table 22. The recapture of tagged salmon in three differént.regions (north of 59 °N, 56 ° to
59 ° N, south of 56 ° N) as percentage of the total catch in all regions.-
(Recalculated after B. Carlin 1959 a, 1963; E. Reline 1961)1.
Home river
. Indalsâlv Luleglv .
Oulojoki
Age group Months - - 1954 1959 1959 1959 •
59 ° 56-59 (,) 59 ° 59 ° 5 6-59 ° 56° - 59 ° 56-59 0 56° 59 0 56+59° 56 0
V-VI 100 100
. VII-VIII 100 0 86 14
A.0 IX-XII 25 SO 25 81 5 14
I-III 75 25 40 40 20 100 66 34
IV-VI 11 22 67 - 29 43 , 28 100. 100
A.1-A.3
VII-VIII 80 11 5 88 12 95 5
IX-XII 12 40 48 26 46 28 56 33 , 11
I-III 11 89 7 35 58 31 35 " 34
IV-VI 5 22 73 33 47 20 55 27 18
A.0 Total i 48 27 25 92 3 5
A.1 Total 14 20 66 26 • 46 28 58 28 14 47 35 18
A.2/A.3. Total 17 32 51 - 32 30 38 61 26 13
1 The percentage values of the sea year class A.0 are based on recaptures of 3 to 34, on
an average of 12 salmon. The older classes are based on about 50 salmon.

•
- 94 -
of these six = 40 "Per cent have been reported hitherto. Pive of the fish
had at the time of recapture not moved from the fishing ground 5 after a
maximum of 12.months, one fish had migrated into the Lulettiv to spawn
(Fig. 24 a).
In the Danzig Deep 33 salmon have been liberated in November/
December 1959 and in December 19 6 2. Of the fish recaptured at sea some
.had not moved farther during 11 months than others in one month after re-
lease. (Three fish of one experiment of February 1964 in the same area
were recoverèd like the others in the Danzig Deep or off the Pomeranian
coast, respectively.) Two other fish had migrated into the rivers Lule
and Torne& after 7 and 19 months, respectively, in order to spawn.
In a third experiment in November 1960, 52 salmon were tagged
near Memel. Six of these fish have been recovered at sea. Of these four
had moved into the Danzig Deep and two to Bornholm. A further six salmon
were captured 7 to 8 months later during spawning migration in the rivers.
Three of these were caught in the Gulf of Bothnia(lingermanalv and Indals-
alv, respe-ctively) and three in the Bottenwik (Torne. and Kalix, respec-
tively).
Besides the spawning fish, no other fish have been recovered
fn the three experiments that had moved north and crossed the 56th par-
allel or had even reached Gotland. In the first experiment the fish had
moved a maximum distance of 40 nautical miles from the place of release
and had remained around Bornholm. The fish in the second experiment did
not move farther to the south or to the west than 80 nautical miles and
remained in the Danzig Deep or off the Pomeranian coast. Even in the third
experiment there was only a maximum movement of 140 nautical miles after
13 months. It cOuld not be established that the fish caught last had traV-
eled the greatest distances.

•
II>
Three conclusions can be drawn from these results:
(1) The recaPtured salmon of the first two experimental series have carried
out astonishingly short movements and have remained very close to the
pdint of capture and release.
(2) A large part of the recovered fish of the third experiment were cap-
tured in the rivers.
(3) The other fish of the third experiment had travelled the greatest dis-
tances (a maximum of 140 nautical miles) and visited the Danzig Deep
as well as Bornholm.
These results support the conjecture that the salmon do not make
far flung travels or annual periodic movements once they have reached the
Baltic Sea proper. One has rather to assume non-periodic local movements
after the fish have reached a feeding ground. This will be investigated later.
4.1.3.
[P. 286]
In the third experiment mentioned above the high percentage of
spawning migrants is striking. At the time of tagging these fish were res-
iding in the Baltic Sea in their second year (A.11-) and they did spawn in
the course of their third year. Since of the total catch only the smaller
fish (under 75 cm fork length) have been tagged, it is possible that of
the remaining fish still more than one-half did migrate to spawn. Con-
sequently one could explain the results of this tagging as follows:
A few salmon in the southern Baltic Sea, of which the majority
did spawn a year later, had moved in November 1960 already to the west of
Memel. When the maturing fish wandered in the spring of 1961 towards their
home rivers, the juvenile fish returned in part to the Danzig Deep and in
part to Bornholm. In any case it must be stated that the sPawning migrants
associated in the fall before their spawning migration still with juvenile
- 95
-

•
66
65
64
63
62
61
60
59
58
57
56
55
54
Recapture of tagged salmon. Released
near Bornholm, Nov. 1960.
- 96 -
[p. 283]

•
6
65-
64 -
62-.
61 -
6
. 5
.
591-
576
5
55
$4
•
1 1 I_ _I_ 1 _I
10 15 20
Fig. 24 12. Recapture of tagged adult salmon.
the Danzig Deep, Nov./Jan. 1959, Dec. 19 6 2,
/'
f
1 .
25
Released in
Feb. 1964.

•
66
65
64
63
62
61
60
58
57
56
55
54
10 15 20 - 25
Fig. 24 c. Recapture of tagged mature salmon. Released
near 14emel, Nov. 1960.
- 98 -
[P. 285]

•
- 99 -
fish. The tagging does not give any information about the course of the
later movements until the fish ente r . the home stream. We do know, however,
through the analyses of the stock, that the age composition changes each
year beginning in April/May on account of the emigration of the spawning
fish. This is also clearly indicated by the reduction in the average weight
(Table17). The change caused by the emigration of the larger fish extends
into June.,(There are n4 data for July on account of the cessation of the
fishing.) It is, however, not known that the share of the large fish does
increase at this time On the fishing grounds 4 or 5, which have to be
crossed by the maturing fish.
Table 23. Number of salmon of more than 5 kg weight
on various - fishing grounds as percentage of
the total catch.
Bornholm
Month 58 .5.2 (60) 61 Mean 58 .52 60 61 Mean
59 60 (61) 62 59 60 61 62 •
Nov./Dez. 60 55 (27) 29 48,0 37 31 38 19 31,3
Jan./Febr. • 55 31 (44) 26 37,3 41 36 24 13 28,5
MârziApril 39 15 10 21,3 36 21 40 31 32,0
On the Pther hand, Table 23 indicates that the share of the fish
over 5 kg in weight in the catch near Bornholm diminishes during the course
of the season. This phenomenon could perhaps be explained by the beginning
of the emigration of maturing salmon.
Danzig Deep
Many papers have been published about the "homing" of the sal-
mon about to spawn. Especially important are the results of A. D. Hasler
(1954, 1960), who could demonstrate a "sun-compass mechanism" and, among
other things, a long-persisting olfactory memory in Pacific salmon. J. B.
Brett and C. - Groot (1963) speak of the innate ability in sockeyesalmon
(Oncorhvnchus nerka) to be able to keep s8..u. sun-compass diredeon and they

River Ap. May Jne. Jly. Aug.
Tornea 25 ' 74
• Lima 4f 55
Dal 23 64 12
tvliirrum 6 35 35 23
- 100-
attribute to it.a rythmic sense that is attuned to diurnal periods. Accor-
dingly one reckons today with the ability of the maturing salmon to orient
themselves at sea with the aid of their "biological clock" and the sun until
they perceive the emell of the home waters. After this they find their waY
by their chemical sense organs. These abilities enable every individual
salmon to attain the goal of its travels quite independently of its com-
panions. This leads to a behaviour that is different from that known in
gregarious fish (e.g., sardines). In the clupeids the reaction of the in-
dividual is governed largely by the behaviour of the school. From this point
[13 . 287]
of view it is perhaps not appropriate to talk about a "spawning school" of
salmon. It is certain that the common time of migration and the same goal
brings the fish together gradually; the movements of the individual fish,
however, are determined through the individual orientation. This behaviour
Table 24. Monthly yields of may be a cause of the fact that no large
salmon in Swedish rivers as
percentage of the annual catches are made during the migration of
catches.
the salmon into the rivers.
The monthly yields of salmon in
the Swedish rivers have been assembled in
Table 24. From this it can be seen that
the rise of the salmon into the rivers of
the Bottensee takes place during May to July and in those of the Bottenwik
from June to July. When the salmon of the southern Baltic Sea begin to
migrate between April and June, then they have not much time left to reach
their home river. Oné can therefore assume that the spawning migration is
being carried out rather fast. Travelling speeds of 100 km/day have been
, observed in salmon ready to spawn (Suvoràv 1959) . Nothing definite is known
about the routes of travel of the maturing salmon. E. Halme deduces from

- 101 -
tagging experiments'that salmon from the Oulujoki return along the Finnish
coast of the Gulf of Bothnia.
4.2. Local movements
In general we must assume that the hourly and daily movements
of the salmon in the Baltic Sea are determined by the search for food. There
can be no doubt that these local movements are of the utmost interest for
the practical fishery, because they are the cause of the short-period
fluctions in the yield. The ascertaining of such local movements and of
their immediate causes requires, however, an extensive material that can
be obtained only with difficulty. If we want to learn more about the causes
of these local movements, we have to have recourse to the results of the
critical examination of the captures per unit effort. We could start from
the fact that the catches can be influenced on the one hand by the specific
effects of the fishing gear and on the other hand by environmental factors.
The latter have the effect to induce the salmon to stay at certain places
or to travel. We found such factors to be:
(1) temperature,
(2) wind conditions,
(3) competition for food,
(4) occurrence of cod.
We can neglect the temperature conditions because they lead to
seasonal vertical movements of the salmon. The catches with nets are af-
fected only by the wind conditions, the line catches, on the other hand,
are affected by all other factors. If we now enquire which of them can
cause local movements of the salmon, we are left with only the food and
perhaps also the wind conditions and currents.
It has already been pointed out that a pelagic gregarious fish,
•

IS° 16°
- 102 -
the sprat L is, besides other animals, the most important food of the
salmon. These clupeid, in turn, feed , on plankton. The starting link in
1.1).288]
this chain is represented by the primary producers, the phytoplankton,.the
production of which is governed by the nutrients. The nutrients as well
as the plankton and to a large extent also the sprat are dependent in their
occurrence on water currents (which are mainly wind-driven in the Baltic
Sea proper) and of their discontinuities (divergencies, etc.). It is also
clear to assume an influence of the wind on the offer of food. Even if we
cannot define exactly a connection between wind conditions and the occur-
rance of salmon, an indirect relation may be assumed (see 2.3.3.2.). In
this connection an example may be offered that can also give other infor-
mation.
Fig. 25. Fishing positions of salmon cutters south
of Dueodde, Febr. 22 to March 4, 1962.
From February 22, 19 6 2 on, a fleet of six to ten vessels was
.fishing with driftlines on a fishing ground south of Dueodde near the

- 103-
Renne Bank in about 60 m depth of water (Fig. 25). During the first three
days stormy northeast winds prevailed, followed by east winds that sub-
sided after February 27. Between March 1 and 4 light winds from various
directions prevailed.
During the period of the northeast storms and the east storms
it was possible to fish only with lihes. The captures per unit effeort
were more than 20 salmon per 1000 hooks and thus rather favourable, but
they dropped with the diminishing winds to fewer than ten salmon per 1000
hooks. The favourable winds allowed to employ driftnets beginning on March
1, 1962. The Catches amounted to 130, 40, 5, and 2 salmon per 100 nets
between March 1 and 4 and. yielded on March 1 a total of almost 1500 fish
(Table 25).
It cannot be established with certainty whether the large num-
bers of salMon were present on the fishing grounds prior to March 1, when
lines were still used for fishing. It must, however, be assumed that in
that case the catches with lines would have been much greater. It is thus
very probable that the fishing on March 1 encountered a very numerous
acktkes
group of salmon that happened to pass through at that time. The -e-etp-tttre-e
[P. 2891
per unit effort show that on the second day only stragglers were still
being caught. On March 1, the catch amounted to 30 salmon per 1 km 2 of
fished area, on March 4 it was only 0.45 salmon.
Let us attempt to draw a conclusion from the known facts in
regard to the behaviour of the salmon.
The fishermen had taken up their driftlines on the afternoon
of February 28. These had been set out around 0400 h in the morning and
had yielded on an average 6.9 salmon per 1000 hooks. In the afternoon the
wind had dropped so much that already at sundown of the saine day it became

•
•
- 104 -
possible to begin with putting out nets. After about 12 hours the gear
was on board again the next morning.and had caught on an average 130 salmon
per 100 nets. About a further 12 hours later the driftnets were in the water
again and yielded until the next morning 40 salmon per 100 nets. The first
travelling salmon were swimming in large numbers across the fished area
at the earliest on the evening of February 28 and at the latest around
midnight. The swarm may also have persisted during the day on March 1. The
number of fish, however, did decline, because on the next morning only 40
salmon were caught per 100 nets. On March 2 the swarm had definetely passed,
because the catch during the following night yielded only 5 salmon per 100
nets. In its longitudinal grouping the swarm had such a shape that the
salmon were concentrated most densiely at its front in the direction of
travel.
Let us also attempt to learn something about its lateral com-
position. The catch of 130 salmon per 100 nets or of almost 1500 fish per
1 km 2 of fished area constitutes a rare event in salmon fishery. It leads, •
however, easily to the unwarranted conception that the salmon had travelled
in a very dense swarm. The best catches, however, brought only 1.7 to 2.0
salmon per net, the emallest 0.2 to 0.4 fish. This means that the fish were
caught by the nets in such a manner that they were at a least distance of
on an average 12 to 14 m and at a greatest distance of 60 to 120 m from
one another. We cannot assume that the fish had been swimming in a line
[P. 29 0 ]
and so got caught simultaneously. That means that the salmon were swimming
in the water at inter -ials of more thenan average of 12 m. On the other
hand.one cannot reckon that all fish were caught that encountered a fleet
of nets. Thus there were more fish present than were caught and they must
have been travelling closer together.

•
9:1
0
a)
el-4
o
(XI
-P
CNI
4-
o
4-,
\
crs
0
P
■,
0
CD
o
CH
•ri
(/)
•H
ro
Ei
o
Si
N
sO
en • rci
*.g
,1
Fi
tn
0
Cr3 -1?
N. •• cr," s.o
9
.ul E u,
1-4 •4-

•
- 1 06-
catches of Pacific Salmon, considers an aggregation of four to six fish
as a great school, whereas he calls . the appearance of two fish together
a normal size of a school. Such relations are quite applicable for the
Baltic Sea salmon. It happens frequently that several salmon are caught
in one or two nets and that only after a distance of 500 or 1000 ,m there
will be again some salmon in a net. Good orexceptional catches are ex-
perienced Only when a number of these small groups come together.
In the present case it is not possible to state with certainty
the causes for the concentration of the fish. There were no observations
by echo sounder of the occurrence of food fishes. Let us therefore ex-
amine the wind and current conditions on the fishing grounds (Fig. 25,
Table 25). The northeast and east windstorm that prevailed since February
22 undoubtedly caused a damming of the water against the east coast of
Bornholm, which resulted in a current directea to the southwest. Under
the influence of the topographical conditions it is possible that the
water became dammed again in front of the Renne Bank and the Adlergrund
until the dropping of the wind made it possible for the water to flow
to the south and east. During the first phase several smaller groups of
salmon may have been conveyed to the coast of Bornholm by the wind drift
where they were thrown together by the damming and from where they then
drifted with the current towards the south. In the case depicted we thus
had a. relatively large and.fast-moving group of salmon that had been formed
perhaps under the influence of the wind conditions and of the topographical
relations. Under these Circumstances it cannot be excluded that there were
also schools of clupeid present that behave much more passively in relation
to currents than the. salmon.
In other cases the wind can hardly have played a role, as is

14,3
14,3
30,7
31,3
27,7
6,0
15,0
104,3
47,5
50,0
4,3
2,4
j9,1
34,9
96,5
156,0
32,1
10,7
43,7
10,5
- 107-
shown in Table 26. The results of line fishinir near Memel during January
and the beginning of February in weather with light to strong winds had
been fair. When it fell almost calm, the net catches between February 7
and 9 became very good and after a short-lived recession they became even
excellent. Four days later the fleet had moved 30 to 40 nautical miles
farther south into the Danzig Deep. There excellent line catches were made
for a few days with rapidly increasimg westerly wind storms. Unfortunately,
there are-no exact records of positions and echo soundings. It is, however,
certain that in regard to the net catches neither the preceding light winds,
nor the light winds prevailing during the fishing with nets had any con-
[p. 291]
nection with the excellent results. It is therefore probable that the presence
Of food fish played a role here.
Table 26. Salmon fishery in FebrUary 1959 near Memel
and Briisterort.
Febr. Number
of Wind
1959 Cutters
1.
2.
6 N W. 2-.6
West of Memel
80-75m water depth
Salmon Salmon
1000 hooks 100 nets
7,3
43 . j
5.
6:
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
p20.
21. .
22.
23.
24.
25.
5
4
2
2
2
2
2
3
3
3
2
I
1
4
4
1
3
5
4
5 .
W3 6,6
Stale = C8,1111 4,3
um1 ' =
S
variable
1
Si
Si
SO 1
SO 1
SOI
S2
SW 4 .
NNW 4
SW 6
W5
W6
W8
NW 8
NW 6
NW 3
W7
W4
West of
Brasterort
100m w.d.
Salmon
1000 hooks

•
- 108-
This cause certainly must have affected the catches on the
Mittelbank in April 1963. There the best catches were made in depths of
20 to 30 m. The salmon could even take up hottom-dwelling food animals.
According to the statements by the fishermen they had eaten besides stickle-
backs also sprat and small crustaceans (Table 27).
Table 27. Salmon fishery in April As a final example will be
1963 on the southern Mittelbank. discussed the catches in the Danzig
Apr. Number Aver. Salmon Bay of February/March 1964 (Table 28).
of Wind depth per
1963 cutters m 100mets- In contrast to the previous examples
18.
19.
20.
21.
22.
1
7
8
6
4
umlf. 19
unilf. 28
NO 2 .„„,_28
25
turtIClableo
23,2
26,2
13,7
8,0
3,9
no exceptionally large catches were
made there,.It was, however, possible
to ascertain all attendant circum-
. stances. During the entire period there
were no fundamental changes in the wind conditions. The water was flowing
continuously towards the south-southwest, as was shtwn by the anchored .
cutters. Until February 28 the average yields were rather uniform at about
3.3 to 4.5 salmon per 100 nets. Afterwards the catches increased and yielded
on an average between 13.9 and 17.5 salmon per 100 nets from March 2 to 4,
• [p. 293]
only to diminish again later. The fish had eaten mostly benthic.amphipods
and sticklebacks. Because the fish become often badly tangled in the net
it is difficult to determine from which side each salmon has approached
the net. In this case there appeared to have been no preference for one
side of the net, so that no direction of movement could be inferred.
, The available data give a picture that is entirely different
from the.previous examples. The yields do not jump up suddenly, but in-
crease slowly. Good.catches are made not only on a single day, but per-.
sist for some time. With uniform current conditions and hardly changing

Table 26. Catches of salmon in the Danzig Bay, NNW of Kàhlberg, 45 to 82 m water depth,
current WSW.
February 19 64
March 19 64
24 25 26 27 28 29 1 2 3 4 5 Total
Number of vessels 11 10 13 12 10 13 12 12 12 14 14
Wind S03 S03 S03 SOS S4 SO 2 0 2 01 W3 W3 N4
Salmon/100 nets 3,8 4,5 3,3 3,5 3,9 7,9 9,3 15,8 13,9 17,5 8,5
Tot. no. of salmon 136 151 138 134 145 338 390 689 604 682 435 3841
Tot. no. of salmon 704 338 279-i 3841
Date
Date
Table 29. Food of salmon, March 1964,'Danzig Bay.
Number of salmon Food per salmon
examined with food MYsids Sticklebacks Clupeids Fish Ammodytes Reeds
Number Number Number Number
I. 3. 21 4 1,0 0,3 0,3
2. 3. 75 16 0,5 1,0 0,4 0,1
3.3. 54 9 4,5 0,7
4. 3. 38 16 • 3,0 0,6
5. 3. 26 6 • 1,0 1,5 0,2 0,2
o
%JD

winds, the data
fishing grounds
a while, eating
the upper water
• •
•
O
29,I Lochs' goo Nitre
18.3 LicAsellOONetze
•
S4MOn/100'netS
•
O 16,0 LachsellOONetze .•••
o
1..7 LachselICION•frp' ..'
....• • "• •
• e
- 110-
give the impression as if the salmon had arrived on the
rather hegUeingly and gropingly. They remained there for
during the - day benthic food in the depths and coming into
layers at night. After a few days they moved on slowly.
Fig. 26. Distribution of salmon in the Danzig Bay,
March 2 to 4, 19 6 4.
Let us examine the yields of March 2 to 4, which were the higheet,
in more detail. InsFig. - 26 has been drawn a map of the distribution of the
salmon based on the positions of the participating cutters and their cap-'
tures per unit effort. According to this the greatest concentration of the
fish occurred in the southeastern part of the fished area (25.4 to 34.4
salmon per 190 nets). In the northern, eastern and southwestern parts the
catches were not substantially higher than during the previous days (3.3
to 8.9). From the centre of the distribution extends an area towards the
north,-northwest with strongly scattered captures per unit effort, which,
.however, were all higher than on the days before (8.9 to-27.2). From the •
distribution in Fig. 26 can be deduced that. the area of strong scatter

- 111 -
between Hela and Kahlberg represents either the route of inward movement
or the route of outward movement of the salmon. Let us examine in this
[p. 294]
connection the positions of the.greatest concentrations of salmon be:4een
March 1 and 5 (Fig.'27). The best results with an average of 14 salmon
Fig. 27. Positions in the Danzig Bay where were made
the best captures per unit effort between March
1 and 5, 1064, with number of salmon per 100 nets.
were obtained at the eastern edge of the fished area. The positions of the
best catches remafned in about the same region during the next three days .
(Fig. 26), whereas the centre of the greateet concentration of salmon had
shifted farther to the west on March 5. These results suggest with great
probability that the salmon were mOving from the northeast very slowly
with the current into the Danzig Bay. During the day they prébably were. .
feeding in deep layers of water on mysids and at night on the pelagic stick+
lebacks. The salmon then .left the Bay gradually in the direction of Hela.
Within four times twenty-four hours the group moved on an average Imam
. than four nautiéal miles (seven km). Direction and velocity of this movement

•
- 112 -
must be considered to be the resultant composed of the daily periodical
vertical movement and the horizontal feeding movement.
In this connection it can be mentioned that among others 23
tagged salmon (58 to 77 cm total length) were liberated on March 2. One
fish, liberated at about 1400 h, was discovered two hours later in another
net about 2 km distant, after it had swum in an easterly direction and
passed a further fleet of nets.
The findings about the local movements can be summarized as
follows: the hoUrly and daily local changes during the period of feeding
movements are determined by the search for food organisms and the pursuit
of the prey. In addition they are probably connected with wind and current
conditions. Such movements are indicated by sudden increases in yield that
[p. 295 ]
usually last only one or two days. On the other hand there is a gradual
transition to the better catches that per:tee longer, these are caused by
pure feeding wanderings.
The salmon form generally.small groups of 2 to 10 individuals
that may be encountered everywhere in the Baltic Sea proper. From time
to time larger associations occur that are composed of several gmaller
groups and that weie formed under the influence of food supply andwind-con-
ditions. The single individuals are separated on an average by more than.
10 m even in the greatest concentrations. The distances resulting from the
local movements are never very large and probably do not exceed 10 km per
day.
In general it has been established that the salmon, in the same
manner as the sprat approaches the coastal waters in the fall and spring.
Apart from a probably daily vertical movement no periodicity of the local
. movements could'be found.

•
- 113-
5 .. Age and growth of the salmon in
the main basin of the Baltic' Sea
For the determination of the individual growth of fish it is
necessary to obtain the increase in length or in weight during a known
period of time. That is possible in general only with the aid of tagging
certain individuals. When it is . desired to ascertain the increase for a
group of fish, then determinations of length, weight, and age are re-
quired. On account of this close connection, age.and growth will be treated
together in this chapter.
5.1. On the terminology of age and growth analysesl °
The numerous developmental stages of the salmon have had of old .
definite names, especially in the English language. A small fish, freshly
hatched from the egg is called "alevin" (yolk-sack brood)'. After the Yolk
sack has been absorbed and after theflah begins.to feed, it.is.called
"fry" (brood able to feed). During the following period of life, salmon
have the outward appearance of trout and are designated parr until the
transformation into smolt. Since the parr stage extends over several years,
the additional terma "fingerling", "summerling", or one-yeax x-year parr:
were introduced, according to the size and aee of the fish.
In the post-smolt stage (for development of smolt. see 4.1.1.)
the young salmon in the first year'in the sea ("speitzgen") are called
"mielnica". Grilse (Jacob!s salmon) are those fish that spawn already
after only two summers in the sea. Mentioned must be further the names
"kelt" (a salmon thai has spawned, but preserved its nuptial colours)
10 The essential deSignations have been taken from the paper by T. H.
Aria and . W.-J. M. Menzies "The interpretat ion of the zones on scales
of salMon...." (Rapp.Yroc., Vol. XCVII, 1936).
,
) •
"

• and
- 114-
"mended kelt" (aealmon that has spawned, has a silvery colour, but
is still in very poor condition, in German "lager").
The transition from the life in the rivers to that in the sea,
constitutes for the salmon a change that is penetrative in every respect.
It has therefore been agreed to designate the age of the salmon by two
symbols, A.B, which are separated by a full stop. "A" denotes the number
of years spent in the river and "B" stands for the number of years spent
in the sea. When at the time of sampling the year of life has not yet been
completed, the full number of years is given with the symbol "+" added.
If the fish has already spawned, the event will be indicated by inserting
a "G" into the formula, whereby G counts for one year. A salmon with the
age formula 3.2G1+ has spent three years in the river and two in the séa Lia. 29 6 ]
before it migrated to spawn. After the return from the river it spent more
than one year in the sea; it is thus over seven years old altogether.
April 1 /B .-the key-day from which are counted the full years of life.
Since we are treating priWcipally the life of the salmon in the sea, often only
the number of years spent in the sea will be given. When we say that a fish
belongs into the sea year class A.2, this means that this fish has spent
already two years in the Baltic Sea since it emigrated from the river. We
talk of age groups, when the ruiraber of years spent in both fresh water and
in the sea has been given.
5.1.1. The relation between total length and fork length
ICEs
During a session of (the International Council for Oceanography
in 1933 it had been recommended to carry out the measuring of the length
in salMon in such a manner as to give the fork length, that is,'the dis-
tance between . the point of the snout and the central (usually shmefflt) ray
of the tail fin. In contrast to this, fishermen and market employees use
•

cm
100
80
60
40
- 1 15-
customarily the total length from the point of the snout to the end of
the dorsal (mostly longest) ray of the tail fin.
In order to be able to compare the two statements, we have
taken both length measurements in 250 salmon and calculated the obvious-
ly linear relation (Fig. 28). The measurement of the total length and of
the fork length has been carried out in such a manner that they were based
in every case on centimetres rounded off downwards. The fish of the group
20
50 ' m 90 lIC Lcm •
Fig. 28. Relation between fork length (11.) end
length (Lt ).
•
[1). 2971
72 cm are thus on an average 72.5 cm long. This correction has been ap-
plied in all oases before an evaluation was carried out. The statements
given here.are all corrected values.
total length Lt
The following relation exists between fork length Lf and the
Lf m -1.2256 0.9578 Lt
t 1.2796 + 1.0441 Lf.
L
•

- 116-
This result is based essentially on the measurements of salmon
of length 60 to 110 cm, although also onfish of a total length of between
40 and 60 cm. The equation contains an additive term. It is therefore not
valid for the early stages. The measuring of such small fish" shows that
the alevin with a mean length of 20,3 mm have not yet a forked tail fin,
when they are freshly hatched. Slightly older alevins-showéd the forking
of the tail fin already plainly with 26.62 fork length and 26.95 total
length. In fry (brood without a yolk sack) the two measurements were found
to be 28.08 and 29.05 mm, respectively. The difference between the two
lengths is 1.2 per cent in alevin, 3.3 per cent in fry, 6.5 per cent in
salmon of a length of 61 cm, and 5.4 per cent at a length of 100 cm, all
Calculated as percentage of the total length. The percentage of the dif-
ference thus reaches a maximum value and then diminishes linearly. On the
basis of the knowledge of the developmental history wf,, can assume that the
maximum value is attained in the smolt stage. This means that the equation
given above is probably valid for the entire period of life in the'sea.
5.1.2. The gutted weight
Since the Danish and German salmon fishermen extend their fishing
cruises to a maximum of 13 fishing days it is necessary to gut and clean
the salmdn on board. Very many Swedish fishermen, as well as the Russian
and Polish fishermen land their daily catches frequently whole (fresh weight
= Wf). In order to make possible a recalculation from gutted weight to
fresh weight and vice versa,'we have measured on board both weights in 34
salmon. It appeared at first that the number of 34 salmon would be too
gmall to calculate the relation between fresh weight and gutted weight.
It was found , , however, that the relation is very tight, so that the values
......■•••••■••
11 The fish had kindly been put at my disposal by B. Carlin.

found can be used for the recalculation.
- 117-
Fig. 29 shows, as was to be expected, that a linear relation
• exists that leads through the use of the method of least squares to
W = -0.0241 + 0 .91 80 lélf
Wf = 0.0263 + 1.0 893 Wg.
Here W is the gutted weight and Wf is the fresh weight. The
straight line does not pass exactly through the origin, but cuts the neg-
ative abscissa. To be sure, we must expect this result, because one could
'already speak of gutted weight'in case of an embryo, as soon as the ento-
derm has been organized. The additive term, however, makes difficult the
recalculation. We shall therefore examine how large is the error when we
omit the additive constant and alter the slope constant correspondingly.
The'equation then becomes
W = 0.9114 Wf
WÉ = 1.0972 Wg .
Compared with the first equation, the recalculation from fresh
weight to gutted weight results in an error of + 1.96 per cent for a fresh
[1).- 298]
weight of 1 kg, -0.20 per cent for a fresh weight of 5 kg, and -0.46 per
cent for a fresh veight of 10 kg. The difference is thus largest for the
'smaller salmon. For body weights between 1.6 and 20 kg the error lies below
1 per cent, for those between 2 and 10 kg even under 0.6 per cent. On the
fish markets the weight of salmon is given in the great majority of cases
only within 100 g. This means that the error for these figures is generally
higher than 1 per cent and is higher than 2 per cent for small fish. It is
therefore justified for single recalculations to make use of the above
simplified . relation and.to neglect the additive constant. One can proceed thus
-Fresh weight = gutted weight + 9.72 per cent
Gutted weight = fresh weight - 8.86 per cent.

