Wildlife re-introduction projects are becoming more prevalent. Good monitoring goes a long way towards allying community concerns when it comes to ecologically important – but socially questioned – wildlife management.
The European beaver (Castor fiber) was once found in watercourses throughout Britain. Over-hunting led to its extinction, which – although not precisely recorded – likely occurred in the late 18th Century.
The beaver is recognised as a keystone species – having a disproportionately large effect on its environment in relation to its own abundance. Their well-known waterway engineering creates habitats and entire ecosystems – and the prehistoric British landscape, and its riparian-dwelling plants and animals – evolved within such environments.
Removal of the beaver and subsequent major alterations to British hydrology led to the development of a highly productive agricultural landscape – at the expense of riparian wildlife.
In 2009, the Scottish Beaver Trial was the first such enterprise to re-introduce beavers to the British landscape. Following this, several such trials have been implemented.
In February 2015, the Devon Wildlife Trust issued a licence for the River Otter Beaver Trial (ROBT) to release beavers into the wild. This followed the discovery of a wild breeding group of beavers living on the River Otter in East Devon.
As part of a campaign supporting the retention of these wild beavers, the re-introduction project aimed to assess the impacts of beavers on the Otter catchment; its wildlife, local economy and people. Scientific assessment of these factors was hoped to provide a sound evidence base in order to determine the future of the population.
A robust monitoring programme was designed to assess the positive and negative impacts of beavers in the River Otter Catchment, and the five-year study was implemented.
Monitoring Programme Results
With the set term ending in March 2020, the results offer future guidance on beaver re-introductions in Devon – with outcomes pertinent to the rest of the United Kingdom.
The study has shown that the beaver population in the River Otter Catchment is increasing, and 13 separate territories were identified by 2019; stemming from the two family groups that founded the project in 2015.
The population has dispersed through the River Otter and smaller River Tale, as well as lesser tributaries – and shows that the Catchment can support a self-sustaining beaver population.
This population expansion has led to 28 beaver dams recorded in 2019 – predominantly in smaller tributary streams as the main stem of the Otter River is too large. The Tale experiences temporary, dynamic dams which are washed out in seasonal high flows.
Of the 594 kilometres of watercourses within the Catchment, 1.9 kilometres (representing 0.3% of waterways) were impounded by beavers when assessed in October 2019.
This activity has of course impacted surrounding land use to some extent. Management of several spillways, culverts, agricultural land and waterways close to roads and access tracks has been required to keep water levels at acceptable levels.
In one instance, riverside orchards were impacted by the feeding behaviour of beavers, as well as maize crops – which could be managed with minor visual disturbance to the areas (from such devices as tree guards).
Several trees were also felled over public footpaths and subsequently cleared.
As for benefits gained, beaver activity has delivered significant ecological benefit – with new wetland habitat created and managed. This in turn has benefited amphibians, wildfowl and water voles.
Fish abundance was found to be 37% higher within a beaver dam pool on the River Tale, as compared to upstream and downstream sites. Increases in minnow and lamprey populations were observed. Comparatively, the habitat and flow dynamics formed by washed-out dams created favourable habitat for juvenile trout.
It remains unknown as to the impact of dams on migrating salmonoids in the Catchment; however trout were observed navigating past dams during high flow events.
One village at risk of flooding saw a reduction in peak flows due to a series of dams constructed upstream, which spread water over the floodplain.
The results of the five year monitoring program show that the costs of beaver activity – while present and requiring acknowledgement and management – were outweighed by the benefits provided to ecosystems and communities.
It’s recognised that, at a catchment scale, the benefits incurred can accrue at the same locations as the cost (in such examples as biodiversity gains due to wetland creation) but also in other locations (such as flood threat reduction downstream of dams). This is of importance as those who benefit most from a factor mightn’t be the ones bearing the cost.
Increasing public acceptance of the beaver re-introduction project was also shown through the monitoring. This is a positive outcome showing that attitudes can and do change in regards to wildlife management – as long as information is accurately collected and demonstrated to those concerned; and appropriate management is put in place.
Joe Brennan