To explore the gillnet selectivity for swimming crab Portunus trituberculatus , six mesh sizes (100, 110, 120, 130, 140 and 150 mm) were tested to determine the optimal mesh size for swimming crab. The experiments were conducted in the traditional area for fishing crab in the East China Sea from 25 to 29 July 2018. Four kinds of selectivity curves were used for fitting, and the maximum likelihood method was used to estimate the model parameters. In this experiment, 436 swimming crabs were caught with six different mesh sizes. The carapace length range was 46.2–83.7 mm, and all crabs were caught by entanglement (i.e. body or limb). When the mesh size was larger than 100 mm, the proportion of juvenile crab (carapace length < 60 mm) was less than 20% of the total catch. A linear relationship was observed between the carapace width and height and the carapace length of the crab. Gillnet selectivity for swimming crab was well described by the normal model based on the smallest Akaike information criterion value. The optimal lengths calculated by the normal model were 49.8, 54.8, 59.8, 64.8, 69.8 and 74.8 mm for the six mesh sizes, respectively.

中文翻译：

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东海三疣梭子蟹刺网选择性

为了探索刺网对三疣梭子蟹的选择性，测试了六种网孔尺寸（100、110、120、130、140 和 150 毫米）以确定游泳蟹的最佳网孔尺寸。试验于2018年7月25-29日在东海传统捕蟹区进行，采用4种选择性曲线拟合，并采用最大似然法估计模型参数。在这个实验中，436 只螃蟹被捕获到六种不同的网眼尺寸。甲壳长度范围为46.2-83.7毫米，所有螃蟹都是通过缠结（即身体或四肢）捕获的。当网目尺寸大于100 mm时，幼蟹（背甲长度< 60 mm）的比例小于总捕捞量的20%。观察到螃蟹的背甲宽度和高度与背甲长度之间存在线性关系。基于最小 Akaike 信息准则值的正态模型很好地描述了对游泳蟹的刺网选择性。正常模型计算出的六种网格尺寸的最佳长度分别为 49.8、54.8、59.8、64.8、69.8 和 74.8 mm。