Community structure of mesopelagic fish species in northern slope of South China Sea

Based on the fisheries resources data collected from two mid-trawl surveys from the northern slope of the South China Sea (111°00′E−120°00′E, 18°00′N−22°00′N) during August, 2015 and December 2015−January 2016, we investigated the community structure, dominant species and diversity of fishery resources in that area. A total of 273 fishery species were recorded, including 205 fishes, 50 crustaceans and 18 cephalopods. The index of relative importance (IRI) analysis shows that Ceratoseopelus warmingii and Oplphorus typus were the dominant species (IRI≥500). Diaphus brachycephalus, D. Phillipis, D. mollis, D. malayanus, Bolinichthys longipes and Lampanyctus tenuiformis were identified as the main species (100≤IRI < 500). The average Shannon-Wiener diversity index (H′), Pielou evenness index (J′) value and Margalef richness index (D) of fishery resources were 4.34, 0.70 and 3.41 in summer, respectively, and were 5.26, 0.79 and 4.03 in winter, respectively. Generally, the diversity index of winter was higher than that of summer. The diversity index was positively correlated with seawater depth, but negatively correlated with seawater temperature, indicating a certain environmental gradient in distribution of community diversity.