Translation Series No.1211

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salmon . switch over to the compact food of crustaceans and fish. This doesnot
man H that crustaceans and fish do predominate in the food only after the:fish
have reached a length of 30 or 40 cm, but that they are decisively respon-
sible for the attainment of this size and are therefore eaten alreaey
earlier in greater amounts. One can deduce furthermore from this finding
that the final growth performance of the salmon is dependent to the largest
extent on the moment when the post-smolt switch to fish food.
6.4. The relation between the behaviour of the prey and the composition
. of the food of the salmon
CobOrSe
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• (On hand)of the food investigation could be established that in
the Danzig Deep the proportion of sprat is smallest from December to March,
whereas the proportion of herring increases simultaneously. This finding
agrees with the yields. The greatest catches of sprat are being madeduring
the time of spawning (May/June) and the best catches of herring are during
spring and fall (FL Berner 1963). The sprat make daily vertical movements
during the warm season and feed., at night on plankton in the upper layers
of water. In contrast,-they remain in winter principally in the layers near
the bottom (E. Ehrenbaum 1936, K. Bahr 1936b). Only amall amounts of sprat
were caught from 1953to.1960 to the southeast of Bornholm. The catches
in the Bornholm Basin were also relatively mall. This fact coincides with
the amall importance that the sprat has as food for salmon on the fishing
ground 5. In all'areas of the central and southeastern Baltic Sea, the
best catches of sprat per unit effort are made in May to lugust, with
maximum values in June and July (M. Berner 1965e J. Elwertowski 1959).
Belona and sand eel stay during the summer in the ûpper water
layers in order to eat plankton. Some individuals, however, carry out
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