How do fish functional traits respond to dams at the global scale?

Dams are undoubtedly a primary threat to global freshwater fishes. However, how fish functional traits respond to dams at the global scale remains poorly understood, which hinders a general understanding of related ecological processes, conservation, and management. By synthesizing fish data from 4040 relevant publications, this study investigates the species compositional and functional differences before and after dam construction, aiming to obtain general fish response patterns to dams and to propose pertinent conservation suggestions. The mean values of body size and trophic level of the occurrence-increased (OI) fishes and occurrence-decreased (OD) fishes were found to be larger than those of global freshwater fishes obtained from FishBase, respectively. In terms of mouth orientation, most OI fishes have terminal mouths, while a large proportion of the OD fishes have inferior mouths. The sensitive functional traits that respond to dams are habitat preferences and reproductive traits because the OI fishes are mainly lentic-adapted, warm-water, non-migratory, and produce demersal eggs, while the majority of the OD fishes are lotic-adapted, cold-water, migratory, and produce floating eggs. These results indicate that functional trait-based evaluations are essential for predicting the impacts of dam development on fish assemblages and guiding global biodiversity conservation, management, and sustainability. [ABSTRACT FROM AUTHOR]