Beavers benefit fish by building dams in Scottish rivers

Beavers benefit fish by building dams in Scottish rivers - University of Southampton

Image: Beaver dam in Scotland. Credit: R Needham

Modification of river habitat by Eurasian beavers helps fish in small upland streams, according to a new study led by the University of Southampton.

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, conducted by scientists at the University of Southampton, and published in the Canadian Journal of Fisheries and Aquatic Sciences, monitored the fish that inhabited two Scottish streams in Inverness-shire 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.
PhD student Robert Needham, from the International Centre for Ecohydraulics Research at Southampton, explained: “There has been a great deal of concern about the possibility of beaver dams blocking the upstream and downstream migration of Atlantic salmon and trout as they move to and from their spawning grounds, as well as impacting habitat quality. This study explored how brown trout respond to beaver activity.”

Read the paper ‘The response of a brown trout (Salmo trutta) population to reintroduced Eurasian beaver (Castor fiber) habitat modification’