Translation Series No.1211

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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