26/2/2021

Environmental engineer or a waterway menace?

Our Head of Fisheries Dylan Roberts looks at the reintroduction of beavers into the British countryside and the consequences for the existing wildlife

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There has been much media coverage about the reintroduction of Eurasian beavers into the countryside, but are they clever engineers whose dams benefit other species or are they a waterway menace? Beavers became extinct in the UK in the 16th century, and almost extinct in the rest of Europe, mainly because of hunting for their fur, meat and ‘castoreum’, a secretion used in perfumes, food and medicine.

Over the last 60 years they have been reintroduced into a number of EU countries, and were reintroduced into Scotland as part of a trial at Knapdale in 2008, where they were granted legal protection status in May 2019. In recent years, beavers have been reintroduced into England under licence from Natural England (NE) mostly in enclosed (fenced) environments. Several ‘wild’ populations have also illegally established, including one in the River Otter in Devon, which was subsequently licensed as an unenclosed, five-year trial to assess the likely impacts (positive and negative) on riverine ecosystem functioning and biodiversity. The GWCT has sat on both the Management and Fisheries sub-groups of the River Otter Trial since 2016.

Beavers are large powerful rodents weighing up to 30kg and live in the deep pools of rivers and lakes. However, if there is no deep water available, they will create deep water by building woody dams, which tend to be on small rivers and streams less than 10 metres wide. They build a main dam where they also construct a ‘lodge’ to live and breed, and then build subsequent dams upstream to ensure that they have long lengths of continuous deep water to access the bank for feeding. Dams are created by cutting down trees, cutting branches and pulling them into the water and made watertight by puddling the upstream side with mud. Dams vary considerably in height from a few inches to over six feet and the subsequent ponds and deep glides can cover large areas.

Their preferred diet is willow, but if it is unavailable, they will cut down and feed on the succulent small branches of most trees and shrubs. As they are rodents, their teeth continually grow, so they will also target the bark of very large hard wood trees such as oak and beech to gnaw. The change in river structure to ponds and deep glides has many benefits for wildlife. They create habitats for pond loving creatures like frogs, newts, waterfowl, wetland plants and fish such as minnows, sticklebacks and lamprey. The ponds can also store sediment and the associated nutrients which are often washed in from ploughed farmland, which can be detrimental to a river’s ecology.

Understanding the challenges

Although there are benefits, beavers also come with a number of challenges and can cause problems to agriculture and forestry where land and crops can be flooded, and trees are felled or damaged. They can burrow into flood defences and the debris from their dams can block flood relief culverts and small bridges. They can also be territorial and aggressive, particularly between May and July when they have young, and attacks on dogs and even people have been recorded. In addition, there can be negative impacts on fish.

Most salmon and sea trout populations in England and Food and Rural Affairs, Defra and Natural England who Wales are under severe pressure and classified as ‘at risk’ by the Environment Agency and Natural Resources Wales. Beaver dams can often prohibit their access into important breeding areas in the tributaries of rivers and also unfavourably modify their nursery habitats. Consequently, in many countries, beavers are actively managed to control numbers and mitigate impacts: in Latvia and Lithuania (respectively 25% and 15% of the area and population density of the UK) beaver populations are 70,000-120,000, and 20,000 to 30,000 are culled (shot) annually under a hunting licence.

The River Otter Beaver Trial

The River Otter Beaver Trial (ROBT) has now reported to Natural England and Defra and we feel that its beaver management process is flawed from a fisheries perspective. The trial was also too narrow in scope to provide robust evidence to inform decisions on further unenclosed reintroductions, and too short to understand the full implications of reintroducing beavers into open catchments. The emphasis was on benefits from beavers to the rural economy and ecotourism, and in providing nature-based solutions to flooding, but not on biodiversity loss arising from construction of dams and other beaver activities.

Given our concerns, particularly on the impacts of their dams on migratory salmonids, we are working with the Angling Trust, Salmon & Trout Conservation, Atlantic Salmon Trust, River Otter Fisheries Association and the South West Rivers Association. We collectively commissioned Professor Ian Cowx (University of Hull International Fisheries Institute) to independently review ‘wild’ beaver impacts on salmon, trout and sea trout with particular reference to UK rivers, including the published science and evidence report from the ROBT. Professor Cowx’s report is now published and has been sent to George Eustice, the Secretary of State for the Environment, Food and Rural Affairs, Defra and Natural England who are due to open a consultation in spring 2021.

Looking to the future - the GWCT position

Based on the report produced by Professor Cowx our position is:

  • Managing beavers and their dams for fish conservation needs to be an integral part of any future beaver management strategy.
  • There is currently insufficient scientific evidence to develop a robust strategy to manage interactions between beavers, their dams and fish.
  • There needs to be fully funded research, including telemetry studies, on the upstream and downstream possibility of a range of dam types, including cascades of dams, and for a full range of species.
  • There should be a cessation of open and enclosed beaver releases until a funded management strategy based on research is produced.
  • Any future management strategy should be simple, low in bureaucracy and similar to other species like deer and foxes.

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