W kg
W 9 = -0 020 + (4919W,
Fig. 29. Relation between gutted weight (W ) and fresh
weight (Wf ).
5.2. Materie and method
15
,
- 118 -
Age determinations have been made by examining the scales of
the salmon. For this purpose complete.catches of the fish have been ex-
amined in January of every year since 1958 on the Kiel Market for Sea Fish. \
The length and weight of every salmon were ascertained and several scales
were collected from every fish. According to a recommendation of he In-
ternational Council for Oceanography) as far as possible, only such scales
should: be used ihat are situated at the height of the posterior half of
the dorsal fin above the lateral line. We have always taken the scales
from this place, providing the salmon was not 'damaged there.
The scales were treated in the following manner..They were
first cleaned and examined under a stereoscopic microscope. Here speial
A
attention was paid to the sclerites developed during life in the rivers.
We then selected the best scale and mounted it with others from fish of
the sanie length on a slide. To finish the preparation, a second slide
was fastened "over the scales. We now carried out the examination proper

v 0 00 0
I I
- 119-
of the scales. Generally we used a binocular microscope at a magnification of
40 to 150, but we have now switched to a scale projector “BT, Krauss,
Paris).
5.2.1. The arrangement of the scales
In order to answer the question of where the first scales are
being laid down on the body of a salmon, we have examined samples from 40
positions on one side of the body of a salmon (Fig. 30)..With the aid of
a scale projector we measured the radius from the centre to the uppermost
margin of the scale (Fig. 31). It is found that the largest scales . are
situated in the anal region closely below the lateral line. There is prob-
ably the initial zone of scale formation. The next smaller scales are to
be found in a band that extends from there below the lateral line as far
as the pectoral fin. After this follow the dorsal and ventral regions of
the body. The last scales are developed in the regions of the nape and of
the throat, as well as at the stem of the tail.
IBM Schuppenradius 92-M0 % der eel) fen Schteen
= radius of = of the largest
saie
85 - 92% sa l es
75 - 85%
50- 75%
25 - 50%
Fig. 30. The size distribution of
• the scales on the body of the
salmon.
In the largest scales the radius is almost four times as •
P. 299]

- 120.-
large as in the smallest. Winter bands and summer bands, however, are
uniformly developed on all scales, so that in general the gmaller scales.
also are suitable for age determinatibn. Therumber of the sclerites, how-
ever, is very variable. Thus their number on the small scales is smaller
by about one-fourth than bn the large ones. For comparative investigations
the samples should always be taken from the same place. This is to be rec-
ommended also for age determinations; because all irregularitieà on the
scale that are the expression of various events, show up the more distinctly
the larger are the number of sclerites.
5.2.2. The significance of the sclerite rings for age determination
It is to be the goal of the examination of the scales (W. J. M.
Menzies 1925) to recognize the entire course of the life of the salmon,
• because the essential events have left their traces on the scales. The pic-
ture of the scale is formed by the sclerite rings, which are laid down con-
currently with the entire process of growth. During sloweroWth, the rings
are very close together, during fast growth they have greater distances be-
tween them and at a sudden check the growth of the scales also ceases. The
fundamental picture .of the scale is determined by the different growth in'
fresh water and in salt water, as well as by seasonal effects. This makes
it possible to ascertain the number of years of life, as well as to dis-
tinguish the period in fresh water from that in salt water.
[p. 300]
This simple pattern, however, is being complicated by secondary
effects, the causes of which .we do in general not know. Thus there appear
frequently during the first summer in the sea cessations of growth, the
so-called summer checks that cannot readily be distinguished from a winter
band or annulus: . On the other . hand, the annuli.occasionally are lacking.

- 121 -
The interpretation of the years in fresh w .- ter is especially difficult.
On account of the slow growth in fresh water, the sclerites are lying
much closer together than during the sea stage. It is therefore sometimes
impossible to identify a period of growth with certainty. Occasionally
Fig. 31. Scale of a salmon of a total length of 63 cm
(A.Gr.2.2) (after B. Carlin).
checks OCCUT durine—the first year in fresh water that are hard to dis-
tinguish from true annual rings. It is therefore necessary to search always
for aids that can support the age determinations and that confirm the in-
terpretation and decisions of the examiner. The often cited "necessary
experience" is doubtlessly important and useful. It can, however, play a
role only when the experience is supported by measurable foundations.
Such foundations can be obtained through tagging experiments. Such results
are available only for the sea phase, whereas the results of tagging are
very hard to.obtain for the life in the rivers.
In the search for further aids we shall consider the sclerite

•
•
- 122-
rings. M. N. Lishev (1958) demonstrated in salmon of the rivers in Latvia
that there exists a clear relation between the.number of sciantes and
the length of parr. There is supposed to be no relation between the age
of the Parr and the number of sclerites. This statement is surprising.
Since the length of the fish depends on the age and there is supposed to exist a
clear correlation between length and number of sclerites,then the number of
sclerites should depend also on the age of the salmon.
In this connection let us examine a partial material of our age
determinations of 1959 to 1961, which comprises 2756 salmon, and that of
January 1962, which concerns 731 fish. In the first instance the numbers
of sclerites were ascertained that were laid down during the first year
Of life, in the second instance the numbers have been ascertained that were
present after leaving the river. If one presents the average number of the
sclerite rings in relation to the duration of the life in the river as a
log-log graph for the first instance and as s simple graph for the second
instance (Fig. 32) one obtains an approximately straight-line relation.
The coefficients of correlation are
r 1
= -0.595 ± 0.0123 •
r
2
= 0.642.± 0.0217.
[1). 3 0 1]
This means that the numbers of sclerites can perhaps serve as
an aid in the age determination.
The individual values, however, show a very strong scatter and
à frequency diagram shows no gaps between the different age groups. It is
therefore necessary to develop an artificial auxiliary model, in which the
age.groups are separated more or less arbitrarily according to certain num-
bers of sclerites (Table 30). When one divides the salmon according to this
'method the following deviations are found from the age determinations. For

•
- 1 23 -
the age groups 2.B to 4.B the deviations from the age determinations are
less than 5.6 per cent and those for the age group 1.B amount to 10 to 11
Per cent. On account of the large deviations, the system cannot.be used
for the 5L.year old smolt.
M Skkriteazel
im Jo&
40
2,0 4-
log number of sclerites in the 1st year
0,5
1,0 In des Smoltalters
45
log age of smolt
Fig. 32 a. Relation between the mean number of sclerites
after one year in fresh water and the.duration of the total
sojourn in the river (mean values of the age group).
We have now to enquire whether deviations of 5 per cent or
even 10 per, cent are permissible in our determinations. Doubtlessly, that •
is not so. The data in Table 30. have, however, not been assembled in
order to replace the investigation of age by the classical method, but
1p.' 302]

•
Sleritenzel
im smoltistage
Smair
40 4-
30 '
20 +
70 4-
number of sclerites in
- 124 -
to make them easier. When there is any doubt in the determination whether
a salmon has spent two or three years in fresh water before migration, the
number of 14 sclerites after the first year or of 26 sclerites at the time
of emigration indicates a smolt age of two years...A deviation of 5 per
cent becomes thus effective only for fish to which the above pattern has
been applied. To this must be added that one can use for orientation the
number of sclerites after the first year in the river aswealas the number
in the smolt age (at the time of emigration). This serves to reduce the
possibility of an erroneous determination still further.
2 3 4 5 Smoffler
age or smolt
Fig. 32 b. The mean number of sclerites
in the smolt age in relation to the
duration of the total sojourn in the
river. (i4ean values of the age groups).
It must be mentioned in this connection that the recalculation
with the aid of the body-scale relation can provide important pointers for
age determinations. A. Lindroth (1963a) has investigated in detail the
growth of the scales as a special case of the relative growth of body
parts. According to this, the scales of Parr show in all dimensions a

•
L s - L c r s 0.85 Smolt Ls = length as smolt to be determined
rc
= length as parr to be determined
Lp -t(
Ls r-18) r
s P Parr
- 125 -
weak tachyauxesis 12 ,' which is present in adult fish only in the vertical
direction, whereas the length of the scales shows bradyauxesis 12 . Apart
from weak, individual fluctuations that are of small interest in this
connection, the change in the body-scale relation that occurs before and
after the transformation into the smolt stage is important for us. Accor-
ding to Lindroth, this causes different linear relations for parr and.
adult fish, as far as the anterior radius of the scale is being measured.
L rA
LA c
rc
Adults L
c
length at catch
L
A =
length during.sojourn in the sea to
be determined
rc = radius of scale at catch
r A = radius of scale at length L A
r
s
radius of scale as smolt.
r radius of scale as parr
p
•
[p• 30 3]
The scales of an adult fish can be used forthwith for the cal-
culation of the lengths during the stay in the sea by employing a simple
proportion (equation for adult salmon). For the determination of the size
of smolt L s the value calculated for adult salmon has to be multiplied by
0.85 (equation for smolt). Through inserting the length of smolt Lg and
the measured scale radius r s into the equation for parr one can calculate
every length during the stay in fresh water.
After one has calculated the lengths for Parr for a fish at the
end of the 1st, 2nd, etc. year, one needs to know the natural.griowth
in the river in order to confirm the determination of the age. • 171- 4 erg-
12 Isauxesis, tachyauxesis and bradyauxesis are cases in which the growth
of the part of an organism takes place in part with the same speed, or
faster or slower; in comparison with the entire organism, or with another
part (Huxley, Needham, Lerver 1941, after Lindrôth, 1963a).

•
cr-I
0
4—/
cd
cn
• •
+3 CO
41-1 H
• 0.)
0
r-4.m1
O 4
CH
• +3
■
f•-
O -H
9 a e •-1
a)
e
Q)
0
-P
cd
a)
re%
cd
E-1
co
(p. p.
.fl N: ô
-4r
•
4.1-4
o N... Kb '
1—■
IT I.
ob
N
Lr■
,
4-)
Q 1-1 0'
0 .., 0 .-4 p..
er it s 4 i 4- ,-r
i
.
a
N 9_1
ce
N
en
se;
•i•
N
'e'l•
leb
qs N
....1--
▪
oo •
ou
à
.4. cr. -t- e4 oo -r
.v ..... .
, •
I
coHI
o
,,, *
al w po • -4;, ..n., ,
lea ›. VS' V 0 .11
. ri
• ul
0 g
. 0 MI,
• (1,
c›...%D.,
e--
MD
4 'H n. 44% c4 4/1
...
e
.
o-' cr.'0 IN
,0 0%.„ >à i3;., 7-1 N., el
I ,-r ,,, ,c. I -4- -r
ci■ Ln _p I N VI
+
co
a■
T.".
• a....e
nt scr
t'i
es-
N
H '...
0
oo
i
ni
0,
•1" 4.n
4-4
I •
00 • +3
. Cr,
o..4.4 cU ot 00 oo oo..
... .6 .., rsi .... 4 cr.
r-1
•
• •
r4 ~i
er—cd1 o
.00 eme com m
ca 0 +, p 0 0
•
• :1
.w.w e
a) a) ca 4
A +
-P
e
0 0 H
0' -P c5 (o • §
..-1 › a) El
F-1 -P • H u-■
(1.) 0 CH r4 r-I
P.4 r-i 0
• 0.) • 0 •
CO Cr) (I) C \
O -P X
0 4-i.1-1 u)
P:1 9-1 0 0 0 0 r.
-P4-, •r•I 4-1
r-I • rl O a -P
0 ca 0 • 0
0 0
g 9 `.1
•ri Z A •ri
CJ N%4 LC-NU)
and counts of sclerites have been
— 126-
If the recaciculated.lengthS of parr are, e.g., 5, 11 and 17 Cm, and if
the results agree with the amounts of growth that have been ascertained
otherwise, then this result indicates
a correct . age determination.
Unfortunately,.things are not
quite as simple, since hardly any meas-
urements of lengths in the natural
stock of parr have been carried out.
•All figures for the mean lengths of'
parr that are available have been ob-
tained through recalculation (W. J.
Menzies 1925, G. Alm 1928a, F. Chrzan
1959b). Furthermore, we have here as-
sumed a simple proportionality, so that
changes in the body proportions have
not been taken into account. However,
even these statements .can help us in
making a step ahead. When the analyses
give the same result or a similar one
as the investigations of other authors,
then the possibility of an erroneous
'determination is slight, even when the
recalculation does not result in the
actual length.
In every case recalculations
carried out for the presentage deter-
minations. In addition the entire material has been - determined twice.

5.3. The'age composition of the German catches
- 127-
Age determinations have been carried out in salmon of the
Baltic Sea principally by T. H. ervi (1938, 1948) and G. Alm (1928a, 1934)
and later also by J. Jokiel (1958), M. N. Lishev and E. J. Rimsh (1961).
These, however, concerned,ascending spawning fish. The pelagic stock of
salmon has been investigated by D. Dixon (1931, - 1934) and A. Willer and
W. Quednau (1931), but, to be sure,, only on hand of a very mall amount Of
material. P. Brandtner (1938), who received, among others, material from
Quednau and Bahr (catches from the Danzig Deep), could carry out slightly
more ample analyses. The . results of F. Chrzan (1959b) and of R. Kgndler
and M. Whmann (1957), the work of whom was continued by F. Thurow (1960),
were based on numerous samples of scales. A considerable material has been
worked over recently by . 0. Christensen (1963, 64).
5.3.1. Results of the analyses of January catches.
When the age determinations are to be.evaluated iicyrespeot
the study of the stock of salmon, te questions will be of interest: the
l'ety-dAsses (1)..0bei
strength of the -yea-r-La.-sats and the strength of the sea year classes. From
Table 31 can be seen that the members of a brood year class can reach the
smolt stage after very variable periods of life. A small part of the fish
of a certain year class x emigrates already after one year from the rivers
and thus joins with two-year old emolt of the year class xr1, as well as
with three-year, four-year and five-year olds of the year classes x-2, x-3
and x-4. Salmon of five different year classes form together in general
one sea year class. In the following year smolt of the.year classes x + 1,
x, x-1, x-2 and x-3 unite into a further sea year class. The analyses of
tyabti_ eet, dASSCS
. age..of catches.at sea thus show always that yeerLd-eem as well as sea
year classes are groups of very heterogeneous composition. The sea year
[P. 304]

- 128-
. A
r i" 'MAY etkeiS
classes consist of different--yearta, but they show an extensively
by-boet yetw•-c&sses
uniform growth in the . sea. On the other hand, the yeaele-eete contain fish
of the same age, but of very variable growth. From the point of -view of
C.11, 5% C.
the study of the stock we shall investigate the brood year's-se-43-, because
we are interested in the number of the fish of one population. Wé analyse
the sea year classes on account of the growth.
cLtses
5.3.1.1. The brood year t -s-se4e
In Table 31 the percentage composition of the catches has been
CetekeS
recalculated as the corrected line eaetuxes per unit effort of Table 15
in order to make possible quantitative comparisons. To begin with, it can
-4ew-ekts
be established that a -year-l-s-ae-t can be represented in the catches for a
maximum period of eight years. The first of the fish,to be captured are
those that emigrate from the river already after one year, and that were
thus in the first year of stay in the sea. During the following four •
years are added to these those salmon that lived for two, three, four or
even 5 years in the river. The oldest of all the fish ekamined waenine
years old and belonged in the-age groUp 3.6. The fish thus remain at Most
for six years in the Baltic Sea.
However, the salmon do not enter iMmediately ifter.reeping the
Baltic Sea into the exploited phase. There axe only - very few fish that
are caught already in the first year of their stay in the Baltic Sea.
Their share in the total catch lies in general below one per cent. Only
during the third year after hatching is the caught share in the year%t
cc% more than one per cent and after the seventh year it .1a1ready lies
again below one per cent. In this connection each year- 1-&-e-e4 becomes ef-
fective . only during five fishing periods. However, it plays a decisive role .

-129-
with shares in the catch of over 10 per cent only during three years,
namely in the fourth, fifth and sixth year after hatching. During the
fifth year the share amounts on an average toet0 55 Per cent, whereas the
shares during the fourth and sixth year amount to 17 to 32 Per cent each.
If flow from one year to the next a new group of salmon of the
flame agé enters the exploited phase of the brood ear- eet-, then the
entire composition of the catch changes with the average age of the smolt.
e.■,v - elk 'IS el
One can therefore not inôlude the fish of the different ycar's mete that
appear during a fishing season in a quantitative- comparison. That follows'
yeee-e-Lts e-C
from the average smolt age of the individual brood yeer4-ee4e in subse-
quent fishing periods (Table 32). It is seen that in the very important
fourth, fifth and sixth years of life the smolt age increases on an average
by 0.9, 0.6 and 0.6 years. In an investigation of the strength and of the
yeey -clAsses
smolt age of different brood jeari se-tie., only the entire span of life Or
a comparable section of life that should be as large as possible can be
used.
L. bsterdahl (1963). has analysed the stock of salmon in the
[P. 30 5]
:yew-
Bicklean. He found that the determination of the mean smolt age of a yetela
— el Ls
-ales.
„e
with the aid or the scales of adult fish is subject to errors, because
the mortality of the smolt is dependent on size. The recapture of fish that .
had been tagged as smolt was the higher the longer the fish were at the
time of tagging. B. Carlin (1963) arrived at the saine result on hand of
numerous taggings. 8sterdahl concludes from this that the counting of scale
rings gives a smolt age that is too high On an average. The results indicate,
however, that the error is not very large. In addition, a mort•ity that
may possibly be affected by the tagging has not been taken into account.
■■■■
71e,

•
- 130 -
The conclusions that have been drawn from Table 32, will remain
unchanged in any case even if the mortality is dependent on size. Because
the smaller fish fall prey to predators only during the first monthS, all
values would be slightly lower. For the saine reason it is possible to com-
pare the mean smolt age of all fish in different fishing seasons with one
another. It is found that the fluctuation are very small and amount at
most to 0.25 years. The lowest smolt age could be established as 2.54 and
2.51 years, respectively, in January195 8 and April 1963. It was . highest
with 2.78 years in January 1962 (Table 31).
yeee - cLue s
It might now be attempted to compare the brood y---set. with .
one another in regard to their average smolt age (Table 31). Since age
-yet.e-eieLes
*analyses for the entire life in the sea are available only for the year l o
of 1955, a period of that length cannot be used as the basis for a
yew-eLss
comparison. It is true that this is not necessary, because a brood year's
ite4..plays : a role for the catch only during five years and is of importance
even for three years only. More than 90 per cent of the tetal-yields from
yea. - 'J
a yeeeLs-set are obtained during this period.
yeev - S
Let us consider first the year's-meta that can be followed com-
'yeee -akcs
paratively for five years, namely 1955 and 1956, and then the yearle-sete
yege-dA.s.r
1954 to 1957 that can be compared> for three years. For the yearts-set.
1955 is found an average smolt age of 2.36, 2.41 and 2.42 years, when 3,
5, or 6 years, respectively, are used as basis. On the other hand, the
etét.ee •
yesei-e-sett 1956 shows a smolt age of 2.93 or 2.82 years, respectively,
when 3 or 5 years of life are taken into account. Thus, the values change,
because the fish with a smolt age of one and five years are not taken care
of sufficiently in the composition that is obtained during the fourth to
'sixth years of life. The deviation, however, is not large so that wescan

"ervoct.
Yeer-Le-
-e-t.
'4.y-c.1*.e.,s
2nd 3rd 4th 5th 6th 7th 8th 9th
7 131 -
compare the four year's sets 1954 to 1957 on the basis of three fishing
periods. According to this, the smolt age was 2.7, 2.4, 2.9 and 2.8 years.
That are rather . considerable deviatiensamditds questionable whether such
fluctuations, when the share of every river remains the. same, can be at-
tributed to changes in all rivers, or whether they are to be attributed -
to changing shares of thé rivers.
[p. 308]
It has already been shown (4.1.2.) that the salmon of the nor-
thern Gulf of Bothnia show the tendency to migrate later and not as far
to the south than fish from more southerly rivers. In this connection we may
• yefee7cLues
Table 32. Mean smolt age of different j.earLs-gete in the sea
in consecutive years.
1950
1951
1952
1953
1954 •
1955
1956 .
1957
1958
1959
1960
1,0
1,0
1,1
• 1,1
1,1
1,0
1,0
1,0
,
1,9
1,9
1,8
1,9
1,9
1,9
2,6
2,8
2,6
2,9
2,9
2,7
3,1
3,4
3,2
3,4
3,7
3,3
3,4
4,1
3,8
4,0
4,6
3,6
3,8
5,0
3,7
3,0
3,5
3,4
3,0
.
.
• -
Me an
smolt age 1,0 . 1,05- 1,88 2,75 3,34 3,92 3,73 3,0
Difference 0,05 0,83 0,87 0,60 0,57
make a comparison with the figures for smolt ages by G. Alm (1928a).
Rivers north of 65 ° N . had an average smolt age of 3.15 years in 1915 to
1944. The corresponding value for rivers between 61 ° and 64 ° N was 2.54
years.and in the lerrum, 56 ° N (1919 to 32) it was even 2.03 years 1 3.
13 It is possible that the actUal smolt age has been lower - in all regions,
on account 6f the mortality dependent on size; however, the values remain
comparable with one another and aléo . with the data presented here.

Table 3.1. Composition of the German salmon catches by brood year's sets, January 1958-62,
as number of salmon per 100,000 - hooks according to the line catches per unit effort
of Table 13.
Brood Years in Year of investigatibn Composition
year's .fresh 4th - 6th year 3rd - 7th year
set water 1958 1959 1960 1961 1962 1962' Iiiee -Nùàber Smolt p .ç . Number Smolt
Etee age •
3 3
1950 4 1
5 2
2 5
1951 3 20 .
.
4
5 -
17
4_ 7
.
2 34 1
1952 3 150 20 2 1
4 47 31 1
,5 29 2
1 - 6 1 (4)
2 214 31 - 2 (27)
1953 3 299 270 9 1 (48) (1380) (2,86)
4 272 54 (21)
' 5 4
1 26 11 1 2,8
V
2 195 171- 10
2 27,4
1954 3 747 163 5 66,3 1372 2,71
4 2 45 19 • 3,4
5 1 6 2 0,1

1955
1
2
3
4
23
3
61
506
7
3
135
211
2
5
105
68
2
3
2
'
5
'
5,8
58,6
29,3
6,3
1103 2,36
7,6
55,6
27,7
6,0
1172 2,41 *
5 36 3,1
1 67 40 1 3,9 9,4
2 11 123 79 3 • 2 19,6 19,0
1956 3 . 530 62 6 56,6- 1048 2,93 52,2 1146 2,82
4
.
210 • 10 20,0 19,2
• 5
2 0,2
1 7 28 30 1 2,7
2 2 201 49 • 2 21,8
1957 3 742 79 71,0 1156 2,77
4 • 52 4,5
1
1958 2
3
1
1959 2
3
1960 1
28 30 .2
1 368 80
246
69 , 18
261
1
1 55 146 74 59 101 55
Average 2 451 719 273 286 425 345
0 3 472 1044 385 642 806 337
4 65 305 102 87 210 62
5 6 36 7 6 38 • 2
Total 1049 •2250 • 841 1080 1580 801
Mean smolt. 2,54
2,72 2,64 2,72 2,78
...
2,51
age
34
(890)
6,5 490
32,9 2499
48,5 3686
10,9 831
1,2 95
1 Analysis of catch of November 1962, cf. Table 40 and the conclusion of Chapter 5.5.3.
7601
2,68

- 134--
Within one and the same river the figures vary in the different periods
by a maximum of 0.35 years.
The mean emolt age of the salmon examined from 195 8 to 19 6 3
was 2.68 years. According to the statements of Alm for the Gulf of Bothnia
the salmon of the southern Baltic Sea are being recruited to about only
one-quarter from the rivers of the Bottenwiek, whereas most of the fish
come from the rivers of the Bottensee. The Swedish restocking measures
undoubtedly have lowered the present-day mean gmolt age slightly, because
the artificially reared salmon are being released already at the age of.
two years. Most of these fish have been released in the rivers of the Bot-
tensee, so that the above statement remains valid. This:result agrees with the
figures of Table 22.
Let us return once more to the individual statements. The Yer-t-B ee-
desses
-sets 1955 and 1956 show a smolt age of 2.4 and 2.9 years, with a difference
of 0.5 years. This considerable difference has been caused by the fact
that in one case more than 55 per cent of the fish examined did emigrate
as two-year old smolt, whereas in the other case they did not even amount
to 20 per cent. It has already been indicated that two causes may be res-
ponsible for Ëuoli changes. If only fish from the Bottensee and no salmon
from the northernmost rivers occur in the southern Baltic Sea, then the
.average smolt age of a lilalet-e—ae -el"s t could drop to 2.54 years. This effect
can, however, also be caused by tne salmon emigrating from the rivers on
• an average at an earlier date than in other years. Finally, the influence
• [P. 309]
can have been caused by the living conditions being more favourable after
the emigration in one year than in others so that a higher perdentage of
the younger fish managed.to survive.
Sirice the absence of the northern salmon does not suffice for

- 135 -
yeAy-ctt4
thé explanation for the low smolt age that is shown by the yèeele-eet of
1955, we have to suppose that the main cause.was that the smolt emigrated
earlier. If we assume as before that the share of the northern salmon (be-
eiond 65 °N) was 25 per cent and if we assume further that they emigrated
0.3 years earlier, we obtain with the•aid of Alm's (1928a) average values
for 1915-1944:
Smolt age north of 65 ° N 1 3.15 years - 0.3 years = 2.85 years
Smolt age 61° - 64 °N 1 2.54 years - 0.3 years = 2.24 years,
total average weighted smolt age 4 2.39 years.
s{Cee — elitSSGS ,
Let us now make a comparison of the strengths of the yeealls
'Pe t . In order to include as many of them as possible, we shall again use
as basis the figures for the fourth to sixths years of life. It has already
been pointed out earlier (F. Thurow 1960) that the ye;45.2e4 of 1953 was
very rich in individuals. Only fish in their fifth and sixth year of life .
have been used in Table 31. Nevertheless, we shall•attempt to include them
- cUss
in the comparison as well as the fish of the yeel-e-eet of 1958. With the
aid of Table 31 we can state that on an average 26 per cent of the total
number of the fish in their fourth year of life are caught and an average
of 18p cent of ihe total nUmber are caught in their sixth year of life..
yew- s 5 •
In order not to overvalue in the comparison the yéar's set of 1953, we f-
shall assume that the share in the fàurth year of life is only 16 per cent.
yet.y--chas .
Wé shall apply to the yearlo pet of 1958 the intentionally reduced percenr.
tage of only 15 per cent for the sixth year of life. Thus are obtained the
sie&Y- tb,ts
comparable figures for the six yintr-1-a--ee4a. from 1953 to 1958 in Tkble 31.
yeey: eha se
According to this, the yéeel7e-aete 1953 and 1954, with their high yields
of almost 14 ealmon.Per 1000 hooks stand far aboVe the group 1955 to 1957,
which is in coniparison rather uniform (about 11 salmon Per 1000 hooks).
'

- 136 -
rw-d4ss
The -yeamla-ael of 1958, which yielded about nine salmon per 1000 hooks,
must probably be designated as weak. Even an increase of its share in the
sixth year of life to 20 per cent results only in a number of 9.5 salmon
per 1000 hooks.
In conclusion let us follow up how the appearance of the ill,-
yeer-Ciat.e
dividual ye-axle-es-to affected the yields of the various fishing periods.
dAse:k
Whereas every yeeele-the't contributes the highest amount to the catches
mostly during the course of the fifth year of life, the salmon that had
hatched in 1955 aPPeared already in the fourth year of life ', that is,
during 1958/59 in the largest number of individuals. At the same time the
dess
good yeau'iy, bet, of 1954 reached in the fifth year of life the maximum of
crebel,e.s.
exploitation. In this way the very good captures-per unit effort of 22.5
Salmon per 1000 hooks were realized.
Since the fish that had hatched in 1955 had passed the peak. of
exploitation already in 1958/59, that is a year earlier than normal, a
group of similar strength was missing from the catches Of the season 1959/
1960. Thus the Oc4ere per unit effort dropped to 8.41 fish per 1000 hooks.
A case similar to that of 195 8/59 occurred during the season 1961/62, when
desses .. •
the two reerks-eets 1957 and 1958 experienced the peak of exploitation,
cettk
which resulted in an average ese44.14e of 15.8 salmon per unit effort. Con-
sequently such a maximum was missing again in the following season 1962/63,
Cabc-iL
in which a oaptuxe-per unit effort of only 8.0.salmon was reached.
. In summary, the above detailed statements show clearly that the
yeev.- . cless .
strength of the brood ytar'o set is of decisive importance for the yields
of the fishery on thé high seas. The annual fluctuations in the catch can
f.urthermore be influenced by the different age of the smolt of the
• thisç es. .
SeertM4 The yter-i-e-sems 1953 and 1954 must be designated as strong, 1955 to
1957 as medium strong and the yle, of 1958 must Probably be deeignated
et4;-Ls -

