Variation analysis of single otter trawl fish community structure outside forbidden fishing line of Zhoushan fishing ground

We investigated the seasonal variation of the fish community structure outside the forbidden fishing line of Zhoushan fishing ground in base of the data collected from bottom trawl surveys in February, May, September and November, 2010. In the surveys, 80 fish species were found, belonging to 13 orders, 49 families and 59 genera, among which 30 species are Perciformes (predominated order). Simpson index, Shannon-Wiener index and Pielou index increase after September then decrease and bottom in May; while Margalef index is relative high in May, which indicates a relative high richness of fish species in May. Abundance biomass curves (ABC) are greatly impacted by dominant species. The ABC is either above its dominance curve of abundance (in February) or the curves intersected (in May). The dominance curves of abundance are above the ABC in September and November. The value of slope of trophic level-average body weight curves reaches the minimum and maximum in May and September, respectively, which indicates that the average body weight, especially for species at high trophic level, increases in September after summer closed fishing, but decreases to a low level after continuous fishing from September to May.