PRELIMINARY TRAWLING TESTS USING A 2-LEVE L BEAM TRAWL WITH SQUARE MESH SEPARATOR AND ITS SEPARATION EFFICIENCY

A two-level beam trawl was developed with a square-mesh separator pane l in it to separate marketable fish and shrimp from non-commercial cra bs and smaller fish. The net-mouth of the lower cod-end in the two-lev el trawl gear was covered with a square-mesh net panel as a separator. Fishing experiments of the gear were conducted with a chartered trawl er off Shimonoseki city in October 1995. Two square-mesh net panels of 40 and 50 mm mesh bars were used in the fishing experiments. The net mouth openings of the upper and lower cod-end associated with the effi ciency of the separator were measured. The total number of animals cau ght in 7 hauls was nearly 2,300. Separation efficiencies defined as th e ratio of the catch in the upper cod-end to the total catch of 11 spe cies were compared by two mesh bar sizes. Non-commercial crabs passed through the separator panel and then entered in the lower one, while s hrimp were caught in the upper cod-end although its body was enough sm all to pass through the separator. Separation efficiencies of the main 6 species plotted versus bodysize indicate that the separator has siz e-selectivity to some extent. Thus, the gear was useful to catch fish of marketable size and shrimp in the upper cod-end.