| Fish supplementary groups occupy a very important position in fish populations.The abundance and spatial distribution of juvenile supplementary groups determine population dynamics.Their distribution is easily affected by environmental factors and presents a certain spatial pattern and closely affects the status of fishery resources.Understanding the recruitment process of a species and its dominant factors(such as predation,temperature,etc.)is fundamental to the study of fish populations and fisheries management.Among them,the chemical composition of otoliths has been developed as an important technique for quantifying the movement and connection patterns of individual fish.Otolith is a stable calcified tissue formed by fish body along with fish.It absorbs trace elements in the living water environment of fish every day and reflects the information of the water environment in which fish live.As an effective research tool,otolith chemistry plays an important role in the study of dispersal patterns in fish life-history stages,and individual dispersal histories can be obtained from chemical information stored in otoliths.The otolith is a bi-crystalline structure in the inner ear of teleost fish that is used to receive sound,determine direction,and maintain balance,and is a stable calcified tissue that grows with fish.When the otolith grows,it incorporates trace elements into the calcium carbonate matrix,and the incorporation rate of some elements(such as Sr and Ba)is related to the concentration of the water environment or other environmental variables(such as temperature and salinity),which record the fish all the time.Information about the water environment experienced by the class.Therefore,otoliths are a natural biological marker that can be used to study the dispersal history of fish.Among them,the otolith core reflects the birth environment of the fish,and the group origin can be determined according to the characteristics of the otolith core elements,and the spatial scale information of the juvenile fish dispersal can be obtained.Small yellow croaker(Larimichthys polyactis)is an important economic species in my country’s offshore ecosystems.It is widely distributed in China’s Bohai Sea,Yellow Sea,East China Sea and the western waters of North Korea.It is a warm bottom fish.There are 3 geographical groups in the waters of my country,among which the ethnic groups in the southern part of the Yellow Sea and the northern part of the East China Sea are the largest.The small yellow croaker population in this area often appears mixed in the period of feeding and overwintering,which affects the judgment of resource quantity.Understanding the distribution and dispersal patterns of supplementary populations of small yellow croaker in the southern Yellow Sea and northern East China Sea,and identifying the main drivers of spatial heterogeneity of juvenile abundance can provide basic information for habitat protection and population restoration and reconstruction of small yellow croaker in the South Yellow Sea and the East China Sea.This paper firstly uses the survey data of small yellow croaker juveniles and the environment in the southern Yellow Sea and northern East China Sea(30°30′N～35°N,120°E～127°E)in August 2019,and uses three generalized additive models(GAM)to explore Relationship between resource abundance of small yellow croaker and related environmental factors.The results show that Delta Gamma-GAM is the best(root mean square error RMSE value is 12014.43,Pearson correlation coefficient r value)is0.461,and the Spearman rank correlation coefficient ρ value is 0.699).The distribution of small yellow croaker is highly clustered in space,and the concentrated distribution range is in the sea area of 32°N～34°N and 122°E～124°E.Among many environmental factors,the distribution of small yellow croaker juveniles was only significantly correlated with water depth,showing a negative linear relationship,reflecting the distribution pattern of small yellow croaker larvae preferring near shore.Then this paper selected the forage populations of the same year in the southern Yellow Sea and northern East China Sea(30°30′N ～ 35°N,120°E～127°E)in August2019,Laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)was used to determine the Sr:Ca,Ba:Ca,Mn:Ca and Mg:Ca values in the otolith margin and near-nuclear region,using unsupervised cluster analysis,random forest classification,nonparametric permutation analysis of variance(PERMANOVA),etc.Methods,analyze the differences of elements at the edge of otoliths,and determine their birth environment according to the similarity of element values in the near-nuclear area.Based on the core elements of the otoliths of the larvae and juveniles in May,the supervised random forest classification method was used to further determine the birth source of the feeding population in August.The results of the Kruskal-Wallis rank-sum test show that there are obvious differences in the edge elements of the otolith of the small yellow croaker between the sampling points,and there are geographical differences between the north and the south.The main factor of North-South difference.The results of the Kruskal-Wallis rank sum test of elements in the nuclear area showed that the element concentrations in the otolith near the core area of small yellow croaker showed significant differences at different capture sites.The results of supervised clustering analysis showed that this part of the prey populations came from two different birthplaces in different environments,and the PERMANOVA analysis showed that the elemental differences of the birthplaces of the two cluster groups were extremely significant(F=66.476,P <0.001),mainly driven by Mn and Ba,the spatial difference in the birth source of juvenile yellow croaker.Based on the core elements of the otoliths of the larvae and juveniles in May,the birth sources of the feeding groups in August were further identified,and it was found that the birth sources were mainly two places along the coast of the South Yellow Sea and the coast of the East China Sea. |
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