• •
_
Table 33. The composition of the German salmon catches by age groups, January 1957-6 2/
Navember 1962. •
Age 19571 1958 1959 - 1960 . • 1961 1962 19621 Total
igTOUP
A.B N. p.c. Num. p.c. Num. p.c. Num. . p.c. Num. p.c. Num. p.c. Num. p.c. Num. p.c.
■111.11•1•■••■11.■••■
1.0+ 2
2.0+ 4 3 1
3.0 + 4 0,3 2 9 1,2 7 0,5 1 0,1 '2 2 0,2 23 0,3
4.0+ 1 2
• 5.0 + 1 . •
1.1 + 30 23 44 35 48 42
2.1 + 249 174 193 248 252 325
3.1 + 673 77,2 381 725 54,2 257 558 72,0 331 646 49,1 651 1026 77,2 509 979 90,5 306 741 74,3 5348 69,3
4.1 + 60 94 71 84 144 65 -
5.1 + ' ' 5 7 8 26 3
1.2 + 34 21 63 37 21 22
2.2 + 273 59 212 97 33 99
3.2 + 186 21,3 191 521 39,0 93 186 24,0 256 618 46,9 129 286 21,5 42 96 8,9 99 233 23,4 2126 27;6
4.2+ ' 21 11 84 23 12
5.2+ 2 2 3 1
1.3+ 8 4 5 1 3
2.3 . + 43 11 16 6
.
2 2
3.3 + 13 1,5 25 77 5,7 7 22 2;8 15 37 2,8 7 14 1,0 1 3 0,3 8 14 1,4 180 2,3
4.3+ 1 1 1
1.4+ 1 1 .
2.4+ 7 11 0,8 4 7 0,5 1 0,1 2 2 0,2 2 7 0,7 28 0,4 .
3.4+ 4 2 1
1.5+ 1 1
2.5 + - 1 2 0,2 1 0,1 1 2 0,1 5 0,1
3.5+ , 1
Total ; 1172 100,0 1338 100,0 775 100,0 1317 100,0 1329 100,0 1082 100,0 997 100,0 7710 100,0 ;
1 cf. Talle 40 and conclusion of Chapter 5.3.3.

as weak.
5.3.1.2. The sea year classes
- 138 -
As we have seen, all the fish that have hatched from the eggs
in the same spring form, in regard to Age, a uniform group, the brood
ysey-dass
ycarts eet. In contrast, the individuals in the sea year classes are those
fish that have transformed into smolt in the same spring and that have
left together the rivers and entered the Baltic Sea. Consequently, one
le6w- Cieeses
can talk
Ye4rof
ycaetc cot,: also in regard to these fish, namely of --yeee 1s
c(4.ss4-s
-
-sate of smolt, which are, however, of very heterogeneous composition in
regard to their actual age.
Let us now follow up the exploiteà sea year classes on ihand of
Table 33. During the - first year in the Baltic Sea (A.+) the .salmén are
practically not caught. On an average the share of the sea year class A.+
[P . 511]
in the catches amounted to only 0.3 per cent during the years 1957 to 1963.-
These fish are hardly ever caught in the nets, because they can slip
through the meshes. It is, however, astonishing that even with small
hooks only very few fish of the age group A.+ have - been captured. We can • .
theref ore assume ihat these amall salmon either live in a region.that ia
different from that of the large fish, or that they do not take the bait.
The latter would mean that they use a different basic food than the older
fish. It has already been established (2.2.3.2.) that the salmon can tiver-
come the sprat used as.bait only after they have reached a length of about
[13. 312]
27 cm. According to Lindroth (1961b) they liVe before that mainly on
flying insects.
It iatheamfore probable that the young salmon live in shallower
waters until near the end of their first year in the sea, where they can

Table 34. Composition by age of catches of salmon
according to various authors as percentage of the
numbers, line catches.
Season Author Sea year classes
A.+ A.1+ A.2+ A.3+ A.4+ A.5+
. .
1945/46 OutzAN 36,4 59,8 9,8
1946147 CHRZAN 16,0 57,0 21,0 6,0
•
; 1947/48 CHRZAN 2,7 41,0 51,8 4,5
1948/49 CintzAH 37,5 38,1 18,8 5,6
1949/50 CHRZAN 7,9 81,6 9,8 0,6 .
1950/51 CHRZAN 9,2 72,3 18.,5
' 1951/52 .CletzAN ' . ••10,8 64,6 22,6 2,0
1952/53 CHRZAN 17,3 66,0 15,8 0,9
1953/54 Clutz.AN 3,5 55,1 36,9 4,0 0,5
1954/55 CHRZAN 0,2 51,3 44,4 4,0 0,1
1954/55 ICINDLER/LCIHMANN 37 58 5
1957/58 CHRISTENSEN 72,9 25,3.
1958/59 CHRISTENSEN • 83,0 16,0
1959/60 CHRISTENSEN 65,4 , 29,6 •
1960/61 .CHRIS'TENSEN 79,8 18,7
1961/62 CHRISTENSEN 83,5 15,6
1962163 CHRISTENSEN 76,8 20,9
1963/64 CHRISTENSEN 0,1 71,3 27,1
. 1957/58 THUROW 0,3 . 54,2 39,0 5,7 0,8
1958/59 THultow 1,2 72,0 24,0 2,8 • •
1959/60 THUROW 0,5 49,1 46,9 2,8 0,5 0,2
1960/61 THUROW 0,1 77,2 21,5 - 1,0 0,1 0,1
1961/62 .THUROW 90,5 89 0,3 0,2 0,1
1962/63 THUROW 0,2 74,3 23,4 1,4 0,7
1928-36 DIXON 24 60 15 - 1
1945-53 CHRZAN . 16,5 60,1 21,0 2,4 i
1953-55 CHRZAN 1,8 53,2 40,7 4,0 0,3
1957-63 l'HuRow 0,3 68,4 28,4 2,4 0,4 0,1 1
• 1957-64 CHRISTENSEN 76,1 21,9 i
. _. .
- 139 -
also capture small food animals on the bottom; they are joining the larger
animais only gradually. This behaviour surely is the cause of the fact that I
it was formarly possible to capture considerable amounts of "speizken" (sal-,
9
mon in the first' year in the sea) at the coast of Pomerania).
The largest share in the catches is provided by the sea year
class A.1+, which amounts to an average of 69.3 per cent. During their
second year in the sea, obviously all salmon are in the exploited phase.
The same is to be expected for the fish of three winters (A.2+), which ac-
count for 27 ..6 per cent of the yield on an average. The percentages ate
very small'of.thè following sea year classes: A.5+ with 0.1 per cent,14+
with 0.4 per cent and A.5 with 0.1 per cent. Among the about 7000 fiàh

- 140
-
that have been analysed there was not a single salmon that had lived in
the Baltic Sea for more than six years. The fishery rests thus principally
on the two sea year classes A.1+ and A.2+, which account on an average for
almost 97 per cent of the yield.
If we cômpare these results with the statements by other authors
(Talle 34), we find that the sea year class A.2+ was exploited the heaviest
until the season of 1952/53, when it brought about 60 per cent of the yields.
The classes A.1+ and A.3+ accounted together for a further 38 per cent.
The picture changed considerable during the subsequent years, so that the
sea year class A.3+ played practically no longer a substantial role, while
the main share shifted from the fish of three winters (A.2+) to those of
two winters.(A.1+).
It must be obvious that the analyses of captures until 1953 •
cannot have given a true picture of the conditions of the stock. Under
average 'conditions the sea year-class A.+ must have the highest number of
individuals in the stock, whereas the number of fish in the following sea
year classes diminishes steadily through fishing and natural waste and
the emigration to the spawning grounds. A. fishery that is exploiting the
stock representatiVely, must also reflect these relations.
Although F. Çhrzan (1959b) has examined-only an average of
160 salmon, a possible error may have been compensated through the for-
[1:4 313]
mation of mean values. He hils established that the changes in the compos-
ition of the catches around 1953 are connected with the use of smaller
fishing hooks. The Polish fishermen changed during this time from hooks
-with an opening of 25 mm to those with an opening of 13.5 and 15 mm.:Since
• at that time.the bait-for the large hooks consisted of herring, it is'pos-
sible that significant differences occurred between the catches with the'

- 141 -
yeAy-cle..es
Table 35. The strength of the ye-are-Es-seta of smolt as number
of salmon per 100,000 hooks according to the line captures
per unit effort of Table 15.
■•■•■■
Number Evaluation
Year's in 2nd Eval- figure re-
A.+ A.1+ A.2+ A.3+ A.4+ À.5+ a. 3rd- uation calculated
set year figure after Kând-
é.;“ott ler 19 64
"Wy)
.
1953 8 .
•
1954 •
• . • 61 ' 2
• 1955
195,6 '
- 409 '62 .
568 . ' 540 • . 23
5 • 1
1 - 4
(1683) 1
1108
(17)
11
1957 3
1958 • 27
1959 6
1621
411 .
833
394
233
143
- 11"
5
11
3 -
6
2015
644
976 -
20
6
i0
12
8
11
,
• 1960
1961
1962
1
2
1425
593 :,
187
•.
•
-
1612
(803)1
16
• • (8)
17
13 .
.
.
0 7 909 318 29 4 1 1225 12
1 •Figures completed through estimates.
[0 = average]
hooks of 15 and 25 mm openings. Chrzan also mentions that the enforced
cowseyve,t,,m,
Hprefferieft4i-ea during the war had thé consequence that there was a larger
share of older fish than before and afterwards. • leaf — ciesses
Let us flow attempt to compare the individual yettele-eebs of
smolt with one another in regard to their strength. With the aid of the
entries in Table 33 and the line •keeee per unit effort in Table 15 com-
parable values have been assembled. ih,Table 35. For an entirely exact com-
Yee-r-ct,ts
parison each ye.selle-se4 would have. tp te taken into account from its first
appearance in the exploited phase until its:disappearance. Since the sea
ye e
year classes A.1+ and A.2+ of every yeer-I-e-set of gmolt supply on an aver-
age more than 95 per cent of the yields, we can use for the compai.ison
also the figures for these two classes. With the aid of the mean numerical
.ratio of A.1+ to A.2+ for 1956-1960 one can in addition estimate the prob-
able total number of the individuals for the capture per unit effort for

déro:
the yeetri-s-zre4s. of 1955 and 19 6 1 (figures in parantheses).
- 142 -
The manner of presentation in Table 35 has the advantage that
it is not necessary to employ the very relative expressions "good" or
"bad". The number of- individuals of the . sea year classes A.1+ and A.2+
that were caught per 1000 hooks provides an absolute comparative possibility.
According to the present results one can consider as average
ww-644see .
those that have an evaluation figure of 10 to 14 (10 to 14
salmon per 1000 hooks a:1day in the sea year classes A.1+ and A.2+). It •
v - eLss
can therefore be dèduced from Table 35 that.the yeler'r-eet-e.of smolt /e
1955, 1957 and 1960 with evaluation figures of 17 to 20 can be called good,
those of 1956 and 1959 (evaluation figures 10 to 11) cari be called average,
and those of 195 8 and 1 9 61 (evaluation figUres.6 to 7) can be called poor.
R. Kandler (1964) has used the average yield of a cruise in
M.S.
order to be able to evaluate the strength of the year-Le-sat. The age*com-
position had been obtained with the aid of weight statistics (cf. 5.3.3.).
According tO this, salmon under 5 kg belong into the sea year class A.2
and fish over 5 kg belông into the sea year class A.3. On account of the
unknown number 'of older fish and of sea trout, as well as on acbount of
the fluctuations in growth, he had to apply annually a correction to the
yields of the cruises. }lis results have been recalculated as evaluation
figures and inserted in Table 35. The two investigations show approximately
yedui7eAses
similar results for the **ele--e -: ;.:e-t& of gmolt for 1959 and 1956. However,
yem, eid4g-see
there are considerable differencesl'or the yeaxle- ete Of 1957, 1958 and
1961. It had already been pointed out hy way of introduction (cf. 2.3.3.1.)
that the number of cruises during a longer period does not constitute a
good measurement for the fishing effort, because the eitmtbe.r of gear per
cutter has risen steadily. This.has also considerably impaired the

- 143 -
•
U7,) tdL
comparablenece of the yields of cruises that had been selected as eapteee
per unit effort.
Let us examine once more the age composition of the Catches in
Table 33 in order to discover the cause of the fluctuations in the catches
yelw-at,s
of the sea year classes A.1+ and Ae2+. In 1958 the average yeeke-la-eet of
• yewgmolt
of 1955 as A.1+ contrasts with the good y arls-set of smolt of 1955
as A.2+. For this reason the share of the sea year class A.1+ WaA onky 54 per
cent. A year later appear together the good yeaele act of smolt of 1957
as A.1+ and the average of 1956 as A.2+. A.1+ accounts therefore for 72
per cent of the catches. In 1960 the sea year class A.1+ is represented
ye,v-éless yeew-
by the poor yearic-cet of smolt of 1958. In comparison with the good yecela
CA.45
Set of 1957 (A.2+) it yields a share of only 49 per cent. In 1961 the av-
erage ycartc7 act of smolt of 1959 as A.1+ in comparison with the poor one
of the year 1958 made up 77 per cent of the catches. In the yeax 1962 the
[P. 314]
good yearls-cet of smolt of 1960 furnished even 90 per cent of the catches,
de,ss
whereas the sea year class A.2+ is represented by the average yeario sot
of 1959. The percentage of the sea year classes in the catches is thus
y eev
alwgys dependent on the relative strength of the yecTlezzeefs of smolt.
5.3.1.3. The salmon with spawning marks
During their spawning migration, the salmon probablycease to
feed already before they enter the rivers. It has, already been stated that
the development of the gonads is accelerated during this period. Since the
fish also have to supply the energy for the spawning migration and for the
spawning, all body reserves are being mobilized. Among other things, there
is a degradation of Substance on the scales (T. H. Jgxvi and W. J. M.
Menzies 1936): This involves a more or less complete resorption along the

- 144' 7
margin (Fig. 33). In those fish that survive the migration and that manage
to return to the sea, this resorption zone is usually plainly visible. It
is called the spawning mark.
Fig. 33. Scale of salmon with spawning
mark, 91 cm, 2.2G1. (After B. Carlin.)
The ntimber of fish with spawning marks that were found during
age determinations has occasionally been employed for the evaluation of
the composition ofe the stock in order to denote the waste. In Table 36
have been assembled the data of F. Chrzan (1956b) and of R. K4ndler . and
M. Liihmann (1957) together with the present data.
F. Chrzan found during the season 1947/48 a very high value of
11.2 Per cent. The figure can perhaps be considered to be accidental, be-
cause in this period a total of only 260, mostly large, salmon were ex-
amined. For the rest, the fluctuations are rather small. G. Alm (1934)
already -found in the catches in the Baltic Sea a figure of 3.2 per cent.
F. Chrzan (1959b) ascertained an average value (1945-1955) of 3.7 per cent,

•
whereas the present data .(1957 to 1963) give 2.A per cent.
- 145 -
R. Kgndler and M. Lehman (1957) have already pointed out that
the share of the salmon with spawning marks 1epends on the age composition
of the sample of catch examined. The older the salmon are that have been
caught, the more specimens with spawning marks will be found among them.
This furnishes also the partial explanation for the fluctuations of the
values in Table 36, when one compares them with the composition in age.
Furthermore, it becomes also clear why G. Alm (1934) and T. H. and (1938)
[P. .315]
found the high percentages of 7.5 and 6.3 per cent, respectively, of salmon
who were spawning again. The percentage of fish with spawning marks in the
total catch thus gives hardly any information other than that obtained
anyway through age determinations. On the other hand, one can answer other,
important, questions:
(1) At which age do salmon migrate to spawn?
(2) How grèat is the percentage of fish with spawning marks in the indiv-
idual age groups?
(3) What percentage of the utilized stock migrate to spawn?
In Table 37 the fish with spawning marks have been divided ac-
cording to time of'spawning and the age at spawning. - The number of fish
that did sPawn in 1962 could not not be taken into account completely,
[p. 316]
because all survivors had not yet returned by the time of the last examin-
ation (spring of 1963); On the other hand, the number of the older fish had
already been reduced through mortality. If we compare the total result with
the age compositions for the years 1957 to 1961 that have been investigated
best, .there is found no substantial difference. About 50 per cent of all
fish on spawning migration consisted of fish that were in the third
•

•
Table 36. Percentage of salmon with spawning marks in the
Baltic Sea.
Author
CHRZAN
CHRZAN
CHRZAN
CHRZAN
CHRZ AN
CHRZAN
CHRZAN
CHRZ AN
CHRZAN
CHRZAN
K.ÂNDLER/LüHNIANN
THUROW
THUROV
!THUROW
• THUROW
THUROW
THUROW
1945/46
1946/47
1947/48
1948/49
1949/50
1950/51
1951/52
1952/53
1953/54
1954/55
1953-55
1957/58
1958/59
1959/60
1960/61
1961/62
1962/63
2,3
4,0
11,2
3,6
2,5
4,3
3,1
2,6
2,0
1,0
2
3,3
4,3
3,3
1,0
0,7
1,9
30
16
3
38
8
9
11
17
55
51
54
72
49
77
91
66
- 146 -
Salmon with Share of sea
Season spawning marks yeax class
in per cent A.1+ in total
catch in p.c.
Table 37. Time of spawning and age at spawning of fish
with spawning marks that were caught in 1957 to 1963, as
number of salmon per 100,000 hooks (percentages in
parantheses), 162 salmon examined.
Time
of
Age at spawning
spawning A.+ A.1+ A.2+ 4.3+ A.A+ A.5+ Total
.
1954 1 1
1955 1 '1 ' 2
1956 9 . 13 5 27
1957 3 14 25 7 1 50
1958 8 38 20 66
1959 1 6 8 7 2 1 25
1960 3 3, 2 1 9
1961 1 6 7 14
1962 1 1
Summe gcsamt 4 (2) 43 (22) 95 (49) 46 (23) 5 (3) 2 (1) 195
Summc 1957 61 4 (2) 32 (20) 80 (49) 41 (25) 5 (3) 2 (1) 164
Summe gesamt - total sum, Summe = suml
younger age group 4.1+ (grilse) and 25 per cent constituted the next older .
age group A.34.

Sin%
0,1 2,8 37,0 96,8 100,0
- 147-
If we compare these results with the series - of Swedish measure-
ments of lengths in ascending salmon (Fig. 22),'we find that the bulk of
the ascending fish here also is formed • y the sea year class A.2+. The
fish that migrated already in their second year in the sea (A.1+) are
grilse. Of the older groups, the sea year class A.2+ on the one hand and
the classes A.3+ to A.5+ on the'other form each a maximum in the frequency
distribution of the Swedish series of length measurements (3.2.3.).
If one collects together correspondingly the age groups of the
Table 37 and neglectF the grilse, then the sea.year class A.2+ constitutes
a share of 64 per cent. F. Chrzan (1959) found on an average during the
years 1945 to 1955 the share of the sea year class A.3+ to be more than
60 per cent.
Table 38. The share of the salmon with spawning marks in
the sea year clsses.
Year of Age groups
-
invest- A.1+ A.2+ A. 3+ A.4+ A.5+ Total
igation Tot. .8 Tot. S Tot. S Tot. S Tot. S Tot. S
1958 725 521 16 77 18 11 10 1338 44
1959, 558 2 186 17 22 14 775 33
1960 646 2 618 17 37 15 7 7 2 .2 1317 43
1961 1026 1 286 3 14 7 1 1 1 '1 1329 13
1962 979 96 2 3 2 2 2 2 2 1082 8
1963 724 342 3 20 8 10 10 1103 21 .
Summe 4658 5 2049 58 173 64 31 30 5 5 6944 162
8 = salmon with spawning marks [Summe = sum]
v/
In the age determination the salmon with spaipng marks have been
incorporated inte the sea yeax classes according to the length of life they
spent after their transformation into gmolt. Since the spawning maturity
is dependent on the condition and thus can fluctuate annually and since
the spawning fish are subjected for about one year to quite different
2,3

•
- 148-
conditions of growth and wasting than the fish remaining behind, it becomes
explicable that thé share of the salmon with epawning marks in each sea
year class changes from year to year (Table 58). On an average the percen-
tage of fish that have spawned increases with increasing years spent in
the sea. The class of the fish with four winters (A.3+) is composed on an
average of 37 per cent salmon with spawning marks. (The share fluctuated
between 23 and 67 per cent from 1958 to 1963.) Of the older fish almost
all salmon have already spawned.
• This result leads us to the question about the number of the
emigrating fish. If the sea year classes A.4+ and older consist already
to about 100 per cent of fish that have spawned, then all salmon of the
Lp. 317]
Sea year class that have not yet spawned must emigrate in the spring of
every year. With the aid of this statement and the Tables 33 and 37, the
share of the emigrating fish can be estimated. For this end we start with
the percentage age composition (Table 39, row 2). We know that the sea year .
class .A.3+ consists to -37 per cent of salmon with spawning marks and we
can assume that the remaining 63 per cent will emigrate-as A.4 and will
epawn as A.4+. In the composition of the fish emigrating to spawn they
• Table 39. Average percentage of fish of each sea year
class that migrate annually to spawn.
Sea year classes A.+ A.1+ A.2+ A3+ AA+ A3+
Composition 1958-63, per cent 0,40 67,08 29,51 2,49 0,45 0,07
Of these to spawn, number .00,98) 25,63 12,04 1,57 • 0,52 (0,115
Per cent . 41 63
account for 3 per cent (Table 37, last row)..With the aid of this relation
it will beeasy to obtain the figure s . for the other age groups, e.g. 63
Per cent of 2.49 = 1.57. Since 1.57 = 3 per cent (A.3+),.23 per cent is
equal to 12.04 (A.2+) and 49 Per cent = 25.63 (A.1 -0, etc. According to

•
- 149 -
these results 38 per cent of the age group A.I+ emigrate (as A.2), 41 per
cent of A.2+ and 63 per cent of A.3+ emigrate to spawn. These percentages
have to . be viewed with reservations on account of the small number of
salmon with spawning marks.
5.3.2. Seasonal changes in the age composition
Except for the fishing season 1960/61, WP have for every season
in addition to the series of measurements in January also those for line
catches in November and for net catches in April (Fig. 34). In January
1963 no investigations could be made on account of the lack of fishing.
Up to now we have evaluated the composition of the catch both according
to the share in the brood --efapis--s4.)..ts and also according to the sea year
yee.e-d& , , e, 4 s,iolt
•
classes (the y-e-a-r-1-..,--s-f—stte-1-t-). On a,ccount of the uniform growth con-
ditions in the sea, the sea year classes are decisive for the fishing.
'Hitherto statements could be made only for the investigations
in january, because no scale samples had been taken from the fish of the
other series of measurements. Although it is possible to estimate the
share of the sea year classes with the aid of the frequency diagrams (Fig.
34), there are no 'exact statements. In the age analysis after the method
of Petersen it is necessary to select an arbitrary separation between the
two maxima Of the frequency distribution that correspond to the sea year
classes A.1+ and A.2+. When there exists no gap between the two classes
on account of the different growth performance or on account of a very
small share of the sea year class A.2+, this method of determination can
cause an error of more than 5 . per cent, in some cases even one of more than
10 per cent.
For Obtaining the age composition of the samples of catches of

- 150-
November and April of every fishing period a different method has been
selected for the present case. At first glance the series of measurements
for a season do not show any Considerable differences in the frequency
distribution. The existing changes must be considered to have been caused
principally by conditions of growth. Therefore the idea suggests itself
to assume that the shares Of the two sea year classes in the transition
zone of a series of measurements for all investigations of a season are
almost equal. For testing this assumption the curve of the frequency dia-
[P. 51 8 ]
gram for November 1957 has been shifted until it coincided with the curve .
for the distribution of.lengths of January 1958 (Fig. 35). Consequently
it could be demonstrated that the series of measurements for November and
January show about the same composition. The sea year class AJ.2+ of the
series of measurements for April as a whole does not fit very well the
series of measurements for April. This must be attributed to the smaller
amount of growth of the older fish (see . 5.4.P.) and the selectivity of the
nets. The gap between the two sea year classes thus becomes smaller.
[p. 319]
In Table 40 has been inserted the age distribution of the sea
year class A.2+ in the transition zone, that has been obtained through the
examination of scales. With the aid of these values can be ascertained
now the age composition of the remaining series of measurements. If one
shifts, for example, the series of measurements for November 1957 in such
a way that coincidence is obtained With the distribution of lengths of
January 1958, then there is seen a difference in lenghts of 4.0 cm between
November and Jannaxy. Compared with the values in Table 40 this means that
the salmon from Noveffiber 1957 belong exclusively to the age group A.1+ up
to a length of 70.9 cm (2-cm-group 70). Of the 2-cm-group 72, 3 per cent
- of the measured -fish belong into the age group.A.2+, of the 2- cm,group
5. Per cent belong to to the. age group A.2+, of.that of 76, 14 percent,

•
•
Number of salmon
J. en1967 872 Alli
Angel
Hook
61111111ellibl■,
Nov.1957 nil 1011 Alimmdie., Angel
Jen.1956 1620MM Angel
Lee---
Apc1958 1390111W Metz
hiAlLifit
Nov1958 .22 Mpg Angel .
Leaddikabb.....
'
Jon.1969 769MIR Mg.!
Apt: 1959 575
1111116111111111111116.--.-. —
Metz •
-..■1111111111 1 IMIlln..-.
Now1959 740 Angel
Jan.1960 1370111aWdhhhAigel
Api:1960 564 Metz
.111111111111111111Mbitur-
Fig. 34. Composition by lengths of salmon caught in
driftnets and by line.
- 15 1 -
and finally, of the 2-cm-group 90, 100 Per cent of the measured fish
belong into the age group A.2+. The age composition for all series of
measurements can be obtained in the same manner.
It had already been pointed out that the gap between the -4wo
maxima can be enaller in April. If the overlapping of the two groups
increases, the transition zone in Table 40 would have to be enlarged.
[p. 320]

... 103
40
so °
60
Lo
Jan Kt 1.192 , Anititi -
Nov 961 1186 Angel
Jan. 962 1224 Angel
Ape
' .
962 714 Netz
Net
•
Nov. 962 .997 Ange In
Apt: 1963 1103 Her
Nov. 1963 . Netz
60
80
Fig. 34, continued.
100cm Tafflimm .
Total length
7 152 -
Such regrouping of the percentage values is, however, difficult and
necessarily faulty. It is therefore suitable . to project the series of
meaSurements for April in such a way that•not the maxima of the age group
A.1+ coincide, but the two.minima between the age groups.
Let us now compare the age composition of the catches of Novem+
ber and January of every fishing Season (Table 'ii). In all cases there is •
'excellent agreeMent for the share of the sea year class A.1+. The difference.
between the two values is in each case only 0.2 to 0.5. Such a* difference •

4.
number
50
e"
•
);
e
e ,
lot
nb
• •" Novondet 1.957
1951
Apnl 9151
7 153 -
..110 one Tocolkinq Jort19‘
Totalkinge, Nov19bi
Tota!k,nge,April 151
• _
Total leegth
Fig. 35. Composition by lengths of German salmon catches 1957/58.
(Frequency diagrams of November and April superposed on the
distribution by lengths of January).
can have its cause in methodology so that we may assume the same age com-
position for November and January during every fishing period.
Matters are different for the series of measurements for April.
In comparison with January, the.catches investigated show higher figures
in two cases and in two cases the figures are lower, and in'one case the
values for the age group A.1+ are about equal. Especially outstanding are
the percentages of April 1960 . and of 1963. How can this be explained?
- It has already been said that the maturing salmon start their
spawning migratioris already in spring. This behaviour has the effect to
raise the percentages for A.1+. The percentage of the age group A.1+ is
going to change in relation to January depending whether the salmon do not
yet begin their migration already in April snd move northwards in only small
numbers, or whether they move already in large numbemintothe rivers at
this time.
• On the other hand, the catches in April that have been inves-
tigated were all taken in nets. According to the curves for selection in
Fig. 10 a numbei, of smaller salmon of the age class A.1+ are not being

70
2
4
6
4
1
7 154 -
caught together with the others, whereas in regard to the age class A.2+ .
the selection is, almost complete. This has the result that the percentage
of the fish of two winters in April is.lower than in November andJanuaxy
when the fishing ià done with hoekS.• •
Now, it has been shown that the age composition of the -catches
in November and Januaxy of every. fishing season is the saine, whereas in
the Spring.it will be'influenced through the emigration of the large sal-
mon on one hand and by selection on the other. Both causes act in opposite.
[p. 321]
direction. One can therefore assume that in April 1960 the emigration of
the older fish was predominant,.whereas in April 1963 the effects of selec-
tion were decisive. .
Table 40. Composition by age in the" transitional sene of
. lengths between the sea year classes A.1+ and A.2+.
Lt Number . of salmon of the sea year class A.2+ . in
. per cent of the total number of one length . class
cm Jan. 1958 Jan. 1959 Ja.1960 Jà.1961 Ja.62 Apr. 63
8 ' . 5, 3 , 12 3 1 4
80 . 14 8 50 5 3 • 4
2 16 ' 13 • 60 14 3 21
4 33 27 • 81 35 6 39
• 6 53 30 91 73 10 45
8 . 74 69 100 87 35 82
90 89 87 96 60 100 • .-
2 98 95 100 100
100 100 . 95
95
[p. 322]
5.3.3. The age structure of the exploited stock in the main basin of the
the Baltic Sea
• Hitherto have been given the results of analyses of the ages
of entire catches. However, it has not been discussed whether these
catches can be considered representative of the total landings and whether

they take account of the annual changes in the stock.
- 155
•L
It is very diffult to find,,the age composition of the total yields
with the aid of the above results. Kàndler has indeed introduced a statis-
tics with six groups of weight (1-2 kg, 2-3 kg, 3-5 kg, 5-7 kg, 7-8 . kg and
pver 8'kg) for the landings at the Kiel Seafish Market, in which all sal-
mon are regiStered numerically (R. Kândler and M. Lâhmann 1957). Kândler
(19 6 1, 1963, 1964) has used the distribution of the groups for obtaining
the age composition. However, a division of the fish landed into the tWo
most important sea yearcaasses A.1+ and A.2+ with the aid of these statements.
is, however, necessarily subject to errors. This is owing to the annual diem.
ferences in growth and to changing sharesof the sea trout. In Table 19 it
had been shown that the percentage of sea trout in the catches varies
greatly and has amounted to an average of 3 to 15 per cent during indiv4.
idual fishing seasons. It is difficult to eliminate these fish because they
are not listed separately in the figures for the yields and their share
in the individual groups is not fixed.
'A division of the.salmon landed with the aid of the statistikos
9f the catches can be carried out in such . a manner that the fish under 5 kg
weight are assignèd to seai.year class A.1+ and the heavier fishto 1.1ti
The actual boundary isectordin:g to wsight . between the twO grouPs‘is, however t
not constant. It shifts during the course of every fishing season as well
'as from season to season.
It is possible to estimate the errors that OCCUT when the age
• composition is determined with the aid of the statistids of the landings.
This c an be done in the following manner: the complete catches that have
been investigated are being divided according to the weight of the fish.
TheSe series or measurements contain also seà trout (Table 42, colleen 3).

