Abstract
The behaviour of fish schools concerning the set-net was investigated in eleven fishing grounds around Japan using a scanning sonar. Taking the fish school's horizontal section as ellipse-shaped, they measured 37m in length and 15m in width except for a few larger sized schools. The mouths of set-nets were almost large enough for the fish schools to enter.
The speeds of fish schools were measured around the set-nets for the six different species. Many fish schools moved slowly at 15-23cm/sec around them. No specific differences in speed could be observed, although Chum salmon were 4 times larger in body length than sardines. How-ever in the area off the set-net, they tended to move faster than in the area near coast. The speed varied depending on the area.
