Simulation Analysis Of Resource Estimation Of Portunus Trituberculatus In The North Of The East China Sea Based On Different Sampling Designs Of Two Kinds Of Fishing Gear

The data obtained from the Fishery-independent surveys are the basis of fishery assessment and management.According to the fishery data obtained by using single trawler survey in the Yangtze River Estuary-Hangzhou Bay and its adjacent waters in 2007,sweep area method was used to calculate the total resources of Portunus trituberculatus in each season and Kriging interpolation method was used to predict the "truth value" of P.trituberculatus distribution in each season,and the dynamic resource distribution base map was drawn.Two main fishing gears,trawl and crab pots,were selected as the study objects in P.trituberculatus' s resource investigation.The algorithms of two kinds of fishing gear were established based on statistical methods,which were used to calculate the probability that each individual of P.trituberculatus located in the fishing gear catching area could be caught.The amount of resources that calculated by the algorithm was consistent with the actual situation.In this paper,computer simulation and resampling methods are used to compare four sampling methods(fixed-station sampling,simple random sampling,stratified fixed-station sampling and stratified simple sampling),each sampling method has many combinations and is called sampling scenario.Three number of stations(9,16 and 24),and three number of reaction distance that P.trituberculatus to the trawl(1.5m,3.0m and 5.0m),three number of crab pots(500,1000 and 3000),the resource density of four seasons is also considered,the scenarios with 16 stations were set in stratification as a control group for comparison with unstratified sampling designs.Therefore,there are 96 sampling scenarios for trawl and crab pots,and each scenario is simulated 1000 times repeatedly to compare the sampling performance of each scenario.By comparing the effect of each sampling scenario,the following conclusions are drawn:1.Stratified fixed-station sampling design is better than fixed-station sampling design,stratified random sampling design is better than simple random sampling design;the survey results of simple random sampling method are more objective;the adaptability of fixedstation sampling design to dynamically changing fishery resources is poor.2.The fixed-station sampling method requires at least 16 sampling stations to obtain relatively stable results;In the simple random sampling method,9 sampling stations can obtain stable and reliable survey results.The stratified sampling design(stratified fixedstation sampling,stratified random sampling)has the highest precision and accuracy,and the results of 16 sampling stations are better than the survey results of 24 stations in the unstratified sampling design(fixed-station sampling,simple random sampling).3.The activity ability of P.trituberculatus varies at different growth stages,and the reaction distance to trawling gear varies in different seasons: the reasonable reaction distance of P.trituberculatus in spring,summer and autumn is 5.0m,while in winter is 3.0m.4.The soaking time of crab pots will affect the capture efficiency.The performance of 9,10 and 16 hours was simulated and compared.With the increase of soaking time,the capture efficiency of crab pots first increased and then decreased.Therefore,the reasonable soaking time of crab pots is 10 hours.5.Comparing the sampling scenarios of 500,1000 and 3000 crab pots,it is found that the change range of REE value and RB value of the survey results is less than 2.00% on the whole,and the change range of many scenarios is less than 0.50%,even within 0.10%.The trend of REE value and RB value is not consistent with the increasing number of crab pots.The number of crab pots has no influence on the effect of sampling design.Therefore,a smaller number of crab pots can be used in fishery resource investigation for the safety of fishing boats,cost saving and resource protection.6.The study found that the resource intensive area of P.trituberculatus has a greater impact on the survey results,which is easy to overestimate the abundance of P.trituberculatus and generate abnormal values,such as autumn in this study.The resource desert area of P.trituberculatus has a smaller impact on the survey results,and the stability of the survey results is higher,such as winter in this study.7.Comparing the survey results of 96 sampling scenarios of trawl and crab pots,it is found that the crab pots has an upper limit on the ability of catch P.trituberculatus,which is easy to underestimate the abundance in seasons with large amount of resources or areas with high resource density,thus the crab pots is suitable for the situation with few target species or evenly distributed.Trawl may overestimate the abundance in seasons with large amount of resources or areas with high resource density,and has good adaptability to various sampling scenarios.Overall,the sampling effect of trawl is better than that of crab pots.This paper aims to provide a scientific and reasonable sampling design for the resource investigation of P.trituberculatus in the East China Sea.At the same time,the work and research ideas in this study can also provide reference for the sampling design of other sea areas and other target species.