Table 41. The composition by age of the German salmon
catches in different months and years in per cent.
- 156 -
Season Month Number of Sea year class
salmon A:+ A.1+ A.2+ ( 11 .3+)+ (A.2+)+
1956/57 Januar 872 77,2 22,8
• 1957/58
November
Januar
April
1090
1620
1398
0,3
54,0
54,2
57,5
39,0 6,5
46,0 ,
45,5
42,2
1958/59
November
Januar
April
823
789
577
1,2
72,5
72,0
71,4
24,0 2,8
26,9
26,8
28,6
November 749 48,7 51,2
1959/60 Januar. 1318 0,5 49,1 46,9 3,5 ' 50,4
April 527 57,0 42,8
• 1960/61 Januar . 1324 0,1 77,2 21,5 1,2 22,7
November 1161 . 90,0 10,0
1961/62 Januar 1225 90,5 8,9 0,6 9,5
April 699 88,2 11,2
1962/63 November 997 74,6 25,4 '
April 1112 0,6 65,7 31,1 2,6 33,7
IIMMOReemol.■••••••111•■•••■••••■■■••■■•••••■•••••••■■■
If one now ascertains the percentage of all salmonids that weigh less than
5 kg,(Table 42,'column 6), one obtains values that have been got according
to the method of Kândler (19 6 1, 19 6 3, 1964). When one compares these results"
with those arrived at through the examination of scales, one finds ,:conbid-
erable deviations that exceed the allowable limite of error (Table 42, column
8). It is not possible to apply exact corrections to the data as long as the
share of the sea trout in the statistical figures is not known. In regard
to the errorErnaused by changes in growth only a very coarse and uncertain
improvement can be made even with the aid of series of measurements. This
method is thus not suitable for an exact analysis. It is, Inwever, of value .
when one wants to obtain a preliminary general view of the stock conditions
quickly - without tedious collecting of sample's and time-consuming examin-•
ation of scales. In this paper no comparison has been made between the
samples of catches investigated and the total landings. It will therefore
•be clarified . in. a different manner in how far the fluctuations in catches

•
-157-
and in the stock are being reflected in the series of measurements pres-
ented. In order to make obvious the regular changes, the general results'
of the investigations will be summarized here (cf. Table 41). During a
fishing season the stock is represented substantially by two year's Sets
of gmolt x and x - 1, that appear as pea year classes A.1+ and A.2+. Both
are represented in the catches of November and January as well as in those
of April 14 . In the succeeding fishing season a new year's set of gmolt
has entered the exploited phase, which forms the new pea year class A.1+.
[P. 323]
It has come neifly into the exploited stock during the time between summer
and fall. On the other hand, the year's set of gmolt x aPPears now.as the
sea year class A.2+ , . whereas only few fish of the year's set x - 1 are
being caught. They have already started their emigration to the spawning
grounds in the spring of the previous season. This annual change. in the
stock has already been touched during the dicussion of the yields (2.3.4.).
Since the renewal of the stock mentioned may not be « quite com-
pleted by the beginning of etery fishing season in August/September and
since new changes take place through emigration in spring, one can consider
the composition of the stock to be unchanged only during the period from '
about November to karch. It is therefore appropriate to use this period
as the basis for comparing the age distribution from season to season.
.These reflections are confirmed by Table 41. Since . the share of the sea
year class A.1+ in the samples of catches of November and January of each
season is the same,.We may assume that these series of measurements detect
.the rather unchanged conditions from November to March.
The questions of the aboVe sections concern the relation between
14 The two classes would have to be designated correctly as A.2 and A.3
in the April'catches, because the years are completed at this time.

Table 42. Share of the sea year class A.1 in the catches, obtained at the one hand with the
aid of the landing figures (weight groups) and on the other hand
obtained through examination of scales.
Date of Number of Of these sea trout Sàlmon with Salmon a. sea trout P.c. sal- Difference
salmonids
examination examined Total ..c5 kg
spawn. mark

Table 43. Mean lengths of age groups and sea year classes in cm total length, Baltic Sea.
ige . January 1958 January 1959 January 1960 January 1961 January 1962 April 1963
group Num. ay. lgth. Num .. av. lg. Num. av. lg. Num. av. lg. Num. ay. lg. Num. av. lg.
•
1.+ 2 51,0 • 1 56,0
2.+ • 4 46,5 46,5
3.+
5.+
1.1 + • 30 70,2
• 2.1 + 249 720
3.1 + 381 73,1 72,6
4.1 + 60 74,4
•5.1 + 5 70,5
. 1.2 + - 34 92,2
• 2.2 + 273 95,6
. 3.2+ 191 97,6 96,2
4.2 + 21 99,2
5.2 + 2 95,3
1.3 + 8 98,0
2.3 + 43 102,9 102,9
3.3 + 25 104,5
4.3 + • 1 94
1:4+
• 2.4 + 7 108,5
3.4 + 4 106,5 107,8
4.4+ •
4 46,8 49,2
2 ,47,5
1 58
23 74,9
174 74,4
257 75,9 75,8
• 94 77,5
10 83,1
21 91,6
59 92,4 •'
93 94,3 93,5
11 96,0
2 91,5
4 102,3
11 102,3 102,4
7 102,5
*
3 51,2 52,5
•
• 2 52,4
1 53
44 73,5
193 '73,5
331 73,2 73,5.
71 74,4
7 78,4
63 95,2
212 96,7
256 97,2 97,0
84 98,3
3 100,3
5 106,8
16 107,4 107,7
15 108,1
1 110
1 109
4 111,7
2 108,8 110,5
1 42 42
35 77,6
187 79,7
677 80,7 80,5
74 82,3
12 85,1
42 94,6
91 94,2
149 95,1 94,9
15 97,3
7 109,0 105,1
6 100,3
• 3 98,5 99,9
1 102
•
48 72,7
252 73,9
509 76,3 75,5
144 76,3
26 76,6
21 90,9
33 95,8
42 97,0 95,3
1 105
2 103,5 103,5
2 114,5
114,5
1 54 59,2
3 58,5
1 62
2 62,0
37 75,7
283 73,7
264 74,3 74,3
56 76,4
3 73,8
26 92,4
115 94,4
116 96,1 95,1
13 96,5
1 100
6 101,0
2 102,5 101,4
11 102,6
1 88
1 105
3 103,8
.6 103,8 103,9
1.5+ ' 1 115 •
1 117
2.5± •
1 117 115,6 1 128 128 1 126 121,0
•

•
- 160 -
the composition of the samples of catches, of the landings and of the [P.325]
stock. Changes in the composition of the landings are shown clearly in
Table 17. This table shows that the average weight-'of the salmon rises •
in the mean of the years 1954 to 1964 from September until about Febm-
ruary and that it thein•dropsé. The increase must - be considered to . be a
result of the growth, the decrease must be considered td be an effect of
the emigration of the large salmon. Changes in the composition of the
landings are thus caused only through the spawning migration. These findings
agree with the results of the investigations of samples as well as with
the conditions in the stock that have been described above.. Since in each
series of measurements on an average more than 1000 salmon-Of comPléte
datches have been examined, we may consider them to be largely represen+
tative for the landings. It is a different questionwhether this agreement
exists to the same degree in regard to the exploitable stock. Although
changes in the stock find expression also in the samples of eatches, it
cannot be proved that the percentage age . composition of the series of
measurements agrees with that of the exploited stock. Nevertheless, it be-
comes clear that the reèults of the analyses of the series of measurements
for January shown in 5.3.1. (Table 33) provide considerable information
about, the dynamics of the stock of salmon in the Baltic Sea and that they
do reflect the changes in the exploited stock of the southern Baltic Sea
(cf. 7.4). •
It hae already been pointed out'that it was not possible to
take scale samples in January 1963 on account of the ice conditions in the
Baltic Sea. This could be done only in April 1963. This sample éag, however,
not considered to be representative, as has just been shown. In its stead
'the series of measurements of November 1962 had to be used. The age composition

•
- 161 -
of these catches has been ascertained with the aid of Table 40 and of the
results of the age analyses of April 1963. With the use of the values from
Table 40 it waS possible to include the age composition of the series of
measureMents of January 1957 in the results (Table 33).
5.4. The growth relations
Investigations of the size of the ascending salmon of the Baltic
Sea have been made by T. H. arid (1938 , 1948), G. Alm (1934), J. Jokiel
(1958) and M. N. Lishev and E. J; Rimsh:(1961). The extraordinarily large
material of Jgrvi (more than 60,000 salmon) has recently again been treated
statistically by A. Lindroth (1961a).
The first investigations of the growth of the salmon in the
southern Baltic Sea were made by A. Willer and W. Quednau (1931), P. Brandt-
ner (1938) and B. Dixon (1934). The small material on which these inves-
tigations Were based was sufficient to give a first, valuable View of the
growth performance of the salmon. The data are, however, not sufficient
for a comparative treatment. Only F. Chrzan (1959b), R. andler and M.
Lehmann (1957) and F. Thurow (1960) investigated a larger material that
was suitable for cdmparisons.
5.4.1. Results of the investigations
The, results of the preseht investigation . have been summaxized
. in Table 43. The results apply only tO the life in the sea.
It has already been pointed out that the two maxima that appear
in the series of measurements (Fig. 34). represent the two important sea
year classes A.1+ and A.2+. The age determinations confirm this. It is seen
that the salmon of two winters have in January of the years of investigation

mean total lengths of 72.6 . to 80.5 cm, whereas those of three winters had
lenghts of 93.5 to 97.0 cm. These measurements agree excellently with the
maxima in the series of length measurements.
100
0,7
cm
rotoffin g e = total length
...,-,:elie,
Alemproe_ -:_
, ,/ xi,
.ir
„...,
, ,/
,
, ,
, ,,
, , ,
, , ,
, „ , ,
, , , , , ,,
, , , , , ,
,
, ,
, , , .
. . ti)t
.
m) m) (I) (.e ' r (.1
x t flS V VIS
XI
A. I.
nu mu nu nu 1961 nu
Year of examination
A 2.
1963
Untersuchungsjahr
• it.. - ttai
Fie. 36. Longitudinal growth of different yca7 t s ccts of
smoi-t-of Baltic Sea salmon.
Months
t I t I
4-4
vet ex ere e PtIonatt
3 4 liettrjohreskla sun
- - •
Sea year classes.
Fig. 37. The average changes in the length-weight
coefficients K for the ye.epele-se-t of smolt of 195 6 to 60 .-
Let » us now follow the loagitudtnali g„. 22t12 of the yeares, st
- 162
-
•
CÂMSeS
[p. 326]

- 163
-
of enolt in Fig. 36. From an assumed length of the smolt of 15 cm the
growth curves rise steeply during the first year. In the following.years
the curves flatten out. The greatest length ohserved was 128 cm. Corres-
ponding to this course of the curves the rate of• growth is greateét in
the first year and after that.diminiéhes steadily. The increase in length
during the first year is on an average over 30 cm, during the second year
about 28 cm, in the third year about 20 cm, in the fourth year about 8.3
cm and in the fifth year about 5 cm.
( SV1N et,v- 46,g) [p. 527]
It may be assumed .that of the sea year class A.+ only the
largest fish had been caught, so that the mean length is actually lower •
than the values in Table 43 show. The difference is, however, probably
not very great. G. Nordquist (1908)'carried out in April/May 1905 to 1907
length measurements on salmon in the Màlm8hus Lân that had been.caught with
narrow sand-eel . nets. bf the 168 fish 151 were under 60 cm long and ob•r
viously belonged . to.the sea year class A.1 (of one winter). These fish had
. a mean length of 47.0 cm. He furthermore cites .a series of measurements
by C. V. OtterstAil that was done in April/Mày 1906 on Bornholm :The 159
fish of the age group A.1 had a Mean length of 47.6 cm. From this can be.
deduced that the,èrror of the stated lengths of the one-wintèr salmon in
36 and Table 43 is not very large.
The growth in weight takès a course quite different from that .
in length. The smallest increas&df about 1 kg is found during the first
year. After a greater increase during the second year (more than Lkg gain)
the highest growth rate is achieved during the third year with more. than
4 kg..During the following years the increase is again smaller.(in the
fourth year over 2 kg, in the fifth year less than 1 kg)(Fig. 38)..
F. Chrzan (1959b) arrived at similar resultein regard . te. the
Fig.

Schlaçhtgewicht
kg •
1957
Fig. 38.
gutted weight
e
.
/
--- 1
• i_
1958 1959 1960. 1961 1962 Jahre irea-rm:
Weight increase in the Baltic Sea salmon.
- 164
-
increase .in weight. He found that the salmon showèd the greatest increase
thiring the third year in the sea. The investigations of the length, how-
• evsr, showed the gredbast increase during the second . year in the sea - in
contrast to the results given above. The same result was obtained by Kând-'
ler and Lfihmann (1957): Chrzan obtained the mean lengths with the aid of
a simple recalculation (cf. 5:2.2.). Furthermore hiasamples of catche,
as well as those Of Kândler and ahmann, were not taken at a certain date,
but durinithe entire season. It is therefore not possible to make a Closer
. comparison between the iesults of these authors and of those of the present
investigations.
•
The Figs. 36 . and 38 show, the characteristic annual course of
growth very plainly, the rapid increase during the summer and the check
[p.528 ]
in the winter. These differepées are the more distinct .theyounger'the
fish. In the older salmon a slowing down of growth during the winter is •
hardly perceptible.
A comparison of the growth in length and weight . shows that the

--165 -
increase'in weight is more retarded dUring the winter than the increase
in length. The •two different processes, the predominance of the increase
in weight in summer (rise in condition) and the predominance of the in-
crease in length (loss of condition) in winter regulate the changes in
the length/weight coefficient K (Fig. 37).
•Yeefe - ei"-s 5
. If one follows the performances of each individual yeer-Le-ect,
one finds - very different. forms of the course of- growth (Table 44). The
'yeef-a.sse • -
yeaele,--s494e 195 6 and 1961 attained as•sea year class A.1+ in November the
Very small average length of 68.7 and 68.3 cm, respectively. In contrast,
all other ye-aels. were already over 70 cm long in November as A.1.
Thus the yee,r'o act of.smolt of 1957 had a length of 74.1 - cm as A.1+ in
•November and so was 5.4 cm longer than the year's set of 1956 in the
s.
previous year. The yeeple-set of 19 5 6 managed to reduce this difference
to 1 cm, bees:Use it had Made an average gain of almost 9 cm in length.
yek.m-e..144:
On the other hand the year's cot of 1961 grew during the winter by only
6 cm and that of 1960 even bY only 4 cm. Especially outstanding is the
performance of the et1=tj4t of smolt of 1959 that has been peinted Out
. by Kandler (1961). This ye,aele-ae4 was 80.5 cm long as A.1+ in January .
1961 and had thussgrown at least 5 cm more than any other e444-%-e4
Surprisingly, this advantage finds no longer an expression ,in the4ssea
Year - claas A.2+ (1961/62).
• The growth in the sea is dependent predominantly.on the duration
of the -sojourn in the sea. As is 'shown in Table 43, the influence of the
brood year's oc t is still plain; because the mean lengths increase in
general witnin . a sea year class with increasing duration of the stay in
' the rivers. On an average, during the years 1958 to 1963 the difference
- between the'age groups 2.1+ and 3.1+ is about 1 cm. This phenomenon has

- 166 -
already been pointed out several times (T.H. Jgrvi 1938,.B. Dixon 1954 ,
F. Chrzan 1959b, F. Thurow 1960).
5.4.2. Discussion of the findings
A. Lindroth (1961a) has ascertained in his extensive analysis
of the iaaterial of Jârvi that the size of a fish at a certain age is det-
ermined by font. factors,.namely, the genetically fixed growth potential,
the intake of food, the chemical and physical environment (especially tem-
perature) and'the initial size that it had at.a certain time. The last
point is obviously valid only when a limited period of life is under con-
sideration. As in the present case, the life of salmon in the sea. Apart
from the innate growth potential the three points are not primary factors.
In . their changes they are rather subject to other factors. Thus, for ex-
ample, the intake of food depends on the numbers of prey available, on the
time of their appearance and on the number of competitOrs for the food.
5.4. 2. 1. The rate of growth
Before we consider some phenomena that are indicated'by the
matérial presented, the general features of the growth process must be
reviewed. The course of both the increase in length and in weight shows
that the rate of growth dScreases considerably during the fourth year in
. the sea. It is a general feature Of fish that they grow during their,entire
life. Only in rare cases, when they, are forced to cease feeding, is it
possible for the weight to decrease. .
11). 329]
In the treatment of the salmon with spawning marks it has been
éstablished that the sea year class A.3+ (that of the fourth year in the „
Baltic Sea) cc:insists already . Of 37 per cent of salmon with spawning marks.. .
•
• 0

•
rl
-P
b..0
-e
nzi
-ri
r-1
gl
a)
of smo lt, to tal
Table 44. Growth of .
\ID
o
Cr■
.I.fl
a Ln 0 Ln
»,-11 ■In' '2 4-'.: -›'.
A marks and 110.8 for those fish
that had not yet spawned. In
January 1961 these lengths were even 93.8 and 109.3 >cm, respectively. In

- 168-
spite of the changes that the curve of growth undergoes when the fish
are being eliminated that have aiready spawned, the reduction in the rate
of growth in the older fish can be demonstrated ..
In a paper On the fluctuations Of quality in the Baltic Sea
salmon (F. Thurow 19 62) it could be shown that at a certain body length
[p. 330 ]
the salmon have finished a decisive phase in their development that serves
as preparation for the spawning migration. Since most of the maturing fish
have emigrated before the third year in the Baltic Sea, it suggests itself to
consider here the salmon of the class A.3+ to be such fish that had in
the previous year just failed physiologically to obtain the readiness for
. the spawning migration, beCause they had not reached the condition neces-
sary for the Spawning migration.
5.4.2.2. The growth of the year's set of smolt of 1959
n the preceeding it has been demonstrated that the-
of gmo•t of 1959 as sea year class A.1+ had attained an outstanding mean
lengthof 80.5 cm. A length that had not been attained by any other year is
etss
---sigt for a long time (Tablas43 and 44). The salmon of two winters that had
been examinalby Kgridler and Whmann (1957) had in 1952 to 1955 lengths of
69 to 73 cm. F. Chrzan (1959b) found, it is true, a corresponding mean
length of 80.6 cm. However, he could examine only 16 salmon of this sea
year class A.1+. Furthermore it has' not beenstated whether. the material •
examined originated in winter or spring. In any case the growth of the
e.,Le5
year's ..sre4t of smolt of 1959 deserves a closer examination.
T. H. ervi had pointed out in 1948 that the mean size . of all
salmon had diminished considerably since 1942 to 1944. According to Lind7
. roth (1961a) this reduction became obvious for the first time in the year%

- 169 -
CLA‘s
set of smolt of 1939. He could show that the limited annual fluctuations
of the mean lengths were highly significant, but that they had little to
do with the changes since 1939. Lindroth is of the opinion that changes
in growth are caused by factors that are effective during the first.year
in the sea. Food together with population density, as well as temperature
conditions are cited as possible causes. A previous reduction in the length
of the smolt is not being excluded.
aess
Let us now follow the growth of the vearts. -b-et of 1959. A mean
see5
length of 80.5 cm means::anincrease over the mean of the year's Set.s of 1956
to 1961 of 6.7 cm (9.1 per cent). In contrast to this the weight increases
by 38.6 per cent tc4.17 kg. This shows that this.growth performance is not
only of scientific interest but also of commercial interest. By taking as '
basis the age composition of the catches 1960/61 it is seen that the yield
CIA.ss
in weight bythe mean weight of the sea year class A.1+ (yeails-Bet of smolt
of 1959) ivas 22.3 per cent higher than it would have been for a "normal"
mean weight of 3;01 kg.
.What did cause this good growth? The sea year classes A.2+ and
A.3 + that appeared together with the yearis of smolt of 1959 in Janu-
ary 1961 did not show an especially good growth. It must therefore be as-
• not
Slimed that the phenomenon did/affect uniformly all age groups that appeared
at the same time, but that it was caused by an effect that influenced only
C6.-css cbt.ss
a single yeaeb,sSt. When one follows the yeart backwards, it Can be
de.s$
shown that the year"s,>e,„t of snolt of 1959 probably had grown well also
during the first yearin the Sea.(Fig. 38).
We face now the question, in which stage of life the special
' increase in growth had been realized for the first time. Let us consider
• in this connection the following three possibilities:

- 170-
(a) the good grciwth . of the year'aet of smolt of 1959 took place for the
cf.4e,s
first time in the sea. All age classes of this year'e set must then
dees
have grown very well . No' age group of other yearPss, ee ts should show
a similar result.
(b) The good growth was induced already in the rivers. Only one brood yearm-fd
has grown up under optimum conditions and has later as one of the
age groups 1.B to 5.B exerted a decisive influence on the mean length
ae,“
and the mean weight of the year",>s 'eet of smolt of 1959: The other age
groups do not show such outstanding results of growth.
d. [p. 331]
(c) The good growth was induced in the rivers. Several brood years ee4s
did live under favoilrable conditions and constitute the cause of the
CIAS
good growth of the year"R--eet of smolt of 1959. Therefore, several of
its age groups show special gains. Since the age groups in question
did not only contribute to the formation of the year's, 'eat of smo.1À
of 1959 , but formed also age groups of other year's eets, these.also
should shoW good results.
• eisv-6ie't4S
Let us now follow the brood yeerem-ee4s during the corresponding
cLees
years. The age groupS of the year'sr-eet of smolt of 1959 are made up of
c-1,,Ç es
parts of the five lœood year't-rete 1954 to 1958.
-ctas4cs
As is shown by Table 45, four of these brood year'b bets take
-ciass
part in the formation of the . yearl-e-eet of smolt of 1958. If growth-prom-
oting influences were active in the rivers during the period cited, then
they Should be apparent almost as strongly in the yearie-tôf-âmet'.of
1958 as in that of 1959. Let us inspect Table 43 in this connection and .
-d&ases
compare the mean lengths of the age groups of the year 's-re-S. of smolt of
1958 (January 1960, age group 1.1+ to 5.1+) and of 1959 (January 19 6 1,
elos
age groups 1.1+ to 5.1+). It is seen that the fish of the yeare-e-eet of
•gmolt qf .1958 are very much smaller and show in comparison with the age

Year's sets
of smolt
CILS
present
7 171 -
groups of the yearem-sst of smolt of 1959 the very great differences in
length of 4.1 to 7.9 cm.
•
Table 45. Brood year's sets that appeared together in the
rivers during the years 1954 to 1959. •
1955 1954 1953 1952 1951 1950.,
1956 1955 1954 1953 1952 1951
1957 • 1956 1955 • 1954 1953 1952
• 1958 1957 1956 1955 1954 1953
•
1 ,)59 1958 1957 1956 1955 1954
1960 • 1959 1958 1957 1956 1955
For the sake of completeness let us also inspect the yeart'u
-of smolt of 1960. In case the decisive factors were active only in the
year 195 8 , then the brood year4ASs4ise.. of 1954 tà 1958 have been 4fluenced
ekts
. by them. That means, however, that apart from the year'b bet of 1959, the
.year‘s--met of smolt of 1960 also would have profited by it, because four
of the affected brood year's-sets took part in its formation. Let us there-
fore examine also the mean lengths of this yearLs-set of smolt in January;
clAss
they are 4.4 to 8.5 cm lower than those of the year"r-sset of smolt of 1959.
. Let us .now attempt to obtain a last pointer for the answer to
this question. From Table 33 can be seen that the yearl-s-sst of smolt of
1959 . as A.1+ contained 63.5 per cent of three-year-old smolt, wheras the
proportion of these in the year -"s-set of, 1960 was 52 per cent. When one
now obtains through simple recalculation the lengths of-smolt for these
brood \eallâai that are represented most strongly, one obtains 14.4 cm
for the former and 15.3 cm for the latter, that is a smaller length for
- cl.ss
the main component of the year's-*et of smolt of 1959.
According to these statements it must be considered to be most

- 172 -
improbable that the promotion of growth took place already in the rivers.
, The decisive impulse was received rather certainly during the first year
yeme-c..4,43
in the sea (1959). However, at this time the .scri-s—set of smolt of 1958
was also represented in the Baltic Sea (as A.14.), which did not show any
very great growth. One must therefore assume that special circumstances
did influence the year's-set of smolt of 1959.
Let us examine once again from this point of view the four
factors that influence the growth, mentioned earlier. A change in the
growth potential can here be excluded. The influence of the initial size
must also be denied according to the above statements. It is furthermore
true that the post-smolt could not have lived under different conditions
of tekperature or thet they were influenced by them differently than the
larger fish. Thus there remains as decisive influence the complex factor
of 'food.
' A. Lindroth (1961b) has shown that the young salmon feed in the
sea at first on flying insects and pursue fish only later. According to
our investigations (2.2.3.2.) salmon of a length of hardly 30 cm take
already the baited hooks. The size of the maeh opening certainly plays
a role in the trabsition to fish food. At this time the young fish are
living already under the same conditions as the Older salmon. For this
dass
reason we assume that the extraordinarily good growth of the yeart-s—ee.t..
of smolt Of 1959 had as its cause' the excellent supply of food fbr the
post-smOlt during the first period of their stay in the sea. Thus the
same factor (food supply) is responsible for the unusual growth of the
yearLe—sett of Smolt of 1959 as that cited by Lindroth as the cause of the
c,14es
very poor growth of the year's-set of 1939.
HoWever, before this question can finally be settled it is
[P. 332]

- 173 -
necessary to follow the growth beyond the sea year class A.1+. Here, how-
,I)ew-c,144s
ever, it is found that the year's-ret of smolt of 1959 as sea year class
À.2+ does no longer show a sPecial size. This phenomenon cari be explained
only by the fact that very many, and especially the laxgeet fish have al-
ready emigrated after a stay in the sea of only two years, in order to
spawn in the fall/winter of 1961. The increase in the Swedish river catches
from 110 t in 1960 to 209 t in 1961 provides a hint for this assumption.
5.4.2:3. The influence of the size of smolt on the growth in the sea
It has' already been mentioned:that the smolt are the larger, the
longer the duiation of the sojourn in fresh water and that these differences
Can.still be observed in the adult fish in the sea. Lindroth (1961a) alao
has investigated this question. He arrived at the result that an influence
of the smolt age on the size of the adult salmon could not be proved as
significant in 13 outof 14 cases. Seen from a certain point Of view, it
.seems to be of value, to examine this question.once more on hand of the
• German material of observations.
With the aid of Table 43 we can ascértain the mean annual in-
crease in the age groups 2.2 and 3.2 (the difference between 2.2+ and 2.1+,
and between -3.2+ and 3.1+) and we obtain values of 20.00 and 20,01 cm.
A rate of growth .that agrees that closely for thé two most important age
groups 2.B and 3.B indicates that differences in the mean lengths that
exist already, remain in existence also in the sea.
An important hint, regarding the question,.whether the size of
the smolt can influence the mean lengths of the sea year classes . , is prov-
ided by the figures of Table 33. When one examines the percentage share of
des
'the age groups in the sea year classes for every year4--8--met of smolt, one

Year's
set
1956 • A.1 +
4 34 53 8
1
A.2 ±
11 32 50 6
1
1957 A.1 +
A.2 +
1958 A.1 -I-
A.2 +
'At +
• A.2 +
3 24 64 8
' 22 • 34 44
1959 1
1960 A.1 +
A.2 ±
•Avérage
1956-1960
A.1 +
A.2 +
- 174 —
obtains the values in Table 46. It will be seen that the shares of the
elass
age groups of a yeal-4-s—ee4-of smolt change with increasing age.
The percentages of the older fish (3.14 4,B and 5.B) become.
.smaller at the rate at which the shares of the younger fish (1.B and 213)
increase. These changes have no other explanation than that the older
fish emigrate in order to spawn. That means that the sexual maturation
is being determined not only through the duration of the
but also through the duration of the stay in the rivers.
not the du;s.tion of one of the two periods by itself is
total age.
stay in the sea,
LP.333]
In other words,
decisive, but the
Table X. The percentage composition of the sea year classes.
Sea yeax Share of the age groups in the sea
year classes in per cent
class • 1.B 2.B 343 4•B 5.B
4 31 46 17
10 34 41 14
30 51 11
13 34 45 8
5 26 52 15
10 42 43 5
5 29 53 12
13 35 45 7
• At other places it has been pointed out repeatedly' that the
'emigration is connected with the size of the salmon (3.2.3). Applied to
the above statement, this does mean nothing else but that within a sea
,.year class and within its age groups the larger fish mature earlier.
It is therefore possible that the statements about the existing stock are
'correct when calculating the mean lengths. The rates of growth that have
2
1 '
1
2
1

