东海张纲张网网囊网目选择性研究

张纲张网是我国近海渔业的重要作业方式,当前渔业管理中规定了张纲张网网囊最小网目尺寸,但渔民实际使用的网目尺寸与之差异很大,造成渔获中幼鱼比例大。为了更好地掌握网目尺寸对主要捕捞对象的尺寸选择性,于2012年秋季和2013年春季使用平行作业法开展了不同网目尺寸(35、40、45、50、55 mm)网囊的选择性试验。试验结果显示,网囊对小黄鱼(Pseudosciaena polyactis)、带鱼(Trichiurus haumela)和银鲳(Pampus argenteus)的50%选择体长L50随着网目尺寸的增大而增大,表明放大网目尺寸能有效减少幼鱼渔获,L50与网目尺寸(Me)的线性关系为:小黄鱼L50=2.79×Me-1.45,带鱼L50=4.27×Me-38.28,银鲳L50=1.79×Me+28.66。此次试验不同网目尺寸网囊的L50相比其它研究结果较大,推测试验方法的不同可能是导致这一差异的主要原因。结合当前东、黄海主要捕捞对象的可捕规格,认为目前55 mm的网囊网目尺寸能实现张纲张网对3种主要捕捞对象的管理目标。

Study on the fish size selectivity of codends of canvas stow net in the East China Sea

The canvas stow netting fishery is one of the most important fisheries in the East China Sea.At present,there is of great variance in the mesh sizes of codend of canvas stow nets used by fishermen,which causes the issues of large proportion of juvenile fish in total catching,although the legal minimum mesh size of codend has been regulated.In order to understand the reguations of size selectivity of mesh sizes of codend for main catch species in more details,a selection experiments with different mesh sizes (35 mm,40 mm,45 mm,50 mm and 55 mm) codends were carried out by the parallel haul method in fall of 2012 and spring of 2013.Catch frequencies of total 11 hauls were used for the analysis of the size selectivity of different conends based on the SELECT analytical model and Logistic selection curves.The results showed that 50％ retention lengths and Ls0s of codends for Pseudosciaena polyacti,Trichiurus haumela and Pampus argenteus increased with the increasing in mesh sizes,which demonstrated that the enlargement of mesh size could reduce the catch of juvenile fish effectively.The linear relationships between Ls0s and mesh sizes(Me) were L50 =2.79 × Me-1.45 for P.polyactis,L50 =4.27 × Me-38.28 for T.haumela and L50 =1.79 × Me + 28.66 for P.argenteus,respectively.Compared with the results from other similar studies,the L50 s in the present experiment were relatively larger,and it was speculated that the different experiment methods (covered codend method was used in the other studies) might be the main reason for this discrepancy.Taking the recommended minimal landing sizes for the main catch species in the East China Sea and Yellow Sea into account,it is suggested that the present legal minimum mesh size (55 mm) of codend is able to achieve the management objectives in the 3 catch species in the canvas stow netting fisheries.