冬季长江口渔场游泳动物群落种类组成和多样性的年代际变化

根据1991—2011年间3个代表年冬季长江口渔场的调查数据,对该海域游泳动物群落的年代际变化进行了研究。结果表明：1991—2011年,游泳动物种类数总体表现为升高的趋势,其中鱼类的增加幅度较小,甲壳类和头足类的增加幅度较大。以重量和尾数为代表的资源密度指数均表现出先下降后升高的趋势。平均体重先呈现急剧下降然后继续小幅下降的趋势。1991年优势种类数为7种,2001年为9种,2011年为7种,后2个年份和1991年相比,优势种发生了较大的更替。细点圆趾蟹（Ovalipes punctatus）和龙头鱼（Harpadon nehereus）为3个年份的共同优势种。游泳动物的站位平均种类数呈现持续升高趋势,而站位平均丰富度指数、多样度指数和均匀度指数则呈现出先升高再降低的趋势。1991和2001年、1991和2011年之间的平均相异性较高,均超过60%,而2001和2011年之间的平均相异性较低,为36.05%;引起群落差异的主要种类数呈增加的趋势,生态类群也逐渐扩大。游泳动物长度谱呈现逐渐变窄的趋势,主要是由于群落中的生物种类演替、小型鱼类数量增多和大型鱼类的群体年龄结构降低等原因造成的。

The Inter-Decadal Variations of Species Composition and Diversity of Nekton Community in Yangtze Estuary Fishing Grounds in Winter

According to fishery survey data in the Yangtze estuary fishing grounds in three representative winters from 1991 to 2011, the inter-decadal variation of the nekton community in the area were studied. The results showed that the composition, the fishery resources density, the dominant species, the diversity and size spectrum of nekton species all changed significantly from 1991 to 2011 in the Yangtze estuary fishing grounds. The number of the nekton species overall showed an increasing trend, in which the number of fish species increased a little, but the number of crustaceans and cephalopods increased greatly. The density indices, including weights and individual quantity, all had increasing trend after a falling trend at the beginning, but the amplitudes of them were different. The average weight fell sharply at first and then kept dropping slightly. The number of dominant species was seven, nine and seven in 1991, 2001 and 2011 respectively, and the dominant species changed dramatically. The common dominant species in the three years were Ovalipes punctatus and Harpadon nehereus. The average number of nekton species at all stations showed a sustained increase, but the average richness, the diversity indices, and the evenness indices all firstly increased and then decreased. The average dissimilarity were higher than 60% between 1991 and 2011, 1991 and 2001. But the average dissimilarity between 2001 and 2011 was lower (36.05%). The number of main species which caused community difference was increasing, ecological groups have gradually expanded. The nekton size spectrum was gradually narrowed, mainly due to the species succession in the community, the increasing of small fish population and the decreasing of large fish population age structure etc.