Development of Species Separation Devices for Coastal Trawl

Abstract

A series of fishing trials for development of species separation devices to separate shrimp and unwanted juveniles of finfishes was carried out for coastal trawlers in Choshi, Chiba. Double codends with a separation panel were designed and four types of separation panel (43.5mm/bar square mesh, 55.0mm/bar square mesh, 24.6×49.8mm rectangular mesh with a PE frame and 24.6×101.8mm rectangular mesh with a PE frame) were tested. Newton's separation efficiency which was applied to shrimp and flatfish juvenile (<150mm) was highest when the 24.6×101.8mm rectangular mesh with a PE frame was used for the separation panel. However, even when this device was used, 35% of shrimp were separated into the upper codend which was designed to catch flatfish juveniles. All the devices had size selectivities which separated bigger individuals into the upper codend. From these results, because of the multi-species and sizes targetted by Choshi trawlers, these devices in their present form are not applicable for industry due to a loss of marketable fish and shrimp.