Stream fish assemblages in relation to landscape position and local habitat variables

The relative influence of local habitat variables and stream network position on fish assemblages was evaluated in this study of first-order through third-order streams within the Beaverkill-Willowemoc watershed in New York. We compared fish distribution and abundance over local and landscape scales by surveying 69 randomly selected tributaries within this 775-km(2) watershed. We used watershed-level metrics of stream link magnitude, branch link, confluence link, downstream link, and stream order to evaluate the importance of stream network position upon fish assemblages. Results of canonical correspondence analysis indicated that six factors significantly influenced fish species abundance in our study watershed. The proportion of fine substrate, canopy cover, in-stream vegetation, and water temperature were the four local habitat factors related to the abundance of fish species in this watershed; confluence link and stream order were the stream network position measures with the greatest influence on fish assemblages. Our results show that stream fish assemblages in the study watershed were influenced by a combination of small-scale habitat variables and stream position within a watershed network. The significance of confluence link relative to that of other link measures designed to evaluate stream network position has never been previously established in a direct comparison. The usefulness of confluence link to characterize fish assemblages is consistent with efforts to identify metrics that are relevant to both watershed network geomorphology and ecology.