Effects of local, river-network and catchment factors on fish assemblages in the headwater streams of the Xin'an basin, China

Identifying the spatial pattern of fish assemblages and the correlation between fish assemblages and environmental factors is basic for conserving and managing stream fishes. Based on data collected from 91 sampling segments within first-order through third-order streams of the Xin'an basin, China, we examined the spatial variation of fish assemblages in this area and related it to local, river-network and catchment factors. We found that fish species richness significantly increased from first-order to second- and third-order streams, but assemblage structures showed no among-stream variation. When the independent influence of the three categories of factors was considered, fish assemblages were significantly related to local habitat (e.g. wetted and substrate heterogeneity), tributary spatial position (e.g. confluence link and distance from mouth) and land use (e.g. agriculture and urbanization areas), respectively. However, when the effects of the these factors were considered jointly, local habitat and tributary spatial position were more important in influencing fish assemblages than land use. Our results suggest that fish assemblages in the headwater streams of the Xin'an basin were mainly determined by both local and spatial factors. The landscape data should be further refined in the future to provide more information for assessing how land use influence stream fishes