Landscape Influences on Stream Habitats and Biological Assemblages

Abstract

<em>Abstract.</em>—We investigated the effects of channel shape on the fish assemblages of 51 streams in Michigan’s Lower Peninsula. We considered three measures of stream channel shape: the low-flow hydraulic radius, channel incision, and a measure of channel fit (bank-full over lowflow stream width). Covariance structure analysis (CSA) was used to quantify relationships among fish assemblage properties, channel shape variables, and a number of other reach and catchment scale measures, including stream slope, catchment area, and the proportions of agriculture and coarse surficial geology in stream catchments. Our analyses showed that with increasing channel incision, total fish biomass decreased and that decreasing low flow hydraulic radius led to a reduction in the biomass of intolerant fishes. Our analyses emphasized the ways that catchment and reach scale measures affected fish assemblages through their effects on catchment hydrology, stream hydraulics, and stream channel shape. Catchment area was positively related to species richness and the average weight of fish; coarse geology was positively related to the biomass of the intolerant assemblage and to the average weight of intolerant fishes; and stream slope was negatively related to species richness and the average weight of individuals. Catchment agriculture had negative effects on the average weight of fish, yet species richness was found to increase with this measure, possibly due to the positive relationship between catchment agriculture and stream temperature. By investigating the effects of large scale factors on measures of channel shape and stream fishes with CSA, this study provides insights into the mechanisms by which the landscape influences stream fish assemblages.