A Review of Beaver–Salmonid Relationships and History of Management Actions in the Western Great Lakes (USA) Region

Abstract

Within the western Great Lakes (WGL) region of the USA (Michigan, Minnesota, and Wisconsin), the ecological impact that the North American beaver Castor canadensis (hereafter, "beaver") has on coldwater streams is generally considered to negatively affect salmonid populations where the two taxa interact. Beavers are common and widespread within the WGL region, while coldwater streams that support salmonid populations are scarcer landscape features; as such, all three states currently prioritize the habitat needs of salmonids in portions of each state by conducting beaver control in coldwater tributaries. In this paper, we review the history of beaver-salmonid interactions within the WGL region, describe how this relationship and management actions have evolved over the past century, and review all published studies from the region that have evaluated beaver-salmonid interactions. Our review suggests that beavers' impact varies spatially and temporally depending on a variety of local ecological characteristics (e.g., stream gradient and prevalence of groundwater inputs). We found that beaver activity is often deleterious to salmonids in low-gradient stream basins but is generally beneficial in highgradient basins and that ample groundwater inputs can offset the potential negative effects of beavers by stabilizing the hydrologic and thermal regimes within streams. However, there was an obvious lack of empirical data and/or experimental controls within the reviewed studies, which we suggest emphasizes the need for more data-driven beaver-salmonid research in the WGL region. Resource managers are routinely faced with an ecological dilemma between maintaining natural environmental processes within coldwater ecosystems and conducting beaver control for the benefit of salmonids; this dilemma is further complicated when the salmonids in question belong to nonnative species. We anticipate that future beaver-salmonid research will lead to a greater understanding of this ecologically complex relationship, allowing managers to be better informed of when and where beaver control is necessary to achieve the desired management objectives. found increased water temperatures downstream of dams, and Twork (1936) reported a decrease in temperature after dam removal; however, stream temperatures did not exceed the thermal limits for Brook Trout (20-24°C). 1208 JOHNSON-BICE ET AL. ate the three anonymous reviewers for comments that improved the manuscript.

Effect of Beaver on Brook Trout Habitat in North Shore, Lake Superior, Streams

“…North American beaver Castor canadensis (hereafter, “beaver”) have re‐inhabited northeastern Minnesota since their near extermination in the 1800s (Johnson‐Bice et al. ) and populations have prospered due to declined harvest and aspen Populus spp., a preferred food of beaver (Allen ; Johnston ), succeeding compositional changes of the upland hardwood forest (Knudsen ; Longley and Moyle ; Johnson‐Bice et al. ).…”

“…) and populations have prospered due to declined harvest and aspen Populus spp., a preferred food of beaver (Allen ; Johnston ), succeeding compositional changes of the upland hardwood forest (Knudsen ; Longley and Moyle ; Johnson‐Bice et al. ). Beaver are often referred to as ecological engineers because of their considerable impact on the landscapes they inhabit and their alteration of ecosystems.…”

“…Beaver impoundments are believed to provide suitable Brook Trout habitat during the first 2–4 years after establishment (Knudsen ); beyond that initial period, organic matter substantially accumulates and decomposition reduces dissolved oxygen levels (Johnston and Naiman ; Johnson‐Bice et al. ). Transforming a section of the stream into lentic habitat leads to increased invertebrate productivity and warmer, stable water temperatures, which provide apt conditions for increased Brook Trout growth and catch rates (Gard ; Knudsen ; Johnson‐Bice et al.…”

“…Transforming a section of the stream into lentic habitat leads to increased invertebrate productivity and warmer, stable water temperatures, which provide apt conditions for increased Brook Trout growth and catch rates (Gard ; Knudsen ; Johnson‐Bice et al. ). Additional positive impacts of beaver activity on Brook Trout habitat include stabilizing streamflow (Parker ; Gurnell ), providing rearing habitat (Leidholt‐Bruner et al.…”

“…; Snodgrass and Meffe ; Schlosser and Kallemeyn ) that alters stream geomorphology by increasing habitat heterogeneity and longitudinal complexity between reaches (Naiman et al. ; Johnson‐Bice et al ). Dam complexes accommodate highly altered flow velocity and depth distributions that contribute to temperature variability and increased habitat heterogeneity (Majerova et al., in press), providing Brook Trout of multiple life stages with a greater selection of places to forage, rest, and avoid high‐flow events (Bouwes et al.…”