Shifts in Fish Assemblages and Yangtze Finless Porpoise (Neophocaena asiaeorientalis) Prey Selection in Poyang Lake During the Early Phase of the Decadal Fishing Moratorium

Yangtze finless porpoise (Neophocaena asiaeorientalis) is the only extant cetacean species in the Yangtze River, a national first-class protected wild animal in China, and a key indicator reflecting the health status of the Yangtze River ecosystem. Environmental changes can induce adaptive trophic responses in animal communities; thus, clarifying the dynamic interactions between fish assemblages and dietary shifts in the Yangtze finless porpoise after the fishing moratorium is critically important. In this study, fishery resources in Poyang Lake were surveyed using triple-layer composite gill nets and cage traps, with samples collected and analyzed accordingly. A total of 81 fish species belonging to 8 orders and 16 families were recorded. Following the fishing ban, the abundance of small-bodied fish species (e.g., Hemiculter bleekeri, Carassius auratus) decreased, while the proportion of piscivorous species among the top ten dominant fish increased from 40% to 60%. DNA barcoding was used to analyze gastric contents of 10 dead porpoises found post-moratorium, and the results were compared with pre-ban data. Gastric content analysis identified 11 prey taxa, and comparative analysis demonstrated that prey selectivity was closely correlated with local prey availability. Concomitant with the structural reorganization of the fish community in Poyang Lake during the early stage of the fishing ban, the Yangtze finless porpoise exhibited adaptive dietary shifts toward benthic and small-bodied fish species, suggesting a potential linkage between these ecological responses. These findings provide direct implications for formulating targeted conservation strategies for this endangered cetacean and highlight the necessity of protecting small and benthic fish populations to ensure their long-term survival.