Abstract
The catch amount of the set-nets was analysed in relation to the observed number of fish schools using a scanning sonar, in the fishig ground of Sagami Bay and Sanriku coast for Spotted mackerel and Chum salmon. The catch of the set-net was expressed by the logarithmic Function of the number of fish schools migrating to the fishing ground. The catch of the set-nets could be obtained when the number of fish schools around the set-nets exceeded a certain level. The capturing efficiency index of the set-nets have a maximum value on the equation. A larger num-ber of migrating schools than this maximum value, results in a lower capturing efficiency of the set-nets. The gear space for capturing was large enough to accomodate a larger catch. There-fore the capturing factor could not only be attributed to the number of fish schools but also to their moving behaviour in the fishing ground.
