Application Of Data-limited Stock Assessment Models To Typical Fishes In The South China Sea

Fishery stock assessment is a basic component of modern management,required to maintain sustainable fishery development.Traditional methods require a large amount of statistical data assessing yield,abundance index,and age structure.Due to limited funding and data for such surveys,only 1%of fish stocks have systematic assessments conducted.Therefore,it is difficult to assess maximum sustainable yield(MSY)or determine allowable catch for most fishery resources using traditional methods.In recent years,stock assessment using limited available data has become a focus issue in the field of fishery resources.It has a wide application prospect,especially most fishery stocks near the coast of China belong to the state of lack of data.Life-history parameters are important parameters in fishery resource assessment method based on limited data.In this paper,data-limited assessment models based on life-history characteristics were divided into four categories:(1)models that only use length frequency;(2)models that only use life history parameters;(3)models that incorporate catch data and life-history parameters;(4)models that incorporate catch data,life-history parameters,and lifespan or age data.The introductions,data requirements,output results,and limitations of each model was reviewed and systematically analyzed.Taken the commercial fish populations such as cutlassfishes,Evynnis cardinalis and threadfin breams in the South China Sea(SCS)as examples,the application case studies of electronic length-frequency analysis(ELEFAN),length-based Bayesian biomass(LBB),a surplus-production model incorporating covariates(ASPIC)and Catch-MSY model were carried out.The main contents and results are as follows:(1)The biological characteristics and development status of Trichiurus lepturus were studied using body length frequency analysis method in the Fi SAT II software based on the survey data of bottom trawl fishery in the northern SCS from 2014 to2015.Results show that the anal length frequency distribution of hairtail during2014-2015 was unimodal,and the dominant anal length groups was 160?190 mm.There was no significant difference in the anal length composition between females and males(P>0.05).The proportion of females in spring was relatively higher,and the ratios of female to male in four seasons were significantly different with 1:1(P<0.05).Their grade of gonadal maturity was mainly at Level 2,accounting for 74.2%of the total.The minimum maturity length was 113 mm,and the estimated anal length at 50%sexual maturity(L₅₀)was 241.5 mm.The asymptotic anal length(L?)and growth parameter(K)calculated by Electronic Length Frequency Analysis I(ELEFAN?)were 585 mm and 0.20 yr^-1,respectively.The estimated total mortality coefficient(Z)and natural mortality coefficient(M)were 1.172 and 0.475,respectively.Compared with the 1980s and 1990s,the population structure showed a trend of simplification,with early sexual maturity and miniaturization.Although the exploitation rate of 0.59indicates that T.japonicus resources are still in a state of overfishing,the average anal lengths of the individuals show signs of recovery.(2)Based on the fishery survey data of Beibu Gulf over the years,the development status of 7 species in 27 groups was evaluated by LBB method.The difference in the evaluation results of the LBB method with or without prior information were studied and compared with the analysis results under Fi SAT II software.The LBB assessment results showed that 17 of 27 groups of data showed overfishing,and 5 groups showed non-fully exploited and fully exploited,respectively.Except the Nemipterus virgatus in 1992,other results showed growth overfishing.The comparison of the evaluation results under Fi SAT II software and the LBB method showed that the asymptotic body length evaluated by the two methods was not significantly different,and the Z/K results was significantly different,which was different in the assessment of population development rate.The comparison results of LBB method and its modified two methods show that the evaluation effect of LBB and LBB-2 was closer,and the evaluation effect of LBB-1 was different.In addition,there will be great differences in the evaluation results with or without prior information.The LBB method is sensitive to the setting of the asymptotic body length and M/K,which should be paid attention to when using this method.(3)Based on the statistical data of marine fishery production in Guangdong water from 1961 to 2018,none-quilibrium surplus-production model of ASPIC software and Catch-MSY model were used to evaluate the total catch of marine fishery resources,the maximum sustainable yield(MSY)and catch of five important economic groups in Guangdong water.Guangdong waters?assessment results showed that the estimated MSYs of Guangdong waters by ASPIC program and Catch-MSY model were similar at 1.64×10⁶ t.Although fishery resources have been overfished from 1996 to 2006,the total catch in 2018 was 1.27×10⁶ t and less than MSY.The MSY results of Schaefer model and Fox model were also similar,and the historical trends of B/B_MSYand F/F_MSY were relatively consistent.However,there was much difference in estimating current fishery status between Schaefer model and Fox model.Results of Catch-MSY model and ASPIC showed MSY of cutlassfishes fishery were14.62×10⁴?15.08×10⁴ t,3.82×10⁴?6.78×10⁴ t for chub mackerel fisheries,5.77×10⁴?6.21×10⁴ t for butterfishes,4.16×10⁴?4.54×10⁴ t for porgies,and17.68×10⁴?19.84×10⁴ t for round scad fishery.The chub mackerel and round scad fisheries are recovering after collapse,and the stocks of cutlassfishes,butterfishes and porgies have also been overfished in recent years.