A Preliminary Study On The Biological Characteristics Of Pampus Echinogaster In Southern Zhejiang

Pampus echinogaster belongs to the Perciformes,Stromateoidei,Stromateidae,and Pampus.It is a cold-water species that widely distributed in the East China Sea,Yellow Sea,South China Sea,the Russian Far East,Japan,etc.P.echinogaster is a common fish species found in offshore China.In order to make scientific and sustainable usage of this economic maggot resource,it is necessary to conduct in-depth research on its population dynamics process and resource status.Base on the data from bottom trawl fisheries surveys in Wentai area in the four seasons of February?winter?,May?spring?,August?summer?,and November?fall?from 2016 to 2018,the heterogeneity of body length and weight relationships,growth and death laws,fish biological reference points,and optimal open fork length were studied,and the following aspects have been developed:?1?The fish body length-weight relationship will change to a certain extent under the influence of fishing pressure,hydrological conditions,climate change and other external factors,which will affect the fish population dynamics.Therefore,the analysis of this heterogeneity is one of the important contents of fish life history research and resource assessment and management.The generalize linear model?GLM?and 9 linear mixed effects?LMEM?models were used to analyze the fork length-weight relationship?W=a L^b?and its heterogeneity of P.echinogaster.The results show that the fork length range of the P.echinogaster in the offshore area of southern Zhejiang is from 53.00 to 238.00 mm with the average value of 128.54 mm.The dominant fork length group was 110?150 mm.The dominant body weight group was 30?70 g.According to the Akaike information criterion,the best growth-fitting model was a combination model that has both seasonal and year random effects on the growth parameters a and b of P.echinogaster;root mean square error?RMSE?results also show that this model has the best prediction effect.In the optimal model,the fixed value of parameter a was 1.75×10^-5,and the fixed value of parameter b was3.083,which indicates that the P.echinogaster was growing at a positive allometry and the body is fuller.The results of optimal linear mixed model showed that the value of a was the largest in autumn,followed by summer and winter,and the smallest in spring,while the trend of value of b was opposite.In different years,the value of a was the largest in 2016,followed by 2018 and 2017;the value of b was the largest in 2017,followed by 2018 and 2016.This chapter analyzes the annual and seasonal impact on the fork length-weight relationship of P.echinogaster through the mixed effect model.It shows that the year and season have significant effects on the fork length-weight relationship of P.echinogaster.It shows that the model has important reference value in the study of the heterogeneity of the fork length-weight relationship of P.echinogaster,and provides a scientific basis for the rational development and management of its resources.?2?The fish population growth and mortality is one of the foundation factors for fishery resource assessment.It is also an important prerequisite for the development and utilization of fish stock resources.Based on the relationship between the length and weight of the P.echinogaster obtained in the previous chapter,this study uses the frequency distribution method of fork length to study the growth and mortality of P.echinogaster in 1980,and estimates its growth and death parameters.The results show that the von-Bertalanffy growth equation parameters estimated by using the ELEFAN I method in Fi SAT II software have a progressive fork length L_?,a progressive weight W_?,a growth rate K value,and a first sexual maturity age t₀ of252mm,443g,0.280,-0.523a,respectively.Meanwhile,using the transform body length curve method in Fi SAT II software,the total death coefficient Z,natural death coefficient M,fishing death coefficient F,and development rate E were estimated as1.24,0.371,0.869,and 0.70,respectively.Compared with historical research,I found that the asymptotic fork length L_?and asymptotic weight W_?of P.echinogaster in the offshore area of southern Zhejiang are significantly reduced,the growth rate K is significantly accelerated,and the natural mortality M and fishing mortality F are greater than that in 1997-2000.At present,the fishing pressure and development status in the East China Sea region are far greater than the sustainable development level of P.echinogaster population,which makes the population under greater threats.?3?In the assessment of fishery resources,most conventional models assume that all individuals have the same growth rate.However,usually the growth rate of individuals is variate,and this variation should be taken into account in the stock assessment.Yield per recruitment?YPR?model has been widely used in the population dynamics of single species of fish.Based on the previous part of this research,I used the dynamic comprehensive model of the incomplete?function catch equation to calculate relevant biological parameters and biological reference points?BRP?,and then analyzes and evaluates P.echinogaster population resources.Results showed that at the current fishery point?F=0.869,t_c=1.953?,the yield per cruitment value for P.echinogaster was 66.49.The dynamic assessment results show that at this stage,P.echinogaster resources in the southern coast of Zhejiang have been over-exploited.Based on a comprehensive consideration of inflection point age,critical age,first sexual maturity age,and protection of fishermen's economic benefits,the fishing death coefficient F should be set as 0.869.Results suggested that the optimal age for fishing of P.echinogaster in the southern coast of Zhejiang should be 2.953a,and the corresponding open fork length should be 156mm.In this case,the yield per recruitment value for P.echinogaster was 69.23,which mean per recruitment of P.echinogaster will contribute a yield of 69.23g at last,and 4%higher than the current status.Therefore,it is necessary to increase the age of catching P.echinogaster in a reasonable range to ensure the sustainable use of P.echinogaster resources.