Translation Series No.1211

• 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 )