Study On Age,Growth And Reproductive Biology Characteristics Of Scomber Japonicus In The East China Sea

Chub mackerel（Scomber japonicus）is a kind of economic fish with abundant resources,which occupies an important position in the marine fishery and is highly valued by the World Fisheries Organization.With the continuous decline of offshore demersal fish resources,the rational utilization of pelagic fish resources such as Scomber japonicus becomes important.In recent years,although the resources of Scomber japonicus are still abundant,there are also great fluctuations from year to year.According to the current research,the reasons for the fluctuation of Scomber japonicus resources are quite complex,in addition to being closely related to marine environmental factors.Its own biological and ecological characteristics and other factors.Firstly,this study summarized the research status of Scomber japonicus population division,age and growth characteristics and reproduction biology characteristics at domestic and overseas.The purpose of this study is to provide a theoretical basis for exploring the age and growth and reproductive biological characteristics of Scomber japonicus in the East China Sea.Under the dual pressures of fishing pressure and environment,the characteristics of age structure change of reproductive population need to be updated.Based on the reproductive population samples of chub mackerel（Scomber japonicas）collected in the central East China Sea from March to April in 2021,the population structure and growth characteristics of Scomber japonicas were analyzed by otolith interpretation,growth back-calculation,and growth equation fitting.The results showed that there was no significant difference between male and female individuals in the reproductive stock of Scomber japonicus（F=0.376,P=0.54>0.05）.The age structure of males and females was 1⁺～7⁺years old and the dominant age group was 1⁺～2⁺years old,accounting for73.63%.The number of females was more than that of males at the 3⁺years old and below.Above 3⁺years old,the number of male and female was basically equal,but the female lacks the old age individual（6⁺～7⁺years old）.The relationship between fork length and body weight was:W=0.8837×10^-6FL^3.474.The linear function relation was the optimal solution of the relationship between fork length and otolith radius,and the relationship was FL=184.09R-112.73.The fork length and age data of four models were used to fit three back-calculation models of von Bertalanffy,Gompertz and Logistic.Among them,the von Bertalanffy equation of Dahl-Lea model had the lowest AIC and BIC,so it was chosen as the best growth equation.The von Bertalanffy fork length growth equation was FL_t=427.18[1-e^{-0.23（t+2.5）}];Body weight growth equation was W_t=1187.20[1-e^{-0.23（t+2.5）}]^3.47.After the second derivation test,age of inflecting point was 2.91 years old,the corresponding inflexion body weight and fork length were 365.03 g and 304.09 mm respectively,it can be used as an important reference for the formulation of the Scomber japonicas catch specifications in the future.With the increasing lowering ages and miniaturization of fish populations,the reproductive characteristics of different age stages can reflect the selection of reproductive strategies of fish.In view of this,it is particularly important to study the reproductive characteristics of Scomber japonicas at different ages.So to rationally utilize Scomber japonicas resources and deeply understand the replenishment law of its resources,the relationship between age and egg size and fecundity of Scomber japonicas was studied,the reproductive population samples of Scomber japonicas collected in the central East China Sea in March or April 2021 were used.The results showed that the reproductive population of female Scomber japonicas consisted of 1⁺～5⁺years old,and the dominant age of 1⁺and 2⁺was 68.54%.According to Logistic equation fitting,the fork length of 50%sexual maturity was 256.98mm.Independent-Samples T Test results showed that there was an extremely significant positive correlation between gonad development and egg size（P<0.001）.There was an extremely significant difference in egg size between the elder age group（3⁺～5⁺years old）and the younger age group（1⁺～2⁺years old）（P<0.001）.The average absolute fecundity of Scomber japonicas was（358202.06±185914.39）grain/ind.The average relative fecundity in fork length was（1101.70±492.21）grain/mm.The average relative fecundity in body weight was（881.13±311.46）grain/g.The absolute fecundity and relative fecundity in fork length increased with age,all of them have an extremely significant positive correlation with age（P<0.001）.There was a significant positive correlation between relative fertility in body weight and age（P=0.017<0.05）.Regression analysis showed that the relationship between the three fertility indexes and age was power function.The absolute fertility contribution rate decreased with the increase of age,and with the increase of age,the annual increase of absolute fecundity decreased continuously at first and then rebounded slightly at 5⁺years old.Although elder Scomber japonicas produced higher egg quality and higher fecundity,due to the small number of elder individuals,therefore,the contribution rate of absolute fecundity is smaller than that of younger fish.In formulating the management and protection measures of Scomber japonicas resources,the protection of elder Scomber japonicas should be paid special attention to.In order to protect the Scomber japonicas resources more effectively,the results of the research on the reproductive population samples of Scomber japonicas collected from March to April 2021 in the central of the East China Sea,compared with the previous research results.The results showed that compared with the last century,fork length,body weight,fecundity,egg size and sexual maturity length of Scomber japonicas were reduced.Compared with the early 21st century,the fork length,body mass and fecundity of Scomber japonicas increased,while the egg size decreased.In view of this phenomenon,this study put forward some suggestions on the management and protection of Scomber japonicas resources,in order to provide scientific basis for the protection of Scomber japonicas resources.