Status analysis of fish community in the lower reaches of the Yangtze River at the beginning of 10-year fishing ban and assessment of fishing ban effect

Water course in the lower reaches of the Yangtze River is bent, and flow pattern is tangled, which leads to diverse habitat, and makes it a good breeding, feeding place and important migration channel for fish. In order to study the fish community structure during initial period of 10-year fishing ban, fish was collected seasonally from April to December 2021, in the lower reaches of the Yangtze River. A total of 84 fish species from 63 genera, 18 families and 10 orders were collected during the investigation, with dominance by Cyprinids (47.62% of total species). Results of the species numbers and diversity indices showed that fish diversity was high in the lower reaches of the Yangtze River, while species are less than historical records. One-way ANOVA indicated that significant spatial differences were found for fish species, number and biomass, while no obvious differences were observed among seasons. Pelteobaggrus nitidus, Parabramis pekinensis, Hypophthalmichthys molitrix, Coilia brachygnathus, Hemiculter bleekeri and other 4 species were the dominant species. Piscivorous (47.62%) and omnivorous (40.47%) fishes prevailed in species number among the 4 feeding functional groups, sedentary fishes (76.19%) predominated among the 3 ecological groups, and demersal fishes (46.43%) predominated among the 3 habitat types. The number of large commercial fishes account for a small part of the fish community, but the index of relative importance is high due to the comparatively large individuals. The Shannon-Weiner index in the lower reaches of the Yangtze River is 3.28, which indicate the fish is relatively diversified. In the present study, the richness index was also high, while community evenness was stable. Overall, the fish continue to become smaller and younger, the fishery resources declined clearly, fish species, diversity index and catch per unit effort increased during initial period of 10-year fishing ban, and effect of the prohibition gradually appeared. In order to consolidate the effect of 10-year fishing ban, promote fish resources recovery, and optimize fish community structure, further scientific monitoring and higher strength patrol were recommended in the Yangtze River. Our study can obtain the basic characteristics of fish communities during initial period of 10-year fishing ban, and can also provide reference for fishing ban effect evaluation and aquatic organisms integrity index assessment.