The Dam Builders: Beavers are Back!

The Beaver Trust has announced that two beavers have built the first dam in Exmoor in 400 years, creating an instant wetland that has already attracted kingfishers! And in August, 15 Eurasian beaver families were given permanent ‘right to remain’ on the River Otter in Devon - the first time that the government has backed the reintroduction of an extinct native mammal in England. The perfect time to take a look at beaver reintroduction across the UK...

A beaver as startled as me at good news in 2020. Photo by Steve Raubenstine

A little bit of history

The Eurasian beaver, Castor fiber, was native in England, Scotland and Wales until 400 years ago, having been hunted to extinction here for its thick waterproof pelt, meat and castoreum (a secretion used in perfume, medicine and food). Widely hunted across the rest of its territory too, by the beginning of the 20th century the Eurasian beaver had become critically endangered, with just 1,200 individuals left in 8 isolated populations across Europe and Asia. Thanks to conservation efforts involving more than 200 reintroductions and translocations across 25 European countries in the second half of the century, beavers had become widespread across Europe once again by the 90s, but had still not been reintroduced to Great Britain.

British beavers

After more than a decade of planning, the first British beavers were reintroduced to Scotland in 2009, where there are now more than 250 of them. This established population is now being used to provide breeding pairs to projects in Wales and England. The beavers on the Exmoor estate were relocated from wild populations on the River Tay and were the first beavers to be released by the National Trust, as part of its Riverlands project to "bring UK rivers back to life". As well as these two dam-builders, pairs have also been released by regional wildlife trusts in Cheshire, Cumbria and Norfolk, with plans for a Derbyshire release too. In July, there was a huge boost to the reintroduction effort with the news that a couple released in Essex in 2019 had bred, with 2 healthy kits spotted with their parents!

These various formal reintroduction projects have been given a helping hand though by wildlife activists; the beavers given the right to remain on the River Otter were not initially part of an official trial. Video surfaced of a beaver with young in 2013 - the first evidence of wild beavers breeding in England in modern times - with no one knowing how they came to be there. Although it is suspected that they were released illegally by so-called beaver bombers, the Devon Wildlife Trust, working with the University of Exeter, managed to persuade the government to run a 5-year study on the population. There are now at least 50 beavers (both adults and kits) on the river which are now not only allowed to stay, but protected.

Beaver swimming with an apple. Photo by Niklas Jeromin

Beaver-cology

Beavers are what are known as a keystone species, that is they have a disproportionately large effect on their environment relative to how many of them there are. They are natural engineers, gnawing down trees and using these logs as well as debris they find nearby to build dams in streams, creating small ponds. They also build themselves complex homes, known as lodges or burrows, with underwater entrances.

With their big rudder-like tails, webbed feet and double eyelids, which act like goggles, they are most at home in the water, but it's not only the beavers themselves that benefit from their dams. The ponds and wetlands created offer many animals shelter and protection from predators, as well as slowing water flow which can help prevent flooding downstream and create reservoirs.

Beavers dams increase biodiversity through the creation new habitats; a 2018 study found that beaver-dammed ponds are even more biodiverse than other wetlands, thanks to the variety of habitats the beavers create through different activities, such as gnawing down trees and grazing plants (1). In Exmoor, scientists have already spotted kingfishers at the new dam and expect to see frogs, insects, bats and even more birds in the future as the beavers expand the network of dams and pools. The River Otter trial showed that over the 5 years, the beavers enhanced the ecology of the river, improving water quality (2). This cleaner, clearer water is thought to be what attracts birds such as kingfishers because they can fish better, and is also responsible for the increase in fish biomass.

Apart from the benefits to biodiversity, there are other potentially huge benefits to humans in terms of flood prevention downstream. Dams slow the flow of water and create additional tributaries to further spread the water to prevent inundations further on that cause flash floods. As the risks of flooding increase with climate change, due to more extreme weather events and sea level rise, it will become ever more important to work out how to work with the land and with nature to prevent catastrophic damage to human settlements. Beavers are a great example of showing how nature can hold its own solutions. Not only do they create the dams by themselves, with all their associated benefits, but they do maintenance work for free too!

Nibbling beaver. Photo by Bruno /Germany from Pixabay

Contra(bea)versies

Although many scientists back the reintroduction of beavers, there are certain communities that are not so happy, particularly anglers and some farmers. Although beaver activity can lead to a general increase in fish biomass, some anglers believe that it can make it harder for game fish like North Atlantic salmon and sea trout to reach their breeding grounds, with the dams acting as obstacles they can't get pass. The National Union of Farmers are concerned about the damage that beavers might do to trees and crops, and also that there could be undesired localised flooding around the dams.

In Scotland, these concerns have led to Scottish Natural Heritage granting licences to cull around a fifth of the established beaver population there, despite the beavers being given protected status in 2019. While SNH claim that the beavers are established and breeding enough for this not to threaten the beaver population as a whole, the Scottish Wildlife Trust has raised concerns at the level of culling. They urge SNH to consider relocation of beavers from areas where they have come into conflict with farmers to low-conflict areas, rather than culling them, which brings us nicely to some other suggested ways round these issues.

A benefit of Great Britain being one of the later countries to reintroduce beavers means we can learn from other countries who have had established beaver populations for much longer, like Germany and Norway. This includes individual measures, such as coating trees with a sand mixture or wrapping them with wire mesh to prevent gnawing, as well as initiatives like creating buffer zones between farmed land and beaver habitat to reduce conflict between farmers and beavers.

At a larger scale, planning to make sure beavers are reintroduced to the right places will be a huge determinant of how successful beaver reintroduction is. In terms of the anglers' concerns, for example, planning should ensure that routes for salmon and trout to reach their breeding grounds are not blocked. It is worth noting here that The Beaver Trust believes that beaver dams do not block travelling fish, thanks to side streams and rivulets around the dams, but it will be important to continue monitoring this.

The beaver reintroduction is just one of a number of reintroduction projects happening at the moment in the UK, but it is perhaps the most well-known, and certainly has a charismatic poster animal. It is therefore incredibly important to get the support of the general public, and take the concerns of landowners, farmers and anglers seriously. It is not just scientific evidence that will make this reintroduction project a success, but tangible benefits to the people that own, manage or live in these landscapes.

1. Willby, N.J., Law A., Levanoni, O., et al. Rewilding wetlands: beaver as agents of within-habitat heterogeneity and the responses of contrasting biota. Phil. Trans. R. Soc. B 373, 20170444 (2018) https://doi.org/10.1098/rstb.2017.0444

2. Brazier, R.E., Elliott, M., Andison, E., et al. River Otter Beaver Trial: Science and Evidence Report (2020)