새우류 어업에서 어구의 망목 크기가 부수어획량에 미치는 영향

Effect of Mesh Size on the Bycatch in the Shrimp Fisheries of Korea

The composition of shrimp and bycatch species caught by two fishing gears (shrimp beam trawl and single-walled tangle net) in the shrimp fisheries of Korea was examined from the major fishing ground during two years between October 2002 and September 2004. A total of 127 species was observed in shrimp trawl and a total of 70 species in single-walled tangle net. These samples were occupied by 74.2% of shrimps, 11.6% of fishes, 7.5% of other crustacens and 4.2% of shellfishes in shrimp trawl, and 88.9% of shrimps and 10.4 % of fishes in single-walled tangle net in terms of total numbers. These samples were occupied by 36.1% of fishes, 25.8% of shellfishes and 14.4% of shrimps in shrimp trawl and by 64.5% of shrimps, 32.7% of fishes in single-walled tangle net in terms of total catch weight. Main bycatch calculated by biomass was Chaeturichthys stigmatias (21.6%), Rapana venosa (21.1%) and Charybdis japonica (12.5%) in beam trawl, and Collichthys lucidus (14.7%), Thryssa kammalensis(11.4%) and Setipinna taty (10.0%) in single-walled tangle net. During the study period, the bycatch-to-shrimp ratio of shrimp beam trawl and single-walled tangle net were 0.87 and 0.24, respectively. Experiment of gear selectivity with increasing mesh size from mesh size in present use to 50% and 100% increase of its mesh size, showed that 50% selectivity size increased and bycatch-to-shrimp ratio are reduced. Measures to reduce the bycatch proportion in the shrimp fisheries are discussed with various management options.