桁拖网不同网目结构的网囊对虾类的选择性

Size selectivity of codends with different mesh configuration for shrimps in Chinese beam trawl fishery

为改善东海近海桁拖网对主要虾类的选择性,使用对比作业法,在吕泗渔场开展了多个航次、不同网目结构(菱形、方形及转向网目)网囊的选择性试验,并进行了选择性分析。在选择性分析中,将几何相似原理运用于选择性曲线模型(Richards曲线),并使用极大似然估计法进行参数估计,同时使用假设检验理论对选择性曲线模型进行简化。选择性模型对哈氏仿对虾(Parapenaeopsis hardwickii)和葛氏长臂虾(Palaemon gravier)渔获数据的拟合结果显示,选择性模型具有较好的拟合性,但存在航次间差异;不同网目结构网囊的选择性曲线模型都可简化为Logistic曲线;对于哈氏仿对虾,相比菱形网目网囊,方形网目和转向网目网囊的L50较大,而SR较小(菱形和方形网目之间差异显著,菱形和转向网目之间差异不显著);对于葛氏长臂虾,方形网目和转向网目网囊的L50较大(菱形和方形网目之间差异显著,菱形和转向网目之间差异不显著)。根据虾类在网囊中的逃逸行为,方形网目、转向网目具有较好选择性的原因在于这2种网目较传统菱形网目不易合拢;不同网目结构网囊的选择性对开展渔具种类选择性研究具有重要意义。

In order to improve size selection for shrimps of multi-codends beam trawls fishing in offshore of the East China Sea, experiments of several sea trials for size selectivity of codends with different mesh configuration, including diamond mesh, square mesh and tumed through 90~ mesh, have been carried out and catch data were collected by comparative fishing method. In analysis of selectivity, the selectivity curves （Richards curves, which could be simplified to Logistic curves by hypothesis test theory） were considered geometrically similar and maximum likelihood method was used as the method of estimation of model parameters. The result demonstrated that selectivity models fit well to the pooled catch data of Parapenaeopsis hardwickii, Palaemon gravieri but between-trials variation was found, and Richards selectivity curves of codends with different mesh configuration could be simplified. The 50% retention lengths （L50） of square mesh and T90 mesh codends for Parapenaeopsis hardwickii were larger than and the selectivity ranges （SR） were less than those of diamond mesh codends respectively. As for Palaemon gravieri, the L50 of square mesh and T90 mesh codends were larger than those diamond mesh codends. Difference in selectivity parameters between diamond and square mesh codends was significant while difference between diamond mesh and T90 codends was insignificant. Based on the escape behavior of shrimp in codends, the reason for the fact that square mesh and T90 codends were more selective for shrimps than traditional diamond mesh codends might be the better mesh openness of square mesh and T90 mesh. The suggestion is that the information of size selectivity of different mesh configuration was also crucial for research on species selection of beam trawls.