Beaver Library

Expansion of populations of beaver Castor canadensis in northern Wisconsin has raised concerns over warming of coldwater fish habitats as a result of impoundments created by the mammals. We examined temperature with a network of electronic thermographs that recorded hourly water, air, and soil temperatures on four headwater streams occupied by beaver during summer 1990 and 1991. Stream temperatures followed air temperatures, even near groundwater sources. There was no consistent relationship between size or number of beaver impoundments and the degree of downstream warming. Large impoundments, although often warming downstream temperatures slightly, dampened temperature fluctuations immediately downstream. Local groundwater inflow and vegetative and topographic shading also dampened warming by impoundments. Several beaver impoundments were removed to evaluate ensuing temperature changes. Removal of beaver dams did not generally reduce the difference between upstream and downstream temperatures; in some cases dam removal increased the warming rate. Direct thermal benefits of dam removal in headwater streams may be outweighed by the potentially disruptive effects on the composition of fish and invertebrate communities downstream. It is suggested that management focus on relating topographical and geographical attributes to the potential for substantial groundwater discharge and to suitable summer temperatures for coldwater species such as brook trout Salvelinus fontinalis.

In degraded river systems, beaver dam analogs (BDAs) are an increasingly popular low-tech treatment used to reduce water velocity, increase floodplain connectivity, activate secondary side channels, and thus increase juvenile salmonid rearing habitat. However, BDAs may benefit non-native species as well, posing a potential conservation risk. In the Lemhi River basin in Idaho, an Intensively Monitored Watershed program quantifies responses of salmonid populations to restoration actions intended to remediate the effects of agricultural development. In 2017, BDAs were installed in Hawley Creek, to improve habitat conditions for native Rainbow Trout (Oncorhynchus mykiss). Non-native Brook Trout (Salvelinus fontinalis) also reside in Hawley Creek. We evaluated native and non-native salmonid responses to BDAs to understand their implications for achieving restoration goals. A BACI analysis was used to evaluate the effects of BDAs on the intrinsic rate of population growth of Rainbow Trout and Brook Trout. Demographic analysis was used to estimate the effects of treatment (i.e., BDA or control) on abundance and demographic rates of Rainbow Trout and Brook Trout. Our results suggested that Brook Trout did not displace Rainbow Trout in sites with BDAs, indicating that BDAs may not greatly change conservation risk to native salmonids. Rainbow Trout abundance and apparent survival in Hawley Creek post-treatment were typically higher than for Brook Trout. Our study suggests that BDAs in degraded western streams did not favor Brook Trout over Rainbow Trout.

I. Schlosser performed a long-term study to analyze changes to species density, fish predation, and precipitation over time in beaver ponds and their associated streams. In addition to an experiment that looked at the effects of these temporal changes on invertebrates. Yearly, there were significant variations in the amount of precipitation. The researcher suggests that dispersal is a significant factor in determining fish density and diversity, as well as effects of their predation on invertebrates.

European beaver dams impeded movements of anadromous salmonids as it was established by fishing survey, fish tagging and redd counts in two lowland streams in Lithuania.

A synthesis of scientific literature and our current level of: 1) understanding of the relationship between habitat quantity and quality and salmon production, 2) quantify the improvements in salmon production and survival that can be expected with different restoration actions, and 3) use models to help identify habitat factors limiting production and quantify population-level responses to restoration.

We have developed and implemented a simple approach that emulates the ecosystem engineering effects of beaver. This approach is less expensive and disruptive than typical large-scale engineering efforts and has the potential to restore both fish habitat and floodplain vegetation more rapidly than simply revegetating and waiting for the riparian zone to mature.  (Pg 246 – 255)

Whether beaver-induced changes of fish populations are beneficial or harmful will depend on the prevailing constraints on local fish species composition and abundance.

Researchers examined interactions between beaver and fish communities in the types of streams selected for Eurasian beaver re-colonization. They found several critical elements of fish communities in these mountain streams that relate to beaver activity and its effects.

A study of beaver control measures to help land management agencies weigh against large-scale removal programs

The goal of this project is to test whether a restoration method developed and tested in Bridge Creek, Oregon will be suitable for restoring streams like Pataha Creek in southeast Washington.

Relocating American beavers (Castor canadensis) from unwanted sites to desirable sites where damage exceeds stakeholder capacity) has been posited as a method to enhance in-stream habitat for salmonids in the Pacific Northwest.

Study that finds beaver-induced changes to habitat quality, stability, and connectivity may increase spotted frog population resistance and resilience to seasonal drought, grazing, non-native predators, and climate change.

Study of salmon and trout movement upstream and downstream of beaver dams, and how the dams effect them

Study of Coho Salmon rearing habitat in beaver ponds vs. non-beaver pools in Oregon

A review by the University of Southampton of how the reintroduction of beaver will affect fish in Scotalnd

Review of research about the positive and negative effects of beaver towards fish

An investigation into whether beaver dams impact the movement of trout

Article that investigates the relationship between beavers and coho salmon in the Mendenhall Recreational Area, Alaska

Manual of culvert design procedures for weak swimming fish

Large-scale experiment to quantify the benefits of beavers and beaver dam analogues to a fish population and its habitat