A study, part-funded by the Game & Wildlife Conservation Trust, has found that modification of river habitat by Eurasian beavers helps fish in small Scottish upland streams.

The project was led by the University of Southampton, in collaboration with the GWCT, Salmon and Trout Conservation, and NatureScot.

Dylan Roberts, head of GWCT Fisheries, said: “We welcome the results of this much needed UK based published work to inform what is currently a very topical debate.”

The research shows that, by building dams in shallow streams, the beavers create deeper pools that increase availability of suitable habitat and abundance of food – benefiting brown trout, which are a commercially and ecologically important species.

As a result of beaver activity, the trout tended to be larger, having grown well throughout the year, with the largest and most mature fish, that are of greatest interest to fishermen, being much more abundant. In beaver modified habitat, the trout also benefit from the provision of sanctuary from predators.

The research, published in the Canadian Journal of Fisheries and Aquatic Sciences, monitored the fish that inhabited two Scottish streams that flow into the same loch.

One stream was modified by beaver activity through the construction of five dams, while the other was left unaltered, providing a unique opportunity to compare the influence of beaver habitat modification on fish.

The University of Southampton’s Professor Paul Kemp, the project lead, said: “This is the first published research of its kind conducted in the UK. Most of our understanding of beaver-fish interactions is based on North American studies which involves a different species of beaver, and different species of fish. The results of this study are important because it is hoped that they will allay fears expressed by some representatives of fisheries interests that beavers may be damaging to fish stocks.”

The study’s findings are significant because reintroductions and natural re-colonisations are gaining pace in Scotland, England and Wales.

The GWCT’s Dylan Roberts, continued: “The fact that numbers of larger trout responded positively to pools created by the beavers is good news. However, there is still much to learn to see if their dams impede the upstream migration of adult salmon and trout on their way to spawning grounds and the downstream migration of juvenile fish.”