<em>Abstract.</em>—We analyzed data from 287 streams in Wisconsin and northern Michigan to evaluate the relative effects of human disturbance levels on the influence of catchment, network riparian, reach riparian, and instream variables on fish assemblages. The streams were divided into high, medium, and low human disturbance groups based on catchment and network riparian urban and agricultural land uses. We used canonical correspondence analyses to evaluate relations among variables at the four spatial scales and fish assemblage composition, abundance, and presence/absence and to partition the relative importance of spatial scales. Catchment and network riparian land uses were among the dominant variables correlated with fish for high disturbance catchments but not for low disturbance catchments. The variations in fish assemblage composition, abundance, and presence/absence explained by catchment factors were substantially higher for high than for low disturbance catchments, although the variations explained by network riparian factors and reach riparian land uses were similar among disturbance levels. In contrast, the variations in fish variables explained by instream factors and the interaction of the four spatial scale environmental factors were considerably lower for high disturbance than for low disturbance catchments. We concluded that in largely undisturbed catchments, fish assemblages were predominantly influenced by local factors, but as disturbance increased in catchments and riparian areas, the relative importance of local factors declined and that of catchment increased. Hence, instream and riparian habitat improvements would be most effective in catchments that are largely undisturbed and catchment scale land-use management would be more effective for improving stream quality in degraded catchments.
Fish assemblage composition and structure in a pampean stream with contrasting land uses.
