Variation in fish assemblages across impoundments of low-head dams in headwater streams of the Qingyi River, China: effects of abiotic factors and native invaders

Identifying and explaining the pattern of how stream fish assemblages vary spatially are basic for the conservation and management of fish species diversity. Although low-head dams may facilitate the native invasions of generalist fishes to headwater streams, few studies have evaluated the impacts of the native invaders on indigenous fish assemblages. In this study, we collected 12 indigenous and 13 native-invasive fish species and measured physical habitats and dam dimensions from 62 impoundments of low-head dams located on headwater streams of the Qingyi River, China. We used linear regression and canonical correspondence analyses to evaluate how habitat and dam variables influenced native-invasive fish assemblages. Our results indicated that invasive fish species richness and abundance were related to elevation and upstream and downstream dam abundances, and their assemblage structures were influenced by substrate heterogeneity, dam height, and upstream and downstream dam abundances. We also used similar analyses to examine how habitat, dam, and invasive fish variables affected indigenous fish assemblages. Our results showed that indigenous fish species richness was correlated with substrate heterogeneity and dam height. However, indigenous fish assemblage structures were not only influenced by dam height, substrate, and downstream dam abundance, but also by invasive fishes. The abundance of one invasive species, Pseudorasbora parva, showed a strong negative influence on indigenous fish assemblages. Our study suggests that the combination of changes in abiotic factors and biotic structure and process following dam-building may determine the indigenous fish assemblages in the impoundments of low-head dams within headwater streams.