箱網揚網実験によるマダイ幼魚の網目選択性

Abstract

Since, in a set-net fishery in the sea off Kyoto Prefecture, small mesh sized net in bag-net (about 15mm in streched size) are commonly used, the juveniles of red sea bream Pagrus major (≤ 100mm in fork length) are caught and are mostly discarded at sea.This paper describes the mesh selectivity for the juveniles of red sea bream. Mesh selectivities were obtained from a series of net hauling experiments using six bag-nets (mesh sizes 13.6, 18.6, 22.5, 25.3, 27.7 and 30.2mm). The mesh selection curves were determined as a logistic function for various mesh sizes. The value of selection span (difference of fork length between 25% and 75% selection) were 7.3 ?? 8.5mm for less than 22.5mm mesh, 4.9 ?? 6.8mm for more than 25.3mm mesh, respectively. The resultant selection factors ranged from 2.32 to 2.93 for various mesh sizes.Through this experiments, it is implied that fish behaviour by their size may have a significant effect on the mesh selectivety.