Abstract:Based on the bottom trawl data in May and August, 2010 in the Bohai Sea, combined with the fishery data and literature in the Bohai Sea since 1959, the succession of fish community structure and the stock dynamics of main releasing fish species in the Bohai Sea were analyzed. The shift of dominant species was rapid, and large sized, high trophic level species (e.g. Trichiurus haumela, Cynoglossus semilaevis and so on) were replaced by small sized and low trophic level species (Setipinna taty, Engraulis japonicus and so on). Rapid shifts in small sized fish species were also found in fish community in recent years, excluding Setipinna taty, which was the dominant species in fish community since the 1980s. In addition, fish community structure was in a fluctuating state versus time according to the analysis of biology healthy index. Fish catch per unit effort in May sharply decreased from 186 kg/h in 1959 to no more than 1 kg/h in the present. Fish stock mainly distributed in the Laizhou Bay, Bohai Bay, and the central part of the Bohai Sea,but much less in the Liaodong Bay, and staggered biomass distribution were found between fish and jellyfish. The biomass of releasing fish species Lateolabrax japonicas and Sebastes schlegeli increased slightly in recent surveys, but that of other releasing fish species showed a decreasing trend since the 1980s. The biomass of a few releasing fish species was restored to some extent by stock enhancement, yet still less than 1% of the maximum biomass in history (excluding L. japonicas). Fish community in the Bohai Sea was dominated by small sized and low trophic level species, indicating that a lot of work needs to be done for stock enhancement.
