Translation Series No.1211

Hempen nets are nowno longer used in the German salmon fishery.
For this reason we are using as basis for the present investigations the
mesh widths of the synthetic nets. The measuring of the mesh of 24 nets
on four cutters gave an average mesh width 2 of 78.75 mm (mesh opening
about 157 mm).
Ldnge
CirCUmYerence
A . eye
D insertion of dorsal fin
N .= nape -
0 = operculum
S = snout
36
• For the determination of the
selectivity of gill nets the catches
with driftlines can be used by way of
comparison. For this purpose I have
line catches of 341 fish and net catches
of 949 fish, for January 1964 from the
Danzig Deep (Table 8). If one calculates
for the groups of length the ratio of
values in the range 85 to 99 cm. If one
Fig. 9. Relation between total
length and circumference in four P uts the mean value of this range equal
salmon.
to 100, one obtains then the percentage
selectivity for the individual groups of length (Table 8, column 5).
P. 245]
the number of netted salmon to the number
of lined salmon, one obtains the highest
O. Christensen (1963) has carried out these investigations with
[p. 246 ]
the aid of Danish net catches and line catches in March 1963. The selec- • '
tivity curves for the two investigations are shown in Fig. 10. It is seen
that the German nets select larger salmon than do the Danish nets.
Only a few large fish escape from the nets, but a substantial
2 Mesh width = distance between the centre of one knot and. the Centre cf the
next; mesh . opening . length of the stretched mesh.