Spatiotemporal Patterns of Echolocation Activity of the Yangtze Finless Porpoises ( <scp> <i>Neophocaena asiaeorientalis</i> </scp> ) Near Mid‐Channel Islands in the Yangtze River

ABSTRACT Understanding fine‐scale habitat use is essential for conservation of endangered freshwater cetaceans in large rivers. Although Yangtze finless porpoises ( Neophocaena asiaeorientalis ) are frequently observed near mid‐channel islands, their spatiotemporal use of different island geomorphic units remains poorly resolved. From January 2021 to July 2022, passive acoustic monitoring was used to investigate echolocation activity of porpoises at three geomorphic units (head, middle, and tail) of Qingjiezhou Island in an anabranching reach of the Yangtze River. Porpoise acoustic activity exhibited significant seasonal and spatial variation. During the wet season, both daily detection rate (DDR) and sequent log window (SLW) were highest at the island middle and tail, whereas activity during the dry season was greatest at the island head, likely influenced by fish aggregation associated with sluice gate operation. Spatial heterogeneity in echolocation activity among geomorphic units was significant during the wet season but less pronounced during the dry season. A strong positive correlation was observed between DDR and mean daily SLW, indicating consistent patterns of habitat use intensity. Our findings demonstrate that mid‐channel islands function as seasonal mini‐floodplains and critical habitats for Yangtze finless porpoises, underscoring the importance of incorporating island geomorphic units into conservation planning for large river ecosystems.