Community structure of nekton in Leizhou Bay using gillnetting

The seasonal gillnetting nekton surveys were conducted in Leizhou Bay during November 2014 and August 2015, and the diversity, relative abundance of the nekton community and the structuring roles of environmental factors were analyzed. Results show that a total of 113 species were identified to five classes, 16 orders, 49 families and 86 genera, of which the fishes (82 species) and Malacostraca (27 species) accounted for 72.5% and 23.9% of the catch, respectively. Among the top 10 important fishing species, there were two pelagic and benthic fishes, and six crustacean species. The diversity indicators was relatively high, increasing from the inner to the mouth of the bay, and the taxonomic diversity (TD, Δ) was related with the Shannon-Wiener indices (H′) and Pielou eveness indices (J′) by Pearson test significantly (n=12, P < 0.01), and the TD better described the community characteristics. The modeling of rank abundance distribution (RAD) shows that the Mandelbrot model fitted the abundance of nekton species best with the Akaike′s information criterion value of 485, indicating that the nekton community was possibly at a state of equilibrium with higher competition between species. The general linear modeling of biomass per unit of effort(BPUE) and numbers per unit effort (NPUE) with 11 environmental variables show that the dissolved oxygen (DO) had significant effects on BPUE(P < 0.01);the DO, water temperature and its interactions with seasons all affected NPUE significantly (P < 0.05). Neither the length of gillnets nor the geographical variation between sites had significant effects on the BPUE or NPUE (P>0.05). In conclusion, there was no evident geographical and seasonal difference among the inner, middle and mouth of nekton community based on gillnetting in Leizhou Bay, except for the significant effect of seasons on the NPUE (P < 0.05).