Translation Series No.1211

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In Table 9 have been calculated the numbers of hooks that were
required in order to equal the catch per 100 nets on the basis of the cep -
-e unit of effort of sprat (dragnet) by Polinh cutters in the Danzig
Deep (Elwertowski 1959), since sprat are considered to be the most impor-
tant food fish of salmon (see Table 48).
The number of hooks required and the catches per unit of effort
of sprat in the Danzig Deep show a very good agreement for the three catching
periods 1956/7 to 1958/9. During the subsequent years a considerable decline
of the sprat catches took place. Elwertowski (1964) has pointed out that the
availability of sprat in winter depends on the temperature conditions. Eel-
atively cold water delays the time of spawning and therewith the concen-
tration of the sprat into pre-spawning and spawning swarms. It is therefore .
possible that in the years in question only the availability of these fish has
declined, whereas they were still available as food for the salmon. For the
fishing. seasons 1959/60 to 1961/2 we obtain .therefore a new ratio between
the number of the hooks required and the captures per unit àf effort,of
sprat. According to these statements it is not possible to eiclude the pos-
sibility that changes in the dênsite of the stock of sprat can effect. the
line catches of salmon in the spring.
There are only verY few comparable values available for the fall
and winter months. The compa#son betweeen the number of hooka and nets
. that are required for a certain,catch result of salmon, appears at this
time to le much more favourable for the driftlines. It suggestà itself,.
that this fact is due to the scarcity of sprat, because the sprat appear
only in spring iâ larger numbers in the upper layers.of thewater. (see
011apter 6.4w). Annual differences - cannot be demOnstrated..
It has been investigated in how far otherfactOrs than the