Translation Series No.1211

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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
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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