方目网囊对蓝圆鲹和多齿蛇鲻的选择性比较

为检测方目网囊对蓝圆鱼参和多齿蛇鲻的选择作用 ,2 0 0 0年 1 1～ 1 2月在南海北部海域试验了 4种目大的方目网囊。结果表明 ,方形网目网囊有利于释放纺缍形 (如蓝圆 鱼参)、圆形或近圆形 (如多齿蛇鲻 )两种形体鱼类的小、幼鱼 ,且对后者的释放效果更好。当网囊目大分别为 45、5 0mm时 ,蓝圆鱼参的5 0 %选择体长 (L0 .5)分别为 1 2 1 2 2、1 2 8 77mm ;当网囊目大分别为 40、45、5 0mm时 ,多齿蛇鲻的L0 5分别为 1 2 4 1 2、1 2 6 75、1 3 9 3 2mm。通过不同目大网囊对蓝圆鱼参、多齿蛇鲻选择性比较分析 ,发现 5 0mm目大方目网囊的选择效果好于 40、45mm目大的网囊 ,因此 ,在南海区拖网渔业中采用 5 0mm目大的方目网囊是必要的 ,同时建议将 1 5 0mm作为蓝圆鱼参、多齿蛇鲻的最小可捕叉长标准。

Comparison of Selectivity of Square Mesh Codend on Decapterus maruadsi and Saurida tumbil

To determine selectivity of square mesh codend on Decapterus maruadsi and Saurida tumbil ,four square mesh codends with different mesh size were tested in the northern waters of South China Sea from November to December in 2000. The experiments showed that square mesh codend had a good selectivity on smaller and juvenile fish of spindle (such as Decapterus maruadsi ), roundish (such as Saurida tumbil ),even a better selective effect on the roundish fish. When mesh outer diameters of codend were from 45 mm to 50 mm,50% retention lengths ( L 0 5 ) were 121 22 mm, 128 77 mm for Decapterus maruadsi . When mesh outer diameters of codend were from 40 mm to 50 mm with 5 mm intervals, 50% retention lengths ( L 0.5 ) were 124 12, 126 75, 139 32 mm for Saurida tumbil . After comparing and analyzing selectivity of square mesh codends on Decapterus maruadsi and Saurida tumbil ,we think that the trawl codends with 50 mm mesh outer diameter are superior to the other two with mesh sizes (40 mm and 45 mm) and that it is necessary to increase the mesh size of codend to 50 mm in fishing operation. In addition, we suggest that the minimum catch fork lengths of Decapterus maruadsi and Saurida tumbil should be adjusted to 150 mm.