- 175 -
• been ascertained from them are dependent on the number of the emigrated
salmon and may perhaps be greater than stated. Finally, it is very probable
that thè differences in the mean lengths that have been ascertained for
the age groups of a sea year class would be greater when the emigrated
salmon have been taken into account. This could have the consequence that
the statistical treatment of the differences yields significant differences.
The possibility is therefore not to be rejected that the size of the smet may
influence thé length of the salmon in the sea.
6. The food of the salmon of
the Bal tic Sea
The manner of life of the fish is determined in many respects.
by their food.. Thus investigations of the food will suPply information
about certain habits and behaviour. Furthermore, changes in the kind and
, amount of the food consumed influence the composition of the tissues.
Finally, the food forms an important component of the factors that deter-
mine the growth.
• 6.1. Previous investigations
The differences between the life of the salmon in the rivers
and in the sea have also affected the food investigations'. It is easier
[P. 334]
to obtain the material for investigation in the rivers than in the sea.
There are therefore few papers that treat the nourishment of the adult
salmon. •
.6.1.1. The nutrition of the juvenile stages
The nutrition of the salmonids in fresh water has been investigated

•
- 176-
since the turn of the century by numerous researchers. Statements about
the first food of the fry after the yolk sack has'been consumed are, how.-
ever, scarcet.'
Th. Schrader (1928) has inveStigated specimens of Salmo trutta
fario, about 20 mm long and found that they had eaten hardly any plankton
crustaceans, but Mainly bottom crustaceans (Alona), in part also oligo-.
chaetes. In Cumberland, Nova Scotia and New Brunswick H. C. White (1937)
discovered larvae of chironomids in the stomachs of freshly hatched salmon
alevins. A. Mitans (1963) has observed in subsequent years in the Salatza
(Latvia) salmon fry of 38 mm length..In June the fish had eaten chironomid
larvae that were numerically preponderant (100 to 200), but which amounted
to only 21 per cent by weight, whereas Baetis (Ephemeroptera) represented
50 pér cent. Ephemerella ignita occupied with 16 per cent by weight the
third place. •
. 'Fingerlings examined by White contained nymphs of ephèmerids
in summer and in the fall mainly trichopterous larvae. In the older parr
plecoptera play a role in winter, in the spring also Baetis . and EPhemerella,
. as well as trichopterous laxvae.(A. Fritsch 1893, A. Mitans 1963). In his
three-year investiations (1916 to 1918) G. Alm (1919) obtained similar
results. Trichoptera (Hvdropsvche, Philipotamus, Rhvacophila) played the .
important role.for paxr from April to November. Baetis was represented
most
almost.as well and unifotmly. The ptoportions of the other.animals flue-
tuated during the course of the year. In.third place.were larvae of chir-
onomids in May, in July/August imagos of insects, in October/November
.plecoptera, and in April even Asellus.
Caxpenter . (1940) thiffics that the kind of food consleed . depends
on its availability. There is no loss of appetite, only lack of opportunity

(after K. A. Pyefinch 1955).
— 177 —
The largely similar results of the investigations indicate that
there are only slight fluctuations in the basic food of juvenile salmon
in the rivers. This statement conforms to the scientific opinion that there
are hardly any fluctuations in the total productivity of insects, because
the niche occupied by a weakly represented species is promptly filled by
another.
N. C. Morgan and A. B. Waddell (1961) collected the insects
occurring in a trout lake with a floating trap and found differences in
the catches of the same taxonomic groups from year to year that amounted
up to the six-fdld. In contrast to the scientific opinion it was found,
however, that the catch in 1956 was substantially better than that in 1955
and in 1957.• The period of the main emergence of the insects extended from .
April to September. Correspending to this, the salmonids ate during the
winter at the bottom Gammarus, Asellus, Limnea, in the spring they ate
mainly larvae of chironomids and and in late summer they lived on flying
insects.
6,1.2. The food in the main basin of the Baltic Sea
For a long time there was no information available about the .
food of the salmon in the sea, because material for investigation was dif-
ficult to Obtain. Thus L. Roule (aecording to H. Henking 1929) was still
of. the opinion that the salmon would seek out the depths of the sea after •
.their émigration from.the rivers and feed on the large supplies of •
benthic animals of the Atlantic shelf.
It is probable that the first investigations of the food of sal-. .
hai 335]
'mon that had ben caught in the Baltic Sea along the coast of' Pomerania

- 178-
were published by Eichelbaiim (1916). The results of his investigations •
are. ?till of importance today, because he reports about the nutrition
of the salmon during their first year in the sea. Twenty-nine emigrating
smolt (14 to 27 cm) had lived from March till May principally on flying
insects (Coleoptera, Diptera), besides on larvae of chironomids and gam-
marids and isopods. Another 22 amolt of a length of 14 to 21 cm that had
been caught in the sea .hetween May and October also contained Coleoptera,
Diptera and gammarids. Of exceptional importance is, however, the finding
that they had eaten in paxt'also Ammodytes. Some larger fish of a length -
of between 36 and 60 cm, mostly, however, 41 to 51 cm long, were caught
in March and April. Among the fish With stomach contents, 53 per cent had
eaten preponderantly Ammodytes, 24 per cent had eaten mainly Gammarus and
23 per cent had eaten Ammodytes as well as clupeids. •
Similar investigations have been carried out by Henking (1931)
on 134 salmon that had also been caught from 1914 to 1920 at the coast of
farther Pomerania..During the months of February to May no decisive changes •
were observed. In seven smolt of a length of 12 to 18 cm only flying in.,
. sects were found. Of the remaining 127 salmon (36 to 52 cm length) more
than 50 per cent had eaten Ammodytes (on an average 1.9 fish), 30 per cent
contained Gammarus (1.9 specimen), 24 per cent had remainS of fish, mostly
clupeids. Occasionally isopods and Crangon were found.
The latest investigations of the stomach contents of smolts in
-the Baltic Sea have . been made by Lindroth (1961b). The fish of a length
of 13 to 22 cm were caught from June to August along the Swedish oixIst in
the Bottensee. Almost all fish had eaten flying insects (300 to 500). One
gmolt, 20 cm long, contained a fish.
B. Dixon found in small'Eetic Sea salmon (mielnica) Ammodytes,

•
gadids and sticklebacks (after K. Bahr 1936b).
- 179 -
K. Bahr (1935b, 1936b) was -the first to report on the stomach
«content of large salmon in the sea: Among the fish investigated'were 139
salMon of lengths between 73 and 116 cm. He was able to demonstrate that
the changes in the composition of the food are related in the main to the
seasonal vertical movements of the sand eel and of the sprat. During Jan-
uary apd February the always pelagic stickleback was preponderant. With
the warming up of the surface water , sand . eel and sprat moved up into the
higher layers of water so that they can be captured by the salmon. Numers
ically the stickleback was most common and was also most often eaten by
the salmon.
This result that is very impressive on account of the causal
information, can, however, not be generalized and is not valid for all
fishing grounds in the Baltic Sea, as could be demonstrated by Christensen
(1961b) on hand of the hitherto most comprehensive material.(2100 salmon).
In general the sprat must probably considered to be the most important item
in the food during the entire year. They are followed by herring and stick,
leback. The sand eel is of greater importance only to the south and south-
east of Bornholm.'Netted salmon had larger stomach contents than the fish
caught,on hooks. He did not find any food differences dependent on size .
among the salmon of 60-cm to 95-cm length.
F. Chrzan. (1960) has examined 65 netted salmon in the spring of
1959 and 118 hooked salmon in the fall/winter of 1959 /60 from the Bay of
Danzig. He came to the conclusion that the clupeids are the Most important
food of the Salmon in every case. He thinks, however, that the herring
. might play a more important.role than the sprat. Trigger fish and sand .
eels follov behind the clupeids in regard to weight.
•

6.2. Amount and kind of food according to my own
investigations 1957 to 19 6 4
- 180 -
' The present investigations were carried out between 1957 and
1964 on 2400 salmon (Table 47). More than one-half of the stomachs have
been analysed on'land in the laboratory. For the collection of the mat-
erial several salmon cutters were supplied with plastic pails that held
about 70 to'80 stomachs each. After gutting, the fishermen put the entire
intestines in formaldehyde on board. In this way it was possible to det-
ermine also the sex of the fish. No exact statements of length could be
obtained. Instead the length of the stomach was measured. The comparison
Table 47. Number of salmon investigated and their
times of capture
Month Time of capture
1957/8 '1958/9 1959/60 1961/2 1962/3 1963/4
September .
25 23
Oktober - 91 71 66
November • •
221 151 .
Dezember 122 151 .
Janua'r 156 71 54
Februar
36
Mârz •
. 210 . 77 280
April . 157 71 159
. • Mai
151
•
Juni 63 .
•of the frequency distribution of these values with the series of measure-
ments of coMplete catches df'salmon (Fig. 54) shows that a stomach length
of 10 cm corresponds about to a tdtal length of fish of 66 cm and each
further cm to a body length of 2.5 cm.
In every case thé totarweight of the stomach content was as-
certained first and then the weight and number of the individual prey.
It 'was in general possible to identify food items that.had been strongly
. digested with the aid of ooliths or by counts of vertebrae. That.was
• •
•
[p. 336]

- 181 -
especially decisive in, the „separation of clupeids into sprat and herring.
Nevertheless, there remained a small percentage Of clupeids that could not
. be identified and a further part of fish that could. no longer be determined..
.
The former have been assigned to sprat and herring according to the shares
of these two species that had already been ascertained.
In the investigations of food at sea ia was only possible to
count and measure the prey. These figures have later been recalculated into
weightS with the 'aid of the relations that had been established in the lab-
oratory. •
Of the 2406 stomachs of salmon that have been examined,1198
49.8 per cent contained food with a total weight of 36,139 g. Of this 1416 g
consisted of a slimy food mash. The remaining food constituents have been
listed in Table 48. They amountto 34,723 g. Notwithstanding the rather
long list of foo&constituents it is seen that only five specieS of fish
and one crustacean species are of decisive importance. The clupeidP,
especially the sprat, alone made up over 88 per cent of the food,weight,
The sprat was found in 60 per cent of all .salmon that had taken food and
herring in 20 per cent. Besides these two species of fish should be men-
tioned in the order . of their .importance, (2.8 per cent of the
food weight), Ammodytes (2.6 per cent), and stickleback (Gasterosteus,
0.9 per cent). These fish Were found in 5 to 10 per cent of all salmon
that had food in their stomachs. As a last group of importance have to be
mentioned the mYsids, which made up 2 per cent of the weight and had been
eaten by 9 per cent of the salmon.
[1" 337]
Cod, amphipods and Crangon were present in 1 per cent of the
salmon. With the exception of the cod they do nàt play any role, in regard
• to Weight, «nor as to the number of individuals (Table 48).

Table 48. Constituents of the food of salmon
1957-9 and 19 6 1-4.-
Weight Number of sal-
Prey . g per cent mon with the Number
Total 36,139 particular of
Nash 1,41 6 food in rare
per cent prey
"Remainder" 34,723 100.00
Sprattus sprattus 75,51 60
Clupea harengus ' 13,00 20
Belone belone 2,82 8
Ammodytes Spec. 2,56 5
Mysideae 1,96 9
Gadus morrhua 1,79 1 27
Gasterosteus • 0,94 9
Scomber . 0,24 1
Merlangius merlangùs 0,16 -3
Onos spec. 0,08 2
Alosa fallax 0,06 ' 1
.
Amphipod.
0,04 1
Crangon 0,03 1 13
Cottus spec. 0,03 1
Rutilus 0,03 2
Sonseige Fische, Grâten OTHER FISH • 0,75 1
Corixa ' BONES < 0,01 1
DytisCuS < 0,01 1
Luflinsekten flying insects < 0,01 1
Tunikat tunicates

6.3.1. Seasonal fluctuations
36,9
26,1
13,2
12,1
16,9
16,5
10,1
37,5
61,1
36,5
30,3
26,7
70,3
27,7
24,9
10,4
46,5
35,1
61,8
39,5
- 183-
In the treatment of the growth it haF been shown that growth
is Very rapid during the summer months and that it is slower in winter.
Furthermore, there is a loss of condition in the cold season (Fig. 57).
[P. 33 8 ]
These phenomena Can have two causes, the different speed of digestion in
dependence on the temperature and changes in the availability of the food.
If temperature were the only effective component then we could expect the
sanie average condition in winter as well as in summer. If the filling of
the stomach is reduced during the winter with simultaneous deterioration
in condition one can refer -this to the salmon having at their disposal'
less food in the cold season than in summer.
Table 49. Monthly changes of the food weight per salmon in g,
mean of the years 1957 to 59, 1961 to 64, line and net catches.
Mean food weight per salmon in g
Mean
Month
1957-9, 19 6 1-4 0.
'Mean
Christensen
of all -Mean of salmon
(1961)
salmon ' with food
1960/1
September 36,9
Oktober 15,6
Novernber 4,5
Dezem.ber 7,2
Janùar 7,2
Februar. 11,9'
Mârz
April 26,5
Mai 59,0
juni 34,8
Weighted mean 15,1
Simple mean 21,0
In order to test this question it must be established how the
average weight of the stomach content changes from month to month. Here
we meet a difficulty. It has already been said that about one half of the
stomachs.examined did no longer contain formed food or were empty. In

- 184 -
Table 49 have therefore been given two figures for every month. The mean
weight of food has been calculated first for the total number of all sal-
mon examined and second only for those fish who had a full stomach.
Botk figures show that the weight of the stomach content is
highest in fall and spring and_lowest during the winter months, especially
from November to March. The investigations of Christensen (1961b) show a •
similar result. It is therefore probable that the food supply of the sal-
mon is smaller in the winter than in summer. On account of the cessation
.of the salmon fishery in summer, we could obtain no samples in July and
August. One can, however, assume that the values for these months would
not be substantially different from those for May/June.
A comparison.with the results of Christensen shows a consider-
..able difference in the amount of food. His values for the season 1960/61
are on an average almost twice as large as the mean values of my material.
Christensen has investigated fresh stomachs that had been collected on
board and frozen, whereas my material had been preserved in formaldehyde.'
It is, hOwever, quite obvious that the large differences cannot have been
caused by different : methods of investigation, but must have thpir cause
• in the better availability of the food in the season of 1960/61.
ye- tin
A glance at Fig. 36 shows that principally the yeeri-s-set of
smolt of 1959 has profited'from the extraordinarily good food supply of
the season of 1960/61. But also thé good growth of the year's sot of smolt
of 1958 during the third year in the sea can be brought into agreement with
this.
$ince seasonal changes in the take-up of food are probable,
we shall once more refer to the, fact that only about one-halUof the eal-
.
mon investigated had food in the stomach. Chrietensen has indicated that
•
LP. 339] .

•
Number of Months
Gear salmon
investigated IX/X XI/XII I/II III/IV V/VI Total
Line Total
p.c. with food
. _
187 645 263 13 1108
64 44 43 100 48
Nets Total 89 54 941 214 1298
p.c. with food 83 44 41 88 51
Total p.c. with food 70 44 4 3 - 41 88 50
--r
- 185-
the salmon, especially those caught on hooks, are perhaps inclined to
vomit the food in their stomachs. On the other hand, it is possible that
more salmon with empty stomachs are found in winter than in summer, so that
this phenomenon could be explained, at least in part, by the smaller avail-
abillty of the food. In this connection let us examine the percentages of
salmon With full stomachs in Table 50. Between November to March or April,
.respectively,only
, about 43 per cent of all salmon .have food in the stomach,.
60
40
20
Table 50. Seasonal changes in ratio of salmon with empty
stomachs to those with full stomachs.
9 ,4.9...0.0 Stomach contents
G0110 ,10
Ooozg. fol Danzig Deep
0 0 0011004
Fig. 39. Mean weight of food per salmon in g on the
fishing grounds 5 and 6, 1957 - 9 and 19 6 1-4.
mc,,e.- IMemths

•
- 186-
whereas the share was 70 per cent in September/October and even 88 pert
cent in May/june. After this result we may ahmune that the share of sal-
mon with empty stomachs gives an indication of the availability of food.
Therefore all results will be correlated in the following investigation
with the total number of the salmon examined.
6.3.2. Différences on the fishing grounds •
Since the size of the weight of the stomach contents depends
on the season, only such data can be used in the compaxison of different
fishing grounds that take such facts into account. The data on hand orig-
inate frOm the fishing grounds 4, ,5 and 6. From the fishing ground 4 data
are available only for the months September (1962, 1963) and October (19 6 1,
1963). Data from the other two fishing grounds are very scarce as fax as
they apply to the same months* and fishing periods. For this reason means
[p. 340•
have been'calculated froM the values of all years and their seasonal course
is given in Fig. 39. The values from the fishing grounds 5 and 6 show good
agreement from December to April. In contrast, the salmon-had in October
1957 near Bornholm more than twice the amount of food in their stomachs
than had the fish'of the Danzig Deep. The values for October from the fishing
ground 4 (Gotland) agree.well.with thoEe from Bornholm.
• AlthoUgh it is not possible to obtain differences in the food
weight of a salmon that are unambiguously dependent on the fishing ground,
there are found certain variations in regard to the composition of the food
on the individuar fishing grounds (Table 51).
On.ths fishing ground 6 it is true that the sprat predominates
in the food, but it is represented to a smiller extent than on the Danzig
• Deep. It is also found that.Belone, Ammodvtes and even the mysids can form

MagerdW hing
40
, 20
Filling of Stomach
•---,0 nelzgetarigene Lochs, netted salmon
ci—Cr geongelle (ochre hooked salmon
•
•
•,'"
XI XII IV monae•Months
Fig. 40. Pbod weight of salmon, caught in the Danzig Deep
with line and net.
- 187 a -

- 187-
important constituents of the food, whereas in the Danzig Deep only
Belone played a temporary role.
Table 51. The most important food ingredients as percentaes
of the total food weight (without the unidentifiable mash).
Fishing Months Mean
Food . value
ground IX X XI XII I II III IV V VI simp. weig'd
5
Sprattus
Clup. har.
Belone
Ammodyt.
Gasterost.
Mysideae •
57 67 45 36
10 20 31 29
29 9 16
2 4 11
0 2 8 1
0 0
5 90 97 69 58 76
80 7 2 31 26 14
0 7 2
1 I 1 3 • 1
3 0 2 1
8 0 1 0
6
'
Sprattus
Clup. har.
Belone
Ammodyt.
Gasterost.
Mysideae
•
75
25
8 79
39 2
38 19
8 0
0
54 25
7 11 0
1
73
1 1
91 33
40 29
14 16
IO 16
12 15
2 3
21 18
4
Sprattus
Chip. har.
Ammodyt.
Gasterost.
89 96
9 1
1 2
0
93 93
5 5
2 2
0 0
0 = . .< 0.5 per cent
6.3.3. Differences in dependence on the gear employed
No exact comparison is possible between the weight of the
stomach content of salmon caught with line and that of salmon caught in
nets. There are no data for both kinds of gear corresponding to the same
months and years and the same fiehing grounds. In Fig. 40 have therefore
been inserted the mean value s . for the years of investigation on the fishing
ground 5 (Danzig Deep). According to the curve there are apparent no sub-
stantial differences from October to March. Only beginning in April do the
netted aalmon show a considerably-larger stomach content than the hooked
salmon. However, this result has to be accepted with reservations, because
in March only five and in April only eight" hooked salmon from the Danzig
LID. 341]

Deep could be examined.
- 188 -
Christensen (1961b) had a more extensive material at his dis-
position. He examined in October 1960 the stomachs of 147 netted and 192
hooked salmon and in January 1961 thOse of a further 147 netted and 229
hooked salMon. He came to the conclusion that netted salmon contain con-
siderably more food than hooked salmon. The figures were for the northern .
Baltic Sea 50.4.g (netted) and 27.8 g (hooked), for the eastern coast they
were 34.3 and 15.1 g, and for the Bay of Danzig they were 12.8 g and 9.4 g.
9ear
Table 52. Weight of food and proportion of clupeids in
male and female salmon.
Number of salmon Weight of food per salmon
examind in g
Total Clupeids
9 d 9 d 9
. .
Net 334 235 23,2 24,2 20,3 22,4
Linp 204 150 12,4 13,0 10,0 9,6
_
Total 538 385 19,1 19,8 16,4 17,4
6.34. Differences depending on sex
-During. the examination of the stomachs in the laboratory, ït
was always possible to determine the sex of the salmon. The results, as
fax as they concern - the total weight of the food and the proportion of
clupeids, have been assembled in Table 52.
DifferenCes in the amounts of étomach content of -nettedand
hooked salmon can be referred to the months of capture. In regard to the
sexes it is found that thé males show a slightly higher weight of food
than the fémalea. The differences are not.significant.
• 342]

•
6.3.5. Differences in food related to the size of the salmon
Christensen (1961b) did not find a connection between the kind
of food And the size of the salmon when he examined his fish that had
a length of 60 to 95 cm. Neither did he find that the larger salmon had
more food in their stoamchs. He explains the latter by the larger surface
of the stomachs in.the large salmon and the consequently more rapid diges-
tion. The preeent investigations also show no size-dependent differences
in the salmon with lengths from 60 cm to 112 cm.
Table 53. Fàod of smolt and post-smolt according to different
authors (percentage of salmon with food in stomach
in parantheses).
Author Months
Fish. Am- Fly-
Num- L Clup. Amm. Bel. phi- ing
ground ber cm pods ins.
-
-
EICHELBAUM V-X Pomm. Kiiste 22 14-21 + ' + +
HENKING IV-V Kolberg 7 12-18 LI-
LINOROTH VI-IX Bottensee 46 13-22 + +
HENKING II-V Kolberg 127 36-52 -I- (24) 1,9 (50) 1,9 (30)
THUROW XI-IV Danz. Tief 6 28-48 • 2,7 (100) 0,2 (17)
[Pomm. Kiiste = Pomeranian coast, Danz. Tief = Danzig Deep]
The food of the smaller salmon (A.1), which in general are not
yet exploited, is of greater interest. Only six specimen with a length of
from 28 to 48 cm could be.examined. The results have been summariied iri
Table 53, together with the results of other authors. As has already been
stated, thé Smolt in the Balt4o eat to begin with mostly flying insects.
Some fiéh, however, change very soon to a diet of fish. Lindroth fOund a
fish in à emolt of a length of 20 cm and Eichelbaum could_demonstrate Am-
màdytes already in smolt.with a length of 14 to 21 . cm. When they are over
. 30 cm long.one . finds predominantly fish as food.
One can reckon that the rapid growth begins only when the young
- 189
-

- 190 -
salmon . switch over to the compact food of crustaceans and fish. This doesnot
man H that crustaceans and fish do predominate in the food only after the:fish
have reached a length of 30 or 40 cm, but that they are decisively respon-
sible for the attainment of this size and are therefore eaten alreaey
earlier in greater amounts. One can deduce furthermore from this finding
that the final growth performance of the salmon is dependent to the largest
extent on the moment when the post-smolt switch to fish food.
6.4. The relation between the behaviour of the prey and the composition
. of the food of the salmon
CobOrSe
Ut)
• (On hand)of the food investigation could be established that in
the Danzig Deep the proportion of sprat is smallest from December to March,
whereas the proportion of herring increases simultaneously. This finding
agrees with the yields. The greatest catches of sprat are being madeduring
the time of spawning (May/June) and the best catches of herring are during
spring and fall (FL Berner 1963). The sprat make daily vertical movements
during the warm season and feed., at night on plankton in the upper layers
of water. In contrast,-they remain in winter principally in the layers near
the bottom (E. Ehrenbaum 1936, K. Bahr 1936b). Only amall amounts of sprat
were caught from 1953to.1960 to the southeast of Bornholm. The catches
in the Bornholm Basin were also relatively mall. This fact coincides with
the amall importance that the sprat has as food for salmon on the fishing
ground 5. In all'areas of the central and southeastern Baltic Sea, the
best catches of sprat per unit effort are made in May to lugust, with
maximum values in June and July (M. Berner 1965e J. Elwertowski 1959).
Belona and sand eel stay during the summer in the ûpper water
layers in order to eat plankton. Some individuals, however, carry out
[P. 343]

•
- 191 -
vertical movements also in winter. The share of these kinds of fish . there-
fore changes often in the opposite direction from that of the sprat.
Belone and sand eel become more conspicuous only when the clupeids.beoote
scarcer.
6.5. The food consumption of the salmon
For the treatment of this question we have only the mean weight
of food, which was, according to Table 49, at its lowest during the six
months October . to March. For this period we obtain as the simple mean a
value of 8.7 g stomach content. The corresponding amount for the remaining «
four months amounts to 39.3 g. If we assume that the latter value applies
also to the months July and August, for which there is no informatiOn, •
then the annual mean for the weight of food is 24 g.
In the literature available to me (W. O. Côrnelius 1933, H. Mann
1955, M. E. Brown 1957, various authors after E. J. W. Barrington 1957)
are few statements about . the'frequency of food intake in fish and none for
the salmon.-
According to. Barrington (1957) the speed of digestion is smaller
in fish than in memals on account of the lower temperature. At 10 ° C the
.food passes through the - carp in 181Tr, at 26 ° C it does so in 4.5 hr. In
sharks the digestion is supposed to be complete after three days. Karpevich
and Bokova (after Suvorov 1959) state for cod and sea scorpion that the
skin.of fOod fish.that is in contact with the walls of the stomach is in
part dissolved after 5 hr. Cornelius (1933) fed-fingerlings of the , rainbow
trout.With trout fry. He found the first indications of digestion on skin
and fins of 'the fOod . fish. After five hours fins, skin and eyes were decom-
•posed and the body.càvity had.been opened. The body shape was no longer

•
- 192 -
recognizable after seven hours, although the flesh was still adhering to
the vertebral column. After twelve hours it was no longer possible to
recognize remains of the food.
When investigating the digestive processes in various freshwater
fish, Mann (1935) could demonstrate that the speed of digestion depends
on different factors. Among other things, the age of the fish, the tem7
kind and amount of the food taken up play a certain role.
perature and the
Large pieces of food', the surface of which is relatively small, require
h. 344],
a longer time for digestion then do small pieces of food.
The salmon examined in this work are fish that have been cap-
tured during the night or towards môrning and that were gutted generally
towards noon, frequently also already during the forenoon. The pieces of
Belone and the sprat that have been used as bait can be identified unam,
biguously as such; the former because they had been cut into pieces and
the latter because the head . had been damaged by the hook. The bait may
have been exposed to the digestive juices for about two to ten hours
before gutting. Nevertheless, no instances of considerable damage-by the
digestive juicesieceObserved. During the time of investigation the tern!,
perature was seldem higher than 12 ° C.
For a start, let us assume that the salmon takes daily the
amount of food of 24 g that has been cited above. That would amount to a .
yearly total of 8760 g. This amount'cannot be considered to be sufficient
for the metabolism of the salmon. According to Table 43 the increase from
the age group A.1+ to A.2+ amounts to about 4000 g. It can hardly be im-
agined that the salmon should not require.more food than 8760 g for met-
abolism and for the synthepis of 4000 g body substances. The amount of
food actuaily-consumed was probably greater. Let us therefore attempt
•

to discover the annual food intake in a different manner.
- 193 -
M. Brown (1937) found that Salmo trutta of a weight of 100 g
or over at a temperature of 11.5 ° C required a constant'supply of energy
equivalent to about 60 mg fleshier fish and week. The conversion factor
for anabolism at 11.5 ° C was 4.5. In addition to the food for the energy
supply, the fish had to take up 4.5 food flesh in order -to grow by one
gramme of weight. No indications about the energy requirements of large
fish have been given. We may, however, assume that it will rather diminish
with increasing size of the fish than increase. E. Halsband (1953) estab-
lished that the - energy'requirements of rainbow trout are smaller in salt-
water than in fresh-water. Let u s . use the values cited for the calculation
of the food intake of a salmon of the age group A.1+ for one year. That
can give us an idea of the.order of magnitude of the metabolism.Ye obtain
then for the energy supPly (sustaining food) 15,600 g and for the weight
increase of 4000 g food for anabolism in the amount of 18,000 g. Within
52 weeks there is thus required a total of 33,600 g. That corresponds to .
food coefficient of 8.4 (8.4. g food for 1 g increase). Brown (1957)
. cites for brooktrout (Salmo trutta) the food coefficients established bY
different authors as 2.3 to 7.1, whereby .different kinds of food were
being.used as bases. According.to this comparison the figure of 8.4 for
the 'salmon that we just calculated gppears to lie entirely in the limits of
the possible. The average daily food intake Of à salmon in the second year
in the sea would then amount to about - 92 g.
When comparing this figure with that given above of 24 g, one -
has to.consider that surely some salmon.had already,been caught before
they'had the opportuniy !to feed. Probably only few fish have,been cap-.
tured that at the time Of capturé had already taken up -the potential ..
a

- 194 -
amount of food. Under-consideration of the assumption that the requirement
for energy that has been taken as basis may represent a maximum value one
has to view the weight of 92 g as the average maximum amount of the daily
food intake, whereas 24 g represent a minimum value.
-The number of the Baltic Sea salmon in the exploited stock is
estimated on an average for the years 1956 to 1963 as 10 6 . These fish have
taken up as food about 15,000 tà 30,000 t according to the above figures.
[p. 345]
Of this the sprat accounted for about 10,000 to 20,000 t. The total yields
of this fish as the mean for the years 1956 to 1960 amounted to 26,000 t
(Bull. Statistique). According to this the sprat consumed by the salmon
may.be estimated to have amounted to about 50 per cent of the total amount
that the fisherMen have marketed from the entire Baltic Sea.
7 . Attempt at a quantitative
anal.ysis of the stock in the main
basin bf the Baltic Sea
. In the treatment of biological questions the individual has
been the main object of investigation for a long period. It has been con- ,
• sidered as rePresentative of the species in every respect. With the appear
ance of new goals for the work, groups of individual, the communities of
life, moved into the roreground. Not the individual being, but the effecté
of the vital processes of à number of individuals occupied the centre of
consideration. This method has long-played abonsiderkiàs.±ole 111f4hery
ogy asthe study of the stock.
A stock is, howeVer, not a static, but a eynamic unit and the
investigation of it is more of actual valuethan of a historical one. - . The
supervision of' the Conditions of the stock has thereftre to he continuous,
so the it will«be possible to recognize changes and to connect thèm witb

