北洋底曳漁場におけるネットレコーダーによる入網魚群記録と漁獲との関係

抄録

During 6th July through 12th September, 1966, actual trawlings using Net recorder were carried out by a large sized trawl boat in the fishery near Aleutian Islands and in the southern fishery of Alaska Peninsula in the Northern Pacific Ocean.
The following results which will be useful for bottom trawlings were concluded by comparing the recordings obtained by Net recorder showing the fish school having entered the net with the haul of fish correspond to the recordings. It is noted, however, that a large net (height of net mouth: 5-6m, width of it: 30m) was employed and that operations referred to in this survey are limited to those in depth of 150 to 320 meters.
1) It is presumed that the integrated area of fish traces obtained by Net recorder showing fish school entering the net is approximately proportional in linearity to the haul of fish correspond to the area. This means that Net recorder enables us to determine the towing time required by examining the recordings obtained by Net recorder.
2) It is presumed that when both rockfishes and Alaska pollack are 30 to 44cm in total length (Alaska pollack is in its youth), fish school of Alaska pollack is two times as dense as that of rockfishes.
3) Generally, rockfishes and Alaska pollack on the recordings obtained by Net recorder are distinguished, i.e. rockfishes draws lengthways sharp traces almost touching the oscillation line, while, Alaska pollack draws densely sideways semicircular traces on the bottom line.