Relationship between spatio-temporal distribution of Evynnis cardinalis and environmental factors in nearshore waters of Beibu Gulf

Evynnis cardinalis is an important benthic commercial fish in the Beibu Gulf. To explore its nearshore spatio-temporal distribution patterns and the relationships between its resource density and environmental factors, this study utilized bottom trawl survey data from 34 sampling stations in the nearshore waters of the Beibu Gulf in October 2023 and March 2024. The index of relative importance (IRI), swept-area method, and Generalized Additive Model (GAM) were adopted to analyze its resource variation characteristics and environmental driving factors. The results showed that E. cardinalis exhibited a distribution pattern of "low abundance with large-sized individuals in autumn and high abundance with small-sized individuals in spring". It was an important species in autumn (IRI=231.96) and the primary dominant species in spring (IRI=5 207.57). The numerical resource density was significantly higher in spring than in autumn, whereas the mean individual body mass was markedly lower in spring, indicating obvious seasonal variations in population structure. GAM analysis indicated that the optimal model in autumn included longitude, latitude, and pH, with 71.7% of the deviance explained. Among these factors, longitude exhibited a highly significant effect on resource density (p=0.001). In spring, the optimal model incorporated longitude, pH, dissolved oxygen, and phosphate, explaining 75.0% of the deviance, with longitude and phosphate exerting highly significant effects on resource density (p<0.01). Overall, geographic location and environmental factors jointly shape the nearshore distribution pattern of E. cardinalis. These findings can provide a scientific basis for resource conservation and fisheries management of E. cardinalis in the Beibu Gulf.