Analysis on the characteristics of fish community structure in the main stream section of the National Nature Reserve for Rare and Endemic Fish in the upper reaches of the Yangtze River

The National Nature Reserve of Rare and Endemic Fish in the upper reaches of the Yangtze River is located in the lower reaches of Xiangjiaba Dam. With the impoundment of cascade hydropower stations in the lower reaches of Jinsha River and the implementation of the "ten-year fishing ban" policy, the fish community in the main stream of the reserve may change. In order to explore the characteristics of fish community structure in the main stream of the Reserve before the "ten-year fishing ban", based on the catch monitoring data from five sampling sites of this section from 2017 to 2019, the characteristics of fish species composition, ecological types, community similarity, species dominance, biodiversity and community structure stability were analyzed. The results showed that 134 fish species were collected in this investigation, belonging to 7 orders, 21 families and 83 genera, among which 27 species were endemic to the upper reaches of the Yangtze River and 12 species were exotic, accounting for 20.15% and 8.96% of the total species respectively. The fish community was dominated by demersal fish, sunken eggs and omnivorous fish. Cluster analysis and Nonmetric Multidimensional Scaling (NMDS) analysis showed that the fish community types of five sections in the main stream could be basically divided into three groups at a certain level of similarity, as Yibin, Luzhou and Hejiang sections formed one group, Jiangjin section and Banan section formed separate groups independently. There were 14 dominant species, among which Pelteobagrus vachelli was the dominant species in the whole area, with the highest dominance in Hejiang section where the IRI value was 27.00%. Shannon-Wiener index, Simpson index, Margalef index and Pielou index ranged from 2.725 to 3.306, 0.883 to 0.942, 5.833 to 8.811, 0.699 to 0.773, respectively. As a result, fish species diversity and the community distribution uniformity was high in the main stream of the reserve. The results of ABC curve analysis showed that the fish community structure in Jiangjin section was relatively stable, but moderately disturbed in the other section. This study could supplement the basic data of fish community information in the main stream of the nature reserve, and also provide theoretically scientific support for fish resource management and ecological evaluation of "ten-year fishing ban" in this section of the river.