Investigating the population structure of small yellow croaker (Larimichthys polyactis) using internal and external features of otoliths

In this study, we investigated the population structure and potential changes of the small yellow croaker from nine main spawning grounds covering most of the distributional range of the species in China. The geographic variability of otolith shape and increment growth were used as tools for stock separation. Otolith growth was based on the annual increment width estimated for the age 2 groups of the spawning stock. Otolith shape was described by the shape variables and Fourier coefficients, that were standardized to remove any size effects. Significant differences and gradual variation with latitude were observed in both the otolith growth and shape variables among stocks; these patterns were supported by discriminant analysis with correct classifications ranging from 26.1% to 82.3%. These results taken together show that the nine stocks could be divided into four subpopulations which were correctly classified by around 75.8-95.9%; the main difference of average otolith shapes for these subpopulations appeared on the ventral side. In contrast to previous population studies, the East China Sea group was further divided into the Southern and Northern two subpopulations and the Haizhou Bay stock appear to be more similar to the Lvsi stock. Moreover, considerable spatial variation in otolith shape and increment growth implied different environmental factors experienced by subpopulations and limited levels of inter-connection, and suggested that the small yellow croaker might be comprised of a metapopulation structure.