Impacts of Dams on Fluvial Fish Assemblages in Michigan, Wisconsin, and Minnesota: Consideration of Multiple Measures of Fragmentation and Connectivity

Dams can alter many facets of fluvial fish habitat, including hydrology, temperature regimes, water chemistry, stream morphology, and longitudinal connectivity, in turn impacting fish assemblages through multiple complex mechanisms.  To improve our understanding of the influence of dams on fluvial fishes, spatially-explicit measures of dam position were generated for each confluence-to-confluence river reach (N~125,000) in the three-state region of Michigan, Wisconsin, and Minnesota.  These included: distances to nearest mainstem dams in the upstream and downstream directions for a given reach, dam densities in both upstream and downstream directions, and total number of dams between a reach and its terminal outlet (i.e. ocean or Great Lake).  These dam metrics, along with fish community survey data from ~1700 locations throughout the region, were used in an indicator species analysis to identify 1) fish taxa most sensitive to specific metrics, and 2) the dam metrics that are most influential on fluvial fish assemblages within the study region.  Results have shown that species respond differentially to dam metrics, and that these responses vary with stream size and ecoregion.  The complex relationships suggested by this project have numerous and broad implications in the management and conservation of fluvial fishes, including development of dam removal scenarios.