中文摘要：

采用分层随机抽样的方法，调查了2008年南海北部海域拖网渔获物组成，利用Shanon—weiner群落多样性指数（H’）、Pileou均匀度（J’）指数、相对多度（RD）等分析其多样性；根据渔获物季度组成，分析了主要种类的季节更替规律。研究表明，拖网渔获组成多样性指数介于3．36～5．36，均匀度指数介于0．54-0．74，优势度指数介于0．08～0．89，季节更替率介于22．83％～32．50％。另外，经济种类的优质鱼类与低质鱼类的产量比例为21：100，与20世纪80年代相比，优质鱼类与经济鱼类的比率呈下降趋势，优质鱼类个体日趋小型化。

英文摘要：

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 （ H3, 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 spe- cies 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.