Variable Effects of Habitat Enhancement Structures across Species and Habitats in Michigan Reservoirs

Abstract

The addition of habitat enhancement structures to aquatic systems is a common practice by fisheries managers hoping to increase production, spawning success, and angler catch rates of important sport fishes. However, quantitative evaluations of these efforts are few and typically do not include the extent to which natural habitat mediates the effects of habitat enhancement structures. We evaluated the effects of two types of habitat enhancement structure on four fish groups in four reservoirs of the Au Sable River, Michigan. Using a combination of sampling methods, we compared several response variables (including relative abundance, nesting, and angler catch rates) between areas with and without structures, as well as before and after structure placement, across a gradient of natural habitat conditions. The effects of half-log habitat enhancement structures were significant in some cases, but no significant effects were detected for AquaCrib structures. Smallmouth bass Micropterus dolomieu responded to half-logs with significantly greater relative abundance, nest density, and nest success than in areas without half-logs. Other fish groups displayed few significant differences in the response variables between areas with and without structures or before and after structure placement. Habitat effects varied across reservoirs and fish groups but generally influenced the response variables more than the presence of habitat enhancement structures.