SELECTION OF NURSERY HABITATS BY YANGTZE FINLESS PORPOISE IN THE ANQING SECTION OF THE YANGTZE RIVER AND ITS CORRELATION WITH FISH RESOURCE DISTRIBUTION

The mortality rate for the critically endangered freshwater cetacean, the Yangtze finless porpoise (Neophocaena asiaeorientalis), is highest between the ages of 0 and 2. Improving the survival rate of calves is crucial for promoting the recovery of the Yangtze finless porpoise population. The availability of optimal nursing habitats is essential for improving calf survival. Nevertheless, the specific waters selected by Yangtze finless porpoises for nursing remain poorly understood. Based on visual surveys conducted from April 2023 to June 2025 along the Anqing section (Jiyangji–Emaozhou) of the Yangtze River, combined with hydroacoustic survey data on fish resources, this study analysed nursery habitats characteristics and their correlation with fish resource distribution. A total of 357 Yangtze finless porpoise sightings were recorded, including 28 mother–calf pairs, all consisting of one adult female and one calf. The mean monthly calf proportion was 8.2%, with the highest proportions observed in May–June (23.6%) and October–December (41.4%). The core nursing area (50% KDE) comprised 17.12% of the total study area, primarily distributed in Jiyangji, the southern branch of Qingjiezhou, the Dadukou river section, and the E'maozhou Head area. These areas share common features, including extensive non-navigation zones, natural shallow waters, and slow-flowing shoals. Approximately 87.8% of the core nursing area overlapped with the core distribution area of the Yangtze finless porpoise (50% KDE) and was consistently located in the central parts of these core zones. No significant difference was between the distribution density of mother–calf pairs and the overall fish density, nor with the density of small fish (<10 cm in body length) (P > 0.05). The above results indicate significant seasonal differences in the reproduction of the Yangtze finless porpoise, with nursery habitats demand higher quality environmental conditions, representing the most favourable sites for the species. Additionally, the findings suggest that current habitat selection for calf rearing is influenced more by other factors rather than fish resources. The habitat selection and characteristics of the core nursing areas for the Yangtze finless porpoise revealed in this study can provide theoretical guidance for identification and protection of calf-rearing habitats for the species.