南海区拖网网囊最小网目尺寸选择性研究

Selectivity study on minimum mesh size of bottom trawl codend in South China Sea

为了科学地确定南海区拖网网囊的结构和适宜网目尺寸,于2000年11月25日～12月20日在南海北部珠江口以外海域,水深36～70m拖网渔场,对4种不同网目尺寸的方形网目网囊进行了2个航次34网次的网囊套网式捕鱼选择性试验。4种网囊的网目尺寸(Mex)分别为30.3mm、35.2mm、39.4mm和43.6mm。结果表明,蓝圆(Decapterusmaruadsi)、多齿蛇鲻(Sauridatumbil)和条尾绯鲤(Upeneusbensasi)仍是南海拖网渔获中常见的鱼种;4种方形网目网囊的数量平均逃逸率均高于重量平均逃逸率;网囊渔获的优势体长总是大于套网渔获的优势体长;方形网目网囊有利于释放纺锤形鱼类和圆体形鱼类(如蓝圆、多齿蛇鲻、条尾绯鲤)的幼鱼;3种主要鱼种的50%选择长度(L0.5)与Mex之间的线性回归方程为:蓝圆L0.5=57.98+1.80Mex;多齿蛇鲻L0.5=72.71+1.64Mex;条尾绯鲤L0.5=37.62+1.66Mex。经综合分析认为,南海区拖网最好使用方形网目网囊,最小网目尺寸不应小于40mm。

A field investigation was conducted from 25 September to 20 December 2000 in the Pearl Estuary, north of the South China Sea. The water depth of the trawl fishing area was 36-70 m. Four different sizes of square mesh codends were employed to determine the design and optimum mesh size of bottom trawl codend in the South China Sea. The mesh sizes of the four types of codends were 30.3 mm, 35.2 mm, 39.4 mm, and 43.6 mm, respectively. The results showed that Decapterus maruadsi,Saurida tumbil and Upeneus bensasi are still capture species which can be usually found in trawl catches of the northern South China Sea. The mean escape rate is greater in number than in weight for the four types of codends. The dominant body length of fishes in trawl codend is always larger than that in covered codend. Square mesh codends are much more tending to release spindle and roundshaped fishes such as Decapterus maruadsi, Saurida tumbil and Upeneus bensasi. The linear regression equations between 50% selection length (L0.5) and mesh sizes (Mex) in the three targeted species were: Decapterus maruadsi, L0.5=57.98+1.80Mex; Saurida tumbil, L0.5=72.71+1.64Mex; Upeneus bensasi, L0.5= 37.62+1.66Mex. The conclusion is that the minimum mesh size of the bottom trawl codend in the South China Sea should be not less than 40 mm.