Investigation of trawl landings for the purpose of reducing the capture of non-target species and sizes of fish

Abstract

Detailed measurements of fish captured by trawl were made to determine the relationships between codend mesh size and on-deck sorting selectivity at Kuala Kedah, on the west coast of Peninsular Malaysia. Major species landed in this area are Indo-Pacific mackerel ( Rastrelliger brachysoma), Jewfish (Sciaenidae), threadfin bream (Nemipteridae) and squid ( Loligo spp.). Small or low-price fish (‘trash fish’) accounted for about 40% of the total landings. The sorting selectivities were determined for threadfin bream, slender shad ( Ilisha elongata) and squid which were found sorted both as ‘trash fish’ and as commercial catch. The size and shape of the codend mesh are discussed in relation to these findings. Fish shapes were investigated by detailed measurement. Total length where maximum girth is equal to the circumference of the mesh (= 53.2 mm) were ‘trash fish’ sizes for most species. It was concluded that the present mesh size is not suitable for most species captured by trawl and the mesh shape also should be considered carefully due to the variable shapes of target species.