•
- 195 -
external factors.. The investigations of fish populations that are being
carried out at present have the object to oaic the fundamentals for a
planned fishery -. It has to be discovered by what amounts the stock in.-
creases and diminishes annually and to what extent these processes can
be influenced by man. It is of special interest to learn in what manner
can be obtained the best yield without impairing reproduction.
7.1. The characteristics of the stock
• Before one can begin to investigate the conditions in a stock,
to ascertain their changes and the cause:, of these changes, it will be
necessary to define thé stock. However, one can consider one fish popul-
ation to be separate from another only then; when there are criteria in
regard to which the two differ.
• The first question, therefore,'is: what is a stock? A. Bdckmann
(1929) saw'the problem in its widest sense and considered the stock tO be
a unit in regard.to migration, the phenomena of growth and maturation,
as well as the phenomena Of reproduction and waste. Among others, it is
possible to make a demarcation by means of labelling or investigation of
races..Parrish and' Sherman (after Hempel and :ahrhage 1961) designate stocks
of fish as biological fundamental groups, into which the population can be
divided in order to obtain independent units that can be influenced (by
man). According to Hempel- and Sahrhage (19 6 1) the stock of fish is an
independent unit that is closed in itself. The stock Consists of a reprod-
uctive community that is self perpetuing, the - independence of which is
guaranteed.through geographical isolation or reproductive barriers.
Furthermore,. five criteria are named (N. N. 1962), boundaries
of distribution; spawning areas, uniformity of the values of fishing and
r

- 196-
expenditure, composition in regard to age, and morphological, as well as
physiological characters that serve to define a stock. The last definitions
have been offered in connection with population-dynamical investigations.
For the quantitative consideration of a stock it is necessary to delimit
•
lp. 346 ]
a stock less from a biological point of view than from the standpoint of
fishery, in order to ensure that the figures of yield that are used as
basis relate only to a definite population. •
In the present chapter an attempt will be made to carry thropgh
a quantitative, analysis of the stock. Let us assemble the . characters def-
ining the stock that have been cited above and apply them to the salmon
of the Baltic Sea.
A.uniform.stock ("unit stock") inhabits an area that iS frequently
. delimited tbpographically and propagates within this area of distribution.
It can be fished in continuous isolation. Exchange with other populations
has an insUbstantial.influence on the composition of the stock.
If wa now consider the Baltic Sea salmon, we can state at the
• outset that these fish are unambiguously confined in their distribution
(see 4. migrations). The-western Baltic Sea with the Belts forms the western'
boundary of distribution. An'exchange with other regions does praàtically.
not ciecur. Within the area, however, quite a number of rivers are visited
for spawning. This fact, however, does not justify to consider each river
population(as . its own stock, 'because the spawning fish together with other
individuals are- being exploited . in the Baltic Sea before their return . td
. .theirivérs. In addition, several investigators could show that the great
changes:that occur in ébe riverï oan be followed quite uniformly in all
• the others .(G. Alm 1928a, 1928b, 1958; N. llagmann 1938; T. H. anti 1938,
:1948;. Lindroth.1950, 1957; G. Svârdson 1957a).
• -

7 197 `
It has already bee/I .:stated -that the present investigations of
the fishing intensity and the strength of the stock are based only on the
salmon fishery in the main basin of the Baltic Sea. Therefore, we must
restrict oursellies to a part of the stock on account of the limited.data.
Slich' a delimitation can bè carried .out when one considers the immigration
of the young salmon from the Gulf of Bothnia as recruitment and all losses
except natural mortality and loases through fishing as spawning migration.
The recruitment is taken care of through the divers values of the stock
density. The figures that are obtained for the spawning migration com-
prise all salMon that emigrate from the main basin. This part of the stock,
however, becomes subject to shore and river fishery, so that only a certain
percentage of the spawning migrants actually reaches the spawning grounds.
These events, however, are of no interest to us, Since only an unimportant .
fraction of Balm.= survives spawning and returns to the Baltic Sea, all
spawning migrants are counted from the beginning as defdnite losses.
7.2: Lbsses in the eXploited stock
yew e.(a.ss
In the above chapters it has been shown that a-ye-eta-es—set
becomes eiploited for the first time during the fall of the second year
in the Baltic Sea. One has therefore to distinguish between an undisturbed
stage and an exploited phase. Since the fishing season commences in the
fall of each year,.the - transition-between the two sections Occurs rather
suddenly. During the first phase, losses are caused only by natural causes
(enemies, sickness,lack of food), later the losses through fishing are
added. Finally, a Part of the salmon migrate in order to spawn and
- thus leave the exploited phase. At this time there are-three different
causes that work logether_and lead to a reduction of the stock. The total'of

•
- 1 98-
the stock losses are composed of the waste by fishing, the natural mortal-
ity and the losses caused by the spawning mration.
7.2.1. Total mortality
Beverton and Holt (1957) have, among other things, described
the losses in a stock of fish with the aid of a differential equation.
According to this the number of fish that is lost from the stock in the
time t is proportional to the total mortality Z and the number N of the
fish present.
obtain
dN =
dt
Through solving the differential quotient and integration we
W
- t
W
The mortality . thus follows the law of exponential dependence.
N is proportional to t, when t increases arithmetically, N decreases geo-
metrically. Z . is called the exponential coefficient of the total losses.
Equation (1). thus gives the number of survivors at the time t.
. The nuiber of the dead is then
N o _ N t= N o _ oe -Zt
.
• N o -'r t D0 (1 e t)
With the aid of - (1) and . the values available, one can now
calculate the total mortality
11- = 0. e
ln 1.4 = Zt
ln -D = Z:t N
t
(1 )
(2)
(3)
[ p. 347]

•
- 199 -
For the calculation of Z from (3) no absolute numbers are
required. It is only necessary to have the rat::.o of the strength of the
. stock at the time 0 to the strength at time t. It is true that it is neces-
sary to insert the figures for one feecel-s-set in consecutive years. How-
etc el-,
ever, such data are available, since in 2.3.3.2. we consider the e-aptu4te
per unit effort as an expression for the strength of the stock. If we re-
calculate these figures (Table 15).for the corresponding age composition
in per cent (Table 33), we obtain then the figures in Table 54. These
Values show the losses of a .4ici-4-se "s t during the course of two years
(providing there are no errors in the determination of the age and in the
eta,t-f-
determination of the captures per unit effort). If we examine, e.g., the
-y-ea-r-l-s---set-ef-smca-t of 1955, which was present in 1956/57 as the sea year
class A.1+. Of this yeart 18.5 salmon pèr 1000 hooks were caught. In the
following season it yielded as A.2+ only 4.1 salmon per 1000 hooks and an.-
other year:later as A.3+ -e.o..e.* only 0.6 salmon. The total losses during the
second year in the sea amounted thus to almost 78 pèr cent, in the third
year in the sea, they were 85 per cent.
nad,c ,;
If we insert the cieturco per unit effort cited into (3), we .
obtain as coefficient of the total mortality ln (18.5/4.1)= 1.51. For the
fishing periods under'discussion the mean value of the . losses in the . second
year Z 2 ,--. 1.23 and in the third year Z 3 . 2.20. That corresponds to per
centages of 70.8 per cent and 88.9 Per cent, respectively: During the first
year of exPloitation tiremmLsean average of 70.8 per cent are being
sh,ou
. removed from the new y.s.9,-PLe-eat through fishing and other causes. The
losses suffered by the remaining fish amount in the second year of exploi-
tation to 88.9 per cent. Of the salmonthat had entered originally into
'the exploited phase only 3.2 per cent were left after two years. This

NUmber of salmon per Z Weigh-
Season 1000 hooks ted
Tot. A.1+ A.2+ A.3+ A.1+ A.2+ mean
f +f
f 13+1
2
- 200 -'
result agrees.with.the findings that have been obtained on hand of the
age analyses. Only the two sea year classes A.1+ and A.2+ play numerically
any role in the stock of salmon in the Baltic Sea.
LP. 54 8 1
Christensen (1964) could base his investigations on the Danish
s and German:expenditures.He found total losses of Z 2 = 1.33 and Z 3 = 2*.23
that do not.deviate substantially from the above figures.
The individual mortality values in Table 54 show considerable
fluctuations. The value of Z = 0.05 as it has been obtained for the sea
. year class A.1+ in the season 1957/58 cannot possibly be correct, consider-
ing the recorded expenditure of f = 4.44 (Table 5). Let us therefore exam-
ine once more the figures used as a basis. For the calculation of Z were
Table 54. Values of the total mortality in Baltic Sea
salmon .(by using the eartierrey lineyper unit effort).
1956/57 24,0 18,5 . 5,1 0,4 1,51 2,14 1,61 4,91 4,68
1957/58 10,5 5,7 4,1 . 0,6 0,05 1,92 0,36 4,44 3,96
1958/59 22,5 16,2 • 0,6 1,42 3,30' 1,64 3,49 3,94
1959/60. 8,4 4,1 3,9 0,3 0,58 1,47 0,92 4,38 4,56
1960/61 10,8 8,3 2,3 0,9 1,78 2,44 1,89 4,74 5,16
1961/62 15,8 14,3 1,4 0,2 2,02 1,95 2,01 5,57 5,43
. 1962/63 8, 5,9 1,9 0,2 • 5,3 1
Mittel Me an 1,227 2,203 1,41
1 On account of the ice conditions the effective expenditure
Was only 3.62 in 6 months. For 8.8 months we assume here
f = 5.3, because the vessels of other countries could carry
on fishing to the full eXtent.
used the percentages of the age composition as well as the data of Sle
eedei-ree- per unit effort. In regard to the age composition it has already
been established that the results of the present analyse s . correspond rather
well with the actual . conditions. Let us therefore examine what effect is
due to the changes in the eeptures per unit effort. ldhe4 the value of the

- 20 1 -
ceptu.ye per unit effort of 1957/58 increaes bs ten per cent, then Z2 rises
from 0.05 to 0.15. Increases in the capttbre.pr unit effort by 20, 30, 40
per cent result in corresponding values of Z. ) of .0.23, 0.31, 0.39. Even
this amount must be considered as too small. Un the other hand, we cannot
Cc
assume that the -e-sekttte,e per unit effort in 1957/58 should have amounted
to- mere than 14.7 instead of 10.5. It is, however, also possible that not
only the value for 1957/58, but also that for the following season is
affected . by errors. gowever, if both data are changc-sd then we find consid-
erable effects on the results of the -iirculations for the neXt fishing
season. After it has been shown (2.3.3.2.) that the -captures per unit ef-
fart are subject to other influences than that of the itrength of the stock,
and that these influenees cannot be eliminated readily, one has to reckon
after all with certain effects on the calculations of the mortality.
There is still another problem to be considered. The data for
the present estimates are based on the yield of the German salmon fishery
that amounts to only 15 per cent of the total. Changes that were caused
by the efforts of other fleets cannot be expressed in the present data. We
have therefor e . to reckon with incorrect individual values under certain
circumstances.
• The figures for Z that have been obtained with the aid of the
captures by net per unit effort (Table 55) change little. The average
values for Z 2 are slightly smaller; theSe for Z 3 are slightly greater
than. those in Table 54.
[P. 349]
For the determination of the total mortality .can also be used
the method of the virtual population. The virtual population of a certain
V 'Ye '>‘
Yt‘raer4-7--Set is the total ntimber of all captured fish of this ydrarle sct.
The mortality in the year x + 1 is the natural logarithm of the ratio
between the virtual populations of the age of x-+ 1 years and of x years

•
'Table 55. Values of the total mortality (by using the
captures by net per unit effort).
Season
Number of salmon/100nets
Total A.1+ A.2+ A.3+ A.1+ A.2+
_
1956/57
1957/58
1958/59
1959/60
1960/61
1961/62
1962/63
7,5
9,2
13,3
10,5
. 8 , 5
10,0
8,0
5,8
.5 , 0.1
9,6
5,2
6,6
9,0
5,9
1,6
3,6
3,2
4,9
1,8
0,9
1,9
0,1
0,5
0,4
0,3
0,1
0,1
0,1
0,48
0,45
0,67
1,06
1,99
1,55
1,16
2,20
2,36
3,89
2,89
2,20
• Min e . = Mean 1,03 2,45 .
- 20 2 -
(N. N. 19 6 2). The values obtained with this method amount te an aver-
age in the Second year Z 2 = 1.15 and in the third year to z 3 = 2.74..
Table 56. Determination of Z with the aid of the virtual
population.
• Number of salmon caught Coefficient of f -Ff•
Season
-
the total loss
n n+1
-
Total A.1+ A.2+ A.3+ Z 2 z3 2
\ \ \
1956/57 93 200 71 800 19 500 1 800 1,31 1,94 4,68
1957/68 49 700 26 900 19 400 2 800 0,58 2,37 3,96
1958/59 62 600 45 000 15 000 1 800 0,96 2,71 3,94
1959/60 36 900 18 100 17 300 1 000 0,42 3,36 4,56
1960/61 55 400 42 800 11 900 600 1,71 3,67 5,16
1961/62 86 000 77 800 7 700 300 1,94 2,40 5,43
1962/63 47500' 35 300 11 100 700
mind. = Mean 1,153 2,742
•
1 On account of the ice conditions only 32,400 salmon were
caught in six Months. For the determination of Z the cor-
responding figure for 8.8 months = 47,500 salmon had to be
used as basis.
Kandler (1964) has also used the total German landings as basis
for the determination of Z. The division of the yields into the age classes,
howevei", waS carried out with the aid of the divisons by weight (cf. 5.33.).
The mean Value obtained by him for 1958/64, Z = 1.14, agrees quite well
with the values found here.

• 7.2.2.
•
ideeting through fishing and natural mortality
-203-
By way of introduction (7.2.) it had been emphasized that the
losses
total losses are composed of the waet-i4ig through fishing, the natural mor-
tality and the spawning migration. If we designate these losses by F, M,
[p. 350 ]
and T (transport) and when we see them like the total mortality Z asex-
ponential coefficients, we then have
Z = F + (M + T).
The losses through the spawning migration are not found in this
form in other stocks of fish. The migrating salmon are a practical loss .
from the stock in the sea. Thus the total losses are increaSed. To begin
• with, (M + 72) isicAcé considered a unit in comparison with F.
7.2.2.1. The results . of tagging
Tagging of artificially reared and naturally grown smolt has
- been carried out oh a large scale. The recaptures do not, however, give
satisfactory resuits in regard to the mortality during the exploited phase.
The experiments have shown hitherto that the emigrating smolt become con,-
siderably redUced in numbers during their first year in the sea (recruit-
ment phase). It has hitherto not been possible to ascertain exactly the
total losses during this period. Therefore, the number of the surviving
salmon thatreach the exploited phase is not known.
Carlin (1959a and 19 62a),was able to provide the first picture
of the conditions of the stock with the aid of the method of exclusion
and a few assumptions. Of the -tagged salmon that survived the recruitment
phase about 34 per cent were caught during the second .year in the Baltic
Sea; in the following year 48 per cent of the survivors fell prey to fishing..
.(average of the years 194 to 1958). The corresponding figures for later
( 4 )

- 204
experiment were about 40 per cent and 60 per cent, respectively (1958 to
1960). . •
It is.possible to recognize the effect of fishing rather more
unambigUously, when adult salmon have been tagged in the sea. Blair (1955)
tagged in June 1940 6.8 salmon and 386 grilse in the sea near Newfoundland.
After one year 41.2 per cent of the salmon were recaptured and 1.5 per cent
in the second year. For grilse the corresponding figures were 36.6 per cent
(1st year), 2.6 per cent (2nd year) and 0.3 per cent (3rd year). Belding
arid Préfontaine (1961) tagged in June 1938 195 salmon at the northeast
6(0
coast'of Newfoundland, of which 21.8 A were reported back. Along the Irish
coasts 4562 salmon and grilse have been tagged between 1948 and 1961. The
average rate. of recapture was 26.4 per cent (A. E. J. Went 1964). In Nov-
ember 1960 and in December 1962 we have tagged on board of salmon cutters
86 salmon of the sea year class A.1+ and 13 fish of the sea year class A.+.
During tlie first year 18.6 per cent of the older fish were . reported from
the Baltic Sea and 9.3 per cent from rivers or their estuaries of the Gulf
of Bothnia. The recaptures of the gmall fish amounted to 15.4 per cent in
the Ilaltic Sea during the first year. A division of the larger salmon int o .
those that were liberated in good condition and others that were in medium
condition when liberated, gives for the first group 20 per cent recaptures
from the Baltic Séa and 13.3 per cent from the rivers. This material by
*itself is too small for the derivation of the mortality coefficients. It
may, however, be of some value for comparison with other results.-Wé obtain
(Pss
the wes4e through fishing with the aid. of a proportion (Beaverton and Holt
1957). The total number of thé dead stands in the same proportion to the
number of captured fish as the total mortality.to that caused by fishing.
No-Nt Z
F
11 . number at the time t 0 -
Nt = number at the time t..

According to (2) we obtain,from this
-F
• nZ
N0(1 - e -Z ) .
- 205 -
By using the average value of the total mortality of 1.41
(Table 54) one obtains for the salmon in good condition
F = 0.37 for the Baltic Sea,
F = 0.62 for the Baltic Sea and the rivers.
7.2.2.2. Determination with the aid of the intensity of fishing
Wellave already 'seen (4) that the coefficients of the different
rates of loss (M + T) and F add up to the total mortality Z. There is no
'doubt that M is very small for the adult salmon in the Baltic Sea, where
they have practically no enemies 1 5. iiitherto there have been no reliable
investigations of the share of the 'salmon in the sea year class A.1+ that
migrate to spawn (T). The average values that are shown in Table 39 are •
insecure and it was not possible to cOnsider annual changes. In the eXam-.
ination of thé sea year elass A.1+ We dhall therefore considet (H + T) as
constant. Under these premises, all changes in Z must be attributed quan
titatively to corresponding changes in F. Since the loss through fishing
is proportional to the intensity of fishing f, respectively to the ex-
penditure, we fine from (4)
Z = cf + (M + T).- •(5)
When Z and f are known, c and (M + T) can be obtained by the
methoe of least squares.
In thè.calculation of Z we had assumed that the values of the
15 .
landroth (1962) was able to demonstrate that the harbour porpoise, long
considered *to be a salmon predator, does not eat salmon.
:ID • 351 I

- 206-
strength of the stock N pertain to a certain time t. If, however, the
density of population is specified as the mean value for a fishing period
U,thenthe Z-values are not quite correct. The average annual number of
fish amounts to (Beverton and Holt 1957):
= _E_ ( 1 _ e t).
• Here N is the number of fish at the beginning of the period t.
For the years 0 and 1 one obtains; •
° ' '112 ( 1 - e - Z0)
Zo
= -1 (1 - e1)
Z1
The division of the two equations, whereby, according t
•
one sets N 1 = No e. Zo, results in
. --
e—Z)
zn — In + ln
Z1 (1--e-zo) and . on account of (5),
No•, (cfo + M + T)(1,—e--(cf, +M . 11')).
,= In
In (cf t + M + T) (1 — e-(cr.0 m +T))
( 1 ) ,
In order to çalculate Z the second 'term at first approximation
is set equal to 0 and we obtain
cf o + (M+T) = Zo. = In
iNt
. .
One can now calculate c and (M + T) with the values for Z and
1 • Inserting these into (6), one obtains new results for Z, which are
b. 352]
used once more td -obtain improved results for c and (M + T). The three-
to four-fold repetition of this procedure leaàsto constant results (iter •
àtive method).
Beverion and Holt (1957) used the iterative method to calculate
F. If one uses this•equation for the values Of Z and f in Table 54, one
obtains a négativaresult for (M + T). The failure'of the method can have
two causes. Eiiher the changes in Z are not caused or not caused solely '
(6)
. •

•
- 207 -
by changes in the intensity of fishing f, or the scatter of the values of
Z and f (that is, their error) is so large that the method remains without
success.
On the' other hand, Christensen (1964) was'able to obtain with
the aid of the iterative method results of F 2 = 0.73 and (M + T 2 ) = 0.60
(cf. 7.2.1.). If we now compare the data on which the two cases are based,
in order to find an indication of possible sources for errors, we find that
the correlation of the values for the -e-ap-te per unit effort (line) gives
a correlation-coefficient of rc = +0.93. There is also a high correlation
with ra = +0.94 between the two determinations for the age composition
c.lutbi-
e-84 per unit effort of A.1+). On the other hand the correlation Coef-
ficient for the values of the fishery expenditure is considerably lower
with rf = + 0.82. This indicates that the German figures for the fishery
expenditure do not represent the total expenditure with sufficient exactness.
'Faloheimo (1961) has developed a linear equation that makes un-
necessary the iterative method in the determination of F and (M + T). For
this purpose the second term in equation (6) has been set . K. When
- ln 7 aZ, then
aZ 1
+ aZ o'
The equation is decisively transfoimed through the determination
of a. For the calculation of the infinite series of
•
- 1.11
-Z
1-e
only the first term was used, whith the . result that a = 1/2. For Z.c1 the
error in - a = 1/2 is less than 10 per cent. Since the value of the second
term in equatiOn (6) is small compared with the first term, this approx-
imation may be permissible. Equation (6) then becomes;

•
N„
Z o = cf„ (M1- T) -- In — 1
No.
cf„ -(M+T) =- In NI +
N o
In NI cf„ (M+T) —
----i--- (Z — Z1)
`)
1
(f0 f1)
1
(fo f1)
N 1
In ° — 2 c U 0 17 f + (g+T)
— 208—
Paloheimo has established that his linear equation is superior
to the iterative method in all bases when deviations are introduced through
ceta-
defective material (age, c-ape per unit effort, figures for landings)
or through changes in c. The cause for this is to be seen in the fact that
Z 1 is not being correlated with f 1 but with 1/2 (f 1 + f 2 ). An improvement
can only be expected when c is strictly constant and when only the cep—
P. 353]
tuegs per unit effort per age group are erroneous. In all .other hypothet-
ical cases the standard deviation of c and M was reduced by from 27 per
cent to 69 per cent in comparison with the iterative method. The application
of the linear equation of Paloheimo to the values of Table 54 results in
the equation
Z2 = 0.2135 f + 0.288.
Since Z 2 7 1.23 on an average for the years 1956/57 to 1961/62
. we obtain (line catches):
Z,
(M + T) 2
1.23
0.29
F
2
0.94
The total mortality that has been obtained with the aid of the
netting values Can also be dorrelated with f according to the method of
Peoheimo.
Z 2 1.03
(M + T) 2 0.28
F 2
0.75
(7)

•
- 209 -
If one uses the method of the virtual population and then cor-
relates the values,of Z.thus obtained again with f after Paloheimo, then
the losses during the second year in the sea amount to
Z 2
1.153
(m + T) 2 0.261
F 2 0.892
Through the above explanations it has become clear that the
available data do not form a reliable basis for the determination of the
'loss coefficients. Since the total - mortalities that have been calculated
after Beverton and Holt and with the aid of the virtual population in A.1+
provided nevertheless rather.goo1 agreement we shall have to reckon with
,
errors in the values of the fis rykxpend ture, as had already been sus-
pected during the comparison with thé results of Christensen (1964). The .
values of F 2 do not agree approximately with the results of tagging. These
will therefore be left out of consideration. The rounded-off loss data are
now
Z, 2 1.2
Ovi + T)
2 0.9
0.3
F
2
None of the methods mentioned so far gives usable values for
the losses in the thi.rd year in the sea. In all cases negative figures were
obtained for M. In order to obtain an idea of the order of magnitude of
the losses, we can use the mean value of Table 54 for z 3 . If we assume
F 2 = F3.. we find
Z . 2.2 .
• 3
0.9
(M .4- T) 3 1 .3.
. Withthese Values We have.now two equations with .the three
•inknowns M, T 2 and T 3 . For the calculation of the natural mortality and

— 210—
the coefficient for the spawning migration, however, three equations-are
required.
When No . = number of salmon at the beginning of exploitation during
the second year in the sea
N t1
« Nt2 =
= survivors'after the second year in the sea
then we have according to (1)
survivors after the third year in the sea
Ntl =
No e- Z 2t 1
No - Ntl = No (1 - e -Z2t1 )
«Nt2 = Nt1 e-Z3(t2 t1)
Nti - Nt 2 = N e -Z 2t 1 (1 _ e - Z3 1 t2 t11)
When one multiplies the total losses (8) and (9) with the ex-
(8)
[P. 354]
(9)
pression T.2/Z 2 and T3/Z 3 , respectively, one obtains the number of spawning.
migrants (Béverton and Holt 1957) after the second and third year, respec
- tively. The division of the equation results in
Ta • Za e • z29(1 — e—zet2
_ T2.. Z3(1 -
C11)
. _
(10)
This ratio oan be taken from Table 37 as 41/80. With this we
have three equations.. Through insertion of the first two equations in (10)
one can calculate the natural mortality. However, with the data at hand,
E becomes negative, Since we know already from.other determinations that
M is very small in the exploited phase, whereas for (M T) in A.1+ a
« coefficient of-only 0.3 has been round, we shall assume for the time being
M as 0.1.
- Christensen (1964)-, who used the sanie method for the deter-
minatdon of M and T, could take the numerical ratio of the spawning migrants
from the Swedish tagging experiments. He arrived at values of M = 0.103, -
T 2.
T 5. = 1..397. .

7.3. Losses in the recruitment phase
- 211 -
We designate here as the recruitment phase the period of life
from the emigration from the rivers to the beginning of exploitation.
This period comprises on an average slightly less than 1.5 years, since
the salmon enter the exploited phase only in the fall of the second year
in the Sea.
7.3.1. The natural enemies
We have a number of papers that treat the enemies of the salmon
fry and of the parr. • here are only a few investigations of the losses in
smolt- White -(1936) found in the river Màrgaree (Nova Scotia) that king-
fisher (Megaceryle) and mergansers (Mergus) had eaten daily more than 40
fish (salmon, sea trbut, sticklebacks). The mergansers alone consumed
390,000 smolts of salmon and sea trout. Huntsmann (1941) could show with
the aid of tagging that the number of. emigrating smolt could : be more than
doubled when kingfishers and mergansers were controlled. Elpson (1962) even
obtained a five-fold increase in the nùmber of migrating smolt.through the
control of kingfisbers and mergansers.
In the Betio Sea similar investigations have been carried out
hitherto by Lindroth (1955a). In the Indalsâlv the mergansers had eaten
preponderantly the Parr of salmon and sea trout. One hundred adult and one
hundred and tWenty-five juvenile mergansers -consumed from June until Sep-
tember 350,000 parr. The annual production of smolt in the Indalsâlv is
around 3504000. These investigations show that the losses of smolt alone
through Mergansers and kingfisheré can amount to 50 to 80 per cent. , •

- 212-
In a further paper Piggins (1958) treats Irish salmon smolt.
With the aid of tagging he ascertained the losses in the region of the
Burrishoàle fishery. A total of 5224 ' -fteh were tagged, of which almost
3100 were smolt, the remainder being parr. One hundred and fifty-six 6f,'
the tags recovered were found in the stomachs of predators.
' According to Piggins, herons are commonly found in the region
in question; These birds have no enlarged pyloric antrum and usually void
the tags within 12 hours. Five birds.examined had four tags in their
stomachs. In order to avoid making to4iigh an estimate of the losses, we
shall assumethat one heron had eaten on an average only two tagged salmon
during the months in question, namely . October to December, which would
amount to 200 fish for 100 bird.
. Of the frequently encountered mergansers 15 birds were.examined,
which contained eight tags. Since these are retained in the stomach for
lengthy periods, one can reckon that 150 mergansers had eaten only 80
tagged fish.
'Cormorants.are very common, but also have no enlarged pyloric
antrum. Although previously up te five smolt had been found per bird, no
tags could be found in 22 birds. We estimate the losses through cormorants •
therefore as only 20 tagged fish.
The pollack (Pollachius pollachius) enters in spring in large.
the estuaries of the Burrishoole region. In 94 pollacks only un-
numbers
marked fish were found On the 1st and 5th of May, whereas the tagged smolt
were first liberated on May 1, and 5. Of further fish examined six pollacks
contained 12 tags at the end of May. According to Piggins all Pollacks eat
gmolt and follow them intô the sea in June. Formerly more than 60 per-haul

- 213-
were caught with seines in Mar. Since they are not being fished at present,-
one must reckon with 1000 fish in the'region in question, these Must have
eaten at least 500 tagged fish.
Brook trout of a length of 23 to 33 cm are represented as the •
most important predators of salmon. These robbers retain the tags in their
stomachs for at least four months. Of the fish examined (total number un-
known), ,20 fish . contained 134 tags. Since the brook trout forms . a strong
stationary stock, one can reckon with 1000 fish, who consumed a total of
2000 tagged salmon.
With these minimum assumptions one obtains the number of 2800
tagged salmon that had been eaten by the predators cited. That corresponds
to a loss of 54 per cent in the estuary alone and principally within,four
months. As has been mentioned above, it is true that a series of parr have
been included in the investigations 16 .
7.3.2. The mortality until the beginning of exploitation
The above statements of the present paper show that the numbers
of salmon in the recruitment phase are being reduced quite heavily. With-
out doubt, the decisive losses take place during the period bêtween eMie
ration and the transition to pelagic fish food. The smolt at that time
constitute a' disturbing element in the equilibrium of the population mech-
anism of the-other dwellers in the sea. They are being forced to learn
an entirely new behaviour for their conduct in life. Instead of the pos.-.
sibilities of hiding that they had in the rivers, now only speed is of
avail against predators. The relations.between predator and prey have
16 According to Piggins, the smolt losses have to be set at 70 per oent
(personal communication).

