Development of species separation devices for coastal trawl

A series of fishing trials for development of species separation devices to separate shrimp and unwanted juveniles of finishes was carried out for coa stal trawlers in Choshi, Chiba. Double codends with a separation panel were designed and four types of separation panel (43.5 mm/bar square mesh, 55.0 mm/bar square mesh, 24.6 x 49.8 mm rectangular mesh with a PE frame and 24 .6 x 101.8 mm rectangular mesh with a PE frame) were tested. Newton's separ ation efficiency which was applied to shrimp and flatfish juvenile (<150 mm ) was highest when the 24.6 x 101.8 mm 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 catc h flatfish juveniles. All the devices had size selectivities which separate d 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 marketa ble fish and shrimp.