Modelling Eurasian beaver foraging habitat and dam suitability, for predicting the location and number of dams throughout catchments in Great Britain

Abstract

Eurasian beaver (Castor fiber) populations are expanding across Europe. Depending on location, beaver dams bring multiple benefits and/or require management. Using nationally available data, we developed: a Beaver Forage Index (BFI), identifying beaver foraging habitat, and a Beaver Dam Capacity (BDC) model, classifying suitability of river reaches for dam construction, to estimate location and number of dams at catchment scales. Models were executed across three catchments, in Great Britain (GB), containing beaver. An area of 6747 km 2 was analysed for BFI and 16,739 km of stream for BDC. Field surveys identified 258 km of channel containing beaver activity and 89 dams, providing data to test predictions. Models were evaluated using a categorical binomial Bayesian framework to calculate probability of foraging and dam construction. BFI and BDC models successfully categorised the use of reaches for foraging and damming, with higher scoring reaches being preferred. Highest scoring categories were ca. 31 and 79 times more likely to be used than the lowest for foraging and damming respectively. Zeroinflated negative binomial regression showed that modelled dam capacity was significantly related (p = 0.01) to observed damming and was used to predict numbers of dams that may occur. Estimated densities of dams, averaged across each catchment, ranged from 0.4 to 1.6 dams/km, though local densities may be up to 30 dams/km. These models provide fundamental information describing the distribution of beaver foraging habitat, where dams may be constructed and how many may occur. This supports the development of policy and management concerning the reintroduction and recolonisation of beaver.

Alternative perspectives of the angling community on Eurasian beaver (Castor fiber) reintroduction in the River Otter Beaver Trial

“…We suggest that an open dialogue about the scientific research about beavers and fish, their effects on the wider ecosystem and how beavers can be managed will go some way toward reducing the potential for future conflicts. We exemplify this approach ourselves by ensuring that all beaver research papers that we have produced are available open-access to all (Puttock et al 2015;Puttock et al 2017, Campbell-Palmer et al 2018Puttock et al 2018, Auster, Puttock, andGraham et al 2020). Even more-so, we argue that a management strategy which supports the possible biodiversity and ecosystem benefits of beaver reintroduction whilst providing a sense of empowerment to respond to possible negative impacts could help to reduce potential future conflict risks.…”

Beaver: Nature's ecosystem engineers

“…2%) and perhaps negligible at the catchment outlet. However, Neumayer et al (2020) modeled the impacts of beaver dams on channels larger than those that other research has shown might support the greatest densities of dams (i.e., Graham et al, 2020 show that dams rarely persist on >fifth-order streams) and thus it is suggested that further modeling work is required into the downstream hydrological impacts of small streams with high dam densities. In addition, further research is required to understand what the cumulative catchment outlet effects might be if beavers return to being widespread and catchments contain multiple dam sequences (i.e., hundreds of dams) in all headwater streams.…”

“…There are, however, a number of challenges experienced where beaver and humans interact. In Europe, these are observed mostly where beaver impacts interact with human interests within the riparian zone (Campbell‐Palmer et al, 2016; Halley et al, 2012; Heidecke & Klenner‐Fringes, 1992), particularly in upper and marginal reaches of watercourses where beaver will undertake the largest‐scale habitat alteration (Graham et al, 2020; Halley et al, 2012). For example, where water is stored behind beaver dams, it may inundate land owned by humans which could lead to a financial cost, especially when associated with agriculture or forestry (Campbell‐Palmer et al, 2016; Gaywood et al, 2015; Morzillo & Needham, 2015; Parker et al, 1999).…”

Beaver dam capacity of Canada’s boreal plain in response to environmental change

“…Some of the parameters the BRAT model does not account for are wet and dry cycles, common in the boreal plain 18 , or the fine-scale variations in habitat features, like the presence of deep pools 51 , that are important in influencing the number of dams a beaver colony will build along a stream reach at any time. Some of these challenges may be overcome by calculating the probability of dam construction within a Bayesian framework, such as was recently carried out in Graham et al 52 . Also, beaver in Riding Mountain National Park compete with ungulates (primarily moose and elk) for woody resources, which would limit their population and thus ability to build dams 53 .…”