Date Published: January 12, 2017
Publisher: Public Library of Science
Author(s): Christine A. Ribic, Deahn M. Donner, Albert J. Beck, David J. Rugg, Sue Reinecke, Dan Eklund, Christopher A. Lepczyk.
The North American beaver (Castor canadensis) is a managed species in the United States. In northern Wisconsin, as part of the state-wide beaver management program, the Chequamegon-Nicolet National Forest removes beavers from targeted trout streams on U.S. Forest Service lands. However, the success of this management program has not been evaluated. Targeted removals comprise only 3% of the annual beaver harvest, a level of effort that may not affect the beaver population. We used colony location data along Forest streams from 1987–2013 (Nicolet, northeast Wisconsin) and 1997–2013 (Chequamegon, northwest Wisconsin) to assess trends in beaver colony density on targeted trout streams compared to non-targeted streams. On the Chequamegon, colony density on non-targeted trout and non-trout streams did not change over time, while colony density on targeted trout streams declined and then stabilized. On the Nicolet, beaver colony density decreased on both non-targeted streams and targeted trout streams. However, colony density on targeted trout streams declined faster. The impact of targeted trapping was similar across the two sides of the Forest (60% reduction relative to non-targeted trout streams). Exploratory analyses of weather influences found that very dry conditions and severe winters were associated with transient reductions in beaver colony density on non-targeted streams on both sides of the Forest. Our findings may help land management agencies weigh more finely calibrated beaver control measures against continued large-scale removal programs.
In Wisconsin, as in many states, the North American beaver (Castor canadensis) is a managed species. Wisconsin’s management plan addresses a wide variety of issues important to citizens of the state, making the plan a compromise of the stakeholders’ concerns . One objective of the plan since the 1930s  has been to protect cold-water trout fisheries (primarily native brook trout). The perception underlying this protection is that beaver dams on cold water streams may cause an increase in stream temperature, which may render some streams unsuitable for native trout . To counter this, Wisconsin’s beaver management plan recommends direct beaver control on trout streams. This protection is primarily implemented in northern Wisconsin, which has an abundance of cold-water streams and relatively high beaver density . The direct control tools used to manage beaver populations in Wisconsin are “regulated trapping” (i.e., permitted trapping by the public for beaver pelts) and “targeted trapping” by government agencies, primarily under direction of Wildlife Services, US Department of Agriculture Animal and Plant Health Inspection Service (USDA-WS). The effectiveness of the beaver management program has not been evaluated, although we do know that regulated trapping of beavers does not always result in reductions of the local beaver population . Moreover, targeted removals comprise only 3% of the annual beaver harvest in Wisconsin . It is not clear, a priori, that this level of effort is sufficient to measurably affect the beaver population of interest.
After 20 years of beaver control, we found a substantial and sustained Forest-wide reduction in beaver colony density on targeted trout streams across the Chequamegon-Nicolet National Forest. The magnitude of the reduction on both sides of the Forest was similar at roughly 60% relative to non-targeted trout streams—the targeted streams were regularly recolonized, but well below pre-control levels. Using the Chequamegon side as the benchmark, it took seven years of effort to achieve the full reduction, which was then sustained over the remainder of the monitoring period. The percentage declines are similar to the declines (but not the numerical harvest levels) documented in beaver pelt harvest records of the mid-1800s when commercial beaver trapping was occurring .