| Fisheries resources survey is the basic work of fishing and fisheries resources management,is the prerequisite to grasp the dynamics of fisheries resources,sampling design as an important link in the fisheries resources survey,according to different survey purposes to choose the appropriate sampling method and sampling intensity,can effectively reduce the amount of sampling effort,so as to ensure data accuracy on the premise of reducing survey costs.At present,in the offshore waters of southern Zhejiang,the research on the optimization of sampling survey design is only based on the relationship between body length frequency distribution and sampling volume,and there is still a lack of comparative research on the number of different stations and different sampling survey designs for sampling different fish populations,and the scientific survey system of offshore fishery resources in southern Zhejiang still needs to be improved.Therefore,it is necessary to carry out research related to the sampling survey design of offshore fishery resources in southern Zhejiang in terms of sampling survey design optimization to achieve a balance between data accuracy and survey costs,and to provide effective data support for the development and implementation of management policies.Therefore,this paper uses the bottom trawl survey data from February(winter),May(spring),August(summer),and November(autumn)2019 in the offshore southern Zhejiang to study and analyze them.In this study,we firstly analyzed the effect of the number of stations on the sampling accuracy and precision of fish community resources and absolute dominant species resources in each season based on simple random sampling(SRS),and explored and analyzed the effect of the number of stations on the species detection rate from the perspective of fish species composition in the survey of offshore fishery resources in southern Zhejiang.The effects of the number of stations on the species detection rate in each season were discussed and analyzed from the perspective of species detection rate.Then,we compared the simple random sampling,systematic sampling(Sy S),and stratified sampling(St S)in the fish community resource sampling survey in each season,and analyzed the effects of changes in the number of sites on the precision and accuracy of different sampling designs.The effects of changes in the number of stations on the precision and accuracy of different sampling designs were analyzed.The results of the study were as follows.Finally,we analyzed the length-body weight composition and length-body weight relationship of the population of the dragonfish,explored the effect of changes in the number of stations on the parameter b of the length-body mass relationship of the dragonfish under simple random sampling,and explored and analyzed the effect of seasonal changes on it.(1)The optimal number of sampling stations for different fishery resource survey targets in the southern Zhejiang offshore.Seasonal differences significantly affected the sampling accuracy of fish communities with the same number of stations.The coefficient of variation(CV)of fish community resources sampling survey showed a seasonal variation of spring >autumn > winter > summer,and the relative estimated error(REE)and relative bias(RB)showed a range of the seasonal pattern of "autumn > spring > winter > summer" was observed.Species detection rate also has seasonal differences,and the number of survey stations required for the same species detection rate varies from season to season.At the same time,the change of the research object will lead to the change of the optimal number of stations.In spring,the range of variation of CV,REE and RB of striped bass is significantly smaller than that of seven-star bottom lamprey,so the optimal number of stations needs to be adjusted according to the actual survey needs.The study concluded that the optimal number of sites for the seasonal survey of offshore fishery resources in southern Zhejiang was 27 sites in spring,24 sites in summer,24 sites in autumn,and 26 sites in winter,based on the premise that REE=10 % as an asymptotic value for determining the optimal number of sampling sites,taking into account the quantified results of community resources,community dominant species group resources and species detection rate in each season.(2)Comparison of sampling designs of offshore trawl fishery resources in southern Zhejiang.The relative resource distribution of fish communities in each season was simulated by using ordinary kriging interpolation,and three sampling methods,SRS,Sy S and St S,were set up to resample the ordinary kriging interpolation data using computer simulation.It was found that when improving the same estimation accuracy,only a smaller sample size increase was required when the sample size was lower than 30,while when the sample size was higher than 30,a significant increase in the sample size interval was required to achieve the same improvement.Overall,the estimation accuracy of the three sampling methods differed,showing an order of SRS < Sy S < St S.(3)Estimation of length-body mass parameters of the offshore Harpadon nehereus in southern Zhejiang.Based on the computer simulation resampling method,simple random sampling was selected as the sampling method,and the length-body mass parameter b was estimated with different number of stations,and the effect of seasonal variation on the estimation accuracy was investigated,and CV,REE and RB were selected to compare their estimation effects.The results showed that increasing the number of stations could effectively improve the estimation accuracy of the length-body mass parameter b.The estimation accuracy was significantly lower in summer than in the other three seasons,and seasonal changes also affected the estimation accuracy.Studies have shown that increasing the number of sampling stations in a certain range can effectively improve data accuracy,and the same sampling design scheme is more difficult to meet different survey objectives.Therefore,the sampling design plan can be adjusted according to different survey objectives to obtain a balance between cost and accuracy. |
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