Stock Assessment Of Scomber Japonicus In The North Pacific High Seas Based On Virtual Population Analysis (VPA)

Scomber japonicus is one of the important marine economic species in China's pelagic light seine fishery.Although China,Japan and the western United States have many relevant literatures focused on the Scomber japonicus fishery in the coastal waters,there are few literatures on age,growth and resources of Scomber japonicus in the North Pacific high seas.In this study,we conducted a preliminary study on the biological characteristics of Scomber japonicus,including age structure,fork length and weight distribution,growth and mortality,and stock composition.The fishery samples collected from commercial fishery in the North Pacific from April 2016 to December 2020.We used virtual population analysis(VPA)model based on age structure explored how to assess the status of Scomber japonicus resources in the absence of long-term continuous fishery yield statistics by high seas fishery data from2016 to 2019.We hope the research results can provide suggestions and references for fishery management and resource conservation of Scomber japonicus in the North Pacific high seas.The main results are as follows.1.Based on the otolith age identification,we got the age structure composition and corresponding fork lengths of Scomber japonicus in the North Pacific high seas.187 mm at age 1,248 mm at age 2,294 mm at age 3,and 318 mm at age 4.the limiting fork length L_?was 447.61 mm,the asymptotic curve rate K was 0.264,and the initial age t was-1.06.the age growth inflection point of Scomber japonicus of North Pacific high seas was age 3,the weight growth inflection point was 310 g,the inflection point of fork length growth was 309 mm.2.The average annual mortality coefficient of Scomber japonicus in the North Pacific high seas from 2016 to 2020 estimated by growth characteristics is 0.74.the natural mortality coefficient is 0.56,the current fishing mortality coefficient is 0.17,and the exploitation rate is 0.24.In conclusion,the fishery resource is not overfished.3.The fork length group distribution of Scomber japonicus in the North Pacific high seas showed a bimodal structure.Fork lengths groups of 189-229mm and269-309mm in dominant position,weight group of females was 50-100g and200-300g in dominant position,weight group of males was 50-100 and 200-350g in dominant position.The age of Scomber japonicus stock consisted of age 1?4,and age1?2 were dominant,accounting for 30.15%and 38.14%.4.Resource status of Scomber japonicus in the North Pacific high seas and the Pacific group of Scomber japonicus was evaluated by the VPA model based on age structure.From this paper of view,if the natural mortality coefficient is assumed to be0.56,the assessment results show the resources of Scomber japonicus in the North Pacific high seas will be abundant in 2020 and later years,the resources are predicted to increase to 33×10~4tons in 2020.But individuals are small.Under the natural mortality coefficient of 0.4,the resources of Scomber japonicus in the Pacific group will show a decreasing trend in 2020,the resources are predicted to decrease to83.3×10~4tons in 2020.