Translation Series No.1211

Number of sprat
Season Oct./Nov. Dec./Jan. Feb./March /cutter/day
8Pring, Danzig Deep
• 1956/57
1957/58
1958/59
, 1959/60
' 1960/61 937
1961/62 1 057
1962/63 519 •
453 11 681
" 1830 82 407
1 383 55 385
1 302 8 1001'
554
728
2 1 400
1 042 r
11600'
4 2001
2 1001
- 38 -
The ddftnet works entirely passively, whereas the driftline attracts the •
salmon by the.bait. Spice the fish pureue also the naturally occurring
food fish, there is competiticin between the artificial and natural offer
of food. If we assume that the population density N and the intensity of
fishing f (that is, the artificial offer of food through bait) are constant
in the years x and x + 1, whereas the natural food fish are present in the
strength p and 0.5 p, respectively. That obviously means that drift-line
catches must increase'in the year x + 1. In contrast to this, the catches
with driftnets remain the sanie in both years. In other words: if in the
year x the • catch by 1000 hooks equals the catch . by 100 nets, then the catch
. by 1000 hooks in the year x +1 is greater than the catch by . 100 nets. When
cate,h-
our investigations show such changes; then we have to reckon that.emeimae
per unit of effort by line is influenced by the ratio between the natural
[p. 247]
and artificial food offer.
Table 9. Number of hooks, which were required during
different fishing periods to equal the catch results
of 100 nets. (Calculated with the simple. Means
. of Table 7.)
1 The data were kindly supPlied by Dr. J. Elwertowski (Institute for
' Ocean FisherY, Gdynia) as. catch in kg per outter . and day. The recalculation:is
based on an average weight per sprat of 9.33 g (P.
F. Meyer-Waarden 1942), all other statements -after J. .Eawertoweki'
1959.