Seasonal Variations in Density Distribution of Larimichthys polyactis in Zhejiang Coastal Waters, China

Larimichthys polyactis, a key species in East Asian coastal ecosystems, shows distinct seasonal changes in density distribution, shaped by environmental factors and migratory behaviors of two dominant populations (East China Sea and South Yellow Sea). This study explored its 2023 density dynamics in Zhejiang coastal waters using quarterly surveys across 83 stations, combined with generalized additive models (GAM) and random forest (RF) models. Results showed that RF outperformed GAM overall, with bottom dissolved oxygen (SBO), salinity, and depth as the most influential environmental drivers. Density peaked in summer (77.88 thousand ind./km2) in central and northern offshore areas, dominated by the South Yellow Sea population migrating into the region. Autumn densities (3.76 thousand ind./km2) declined sharply as populations moved to overwintering grounds, while spring (0.41 thousand ind./km2) and winter (0.26 thousand ind./km2) densities were lowest. These findings highlight the role of seasonal environmental filters and population-specific migrations in shaping distribution patterns. RF models provide robust tools for predicting habitats, supporting seasonally tailored conservation strategies to protect critical spawning, foraging, and overwintering areas, which are vital for the sustainable management of this ecologically and economically important species.