Changes in fish community structure in West Dongting Lake after the operation of the Three Gorges Dam

Abstract

鱼类是湿地生态系统中重要的组成部分,鱼类的群落结构动态直接反映湿地生境及外部驱动力的变化. 三峡大坝运行后,长江中游江湖水文情势发生了变化,西洞庭湖地处洞庭湖西部,是受此变化影响最为直接的区域之一. 为监测西洞庭湖鱼类群落结构变化特征,分析其变化原因,于2002年9月-2003年8月和2012年7月-2014年1月,在西洞庭湖进行了两次鱼类群落调查.共鉴定到鱼类7目17科91种,其中鲤形目最多,为58种,占总种数的63.7%. 两次调查结果显示,三峡大坝运行后西洞庭湖鱼类物种数由85种下降到66种,Shannon-Wiener多样性指数和Pielou均匀度指数分别由5.00和1.11下降为4.14和1.00,鱼类个体小型化趋势明显. 两次调查物种数和个体数量最多的类群均为底层、定居性、杂食性鱼类,且其比例有增加的趋势,而肉食性鱼类、中上层鱼类、半洄游性鱼类和产粘性卵、沉性卵鱼类个体数量占比均有减小的趋势,其中中上层鱼类变化有显著性差异. 三峡大坝运行后10年间,西洞庭湖鱼类多样性呈现下降趋势. 研究表明,西洞庭湖鱼类生境丧失、捕捞胁迫,加剧了一些特定类群的生存压力,并反映于鱼类群落结构的变化.;Fishes, as one of the important components of wetland ecosystem, have been used as the indicator of the wetland ecosystem health. Investigation on its assemblages changes may reflect the drivers of change in the wetlands. After the operation of the Three Gorges Dam, the hydrological regime between the Yangtze River and the lakes in mid-Yangtze River basin has been changed. West Dongting Lake has been directly impacted by the operation of the Three Gorges Dam due to its close hydrological connections with the Yangtze River. To monitor the changes of fish community structure at West Dongting Lake and analyze the causes of the changes, we conducted two surveys, of which the first one was before the operation of Three Gorges Dam, from September 2002 to August 2003;and the second one was after the operation of Three Gorges Dam, from July 2012 to February 2014. In total, 91 fish species were identified, which belong to 7 orders and 17 families. The most specie-rich order was Cypriniformes (58 species), accounting for 63.7% of all species identified. According to the survey results, the number of fish species at West Dongting Lake declined from 85 to 66;the diversity index of Shannon-Wiener declined from 5.00 to 1.11, while the evenness index of Pielou declined from 4.14 to 1.00. Body size of all fishes became smaller after the operation of the Three Gorges Dam. The structure of fish communities were also changed both in the dominant species and assemblages composition. The dominant fish groups include bottom feeders, settling fishes and omnivorous fishes, and its proportions in the assemblages have been increasing. We observed decline in the proportions of carnivorous fishes, pelagic fishes, semi-migratory fishes, and fishes that laying adhesive egg, as well as demersal eggs, among which, pelagic fishes declined significantly. The species diversity in West Dongting Lake declined after the operation of Three Gorges Dam. Our results reveal that habitat loss and over fishing are major threats to the survival of some specific fish groups and have been reflected in the changes of the fish community structure.