Tim Bonner: Beavers build better brown trout

A new study has found that brown trout are more numerous and larger in upland streams that have been adapted by beavers. The research, carried out in Scotland by scientists from Southampton University with support from our colleagues at the Game and Wildlife Conservation Trust, found that by building dams the beavers create deeper pools which increase both trout habitat and food supply. The research focused on two streams running into the same Scottish loch, one of which had five beaver dams whilst the other was unmodified.

Beavers are returning to the British countryside, by one means or another, at an increasing rate. Whilst they seem unlikely to fully deliver the transformational benefits promoted by their more enthusiastic advocates, they are undoubtedly a welcome returning species and this study does point to some obvious benefits for fishermen. What is less certain - and of understandable concern - is what impact they will have on migratory salmon and sea trout. These species are already under serious pressure as a result of habitat degradation, salmon farming, predation and at sea exploitation. More research will be required to study river adaptation by beavers and a precautionary approach taken to the release and management of beavers until its impact on migratory salmonoids is clear.

The recent return of species like otters and red kites to the British countryside, having been extinct in most of it, has revived conflicts that have been dormant for decades. Fisheries have had to invest in mammal-proof fencing and keepers think carefully about habitat creation to protect ground nesting birds from avian predation. The beaver has been absent from our landscape for far longer than the otter or the red kite, for centuries rather than decades, so where such conflicts might arrive is much less certain. Research will be key to identifying issues and mitigating any negative impacts.

That research is happening now and will hopefully build confidence that the beaver can return to rivers across the country without harming other species, especially those that are already vulnerable. What is not helpful is the suggestion of "guerrilla reintroductions" as unregulated transport and release of species has become known. One prominent advocate of the guerrilla approach recently posted on social media that he had bought a box of grasshoppers, intended as reptile food, at a pet shop, and released them on his Devon farm. Embarrassingly it was pointed out to him that the grasshoppers in question were actually an easily-grown Asian strain, rather than a British grasshopper. Far from reintroducing a native species he had actually released a potentially invasive alien. That experience should reinforce the need for a carefully and regulated approach to the reintroduction of the beaver and other species that have been absent from the British Isles. We have sadly been without beavers for 400 years. There should be no issue with managing their reintroduction over just a few more, whilst ensuring that there are no fundamental impacts on other species.