东海近海蟹笼网目尺寸对三疣梭子蟹的选择性

不断壮大的东海近海笼壶渔业对三疣梭子蟹（Portunus trituberculatus）等甲壳类资源造成了巨大的压力，实施养护幼蟹的管理措施已成为渔业管理者和生产者的共同呼声。本研究通过海上对比试验，分析了放大网目尺寸对蟹笼渔获效率的影响，运用SELECT模型估算了蟹笼对三疣梭子蟹的尺寸选择性，结合混合影响模型探讨了作业时间和可捕群体对选择性分析的影响。结果显示，对照蟹笼（网目尺寸32.0 mm）与试验蟹笼（网目尺寸分别为52.3 mm和59.7 mm）的三疣梭子蟹渔获甲宽分布存在显著性差异；SELECT模型拟合结果显示试验蟹笼与对照蟹笼的相对作业强度无显著性差异，网目尺寸分别为52.3 mm和59.7 mm的试验蟹笼对三疣梭子蟹的50%选择甲宽（CW₅₀）分别为86.9 mm和90.9 mm，选择范围分别为15.9 mm和9.2 mm。试验蟹笼的CW₅₀远未达到浙江省等当前的最小可捕尺寸规定，表明蟹笼渔业中仅依靠放大网目尺寸可能难以实现幼蟹的有效释放。结果分析显示，在此次试验中作业时间和可捕群体的数量对蟹笼的选择性没有显著性影响。

Mesh size selectivity of crab pots for swimming crab Portunus trituberculatus in the East China Sea

The increasing fishing effort of the crab pot fishery in the East China Sea has resulted in considerable pressure on swimming crab Portunus trituberculatus resources. Thus, there is an urgent need to implement conservation measures to release juvenile crabs from fishing pots to increase recruitment. In this study, sea trials were carried out to assess the effect of increasing mesh size on fishing efficiency and analyze the mesh size selectivity of crab pots for P. trituberculatus through a comparison experiment. Additionally, the effect of soak time and available population on the selective properties of mesh size was discussed based on the mixed effect model. The results showed that there were significant differences in P. trituberculatus carapace width (CW) distribution caught between the control pot with 32.0 mm mesh size and experimental pots with 52.3 mm and 59.7 mm mesh sizes. No significant difference in relative fishing power between control and experimental pots was detected according to the model fit of the catch frequency in the SELECT analysis model. The average CWs of P. trituberculatus with 50% probability of being retained (CW₅₀) were 86.9 mm for the pot with 52.3 mm mesh size and 90.9 mm for pot with 59.7 mm mesh size, whereas the selection ranges (SR) of CW were 15.9 mm and 9.2 mm, respectively. The finding that the P. trituberculatus experimental pot CW₅₀ was considerably smaller than the minimum landing size set by Zhejiang Province fishery regulations indicated that it may be impractical to effectively release undersized crabs by simply relying on increased mesh size in crab pot fisheries. The results of the mixed effect model showed that the influence of soak time and available P. trituberculatus population on size selectivity of the pots was not significant in this study.