Translation Series No.1211

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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