Fishway assessment and monitoring for endemic migratory fish using multiple techniques in high-altitude river systems: A case study from the Yarlung Zangbo River, Southeastern Tibetan Plateau

The Yarlung Zangbo River (YZR) on the Tibetan Plateau is a prime hotspot for hydropower development in China, yet this inevitably poses risks to river connectivity and the survival of its unique endemic fish species. Fishway installations are often adopted to mitigate the impacts on fish, but their effectiveness especially in high-altitude regions remains inadequately studied. Our study offers the first comprehensive evaluation of a fishway installed on a primary tributary of the YZR from 2019 to 2021, using multiple methods including fish sampling, video monitoring, hydroacoustic detection, and passive integrated transponder telemetry technology. The below-dam fish community was dominated by cold-water rheophilic Schizopygopsinae, Schizothoracinae, and Nemacheilidae. Fish movements exhibited distinct seasonal and diel patterns, with activity rising in April and peaking in May. Approximately 75.0 % of fish movements within the fishway were recorded during daytime (7:00–19:00), whereas the fish assemblage near the fishway entrance primarily occurred during nighttime (20:00–6:00). Telemetric trials on five endemic species revealed upstream- and downstream passage efficiencies of 31.0 % and 61.7 %, respectively. Passage efficiency, transit time, and speed varied substantially among species and individuals, primarily affected by environmental factors such as fishway discharge and water temperature. Our findings provide the essential information on fish behavior and movement patterns for designing more effective fishways in plateau regions and underscore the importance of continuous monitoring and evaluation to optimize fishway performance, ensuring that the conservation of endemic fish species is achieved successfully amid expanding hydropower development in the region.