- 214-
shifted and the fOod supply has changed. There are other competitors.
Finally, the young fish are confronted by an entirely different physical
environment.
If one wants to view this complex multiplicity of phenomena as
a constant cause of the natural mortality, this would obviously mean a
coarse simplification. However, we are today not yet in a position to make
statements about the fluctuations in the stocks of the predators and in
the food supply. We can therefore only attempt to estimate the average
total losses for a longer period.
Kgndler (1958) has used the share of tagged salmon in the total
captures and the number of tagged smolt released in order to ascertain
the number of the emigrating young salmon in 1955 and 195 6 and arrived at .
[pw 356 ]
a figure of five to six million fish. Lindroth (1956) states the natural
production of smolt in the Swedish rivers to have amounted to about four
million Salmon before the building of the power stations. Since the Swedish
share in the production in the Baltic Sea is estimated generally to be ca.
65 per cent, one obtains a total number of smolt of about six and one-half
million of smolt.
If we càrry out the investigations in the manner of Kgndler for .
the average of the years 1956/57 to 1962/63, we find that the weighted
share of tagged salmon in the German captures was 0.902 per cent. Against
this we have the number of 71,600 tagged smolt that were liberated in the
average of the years 1955 to 1961 (B. Carlin 1962a). From these figures
we deduce that almost eight million emolt . emigrated on an average during
1955 to 1961. Ildw Carlin (1962a) has shown that the percentage of recoveries
has increased froffi.year to year. Among other things, this points to a mor-
ftality related tb tagging or to incomplete recoveryreports..If we assume

- 215 -
the share of the tagged fish as one per cent, we arrive at a production
of Seven million smolt.
According to the reports available, one may assume that the
losses are very high during the first three months after entering the
Baltic Sea and that they then diminish quickly until the exploited phase.
Let us once more summarize the data cited. The number of the gmolt migrating
into the Baltic Sea.is about six to -seven million fish. In some Canadian '
rivers running into the Atlantic Ocean and in Ireland the losses during
the smolt migration amount to 50 to 80 per cent.
On the basis of tagging of smolt and by assuming the natural
mortality during the exploited phase as 20 per cent Carlin (1962a) arrives
at a loss figure for the first year in the sea of 83.4 per cent.
7.4. Models of the stock of. salmon in the Baltic Sea
In order to test with what approximation the parameters ascer-
.tained correspond to the actual conditions, it will be most instructive
to present the life cycle of an average UZ-e44
We obtain the number of recruits at the beginning of exploi-
tation by using as basis a migration of six and one-half million smolt
and the figure for the loss of Carlin of 83.4 per cent. For the further
calculations the équations (8) and (9) apply.
The parameters.thus ascertained have been used in Table 57.
Since no coefficients of loss could be calculated for the fourth year,
we have here assumed a loss . through fishing of about 55 per cent. The
number of survivors at the .beginning of the fourth year is very émall,
so that it does not Play a Substantial rdle for the total stock.
TwO items of knowledge can be gleaned from Table 57. The first.

- 216 -
concerns the yield of captures. If we set the total number of the captured
fish equal to 100, we obtain for the three sea year classes shares of 75
22, and 3 Per cent. On the other hand the average values of the age analyses
(Table 33) are 69, 28, and 2 per cent. The parameters ascertained are there-
fore erroneous, so that the model does not agree with the actual conditions.
An alteration of F or of Z changes the percentage of the fish caught in
the second year only unsubstantially. The decisive and important knowledge
to be derived from this fact is the - determinationthat the fishing is sel-
ective, - so that the sea year classes are being exploited - in different de-
grees. The expectatiOn that F is equal in both sea.year ailases is wrong,
P 3 must be greater than F 2 .
The . second . item concerns the number of spawning fish. In Table
57 the number of spawning migrants of the sea year class A.2 issmaller
than the number of three-year-old spawning fish. However, we know already
that the relation is the opposite (5.3.1.3.). With this we have two orit-
! [p. 357]
eria, with the eViofleioh the parameters can be tested. For the final res-
ults it will be of value, to pursue this idea further.
Table 57. Preliminary model of the stock of salmon in
the Baltic Sea.
Coefficients
of
.
Num.
Years at Number Yield of
in .beg,- of fishery
the in. natur..
loss Balt, of losses Number
F T Sea year
. Number
of
spawn. Total
mi-
grants -
1. 6 500 000 5 421 000
5 421 000
0,1
0,1
0,9
0,9
0,2
1,2
2.
.3.
4.
1 079 000
324 995
36 009
62 808
13 134
565 504
118 224
(20 000)
1 700
890
200
125 693
157 628
754 005
288 986
703 728 2 790

• To
1
T.,
T3 • Z2 • e — z2ti (1 — e—z3(12 —(1))
Z3 • T2 (1 - e—z2ti)
— 0,51
— 0,51
- 217 -
begin with, we have to establish which parameters exert the
decisive influence in the numerical ratio of the salmon that migrate to
spawn in the second and third year in the sea. According to (10) we have:
c—zeiZ.) 1 — e-23(t2—ti)
•T3 •
c-Z2t1 Z3
The result of the proportion is determined by T 2 , Z 2 , T 3 and
(ii)
Z 3 . It can be said at once the influence is small of T 3 and(T3), measured
- on T2 and Z 2 . If one accepts as perniissible a deviation Of the result of
0.051 (10.per cent) and tries with the possibilities of combination of.
.the figures of Z 2 .= 0.9 to 1..5; T 3 . 0.8 to 1.4, and z 3 = 18 to 2.5, one
will find that T 2 can take on values of only between 0.3 and 0.6, because
the deviation of 0.51 amounts in all other cases to more than-20 per cent.
Since we can assume that F 2 is not smaller than T 2 , the number of possible
combinations.can be restricted still further.
• Let us now look first at the numerical proportion of the salmon
caught in the second and in the third year in the sea. The value of this
proportion can be taken from Table 33 as 69.364:27.575 = 2.516. One obtains
the nuMber of the salmon captured during the second year in the sea by
multiplying (8) with F2/Z 2 . The corresponding expression for the third
year is obtained by using (9). The division of both equations results in
' N„ (I — e-2z2 , 1)
Z2
F3
• • N„ e e—T2.11 (1 — e—z3(t2—tt.)
. 1 Z3 1
. - .
.(!---(F2 - : W. 1 1 • z.) F 3 1—e—z3(t2---1,) •
- 2,516
No value can be expected for M that . deviates . substantially from 0 .1,
( 1 2)
because . the salmon has no enemies in the exploited phase. The influence

nachafter
00 04
0,3
0,4 2 1
0,5 6 9
0,6 11 15
• 0,7 11 14
0,8 5 3
0,9
T2
_
afte
(31) (12)
0,2
0,3 2 7
0,4 16 16
0,5 13 13
0,6 4 ' 6
0,7
- 218-
of F and z 3 on the result of the proportion can only be small. There-
3
fore the numerical ratio between the salmon caught during the second and
third years in the sea is determined principally by F 2 and T 2 . If we now
try to obtain an approximation to the actual values of the parameters
with the aid of equation (12), then the poèsibilities of combination can
[p. 358 ]
be reduced considerably through the limits for T 2 that have been obtained
with the aid of (11). A.deviation of .± 0.126 (5 Per cent) for the value
of the proportion will be considered as permissible. The remaining pos-
sibilities result in the following distribution of frequencies for F 2 and
T 2 :
one obtains:
ana T,:
The weighted mean of these series amounts to for
F 2 = 0.63
T 2 = 0.45
. With M = 0.1 it is then
Z 2 = 1.18.
When these values are inserted in the equations (11) and (12),
Z3 2,0901 F3 (1 — e—zs (t2—ti))
Z3 2,2$05 T3 (1 e—zs (t2*tI))
The division of the two expression results in:
Since
1,0911 T3
Z3 F3 + T3 «
Z3 = 2,1911 . T3 '
We thus have three equations from which we can calculate F3

E3 = 1,61
T3 =-- 1,48
M = 0,1
4 3,19
and with
we have
The values that have been used as basis in Table 57 result in
a yield of the fishery of more than 700,000 salmon. This figure is with-
out doubt too high (cf. Table 16). For the erection of the final model
of thestock we shall start with a number of recruits that results in thè
capture of about 450,000 salmon. . This figure represents approximately the
conditions of the last years. If again the losses in the first year are
• f
assuMed as 83.4 per cent (Carlin 1962a), the number of smolt is 5.1 mil-
lion. This figure is about one 'million lower than the values cited earlier .
(Lindroth 1956, ehdier 1958). This difference can have three possible
causes. (1) The paXameters of the revised model are still too inaccurate.
(2) The number of smolt arrived at hitherto has been too hdgh an estimate.
(3) When the mortality during the first year is higher for the natural
smolt than for the artificially reared ones, then the losses may amOunt
not to 83.4 per cent, but to abolit 86 per cent.
The percentage losses can now be obtained on hand of the revised
results given in Table. 58. On an average the fishery removed about 37 per
cent from the sea year class A.1+ and about 48 per cent from the sea year
class A.2+ of the fish present at the beginning of the year (Canin 1962
figured with 40 and 60 per cent, respectively) . . The corresponding natural
[P.359 ]
mortality was 6 or 3 per cent, respectively. Of the salmon present at the
. beginning of the season, 26 . per cent of the sea year class A.1+ and 44
per cent of the sea year class A.2+ emigrated in order to spawn. The
total losseS in class A.1+ :amounted to 69 per cent; those in class A.2+
were 96 per cent. After two years there were still present 13 per cent
- 219
-

•
1. (5 100 000) (4 250 000) 4 250 000
0,1 0,63 0,45 2. 850 000 49 900 314 352 943 224 543 588 795
0,1 1,61 1,48 3. 261 205 7 852 126 412 948 116 205 250 469
4. 10 736 (6 500) 65
2.-4. Jahr 1 . 121 941 447 264 1 956
- 220-
of the recruits that just entered the exploited phase. The exploited
total stock comprised about 1.1 million fish, of which about 76 per cent
belong into the sea year class A.1+. There exists a difference between
the age composition of the stock and that of the captures (69 per cent
A.1+) because the fishery is selective.
Table 58. Revised model of the stock of salmon in the
Baltic Sea.
• Num .
.
Coeffi- Years at Nàmber
' cients in beg- of
of the in. natur.
loss . Balt. of losses
Yield of
fishery
Number
of
spawn.'
mi-
Total
. M •F TSea year Number t grants
The two most important results of the statements will be
summarized once . -more:
It is of •great iiaportande that the sea year class A.3 is being .
fished . selectively. As a possible cause should be mentioned the selec-
tive effect . of the driftnet fishery. The amount' of the exploitation of
the salmon of the sea year class A.1+ is of extraordinary influence.
Small changes in F 2 have a. substantial effect On the entire stock.
In contrast to .this,changes . in F 3 do not play a great role. It will
have to be the object of further investigations to test the parametera •
presented so . as . to obtain an•unembiguous indication of the extent of the
conservation effects that ean be obtained throngh elhangee in F 2 .

Summary
The fishery on salmon in the Baltic (2)
– 221 –
. There were 3 periods of development in ,salmon fishing. Up to the commencement of the 18th
century only river fishery has been carried .out. From this fishing in the coastal regions was
being evolved. On account of the introduction of drift-lines and the resulting good catches in
the open Baltic, deep-sea-fishing has been;;developed after the year 1945. For the time being it '
is still of greater significance:than river and coastal fishery.
The total fishing effort in deep -sea-fishery his increased since 1955, although the number of
vessels has decreased (Tab. 5). For the time being' about 350 'vessels froin Danmark, Sweden,
Poland and West Germany are carrying out salmon fishing. Of these some 150 are operating
with drift-lines only and 200 with drift-nets additionally .(2.3.3.1.).
The catch Per unit effort is ex:pressed in number of salmon per 1000 hooks or per 100 nets
andiday. It is not an exact expression of abundance, because the data are'biased. by uneven
ditribution of salmon within the stock area by influence of the wind, by food supply, .food
competition and gear selection. Generally. the temperature conditions and the distribution of .
individuals may not influence the cOmparability of the values from year to year (2.3.5.2.).
Food coMpetition of cod (gear saturation, 2.3.5.) may result in an error of not more than 0,5
salmon per 1000 hooks. Variations in the natural food supply do affect the drift line catches in
so far as there is a competition bêtwe.en the amount of natural food and bait (effort) (Tab. 9).
There was no pcissibility to ellininate thé effects of these factors (2.3.3.2. and 2.3.5.), Wind of
more than 5 Beaufort results in better catdies than wind of less than 5 Beaufort (Tab. 10). Drift
net catches are dianging vice versa (Tab. 11), the differences being statistically significant. The
catches are also being correlated with the direction of the wind (Tab. 10, 11).
• Tests with hooks of different size did not result in statistically significant differences of the
•catch. The seleçtion .first of all is in correlation with the size of the bait.. An average sprat has .
a body height of 25 mm and maY be swallowed by a salmon of 27 cm in length.
Drift nets are acting highly selective. Only very few big individuals may escape but a lot
of small salmon are not caught. In case of a mesh%ize Of 78.75 mm between knot and knot for ;
nylon nets the 50%-retention-length amounts' to 78 resp. 105 cm of the total length (fig. 10).
Corrected figures of catch per unit effort are suinmarized in 'I'ab. 15.
The total yield of the salmon and sea trout fishery in the, open Baltic and Baltic rivers are ;
shown in Tab.. 16 and appendix III–V. . •
The sex conditions (3)
'File proportion of sexes is correlated to the changes in thé abundance of the year-classes (3.1.):
Recruitment oocytes with a diameter of less than 0.3 mm and maturing, oocytes, rich in .
yolk are present in eadi ovary (Fig. 15, 16). A discussion of the results of ovary investigations
and estimations of the fat content as well as age determinations of the spawning and the fee- I
shows the following results: Salmon of a fat content of about 12°/s in spring and a . cling stock
mean diameter of the oocytes of more than 1.5 mm will be spawning in autumn of the same
year.
_
The Migrations (4)
After downstream migration most smolts of the Bottnian Bay rivers stay more than 1 year in
the Bottnian-Bay. Later on part of these turn to the Baltic proper together with the 1 year .
; younger individuals from the Bottnian Sea (Tab. 22). No far reaching movements are carried
out there. 'Ile migration is correlated with the search of food and wind (current) eff vets and
the resulting distances do amount to not more than 10 km per day as an average. Normally ,
there are groups of- 2-10 individuals. By influence of wind and food effects crowds :a more ;
salmon are being formed. But . even then there is no shoaling, beause in the densest concentrations
the indiyiduals have an average distance of more than 10 m from cadi other. ,
• .
. Age and growth (5)
The relation between total length i...t and fork length Li is being expressed by '
• Lf = - 1.2256 -I- 0.9578 Lt.
Lt 1.2796 + 1.0441 Lf
the eqùations possibly being valid for the whole stage of sea life (5.1.1.). A linear•relation also
exists betsven gutted weight Wie and fresh weight W.
• . Wic ----- — 0.0241 --h . 0.918 Wf
Wf ,----- 0.0263 + 1.089 Wg •
Using the simple formula: . •
•
• • W g = 0.9114 Wf (Wg -=- Wf — 8.86 °/o) • • '
. Wf =--- 1.0972 Wg (Wf ---- Wg + 9.72 %)

• •em.ilts
- 222 -
in an error Of less than ± 0.6 " 0 as far as salmon o. 10 kg in fresh weight are concer-
ned and less than ± 1 Vo for salmon bet ween 1.6 and 20 L g fresh weight (5.1.2.).
In Tab. 30 the number of sclerite rings formed during the first year of life or during the
total river period resp. is correlated with.age. The corresponding correlation coefficients arc
ri - 0.595 ± 0.0123 or r2 = 0.642 ± 0.0217 resp. (5.2.2.).
As the mean smolt age amounts to 2.68 years (average 1958-1963), salmon of the southern
Baltic are recruited to 1 /4 from rivers of the northern Bottnian Bay and to 3/4 from southern
rivers. A smolt age of 2.4 years for the 1955 fry-year-class is thought to be related to an early
smolt migration (Tab. 31).
' As an average of the years 1957-4963 the proportion of the sea-age-class A.1 -I- amounted
to 69.3%, the A.2 -I- class to 27.6% of the catches (Tab. 33). 50°/o of the spawning migrants
took part in the reproduction after 2 years of sea life, ever 20-25% after one year less or one
year-more (Tab. 37). The A.3 + sea-age-class consists to 37 0/o of individuals with spawning
marks, the corresponding proportion of every elder age-groups amounts to 100 0/0 (Tab. 38y.
The age composition of the stock is changing seasonally . A new smolt-year-class enters the
exploited state between summer and autumn, whereas the maturing salmon start to leave in
April. As a result the stodt composition shown in Tab. 33 is constant during the period November
to Mardi (5.3.2.; 5.3.3.).
The growth rate in length amounts to more than 30 cm during the first year in the sea, to
about 28 cm during the second year, to about 20 cm during the third year, to about 8.5 cm
during the fourth year and to some 5 cm during the fifth year. The corresponding growth rate
-in weight totals to about 1 kg, 2 kg, 4 kg, 2 kg and 1 kg (Tab. 43, 44). The 1959 smolt-yearclass
was shown to mark itself by an extraordinary growth resulting in a mean total length of
80.5 cm in January of 1961 which is related to an excellent food supply during the first year
of sea life (Fig. 36 and 5.4.2.2.).
The size of smolts very possibly influences the growth rates during the sea life. This fact is
not possible to be demonstrated directly, because individuals of higher smolt age are maturing
first, so that the proportion of elder age-groups will decrease in the course of the years. That
appears to result in salmon of higher smolt age apparently not to show a better growth rate
than individuals of lower smolt agè (Tab..46).
The food (6)
Stomach investigations on 2400 salmon show the weight of food to consist of 75 0 /o of sprat
and 13 Vo of herring. Besides garpike, sandeel and mysideae are of little significance (Tab. 48).
The average weight of food amounted to 8.7 g between October and Mardi and to 39.3 g
from April to June and in September (Tab. 49). There is a considerable difference in the food
composition of young (A. -E) and old salmon (elder than A.1 -r) (Tab. 53).
The daily food consumption may be within the range of 24 to 92 g, but very possibly much
higher than 24 g per salmon. The weight of sprat taken by salmon may total to 10 000-20 000 t
per year, that number being 50°/s of the total fishing yield (6.5.).
Stock analyse (7)
Calculation of mortality parameters by means of data on fishing intensity, catch per unit effort
and age composition after the method of iteration resulted in negative figures for M. Better
values have been arrived at from the PALOHEIMO equation (7.2.2.2.). Even these figures did not
iced to a satisfactory model of the stock. But it has been shown, that fishing is selective, F
being much higher in the A.2 + than in the Al + sea-age-class.
Appointing certain ranges to the parameters and inserting these successively into equations
(11) and (12) (proportion of the number caught [12] and the number of migrants [11] of the
two sea-age-classes) resulted in better values:
•
A.1 : M = 0.1 F --- 0.63 T = 0.45
•
A.2 :M 0.1 F = 1.61 T 1.48
In the 'beginning of the season the stock corisists of about 1.1 million individuals, after
.being recruited by 850 000 salmon of catchable size. During the course of the season the fishery
takes about 40 1/o of the stock. Some 31 °/o will leave the Baltic main basin in order to spawn
but will be subject to coastal and river fishery.

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nnd
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- 223 -
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at

•
- 224-
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IThe methodology of fishery - biological investigations of sea fish]
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— 225—
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— 1929: Untersuchungen an Salmoniden. Ibidem, Vol. 61. •
[Investigations on salmonids)
1931: Untersuchungen an Salmoniden, 2. T. Ibidem, Vol. 73.
[Investigations on salmonids, second part l
. _
HicxLING, C. F., and RUTENBERG, E., 1936: Tue ovary as an indicator of the spawning period
_ in,fishes. J. Mar. Biol. Ass. U. K., Vol. 21.
HOAR, W. S., 1957: Endocrine organs (in M. E. BROWN, Physiolugy of Fishes, 1957). Acad.
Press, New York, 1957.
HUNTSMAN, A. G., 1941: Cyclical aimndance and birds versus Salmon. J. Fish..Res. Bd. Ca- •
nada, 5/3.
IntÉR, D. R., and 'BITNERS, J., 1959: Biochemical studies on Sockey-Salmon during spawning
. migration, Cholesterol, Fat, Protein and Water in .the body of the standard fish. J. Fish.
Res. Bd. Canada, Vol. 16/2. •

- 226 -
Paw, T. H., 1938: Fluctuations in the Baltic stock of Salmon, 1921-35. Rap. Proc. Verb., Vol.
106.
— 1948: On the periodicity of Salmon reproduction in the northern Baltic area and its causes.
Rap. Proc. Verb., Vol. 116.
— 1958: Ober die Lachsertrâge im Oulujoki in den Jahren 1870-1948. Acta Zool. Fenn., 94: •
[On the yields of salmon in the Oulujoki in the years 1870to 190]
— and MENZIES, W. J. M., 1936: The interpretation of the zones on scales of Salmon, Sea
Trout and Brown Trout. Rap. I>roc. Verb., Vol. 97.
JOKIEL, J., 1958: Los6s (Salmo salar) Rzeki wisli, Roczniki Nauk Rolniczych, Tom 73-B-2.
The. ALI a vt-1-:c s in,.) u I r ;ref LS
fri b i4-,- /es. Yr 6tDC,k •,011. 115h 54j 4,e. Vo!. "13 - 3-2.
KÂNDLER, R., 1958:. Vorschlâge zur Erhaltung des Ladisbestandes in der Ostsee. Fischwirtsch.
1954/2.
LPropositions . for the preservatiOn . Of . the stocks of salmon in the Baltic
Sea] •
— 1.955: Zut: gegenwârtigen Lage der Lachsfistherei in dir Ostsee. FischerbL 1955/10.
•
[ On . the present •status of the salmon fishery In tne Baltic Sea]
— 1958: Ergebnisse schwedischer Ladismarkierungen in der Ostsee nadi Wiederfângen deutscher
Fischer. Fischerblatt 1958/5.
[Results of the SI;iedish tagging of salmon in the Laitic Sea on hand of
recaptures by German fishermen]
—.1958-1963: The German Salmon fishery in the south-eastern Baltic ... ICES, CM 1958/40,
1959/33, 1961/23, 1962/5, 1963/31.
— 1959-1963: Gerinan Salmon fishery in the Baltic Ann. Biol., 14/210-211, 15/217-219,
16/249-257, 17/238-240, 18/204-205.
— und Lill-MANN, M., 1957: Ober den Lachsbestand und die Ertrâge des deutschen Lachsfanges
in der südtistl. Ostsee. Ber. DWK, 1413.
[On the stocks of -salmon and the yields of the German salmon catches in
the southeastern Baltic Sea]
« KOCH, H., BERGSTROM; E., and EVANS, J., 1964: Studie on the physiological variabilite of the
Salmon. Laxforskn. Inst. Medd., 1964/1.
LARSEN, K.,.1955: Fish population analyses in soine small Danish Trout streams by means of •
D. C. elect'ro-fishing. Medd. Danm. Fisk. Havunders., N. S. 1/10.
LINDROTH, A., 1950: Laxbestândets Fluktuationer i de Norlândska âlvarna..Sv. Vattenkr.
Ftiren. Publ.; 415, 1950 15. -
[l.luctuation of the stocks of salmon in the rivers of Dorrland]
— 1952: Rommângden hos Indalsâlvens lax. Vandr. Fiskundr. Medd. 6. •
IAmounts of roe jn the salmon of lndalsgivj
— 1955a: Mergansers as Salmon and Trout predators in the River Indalsalvem Rep. Inst.
Fr. Wat. Res. Drottningholm, 36.
— 1956: Laxodlingsprogrammet for det nârmaste Decenniet. Vatt. ftir. Publ. 460, 1956/9.
[Program for rearing salmon durin the next deCadel
— 1957: Baltic Salmon fluctuations: A reply. Inst. Fr. Wat. Res. Drottnh., 38.
— 1961a: On growth fluctuations in Baltic Salmon. ICES, CM 1961/7:
— 1961b: Sea food of Baltic Salmon smolt. Ibidem 1961.8. •
— 1962: Baltic Salmon fluctuations 2: Porpoise and Salmon. Inst. Fr. \Vat. Res. Drottningholm,
44. •
— 1963: The body/scale relationship in Atlantic Salmon, a preliminary report. J. d. Cons.,
Vol. 28/1.
LISHEV, M. N., 1958: DitTerences• in the structure: of scales of Baltic • Salmon of various river
populations. ICES, CM 195864.
[ P. 369]

- 227-
— 1961: Einige Gesetzmaffigkeiten der Popula.tionsdynamik des Ostseelachses (russisch). Issl.
Inst. Rybn. Akad. N AUK, Leu. SSR, Riga.
[Some regularities of the population dynamics of the salmon of the Baltic
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MAHLEE, J., und Ilmeru Nu, G., 19.63: Gestehungskosten und Betriebserfolg der Ostsee-FIodisee-
Kutterfischerei. Fischerbl. 1963.7.
[Working costs and operational success of the Baltic Sea / high sea
fishery with cutters]
MAEDA, H., 1953: Ecological analyses of pelagic shoals I. Bull. Jap. Soc. Scient. Fish. Vol. 19.4.
N1ENZILS, W. J. M., 1925: The Salmon. W. Blackwood, Edinburgh/London, 1925. ,
MEYER-WAARDEN, P. F., 1938: Attssetzungen von Regenbogenforellen in die Ostsee. Ber
Deutsch. Wiss. Korn. f. Meeresforschg, (DWK), N. F. 9/2
[Relertses'of rainbow trout in the Baltic Sea]
1939: Versudre mit Aussetzungen von Bach- und Regenbogenforellen in die westl. Ostsec
Rap. Pro.:. Verb., 109.13.
[Trials with releases of brook trout and rainbow trout in the western
Baltic Sea]
•
— 1942: Dic 7eesenfischerei auf Hering und Sprott, ihre 4'ntwicklun g und Bedcutiang fi:r the
Ostseefischerei und ihre Auswirkungen auf den Blankfischbestand der Ostsee. I sch.,
40/4-5. [P.
lThe fishery for herring and sprat, its development and importance for the
fishery in the Baltic Sea and its effect on the open stock of fish in the
Baltic Sea]
MITANS, A., 1963: Studies on the feeding habit of Salmon parrs in the Latvian rivers, NISlir.
MORGAN, N. C., and WADDELL, A. B., 1961: Insect emergence from a small TYOUt 10(11 and its
bearing on the food supply of fish. Freshw. Salm. Fish. Res., 25.
MUIR, S., and.WHITE, H., 1963: Application of the Paloheimo linear equation for estimating
mortalities to a seasonal fishery. J. Fish. Res. Bd. Can., 20/3.
NERESHEIMER, E., 1941: Die Lachsartigen. Handb. Binnenf., IIIA, 1941.
[The salmonicIF1
NIELSEN, J., 1961:Contributions to the Biology of the Salmonidae in Greenland. MedeGronland
Fisk. Unders., 159/8.
Nutor.sxr, G. W., 1957: Spezielle Fischkunde, Berlin.
[Special fish science]
NoaDQutsr, 0., 1908: Die Lângenrnafle von in der siidlichen Ostsee g,etangenen Ladisen und
Meerforellen ais Vorbereitung einer eventuellen Einführung von vereinbarten. MindestmaSen
dieser Fische. Rap. Proc. Verb., Vol. 9.
[The length measurements of salmon and seà trout caught in the southern
Baltic Sea, as preparation for the eventual introduction of conventional
minimum measurements for these fish]
— 1924: Times .of entering of the Atlantic Salmon in ;he rivers. Rap. Proc. Verb., Vol'. 33.
OTTERSTRÔM, C. V., 1933: Reife Lachse in Teichen. J. d. Cons., Vol. 8.
[Mature salmon in ponds]
OSTERDAHL, L., 1963: Tre . ars smoltutvandring i Ridclen. Laxforskn. Inst. Med., 10. '
[Three years of smolt migration in Ricklegn;
PALOHEIMO, J. E., 1961: Studies on estimation of mortalitieS I, Ctirnparison of a method descri-
bed by Beverton and Holt and •a new linear Formula. J. Fish. Res. Bd. Canada, 18 (5).
PIGGINS, D. J., 1958: Investigatio n. on predators of salmon smolts and parr. Salmon Res. Tr:
Ireland, 5, Dec. 1958: •
---: 1962: Some preliminary results of feeding thyroid material to salmon pa'rr. ICES, CM
1962/2.
•

