Changes In Fish Community Structure In West Dongting Lake After The Operation Of The Three Gorges Dam

Fishes, as one of the important components of wetland ecosystem, has been used as the indicator of the wetland ecosystem health, and investigation on changes of its assemblages may reveal the drivers of changes 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 is located at the western part of Dongting Lake, and 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 surveysfrom July2012to February2014, based on the one carried out before the operation of Three Gorges Dam, which was from September2002to August2003.Surveys of spawning ground were conductedfrom April to June2014. In total,91fish species were identified, which belong to8orders and17families. The most specie-rich order was CYPRINIFORMES (58species), accounts for63.7%of all species identified. According to the survey results, the number of fish species at West Dongting Lake declined from85to66; the diversity index of Shannon-Wiener declined from5.00to1.11while the evenness index of Pielou declined from4.14to1.00. The results of the two surveys show that the dominant species are small species; the dominant fish groups include bottom feeders, settling fishes and omnivorous fishes, and theirproportions 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 eggs, as well as demersal eggs, among which, pelagic fishes declined significantly (χ2=8.9069, p<0.005). The number of spawns in each quadrat has significant difference, the dominant specieswhichlaying adhesive eggs, like Cyprinus carpio and Carassius auratus, prefer large leafy plants; shallow grass land and mudflats are their mainly spawning ground. The species diversity atWest Dongting Lake has declined after the operation of the Three Gorges Dam and the community tends to change to groups of smaller species, bottom feeders, settling fishes and omnivorous fishes. 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.During the process of fish diversityrestoration, we suggest that:1. Manage thehydrological dynamic, unblockthefish breeding migration route, protect and restore habitat, andmitigatetheimpactof the three gorges dam operation;2. Strengthen the comprehensive management of ecosystem;3. Strengthen the management and monitoring of the nature reserve;4. Enhancecommunication and education, and crack down on illegal fishing;5. Strengthen the research of ecological system response and its countermeasureunder the river-lake relation change background.