Distribution and drift trend of Collichthys lucidus larvae and juveniles in the coastal waters of the southern Yellow Sea

Changes in abundance and distribution during the fish larvae and juveniles period can affect the size of fish replenishment groups and, consequently, rusult in changes in the size of fish populations.The study of early-stage fish resources has great value for understanding fish stocks recruitment and the assessment of fishery resources. In this study, 47 stations(119°00′-123°00′E, 31°00′-35°00′N) were investigated in the nearshore waters of the southern Yellow Sea from March 2019 to January 2020. Fish larvae were monthly collected using a larval fish net(1.3 m diameter at the mouth, 6.0 m length, 0.5 mm mesh aperture) during the high tide to reveal the spatial-temporal distribution and drifting trends of larval and juvenile Collichthys lucidus. The environmental factors (surface water temperature, surface salinity, water depth) of the surveyed waters were also measured, and the spatial and temporal distribution characteristics and drift trends of the abundance of C. lucidus fish larvae and juveniles were analyzed. The relationship between environmental factors and fish larvae distribution was analyzed by a GAM model. A total of 2385 fish larvae were collected from June to October, with the highest abundance in June (165.15 ind./100 m³) and a decreasing trend month by month. Each month's most dominant developmental stages changed from pre-flexion larvae to juveniles in the order of months, except that only one post-flexion larva was collected in October. The results of the GAM model showed that the deviation of abundance was explained by latitude and longitude with the highest rate of 52.3%, followed by month and surface salinity. We conclude that the inshore waters of the southern Yellow Sea were nursery ground for C. lucidus, with its eggs and pre-flexion larvae dispersed passively. Then, the post-flexion larvae and juveniles drift inshore with growth and development under the influence of environmental factors such as surface salinity, surface water temperature, and water depth. Juveniles dominated in September and subsequently disappeared from the samples, implying potential recruitment success.