Translation Series No.1211

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Selektion Selection
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part of small salmon.can slip through the meshes. Correspondingly, the
50-per cent lengths 3 of the Danish curve are lying lover than those of
the German curve. They amount to about 68 cm or 78 cm, respectively, for
small salmon and 100 cm or 105 cm, respectively, for large salmon.
dânische Netze — - Danish nets
—deutsche Netze (78,75rnm np„rman nets
schenwene
Mésh width
0 0 100 uo cn,
. mowin g.= Total length
.. . .. .. . .
Fig. 10. Selectivity curves for salmon driftnets.
Let us return to the object of our investigation, that is,
obtain comparable data for the density of the stock. The -egelliam e per
unit effort of the driftnet fishery are, to be sure, not representative
in regard to the age composition of the stock being fished. They are,
however, comparable among themselves, if.the mesh width of the nets used
remains constant and if there are no differences in growth. They can
therefore be used as a . measure for the population density.
It can also be stated that the comparability of the
.per unit .effort by line as well as by net sis i not being influenced by the
selective effect.
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However, the two kinds of gear differ in one substantial Point.
3 Fifty percent of all salmon.(of a certain group of lengths),.that meet
the net as Potential objects to be caught, - are retained in the net..