Evolution of fish community structure, cause analysis and implications for ex-situ conservation of Yangtze finless porpoise in Tian-e-Zhou Oxbow of Yangtze River

Tian-e-Zhou Oxbow is ihe first habitats for the ex-situ reserve established for the Yangtze finless porpoise. The rich and abundant forage fish resources are the guarantee for the healthy development of the Yangtze finless porpoise population. Therefore, the change of fish community structure was analyzed with combined of seven fish surveys data in Tian-e-Zhou Oxbow of Yangtze River from October 2017 to April 2021 and historical data before the fishing ban. In view of forage fish of Yangtze finless porpoise, some suggestions were provided for the scientific management offish resources in Tian-e-Zhou Oxbow. During the investigation, 57 fish species were collected. The biomass of large and medium-sized fish such as Culler mongolicus, silver carp and bighead carp increased significantly while the biomass of small-sized fish such as Hemiculter leueisculm and Pseudobrama Simoni showed a declining trend. The dominant fish species gradually changed from small-sized fish such as Neosalanx taihuensis, Coilia hrachygnathm and Hemiculter leueisculm to large and medium-sized fish such as bighead carp, Culler mongolicus and Culler oxycephaloides, in particular, the newly emerged Cutter oxycephaloides population developed rapidly. Meanwhile, the body-weight of small-sized fish such as Coilia brachygnathus and Hemiculler leucisculus was decreasing, but the body-weight of large and medium-sized fish was increasing. Because the Yangtze Unless porpoise feeds on the small-sized fishes and juveniles of large and medium-sized fishes, the decline of their food resources would threaten the maintenance and growth of the Yangtze finless porpoise population. In order to ensure food supply for the Yangtze finless porpoises in Tian-e-Zhou Oxbow, it suggested that rational capture of silver carp, bighead carp, Cutter mongolicus and Culler oxycephaloides should be taken into consideration in order to reduce the food competition pressure of silver carp and bighead carp and the predation pressure of Cutter mongoticus and Cutter oxycephaloides on small-sized fishes. Besides, another measures to increase the small-sized fish resources like strengthening the connectivity of the oxbow with Yangtze River in the wet season to introduce more small-sized fish resources from Yangtze River and laying artificial fish nests in the oxbow to improve the breeding conditions for the small-sized fish species with adhesive eggs such as sharply should be carried out. © 2023 by Journal of Lake Sciences.