Translation Series No.1211

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 %)