Catch composition and species diversity of the bottom trawl fishery in the northern South China Sea in 2008

Using stratified sampling method,the structure,species composition and seasonal dynamics of the bottom trawl catch in 2008 in the northern South China Sea(SCS) were analyzed.It was found that the diversity index ranged from 3.56 to 5.36 for Shanon-weiner(H'),0.54 to 0.74 for Pielou's evenness index(J) and 0.08 to 0.89 for relative dominant index(RD).The seasonal turnover rate of major species communities varied between 22.83 % and 32.50 %.The ratio of high-low quality species has tended to decrease since 1950s,though the ratio begins to declining.Special attentions should be paid that the major high quality species composition has changed and the total trawl catch has decreased although the fishing efforts increased,and meantime the proportion of small fish in the catch has been increasing.