Widespread and strong impacts of river fragmentation by human barriers on fishes in the Mekong River Basin

The Mekong River, a global freshwater biodiversity hotspot, has suffered from intensive barrier construction, resulting in major challenges in safeguarding its fauna. Here, we provide a comprehensive evaluation of the impacts of river barriers on the distribution of 1,032 fish species in the Mekong Basin. Our analysis revealed that 93% of Mekong fish species suffer from habitat fragmentation, and species with larger habitat range requirements experienced higher river fragmentation impacts. Sub-basins along the main channel in the Lower Mekong had high values of species richness but relatively high barrier impacts. Across all migration types, potamodromous fish had the worst habitat fragmentation status (Fragmentation Index, 42.56 [95% CI, 36.95–46.05]), followed by catadromous fish. Among all IUCN conservation status categories, Critically Endangered species experienced the highest habitat fragmentation index (33.34 [12.53–46.40]). Among all barrier types, small dams and sluice gates contribute more to habitat fragmentation than large dams.