Analysis of the escape behavior of juvenile salmon Oncorhynchus keta from the bag-net for by-catch prevention in a setnet fishery

Abstract

The escape behavior of juvenile salmon from nets was investigated in a water tank experiment by using a netting panel with several types of specifications in view of by-catch prevention in a set-net fishery. Twelve diamond mesh nets and four square mesh nets with different mesh size (mesh openings when stretched: 14.0, 15.6, 17.2, and 20.5 mm; hanging ratio of diamond mesh: about 0.5, 0.70, and about 0.8) were used for the netting panel. A comparison of the passing ratio in each hanging ratio of diamond mesh showed the passing ratio of the panel with hanging ratio of 0.70 was the highest in each mesh size. In addition, the diamond mesh with hanging ratio of 0.70 had the higher passing ratio than that of square mesh in each mesh size. From these results, it was determined that the diamond mesh with hanging ratio of 0.70 was appropriate for the prevention of juvenile salmon by-catch. However, the shape of the diamond mesh collapses easily with the tension caused by bag-net hauling, so it is necessary to attach a device and employ a haul technique that allows the by-catch to escape.