Qualitative and quantitative effects of reintroduced beavers on stream fish

Abstract

Reintroduction of beaver (Castor spp) may facilitate rehabilitation of freshwater habitats providing a cost‐effective sustainable means of improving ecological conditions. Despite extensive research, debate and consultation, a general consensus on the impact of beaver on fishes has proven elusive because of variability in biological response. This paper provides a systematic review of the impacts of beaver dams on fishes and fish habitat based on a meta‐analysis of the literature and expert opinion. Research is regionally biased to North America (88%). The most frequently cited benefits of beaver dams were increased habitat heterogeneity, rearing and overwintering habitat and flow refuge, and invertebrate production. Impeded fish movement because of dams, siltation of spawning habitat and low oxygen levels in ponds were the most often cited negative impacts. Benefits (184) were cited more frequently than costs (119). Impacts were spatially and temporally variable and differed with species. The majority of 49 North American and European experts considered beaver to have an overall positive impact on fish populations, through their influence on abundance and productivity. Perceived negative effects related to the movement of aquatic organisms in tributary streams, including upstream and downstream migrating salmonids, and the availability of suitable spawning habitat.

Ecological impact of Eurasian beaver (Castor fiber) activity on macroinvertebrate communities in Lithuanian trout streams

“…The most frequently cited benefits of beaver dams and the ponds they create are increased habitat heterogeneity, rearing and overwintering habitat, flow refuge areas, and invertebrate production [10].…”

A Geospatial Approach for Identifying and Exploring Potential Natural Water Storage Sites

“…Restoring wetlands, reconnecting incised streams to their floodplains through the removal of retired roads or railroads, and installing structures that mimic the ecological services provided by beavers are all examples of natural infrastructure-based methods of slowing runoff and promoting water retention in dewatered basins [15][16][17][18][19][20][21][22]. Previous research on the feasibility of wetlands and other natural infrastructures to attenuate flood and waste water has yielded promising results [14,[23][24][25][26][27].…”

“…Previous research on the feasibility of wetlands and other natural infrastructures to attenuate flood and waste water has yielded promising results [14,[23][24][25][26][27]. Beaver mimicry structures, for instance, can improve water quality and slow water flow, generate riparian vegetation, enhance channel stability and wetland hydrologic processes, deliver ancillary benefits to fisheries, and provide cost-effective natural storage opportunities [15][16][17][18][19]21]. Interflow and percolation of water from flood irrigation are critical to the existence of many wetlands in the West [28][29][30][31].…”

Riparian proper functioning condition assessment to improve watershed management for water quality

“…Presence of beaver dams increases hydrologic complexity and riparian width (Item 4) by influencing the formation of new meanders, pools, and riffles, and improved soil moisture conditions (Burchsted et al 2010), which facilitates riparian plant growth (Items 6 through 12). Increased complexity of streambed morphologic functions affects aquatic biodiversity (Briggs et al 2013;Smith and Mather 2013), including increased habitat heterogeneity, rearing and overwintering habitat, flow refuge, and water quality (Kemp et al 2012;Bledzki et al 2010). Where beaver dams are present, many implications for water quality depend on whether they are stable and Figure 1 Riparian area at risk of channel incision in background and incised in foreground.…”