- 228-
PETERSEN, C. G. .11, and OrrEas -rxeim, A., 1904: Die Ostseefischerei in ihrer jetzigen Lage;
I. Obersicht über die dânischen Gewasser innerhalb Skagens. Pub!. d. Circonst., 13 A.
LThe fishery in the Baltic Sea in its present Ftate. I. Survey of the
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POPE, J. A., MILLs, O. H., and SHEARER, W. M., - 1961: The fecundity of Atlantic Salmon.
Salmon Freshw. Fish. Res.,•29.
PYEFINCH, K. A., 1955: A review of the literature on the Biology of . the Atlantic Salmon.
Freshw. Salmon Fish. Res., 9.
PIECHURA, J., 1961: Température et Salinité des eaux de la Baltique méridional août 1960 -
Mai 1961. ICES, CM 1961/68.
[Temperature and salinity of the waters of the southern Baltic Sea in
Augupt 1960 to May 1961]
SANDMANN, J. A., 1906: Obersicht über die Scefischerei Finnlands. Pub!. d. Circonst., 13 C.
[Y.,urvey of the Finnish sea fishery]
SCHEURING, L., 1929: Die Wanderungen der Fische. Ergebn. Biol., 5.
[The migrations of fish] •
. SCHRÂDER, T. H., 1928: Die erste fiatürliche Nahrung ausgesetzter Bachforellenbrut. Z. f:
' Fisch., 26.
[The first natural food of liberated fry of brook trout]
SHAw, J., 1836: An account of sonie experiments and observations on the parr and ova of the
salmon, proving the parr to be the young of the Salmon. Edinburgh, New Phil. J., 21.
- - 1838: Experiments on the development and groWth of the fry of the Salmon from the
exélusion of the ovum to the age of 7 months. Ibid., 24.
SJÔGREN, S. J., 1962 und 1963. Det svenska laxfisket i Ostersjbomradet. Laxforsk. Inst„ Medd.,
1962/9, 1963/6.
[The Swecish ralmon fishery in the region of bsterse]
SUWOROW, J. K., 1959: Allgemeine Fischkunde. Berlin, 1959:
[General f s'n science]
SVÂRDSON, G., 1949: Natural selection and eg•g number in fish.. Inst. Freshw. Res. Drottningh.
Rep., 29.
— 1955: Salmon stock fluctuations in the Baltic sea. Inst. Freshw. Res. Drottningh. Rep., 36.
— 1957: Laxen och klimatet. Ibidem, 38.
[Salmon and climate]
SZATYBELRO,. M., 1957: Studies of factors influencing catching potential of Salmon and Trout:
fishing gear. Morsk. Inst. 1957/9.
• THukolisr, F., 1959: Die Entwicklung der deutschen Lachstreibfietzfisdierei und die Erprobung
neuèr Treibnetze. Fisdierbl., 1959/9.
[The development of the German salmon fishery with driftnets and the
testing of new driftnets]
— 1960: Untersuchungen über Bestandsfluktuationen beim Ostseeladis. Ber. DWK, 16/1.
[Investigations of fluctuations in the stocks Of the salmon of the Baltic
Seal
— 1962: Ober Qualitâtsschwankungen und die Bedeutung der Fettspeidierung beim Ostsee- •
lachs. Arch. f. Fisch. Wiss., 13/1-2. .
[On fluctuations in the quality of Baltic Sea salmon and the iMportance
of the fat accumulation in the Baltic Sea salmon'
— 1964: . Die Selektionswirkung von Angelhaken in •dei : Lachstreibleinenfischerei. Ibidem, 1964:
• 1-1.2.
. . . •
[The selective effect of hooks in the driftline.fishery for salmon]

- 229-
TRYBOM, F., und WOLLEBACK, A., 1904: Obersicht über die Seefisdierei Schwedens an den südlidien
und iistlichen Küsten dieses Landes. Publ , Circ., 13 A.
[Survey of the sea fishery of Sweden on the southern and eastern coasts
of thiS country]
— 1910: Bericht über die Aufzucht, Markicrung und den .Fang von Lachsen und Meerforellen
[ 1). 371]
im Ostseegebiet wâhrend der Jahre 1904-1908. Rap. Proc. Verb., Vol. 12/6.
[Report on the rearing, tagging and the capture of salmon and sea trout
in the region of the Baltic Sea in the years 1904 to 1908]
TWOMEY, E., and RIORDAN, A. 0., 1963: Novements of Salmon around Ireland, IX. Proc.
Royal Ir. Akad., Vol. 93 B 5.
VLADHLOV, V. D., 1956: Fecundity of Wild Speckled Trout (Salvelinus fontinalis) in Quebec
lakes. J. Fish. Res. Bd. Canada, 13/5.
WENT, A. E. J.; 1956: The Irish drift net fishery for Salmon. J. Dptrnt. Agr., Vol. 52.
— 1964: Irish Salmon, a review of investigations up to 1963. Scient. Proc. Royal Dubl. Soc.,
Ser. A, Vol. 1/15.
WHITE, H. C., 1936: The food of Kingfishers and Mergansers on the Margeree river, Nova
Scotia. J. Fish. Res. Bd. Canada, 2/3.
— 1937: The food of Salmon fry in eastern Canada. J. Fish. Res. Bd. Canada, 2/5.
— 1939: Factors influencing descent of Atlantic Salmon smolts, Nova Scotia. J. Fish. Res. Bd.
Canada, 415.
WISBY, W. J., and HASLER, A. D., 1954: Effect of olfactory occlusion in migrating Silver Salmon.
J. Fish. Res. Bd. Canada, 11/4.
Wn.LER, A., und QUEDNAU, W., 1931: Untersuchungen über den Ladis (Salmo salar L.). Z. f.
Fisch., 29.
[Investigations of the salmon (Salmo salar L.)]

Table I. Captures per unit effort with driftlines under different wind directions and wind
Speeds for the months November to March inclusive.
Wind •
•Season Month
5 Beaufort >5 Beaufort To tal
E Calm Average S W E Aver. mean
• XI 16,1 18,9 . 23,9 22,2 20,3 14,4 24,5 19,5 20
XII 17,2 7,8 3,3 9,4 14,7 14,7 12
1954/55 I 13,9 16,1 3,3 11,1 20,0 13,4 5,6 13,0 12
II 12,2 4,4 8,9 8,5 9
III 18,9 13,0 5,6 17,4 3,3 11,6 12
XI 7,8 7,5 7,0 16,0 4,0 8,5 12,0 7,0 7,0 8,7 9
XII 8,0 4,5 3,0 5,2 19,5 10,7 6,8 12,3 9
1955/56 I - 6,2 5,9 6,3 5,5 4,5 S 5,7 7,9 4,5 4,0 5,5 6
II
III 10,5 18,2 21,1 16,5 1 34,4 49,2 21,4 35,1 1
XI 20,7 11,9 25,6 14,1 29,6 20,4 12,5 27,0 30,3 23,2 21,8
XII 19,6 29,7 15,8 30,8 23,9 22,8 35,2 13,3 23,7 23,8
1956/57 I .10,0 27,5 27,8 7,3 12,7 17,1 46,5 26,3 36,4 26,8
II 5,0 6,6 12,5 21,0 6,5 10,3 45,5 15,0 30,3 20,3
III 14,2 20,3 77,5 16,5 5,6 26,8 36,6 23,4 31,5 20,2 27,9 27,4
XI . 8,9 9,5 17,9 11,0 11,6 10,5 9,5 16,7 12,2 11,9
XII 12,5 13,4 5,3 15,4 11,6 11,7 4,1 19,7 13,9 29,9 16,9 14,3
1957/58 I 14,0 5,5 17,3 6,1 9,6 10,5 19,3 8,8 35,2 25,3 22,1 16,3
- II 3,9 9,4 7,5 3,7 3,7 5,6 1,6 10,7 5,4 5,0 5,7 5,7
III 1,6 4,0 4,5 4,8 3,7 11,8 1,4 2,4 5,2 4,5
13
8
24,0
10,5
tx.1
1-1
•
f\.)
o

X1 12,3 20,9 3,3 9,0 10,8 11,3 34,8 34,8 23,1
XII 14,7 32,7 21,7 14,3 21,6 21,0 2, 1 46,2 34,7 18,8 30,7 25,9
1958/59 I 9,9 12,1 18,9 21,8 21,5 16,9 33,0 34,7 25,0 30,9 23,9
II 10,8 7,3 8,6 4,9 7,9 52,9 50,8 19,3 41,0 24,5
- II I 2,1 15,4 17,7 5,8 • 10,2 (15)
1959/60
XI
XII
I
II
III
7,9
7,3
12,5
6,0
9,1
10,3
8,6
5,9
7,7
' 5,5
1,8
8,2
10,5
9,8
5,7
5,2
•
6,2
7,2
- 6,0
8,5
8,2
8,2
8,5
5,6
7,2
12,2
3,6
11,5
6,7
5,5
7,7
13,0
5,2
12,1
11,6
8,4
9,2
8,8
10,3
11,6
7,6
9,5
7,0
22,5
9,3
9,9
8,1
7,6
7,1
.
.
.
•
.
.
' .
•
•
.
.
•
.
1960/61
" .
•
" .
1961/62
XI
XII
I
II
III
XI
XII
I
II
III
.
9,4 15,1
11,0 13,8
17,8 11,1
10,9 7,8
3,4
_
13,5 . • 11,7
19,0 23,2
11,6 10,2
14,4 12,6
. 6,5 7,1
•
11,2 15,2
12,1 13,8
, .• 6,7
4,9 . .
• •
10,7 -11,8
22,0 • 12,1
20,2 14,8
. 11,2 5,9
3,7 6,6 •
•
9,8
4,3
12,7
12,1
11,8
9,3
4,2
10,4
19,1
14,2
11,0
6,0
-
11,5
11,9. 13,9
14,3 •
8,6 -
. 5,9
,
12,2 18,6
29,9
14,7 35,0
22,5 . 31,1
8,2
-
16,8
13,9 8,2
20,1
.
•
'
10,5 11,3
37,6 15,8
39,0 22,0.
21,3 . 15,4
5,3 5,8
14,2
11,9
17,2 -
8,6
5,9
13,2
27,7
27,7
22,6
6,4
•
.
8,4
13,5
.12,0
14,5
9,0
5,1 .
10,8
11,8
23,4
21,0
16,8
6,2
- 15,8
-
1962;63 XI 9,9 9,8 7,9 9,6 16,1 10,7 10,3 - 8,4 8,3 9,3 9,1 9,9 -
XII 7,3 9,1 9,3 6,5 2 , 4 6,9 10,2 9,4 9,8 8,4
1 The values for March 1956 were left out of consideration when calculating the mean.
The data are based on. short-period, very large catches, which should not be considered
as measure for the strength of the stocks.
2 Obtained with the aid of the average monthly course in Table 7.
9,2
8 2

Table II. Captures per unit effort under different wjnd directions and wind. speeds on all •
fishing grounds for the months February to April inclusive.
Wind .
Season MOnth
Beaufort >4 Beaufort
W N E Calm Average S W N E Mean
1955/56 IV 4,2 12,4 9,9 7,1 8,4 13,0 13,0
1956/57 II 10,8 7,5 ' 9,1 6,7 8,5
III 9,0 4,7 7,4 7,0
- IV 4,3 6,7 5,3 11,1 6,9
8,4" 13,0
5,6 5,6
8,3 • 4,4 • 6,4
• • 5,0 0 2,5
'
.
1957/58
-
II
III
IV
6,3
11,9
8,1 .
19,8
3,8
14,9
11,8
, ,
5,3
7,7
8,5
7,5
5,8
13,6
8,1
f
3,0
,
4,1
1,8
4,8
- 4,1 .
2,4
. .
.
9,2 3,3
1958/59 II 43,3 7,7 8,4 . 22,4 20,5 3,2 - 3,7
• III 13,7 13,6 19,0 9,7 14,0 8,3 8,3
• IV • 4,4 3,6 5,2 4,2 10,0 5,5 • 2,9 - 2,9
13,3 4,8
1959/60 II 20,4 14,9 13,3 13,9 ' 15,6 7,0 3,0 10,6 6,9
III 12,0 25,0 2,7 9,2 2,5 10,3 6,6 5,7 6,2
• . IV 5,9 6,1 5,8 2,8 7,9 5,7 -
2,6 i_( ,
10,5 5,2
1960/61 II 14,4 15,4 10,7 13,5 11,7 23,6 0,5 1 1,9 •
- III . 4,9 14,0 4,4 7,8 6,6 1,7 4,2
' IV 4,3 1,7 . 7,5 2,3 . 5,4 4,2 12,7 12,7
8,5 9,6
1961/62 H 13,1 . 18,1 13,4 ' 1,5 11,5 '8,7 12,1 10,9 10,6
III 9,9 8,4 6,1 30,6 19,5 14,9 5,8 0,5 1,3 13,5 5,3
IV 4 ' 3 5,2 0,6 • 1,0 7,3 3,7 2,6 0,5 1,7 8,5 3,3
10,0 • 6,4
1962/63 IV . 8,2 . 2,5 10,0 8,2 5,0 6,8 4,9 4,3 2,3 3,8
6,8 3,8

Table III. Yields of salmon and sea trout in the entire
Baltic Sea (without the riyers) in t. (For references
. see 2.3.4.)
ear Sweden Denm. Germ.* . Fini. Poland USSR Total
1895 107 . - 69 243 214 633
189 6. ' 41. 132 254 . 191. - 618
1897 - 90 • 88 344 230 752
1898 50 65 250 ' :237- 602
1899 • 30 55 . 175' « 246 ,
506
1900 , 30 52 . 180 .. 154 , •
- .416
1901 . 10 • 55 . 230 56 ',. • 351 '
1902 ''30 • 40 90 .51 • « 211
1903 - 54 18 . .,i, . 70 ..• • 70' ' •
• 210
1904 ..,. 36 21 .• • 70 • - 75 • 202
1905. , 42 ' • 23
80- - 59 204
1906 48 • 21. ' . . 80 92 • 241,
1907 • 69 - ' 25. '43 • 307 444
1908 . • 62 - . 38 • • 79 290 . . • 469 -
1909 120 52 104 '. (350) 626
1910 50 47 . 75 (250) 422 .
1911 ' . 87 .40 . 30 . 111 . . . .
268 -
1912 ' 91 • 41 52 107 291
1913 113 37 -, 83 117 ' 250
1914 ' 170 42 78. . 108. .398"
1915 173 • 66 47 . 152 . 43 8 •
1916. • 124 -- 31 124 . 256• 536
1117 176 ' 25 99 166 . 466
1918 124 • ' 24 • ' 169 137 .454
1919 240 - 78 • 108. (180) : 606
1920 400 .. 88 68 '(250) 806
1921, 425 . 85 • 43 . 245 43 841
1922 , 297 - - 48 • 105 . 195 240 • 885
192 3 • .288 44 ., - 93 184 87 . 696
1924 . 203 • 19 64 228 71 .66L , 651
1925' 160 - 44 68 ' 308 35 64L 679 .
1926 212 60 151 244 - 115 73L 855
1927 310 77 • .202 ' 316 173 - 88L 1166
1928' 306 55 343 • 124 • • 259 . 147 - 1234
1929 ' 206 . 33. 189 135 132 206 901
1930 222 . 52 . 146' • . 180 . 236 . 214 1050
1931 . 401 . 77 • 160 208 81156 1083
1932 350 167 275 • 241 • 86 • 211 - 1330
1933 . 327 . , 142 159 168 • 104 269 • 1169
1934420- 64 - 193. 299 68 162 1206
1935 • 417 71, .118 • 237 70 • 189 1102
1936 350 62 100 • .177. 68 . 118 . 875 .
1937 292 33 55 213 . 32 •178 803
1938 '250 . 34 - - 66 183 • 57 174 • 764
1939 . 287 41 '37 153 12' .144 674.
1940 • 241 52 ' • (35) 162 62 . 517
1941 .. 330 .82 . (30) 413 825
1942 395 , 130 (40) . 403' 928
1943 634 157 • (10) , 323 . 1114
1944 757 147 224 • 1128
1945 1290 162 - 244 11 1707
1946 . 1521 ' .478 • • .475 . 279 79 . 2832
1947 1273 . 628. 395 486. 161 2937
1948 - • 1304 948 • 10 289 406 280 ) 3237
1949 • 1175 8,43 , 68 260 286 185 2817
1950 1470 1323 192 «• 399 367 155 39C6
- 233 -
[p. 375]

•
Yea.r
Sweden
Continuation
Table III.
Year Sweden Debm. Germ. Fini. Poland USSR Total
1951 1175 1099 136 352 128 151 3041
1952. 858 1330 144 « 383 67 149 2931
1953 472 754 ' 75 350 71 117 1839
1954 551 976 112 300 145 96 2180
1955 356 611 157 300 42 182 1648
1956 730 963 287 300 197 128 2605
1957 • 392 896 345 300 185 98 2216
1958 335 898 194 300 204 100 2031
1959 413 935 243 . 293 239 99 2222
1960 501 . 1065 217 300 320 83 2486
1961 561 1386 , ,345 250 193 (100) 2835
1962 (380) 1175 218 341 . 293 (80) 2487
Figures in 0 are estimated
L = Latvia only
Finland USSR Total
Latvia (estimated)
.Oulojoki Tot. only
- 234 -
Table IV. The yields of salmon and sea trout . in the river s.
of the Baltic Sea in . t, annual averages.
(For references see 2.3.4.)
1905-1909 135 11 270
1910-1914 ' 155 8 240
1915-1919 . 148 • 12 290
1920-1924 192 6 .
310
1925-1929 99 7 46 240
1930-1934 100 11 51 240
1935-1939 108 9 34 220'
1940-1944 172 6 290
1945-1949 471 17 54 690
1950-1954 214 45 420
1955-1959 123 29 • • 270
1960-1962 151 • , ' 91 59 340
[P. 376]

•
P
•
Table V. The yield of sea trout in the entire Baltic Sea
without the rivers in t.
(For references see 2.3.4.)
Total
Year Sweden Denmarkl Germanyl Poland Finland a. USSR
estimated
1940 65 . 0 0 0 100
1941 . 63 : 1 ' 0 . 0 • - 100
1942 50.. 2', 0 - 0 - 100
1943 42 , ' 2 ' 0 , 0 100
1944 57 • 2 - ,0 - 0 100
1945 .5/ .. 1 . 0 .; 0 100
1946 47 • 10* t: ' 0. 66 160
'
1947
1948 •
'55 .
56 ' *
15 - - , 0
18 ' ''''' 0.'
'
* .
64
60 '
180
200
1949 • 73 15' • 1 47 190
1950 66 - 25 .- • .2 • . ' 54 200
1951 .
1952
98
68
- 20 1 46 230
. '
1953 .
1954
1955
1956
1957 ' .
•
-
58
67. .
'60
59 ,' . '
52 • .
- 25 •.
15
20 ,
10'
30
20.
1 •
. 0 .
• 1
. 5
10 •
30. . .
24
47
102
26 * '•
41
52
.
.180
180
250
180
200
220
1958
1959
47'
: 55 - .
20
30
2
. ' . 17
'. 69
160
220
320
1960 ' 76 30 33 -. 256 • 450
1961 25 ' - 25 '• 10 ' 142 ' ' 250
1962 ' 30 10 - 7 239 • . 350
lin part after random samples
0 = less than 0.5 t
- 235 -
[P. 377]

Table VI. Ratio between fork le
. Baltic Sea salmon
o,bdiun g e . Fork length
' cm
r11111
.
- 236 -
th and total length in the
cf. 5.1.1.). .
'i'oIalIgc Total length
0 . 1 .2 3 4 6 . 7
30 32,6 32,7 32,8' 32,9 33,0 3 3 ,1 33,2 33,3 33,4 33,5
31 33,6 33,8 .. 33,9 .34,0, • 34,1', 34,2 34,3 34;4 34,5 34,6
32 34,7 34,8 34,9; 35,0 35,1 35,2 35,3 35,4 35,5 35,6
33 35,7 35,8 . 35,9 36,1 • 36,2 36,3 36,4 36,5 36,6 '36,7
34 36,8 , 36,9 37,0• 37,1 . .37,2 37,3 37,4 37,5 37,6 37,7
35 37,8 37,9 38,0 38,1 38,2 38,3 38,5 38,6 38,7 38,8
36 • • 38,9 39,0 39,1 39,2 39,3 .. 39,4 . 39,5 39,6 39,7 39,8
37 399 40,0 40,1 40,2 • 40,3 40,4 40,5 40,6 40,7 40,9
38' • ' 41,0 441 41,2 41,3 . .41,4 41,5 • 41,6 41,7 41,8 41,9
39 • 42,0 42,1 42;2 42,3 42,4 42,5 ' 42,6 42,7 42,8 42,9
40 43,0 43,1 43,3 43,4 43,5 43,6 ' 43,7 43,8 . 43,9 44,0
41 44,1 . • 44,2 44,3 44,4 44,5 44,6 44,7 44,8 44,9 , 45,0
42 45,1 45;2' 45,3 45,4 . 45,5 45,7 45,8 45,9 46,0 46,1
43 46,2 46,3 46,4 46,5 46,6 46,7 46,8 46,9 47,0 47,1
44 47,2 47,3 . 47,4 47,5 • 47,6 47,7 47,8 48,0 48,1 48,2
45 48,3 • 48,4 48,5 48,6 48,7 48,8 48,9 49,0 49,1 49,2
46 49,3 49,4 • 49,5 . 49,6 .49,7 49,8 49,9 50,0 50,1 50,2
47 5 .0,4 - 50,5 50,6 50,7 50,8 50,9 51,0 51,1 51,2 51,3
48 51,4 • 51,5 51,6 51,7 51,8, 51,9 52,0 52,1 52,2 52,3
49 52,4 . 52,5 52,6 52,8' 52,9 53,0 53,1 53,2 53,3 53,4
50 • 53,5 53,6 • 53,7 53,8' 53,9 54,0 54,1 54,2 54,3 54,4
-51 54,5 54,6 -54,7 54,8 54,9 55,1 55,2 55,3 55,4 55,5
52 55,6 55,7 55,8 55,9 56,0 56,1 56,2 56,3 56,4 56,5
53 56,6 56,7 56,8 56,9 57,0 57,1 57,2 57,3 57,5 • 57,6
•54 57,7 . 57,8 57,9 • 58,0 58,1 58,2 58,3 • 58,4 58,5 • 58,6
55 '58,7 -58,8 58,9 - 59,0• 59,1 • 59,2 59,3 59,4 59,5 • 59,6
56 59,7 59,9 60,0 .60,1 60,2 60,3 60,4 60,5 60,6 60,7
57 60,8 60,9 . 61,0 - 61,1 61,2 61,3 61,4 61,5 61,6 61,7
58 61,8 61,9 - 62,0 62,2 . 62,3 62,4 62,5 62,6 62,7 . 62,8
59 62,9 63,0 63,1 . 63,2 63,3 • 63,4 63,5 63,6 63,7 63,8
60 63,9 64,0 64,1 64,2 64; 3 64,4 . 64,6 . 64,7 64,8 64,9
61 65,0 • 65,1' 65,2 65,3 .65,4 • 65,5 • 65,6 • 65,7 65,8 65,9
66,0 66,1: 66,2 66,3 66,4 66,5 66,6 66,7 66,8 67,0
63 67,1 67,2 67,3 .67,4 67,5 67,6 67,7 67,8 67,9 68,0
64 68,1 *68,2 68,3, -. 68,4 68,5 68,6 68,7 68,8 68;9 69,0
65 69,1 69,3 69,4 • 69,5 69,6 69,7 69,8 69,9 70,0 70,1 •
66 70,2 70,3 70,4 70,5 70,6 70,7 70,8 70,9 71,0 71,1
67 111,2 71,3 71,4 . 71,5 - 71,7 71,8 71,9 . 72,0 72,1 72,2
68 72,3 72,4 72,5 72,6 '.72,7 72,8 72,9 73,0 73,1 73,2
69 - 73,3 • • 73;4 73,5 73,6 . 73,7 73,8 73,9 74,1 74,2 74,3
. 74;4 74,5 74,6 74,7 74,8 74,9 75,0. 75,1 75,2 . 75,3
71 75,4 75,5 - 75,6 75,7. • 75,8 . 75,9 '.76,0 . 76,1 76,2 , • 76,4
• 72 . 76,5 76,6 • 76,7 76,8 76,9 77,0 77,1 77,2 77,3 • 77,4
73 77,5 77,6 • 77,7 • 77,8 77,9 - 78,0 78,1 • 78,2 78,3 78,4
74 . 78;5 •78,6 • 78,8 78,9 79,0 79,1. 79;2 79,3 79,4 . 79,5
79,6 79,7 79,8 79,9 . 80,0 80,1 80,2 80,3 80,4 80,5
76 80,6 80,7 80,8 . 80,9 81,0 81,2 81,3 81,4 81,5 81,6
77 • • 81,7 81,8 81,9 82,0 82,1 • 82,3 82,3 82,4 82,5 • 82,6
.78 82,7 - 82,8 82,9 83,0 83,1 83,2 83,3 . 83,5 83,6 83,7
79 • 83;8. 83,9 84,0 84,1 84,2 84,3 . 84,4 84,5 84,6 84,7.
. 80 84,8 84,9 . 85,0• 85,1 • 85,2 85,3 • 85,4 85,5 15,6 85,7
81 85,9 86,0 86,1 86,2 .86,3 86,4 86,5 . 86,6 .86,7 , 86,8
82 . • 86,9 87,0 87,1 87,2 . 87,3 87,4 • 87,5 87,6 87,7 :87,8
•
[P. 37 8 ] I

, •
11111:
•'''"''n'nrse Fork
•
'length
• Continuation
Table • VI
111111 • •
,,.,„-
, - 0 1 2 3
,
c in • ''',, .
•
Tot4Iânge Total length
5 6 7
-. 237 -
. 83 87.,9 88,0 .88,1 88,3 88,4 88,5 88,6 88,7 .. 88,8 .88,9
84 89,0 89,1 • 89,2 89,3 89,4 89,5 89,6 89,7 89,8 89,9
85 90,0 90,1 90,2 90,3 90,4 90,6 .90,7 . 90,8 90,9 91,0
86 91,1 91,2 91,3 . 91,4 91,5 91,6 91,7. 91,8 91,9 92,0
•87 92,1 92,2 . • 92,3 . 92,4 • 92,5. 92,6 92,7 928 93,0 . 93,1
88 93,2 . 93,3 - 93,4 , 93,5 93,6 93,7 93,8 93,9 94,0 94,1
. . 89 94,2 94,3 94,4 94,5 94,6 94,7 • 94,8 94,9 95,0 95,1
90 95,2 95,4 95,5 '95,6- 95,7 95,8 95,9 96,0 96,1 96,2
91 • • - 96,3 • 96,4 -96,5 96,6 96,7 96,8 • 96,9 97,0 • 97,1 • 97,2
. 92 ... 973 97,4 97,5 •97,7 97,8 . 97,9 98,0 98,1 98,2 98,3
93 98;4 98,5 .98,6. 98,7 '98,8 .98,9 99,0 99,1 99,2 99,3
94 . • 99,4 99,5 2 • 99,6 99,7 99,8 - 99;9 100,0 100,2 . 100,3 '100,4
95 100,5 100,6 100,7 .100,8 100,9 101,0 101,1 101,2 101,3 101,4
96 101,5 • 101,e 101,7 101,8 - 101,9 . 102,0 102,1 102,3. 102,4 102,5
97 102,6 102,7 102,8 .102,9 103,0 103,1 103,2 103,3 103,1 103,5
98 103,6 .103,7 103,8 103,9 104,0 104,1 104,2 104,3 104,4 104,5
99 . 104,6 104,7 104,9 105,0 105,1 105,2 105,3 105,4 105,5 105,6
100 105,7 • 105,8 105,9 - 106;0 106,1 106,2 106,3 106,4 '106,5 106,6
101 -106,7 106,8 106;9 - . 107,0 107,1 - 107,3 107,4 107,5 '107,6 107,7
. 102 '107,8 107,9 108,0 108,1 108,2 108,3 .108,4 108,5 108,6 108,7
103 108,8 108,9 109,0 .109,1 109,2 109,3 109,4 109,5 109,7 109,8
. 104109,9 > 1 .10,0 110,1 ..110,2 110,3 110,4 110,5 110,6 110,7 110,8
105 • 110,9 111,0 - 111,1 111,2 111,3 111,4 111,5 111,6 111,7 '111,8
106 - 112,0 '112,1 112,2 112,3 112,4 112,5 112,6 112,7 112,8 112,9
107 - 113,0 .‘ 113;1 113,2 113,3 113,4 113,5 113,6 113,7 113,8 113,9
.108 114,0: - ,114,1 114,3 114,4 • 114,5 114,6;' 114,7 114,8 114,9 115,0
109 • 115,1 115,2 115,3, : 115,4 >115,5 115,6 115,7 • • 115,8 115,9 116,0
110 116,1 " 116,2 116,3 116,4 116,5 116,7 . 116,8 116,9 117,0 . 117,1
111 117,2 117,3 117,4 • 117,5 117;6 117,7 117,8 117,9 118,0 .118,1
112 118,2 118,3 . 118,4 . 118,5 118,6 118,7 118,8 • 118,9 119,1 119,2
113 119,3« «. 119,4 . - 119,5 • 119,6 119,7 119,8 119,9 120,0 • 120,1 120,2
« 114. .120,3 120,4 120;5 120,6 120,7 120,8 120,9 121,0 121,1 .121,2
115 • 121,4. 121,5 121,6 121,7 121,8 121,9 .122,0 122,1 122,2 122,3 .
116 122,4 122;5 .122,6' • 122,7 122,8 122,9 123,0 123,1 123,2 123,3
117 123,4 123,5 123,6 123,8 .123,9 124,0 124,1 124,2 124,3 :124,4
- 118 124,5 • 124,6 124,7 124,8 124,9 125,0 . 125,1 125,2 125,3 125,4
• 119 . • 125,5 125,6 . 125,7 .125,8 125,9 126,0 126,2 126,3 126,4 126,5
120 . 126,6. • 126,7 1 26,8: 126,9 127,0 ' 127,1 127,2 ..127,3 127,4 127,5
• 121 127;6 • 127,7 127,8.« 127,9 128,0 128,1 .128,2 128,3 128,5 128,6
122 128,7- 128,8 128,9 129,0 129,1; 129,2 129,3 129,4 • 129,5 129,6
123129,7 129;8 129,9. 130,0 - 130,1 • 130,2 1.30,3 130,4 130,5 130,6
124 • 130,7 130,9 131,0 131,1 131,2 .131,3 131,4 131,5 131,6- 131,7
125 131,8. .
[p. 379]