Migrating Behaviour of Fish Schools in Set-net Fishing Grounds

Abstract

The migrating behaviour of fish schools such as jack mackerel Trachurus japonicus, spotted mackerel Scomber australasicus, and Japanese anchovy Engraulis japonicus was investigated in set-net fishing grounds by means of sonar image records. The spotted mackerel and Japanese anchovy schools moved at an average speed of 18–19 cm/s, while the jack mackerel schools moved at 29 cm/s. Schools of all species changed their direction of movement at an average veering angle of 19~36°. However, the veering angle of Japanese anchovy schools showed a tendency to be larger than that of the other two species. The average duration of straight movement of the spotted mackerel and Japanese anchovy schools was 2 ~ 2.4 min, while that of the jack mackerel schools was 2.9 min. This confirms a frequent veering of fish schools in the set-net fishing grounds. The jack mackerel and Japanese anchovy schools tend to move along the isobathic route with a depth change ratio of 0.6 ~ 0.8 m/min between the first and final image. In case of the spotted mackerel schools the larger depth change was observed up to 6 m/min. © 1993, The Japanese Society of Fisheries Science. All rights reserved.