Roles of fishing and climate change in long-term fish species succession and population dynamics in the outer Beibu Gulf, South China Sea

A prevailing, controversial hypothesis is that fishing pressure has played a greater role than climatic and environmental drivers, in changing fish species succession and biomass fluctuation in the South China Sea (SCS). Based on otter trawl survey data from 1959 to 2010 in the outer Beibu Gulf (OBG), northern SCS, large seasonal and interannual variation is reported for fish species composition, the proportional abundances of dominant taxa, and fish biomass. Generalized additive models are developed to quantify relationships between fish biomass and the external factors of fishing pressure and climate change. Fishing pressure proved to be the main driver of sharp declines in demersal fish stocks, with high-value species being replaced by low-value ones over time. Abrupt decreases in fish biomass during the years of 1993 and 1998 correspond to El Nino events, with climate change possibly the main driver of proportional representation of pelagic species in fisheries trawl catch. The need to differentiate impacts of fishing and environmental drivers on fish species with different life history strategies is stressed to better understand fish community dynamics.