Seasonal variation of fish community in north central region of Beibu Gulf

【Objective】To study the temporal and spatial distribution of fish composition, density and diversity indexes in north central Beibu Gulf, so as to provide basic data for further research on the long-time dynamic changes and temporal and spatial distribution of fish community structure, and also provide support for the exploitation, utilization and scientific management of fishery resources in Beibu Gulf.【Method】The spatial and temporal distribution of the biomass and abundance of fish resources in north central Beibu Gulf were analyzed by using the data from the four seasonal(February in winter, May in spring, August in summer and November in autumn) bottom trawl surveys in 2016. Sea sweeping area method was carried out to assess the fish resource biomass and abundance. The dominant fish species were in each season were determined by the index of relative importance(IRI). The Shannon-Weiner biodiversity index(H'), Pielou evenness index(J') and Margalef abundance index(D) were used to study the characters of fish community structure.【Result】A total of 152 species of fish were caught in north central Beibu Gulf, belonging to 96 genera, 55 families, 15 orders. All of them were warm-water or warm-temperature fish species. The biomass and abundance of fish resources in the central north Beibu Gulf were uneven, but the variation trend of the biomass and abundance were consistent, both biomass and abundance were higher in spring and summer than in autumn and winter. The value ranges of H', J' and D were 1.952-2.590, 0.481-0.699 and 2.303-3.114, respectively. The decreasing orders for H', J' and D in different seasons were summer>spring>autumn>winter, spring>summer>autumn>winter, and summer>autumn>spring>winter, respectively. The composition of dominant fish species(IRI ≥ 1000.00) was different among the four seasons, with three species in spring, five species in summer, four species in autumn and two species in winter. Parargyrops edita was the common dominant species of the four seasons, Sebastiscus marmoratus was the common species of spring and winter, while Secutor ruconius was shared by summer and autumn.【Conclusion】The temporal and spatial variation of fish resources in north central Beibu Gulf is obvious, the community diversity index is lower than the historical level, and the fish resources are in a state of over-exploitation. The dominant fish species with k-strategy are gradually replaced by those species with r-strategy. It is speculated that the seasonal fluctuation of fish resources is related to the migratory habits of fish, the changes of seawater temperature and salt, the managment of summer fishing moratorium.