DISTRIBUTION CHARACTERISTICS AND ITS INFLUENCING FACTORS OF THE YANGTZE FINLESS PORPOISE IN ANQING SECTION OF THE YANGTZE RIVER

In this study, we conducted a total of 8 visual surveys in the Anqing section of the Yangtze River (Chengying Village - Fenghuang Wharf) spanning from fall 2021 to summer 2023, covering two consecutive years. Our aim was to investigate the distribution characteristics of Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis) in this watershed and the factors influencing them across four dimensions: populations number, cluster sizes, migration patterns, and habitat preferences. During the study period, a total of 555 groups and 1000 individuals were observed, with the largest single assessment recording 192 individuals. Notably, in 2023, we observed 336 groups of porpoises comprising 603 individuals, marking an increase of 53.4% and 51.9% respectively compared to 2022. The maximum observed cluster size of porpoises during the study was 8 individuals, with an average cluster size of 1.8 individuals per group. Our observations revealed that porpoises in the Anqing section of the Yangtze River exhibit a continuous distribution, with distinct hotspots identified. Particularly noteworthy were the North Branch of Zhangjiazhou, the Upper No. 3 Sandbar, the tail of the Lower No. 3 Sandbar, and the head of the Clean Sandbar, which emerged as important habitats, collectively accounting for 19.3%, 4.9%, 12.6%, and 10.8% of total observations respectively. Following the fishing ban, porpoises have displayed increased activity in the estuarine confluence area for more extended periods, with a tendency to spread downstream from the Anhui section of the Bali River. However, the expansion of there habitat is still constrained by factors such as wharf infrastructure and collapsed bank areas. Notably, only the Clean Sandbar area below the Huayang estuary remains as an important habitat for porpoises in the lower river section. Conclusively, our study indicates a significant upward trend in the Yangtze finless porpoise population in Anqing section of the Yangtze River, attributed to a decade-long fishing ban and the frequent occurrence of extreme droughts in Poyang Lake. Additionally, porpoises are displaying improved utilization of migration corridors between important habitat patches, resulting in a more continuous distribution pattern. Based on our findings, we recommend maintaining a proportion of natural shoreline in potential gathering, foraging areas, and migration corridors of porpoise, increasing shoreline improvements, and strengthening control over human activities. Furthermore, considering the temporal and sequential characteristics of Yangtze finless porpoise migration into the river during periods of extremely low water levels in Poyang Lake, we advocate for the formulation of a contingency management plan for the waters from the Hukou estuary to the Huayang estuary.