Current status of community structure and diversity of fishery resources in offshore northern South China Sea

Based on the bottom trawl survey data for four seasons during 2014−2015, we analyzed the community composition and diversity of fishery resources by studying index of relative importance (IRI), Margalef richness index D, Shannon diversity index H' and Pielou evenness index J', so as to understand the dynamics of community structure. Altogether 574 species had been caught in this region, among which Fish had the largest proportion with over 81%. The IRI result found four dominant species: Acropoma japonicum, Evynnis cardinalis, Trachurus japonicus and Decapterus maruadsi. A.japonicum was the only common dominant species for four seasons and the proportion of traditional commercial fish decreased greatly. For temporal distribution of diversity indices, there was significant seasonal variation for D indiex (highest in autumn but lowest in summer), while no seasonal variation was observed for H' and J'. For spatial distribution, high value of D index was mainly in shallow water with depth less than 40 m, similar for H' and J'. Due to the effect of closed fishing and fishing activities, the diversity indices fluctuated sharply during winter but smallest in autumn.