Spatial-temporal distribution and diversity variation of fish in the coastal waters of northern Beibu Gulf

【Objective】The objective of this study was to investigate the spatial and temporal distribution of fish resources and the change tendency of community structure diversity in the coastal waters of northern Beibu Gulf， and provide scientific basis for the sustainable conservation and management and rational development of fisheries resources. 【Method】In 2018，bottom trawl surveys were conducted in the coastal waters of northern Beibu Gulf during January （winter）and August（summer）. Data on fisheries resources were collected from 30 sampling stations. The spatial distribution and diversity variation of fisheries resources were assessed using methods such as area-sweeping，ecological index，and abundance/biomass comparison（ABC curve）. Historical literature data were also used for comparing the fish resource status in different historical periods.【Result】 A total of 140 fish species， belonging to 14 orders， 57 families， and 89 genera， were captured in the northern Beibu Gulf. The dominant group was the Perciformes order，and the composition of dominant species in the ecological community showed obvious seasonal variations. Fish community structure was affected by season variation. During summer，the dominant species were Leiognathus ruconius，Parargyrops edita，and Leiognathus brevirostris，whereas during winter，the dominant species included L. ruconius，Chaeturichthys stigmatias，Pennahia macrocephalus，and Trichiurus haumela. The abundance of fish species in the coastal waters of northern Beibu Gulf exhibited extremely significant seasonal differences（P＜0.01，the same below），with higher abundance observed in summer（146.3×10³ ind/km²）compared to winter（36.8×10³ ind/km²）. However，there was no significant difference in abundance among different sea zones（P＞0.05，the same below）. The biomass of fish species also showed extremely significant seasonal differences，with higher biomass in summer（1394.73 kg/km²）compared to winter（328.24 kg/km²）. There was no significant difference in biomass among different sea zones. In terms of species diversity，the diversity indexes ［Shannon-Wiener diversity index（H'），Pielou evenness index（J'），and Margalef species richness index（D）］of fish communities in the northern Beibu Gulf were generally higher in summer compared to winter，but there was no significant difference among different sea zones. ABC curve analysis revealed that the abundance curve of fish species consistently remained above the biomass curve，indicating a moderate to high disturbance level on the fish community structure. It meant that the dominance of the larger fish was weakened，and the fish that grew faster and were relatively small were the predominated ones.【Conclusion】 The resource quantity and diversity indexes of fisheries resources in the northern Beibu Gulf exhibit a declining trend compared to historical levels，and obvious changes are observed in the community structure. Therefore，future efforts should focus on continuous monitoring of fisheries resources，improving the ecological environment，strengthening fisheries resources conservation and management，and reducing human disturbances to ensure the functional diversity and sustainable development of fish communities.