Study On The Connectivity Of Larimichthys Polyactis Populations In The Southern Yellow Sea And The East China Sea Based On The Analysis Of Otolith Elements And Morphological Differences

The elements on fish otoliths will be affected by environmental factors.The environmental history of the fish’s entire life history is recorded.The morphology and structure of otoliths will also be affected by the environment of different habitats,showing certain group differences.At present,these two research methods are mostly reflected in fish group identification,migration history reconstruction,and group connectivity research.Small yellow croaker(Larimichthys polyactis)is an important economic fish in China,but there are many differences in the group division of small yellow croaker.Therefore,determining the connectivity between different geographical groups of small yellow croaker is very important for the management of the fishery of small yellow croaker.This paper firstly used the otolith microchemical elements to study the spatial connectivity of small yellow croaker juveniles in the southern Yellow Sea(Northern Jiangsu,Lusi)and the East China Sea(Zhoushan,Dachen Island).A laser ablation inductively coupled plasma mass spectrometer(LA-ICP-MS)was used to determine the ratio of trace elements(Sr:Ca,Ba:Ca,Mn:Ca and Mg:Ca)in the otolith edge and near nuclear area of small yellow croaker juveniles.Apply non-parametric one-way statistical methods and PERMANOVA,random forest classification and unsupervised random forest clustering methods.The results show that there is a significant spatial difference in the ratio of the otolith edge elements of young yellow croaker juveniles between sampling stations.The total classification accuracy of random forest classification is 63%,and the classification accuracy of each sampling station is between 50% and 75%.The spatial difference of juvenile fish is mainly caused by the difference of Mn,Ba and other elements.The results of unsupervised random forest clustering based on the element ratios of the near nuclear area of the otoliths show that the birth source of small yellow croaker juveniles mainly comes from the spawning grounds of the southern and eastern seas of the Yellow Sea,and the spatial difference of the origin of the young yellow croaker is mainly driven by Ba.Subsequently,this article analyzed and studied the natal homing of broodstock in the spawning grounds of small yellow croaker in the southern Yellow Sea and the East China Sea using LA-ICP-MS otolith element fingerprint analysis technology.The sampling stations came from the spawning grounds in the north of Jiangsu,Lusi,Zhoushan,and the south of Zhejiang.The sampling time of broodstock was one year apart from that of juvenile fish.The LA-ICP-MS otolith element fingerprint analysis technology was used to analyze the trace elements in the core area of the otoliths of small yellow croaker juveniles.The MANOVA analysis results showed that the element ratios of the otolith core areas of the small yellow croaker juveniles were extremely different at different sampling stations,Sr:Ca,Ba:Ca and Mg:Ca are the element fingerprints that effectively distinguish each geographical group.The juvenile group discrimination success rate based on the three is between 64.7%-87.5%,and the overall discrimination success rate is 77.4%,showing a strong ability to record and identify group elements.The discriminant function set is established based on the core elements of the small yellow croaker juveniles,and the element ratio of the otolith core area of the broodstock taken in 2020 is discriminant and analyzed.The results show that each spawning ground of small yellow croaker has a strong natal homing,with a natal homing rate of 41.38%-75%.The average is 53.67%.Finally,based on the differences in otolith morphology,this study studied small yellow croaker reproduction populations in the southern part of the Yellow Sea(Northern Jiangsu,Lusi)and the East China Sea(Zhoushan,Dongyin Island).The results of similarity analysis(ANOSIM)showed that 4 different samples were collected.There were significant differences in otolith morphology among the reproduction populations of small yellow croaker(R = 0.163,P = 0.001).After comparing the breeding populations of small yellow croaker at different sampling sites,it was found that the differences in otolith morphology between the two groups reached a very significant level(P≤0.01).Based on the analysis of the similarity percentage,the five otolith morphological indicators of ring rate,areal density,radius ratio,FERET ratio,and width to shape ratio are typical indicators of otolith morphology that have a high degree of contribution to the similarity in each breeding group.The dissimilarity between different reproduction populations is mainly driven by areal density,roundness,ellipticity and morphological factors,which to some extent reflects the specificity of otolith morphology in different reproduction populations of small yellow croaker.Through stepwise discriminant analysis,four discriminant formulas for reproduction populations of small yellow croaker were established.The accuracy of discrimination was 36.8% to 74.3%,and the accuracy of comprehensive discrimination was 57.9%.Among them,the Dongyin Island and Zhoushan populations have a better discriminating effect;while the northern Jiangsu and Lusi populations and the adjacent sampling station reproduction populations have greater misjudgments.