In the survey of fishery resources, the sampling design will directly impact the accuracy of the estimation of the abundance. Therefore, it is necessary to optimize the sampling design to increase the quality of fishery surveys. The distribution and abundance of fisheries resource estimated based on the bottom trawl survey data in the Changjiang River (Yangtze River) Estuary-Hangzhou Bay and its adjacent waters in 2007 were used to simulate the “true” situation. Then the abundance index of Portunus trituberculatus were calculated and compared with its true index to evaluate the impacts of different sampling designs on the abundance estimation. Four sampling methods (including fixed-station sampling, simple random sampling, stratified fixed-station sampling, and stratified random sampling) were simulated. Three numbers of stations (9, 16 and 24) were assumed for the scenarios of fixed-station sampling and simple random sampling without stratification. While 16 stations were assumed for the scenarios with stratification. Three reaction distances (1.5 m, 3 m and 5 m) of P. trituberculatus to the bottom line of trawl were also assumed to adapt to the movement ability of the P. trituberculatus for different ages, seasons and substrate conditions. Generally speaking, compared with unstratified sampling design, the stratified sampling design resulted in more accurate abundance estimation of P. trituberculatus, and simple random sampling design is better than fixed-station sampling design. The accuracy of the simulated results was improved with the increase of the station number. The maximum relative estimation error (REE) was 163.43% and the minimum was 49.40% for the fixed-station sampling scenario with 9 stations, while 38.62% and 4.15% for 24 stations. With the increase of reaction distance, the relative absolute bias (RAB) and REE gradually decreased. Resource-intensive area and the seasons with high density variances have significant impacts on simulation results. Thus, it will be helpful if there are prior information or pre-survey results about density distribution. The current study can provide reference for the future sampling design of bottom trawl of P. trituberculatus and other species.

中文翻译：

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底拖网抽样设计对三疣梭子蟹丰度指数估算的影响

在渔业资源调查中，抽样设计将直接影响丰度估算的准确性。因此，有必要优化采样设计以提高渔业调查的质量。根据2007年长江（长江）河口-杭州湾及其附近海域海底拖网调查数据估算的渔业资源分布和丰富度，用于模拟“真实”情况。然后是三疣梭子蟹丰度指数计算并与其真实指数进行比较，以评估不同抽样设计对丰度估计的影响。模拟了四种采样方法（包括固定站采样，简单随机采样，分层固定站采样和分层随机采样）。对于固定站采样和不分层的简单随机采样，假设有三个站（9、16和24）。对于分层情况，假设有16个站点。还假定三结核P对拖网底线的三个反应距离（1.5 m，3 m和5 m）适应于三结核P的移动能力适用于不同的年龄，季节和基材条件。一般而言，与非分层抽样设计相比，分层抽样设计可更准确地估算三头结核对虾的丰度，并且简单的随机抽样设计优于固定站抽样设计。随着站点数量的增加，仿真结果的准确性得到了提高。在有9个台站的固定台采样方案中，最大相对估计误差（REE）为163.43％，最小为49.40％，而对于24个台站，则为38.62％和4.15％。随着反应距离的增加，相对绝对偏差（RAB）和稀土元素逐渐减小。资源密集型区域和高密度方差的季节对模拟结果有重大影响。因此，如果有关于密度分布的先验信息或预调查结果，将会很有帮助。目前的研究可为今后对三疣梭子蟹及其他物种底拖网的抽样设计提供参考。