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

Abstract

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.

Ecology of freshwater shore zones

“…The strength of this effect depends on the species of fish and the amount of structure available in the surrounding area (Bolding et al 2004;Wills et al 2004). There is an active debate about whether such artificial structures actually increase population size, or merely attract fish from other areas.…”

Fish colonization of artificial reefs in a large Neotropical reservoir: material type and successional changes

“…Our experimental reefs were separated from each other by a distance of at least 30 m. Previous experiments with freshwater reefs have used similar distances between replicates, ranging from 3 to 100 m (median ¼ 40 m) (Wilbur 1978, Walters et al 1991, Hayse and Wissing 1996, Rold et al 1996, Samdstro¨m and Karas 2002, Wills et al 2004, Freitas et al 2005, Santos et al 2008. We are confident that our results are not severely affected by confusion with spatial variation or spatial dependence because: (1) the three material types were spatially interspersed (Fig.…”

“…Community change rates indicated that although ceramic reefs were more promptly colonized, concrete reefs benefited from a secondary increase in species gain rates, following the initial decrease which is general of most successions (Anderson 2007). We believe that these differences are not due to confounding environmental variables or the physical complexity and size of the reefs, which have been shown to affect the availability of predation refuges, food, or spawning substrata (Walters et al 1991, Rold et al 1996, Bolding et al 2004, Wills et al 2004), because we carefully matched the dimensions and complexity of the reefs, and we placed the reefs in an environmentally homogeneous area, with no detectable differences in physicochemical features among sites. Although further data are needed to understand the mechanisms generating these differences among materials, ceramic and concrete were more promptly and intensively colonized by periphyton than the PVC treatments (L. N. Santos, personal observation), which also had a different species composition.…”

“…Fishery managers have long recognized the potential of artificial reefs to attract and yield fish (Wills et al 2004). Since the 1930s, the use of artificial reefs in reservoirs has become widespread, especially in North America, where numerous studies have been undertaken to elucidate their role on the attraction, concentration, and enhancement of fishery resources (Bolding et al 2004).…”

“…For instance, depth, temperature, and other environmental variables of the sites where the reefs are deployed may determine their effectiveness (Walters et al 1991). Material type, size, age, and complexity of the reefs are other crucial factors that affect fish colonization (Wills et al 2004). Although habitat management represents an interesting opportunity to mitigate the impacts of dam construction and operation routines , the use of artificial reefs has received little attention in South America.…”