Original research article
Evaluating landowner-based beaver relocation as a tool to restore salmon habitat
- Under a Creative Commons license
Abstract
Relocating American beavers (Castor canadensis) from unwanted sites to desirable sites (i.e., where damage exceeds stakeholder capacity) has been posited as a method to enhance in-stream habitat for salmonids in the Pacific Northwest region of the US; however, no studies have evaluated this method. From September–December 2011, we trapped and relocated 38 nuisance beavers using guidelines available to Oregon landowners. Release sites were selected from models that identified high values of beaver dam habitat suitability and where dams would increase intrinsic potential of coho salmon (Oncorhynchus kisutch). Mean distance moved from release sites within 16 weeks post-release was 3.3 ±0.2 (SE) stream km (max 29.2 km). Mean survival rate for relocated beavers was 0.47 ±0.12 (95% CI: 0.26–0.69) for 16 weeks post-release, while the probabilities of an individual dying to predation or disease/illness during the same period were 0.26 (95% CI: 0.09–0.43) and 0.16 (95% CI: 0.01–0.30), respectively. Dam construction was limited and ephemeral due to winter high flows, providing no in-stream habitat for coho. We conclude beaver relocation options available to landowners in Oregon may not be an effective option for stream restoration in coastal forestlands due to infrequent dam occurrence and short dam longevity.
Keywords
- American beaver;
- Coho salmon;
- Dams;
- Relocation;
- Restoration;
- Stress
1. Introduction
The decline of Pacific salmon populations has prompted efforts to identify factors affecting fish survival. In western Oregon, overwinter-rearing habitat was identified as the leading factor limiting recovery of coho salmon (Oncorhynchus kisutch; Nickelson et al., 1992a, ODFW, 2007), an anadromous fish species given federal protection under the Endangered Species Act. Overwinter stream habitat in Coastal Oregon is affected by fluctuations in stream velocities, resulting from high flow events ( Nickelson et al., 1992a and Leidholt-Bruner et al., 1992). Slow moving stream micro-habitat creates shifts in macro-invertebrate abundance and community structure, providing fish foraging opportunities that are uncommon in less diverse stream sections ( Pollock et al., 2004). In addition, low stream velocity allows fish to expend less energy for foraging ( Pollock et al., 2003 and Pollock et al., 2004). Anthropogenic projects that place large woody debris and boulders in streams, and create channel alcoves, have been used to create pool habitat in coastal streams; however, projects are expensive ( Leidholt-Bruner et al., 1992,MacCracken and Lebovitz, 2005 and DeVries et al., 2012) and have had limited detectable effect on coho salmon recovery ( Nickelson et al., 1992b and Solazzi et al., 2000).
In the Pacific Northwest, American beavers (Castor canadensis, hereafter beavers) co-exist with several anadromous salmonids, including coho. Ponds created by beaver dams create in-stream structure, resulting in greater aquatic productivity than reaches not dammed by beavers ( Leidholt-Bruner et al., 1992, Snodgrass and Meffe, 1998,Collen and Gibson, 2001 and Kemp et al., 2012). In general, beaver ponds are highly productive for fish as a result of high edge-to-surface ratios, presence of vegetation within and near the stream, and high abundance of prey ( Collins, 1993 and Pollock et al., 2004). High water retention from dams prolongs periods of low flow, providing areas of refuge for fish ( Leidholt-Bruner et al., 1992). Reductions in winter habitat for coho smolts were observed at the Stillaguamish Basin in Washington, and attributed to loss of beaver ponds ( Pollock et al., 2004). Similarly, overwinter survival and growth of coho smolts in the Copper River Delta of Alaska were positively correlated with the occurrence of beaver ponds ( Lang et al., 2006). In coastal Oregon, coho fry were three times more abundant in beaver-created habitat than in pools created by other fluvial processes (Leidholt-Bruner et al., 1992). However, beaver dams in the Coast Range are primarily small and ephemeral, with few withstanding high water flows ( Maser et al., 1981 and Leidholt-Bruner et al., 1992).
Pollock et al. (2004) suggested an increase in beaver population size may increase availability of pool habitat for coho smolts. Others have recommended managing for beavers or mimicking their dam-building behavior to augment in-stream complexity (Finnegan and Marshall, 1997 and DeVries et al., 2012). Recent changes in legislation of some western states now allow landowners to relocate beavers as a management tool (ODFW, 2012, RCW 77.32.585, UDWR, 2010). We used the Oregon Department of Fish and Wildlife’s Guidelines for Relocation of Beaver in Oregon (ODFW, 2012), hereafter state guidelines, as a basis for this study. At the time of this study, no state or federal programs were relocating beavers in western Oregon. Thus, we assumed that if state guidelines were used, it would be a citizen-lead program.
Ours is the first study to evaluate beaver relocation as a tool for improving in-stream habitat for salmon. We use the term “relocation” defined by Fischer and Lindenmayer (2000) as “any intentional movement by humans of an animal or a population of animals from one location to another”. Our objectives were to examine post-release rates of survival and cause-specific mortality, and movement of relocated beavers; and evaluate enhancement of coho rearing habitat through dam construction. Our measure of relocation success was construction and persistence of beaver dams at release sites, as dams are potentially important to coho rather than the presence of beavers alone. Although beavers chosen for relocation in this study were taken from areas of human-wildlife conflict (i.e., nuisance beavers), conflict resolution was not an objective or a measure of success.
