Beavers boost fish populations, says study

Beavers are beneficial for migratory fish as they help improve water quality and could help fish populations to grow, according to the initial findings of new research.

 

20th November 2015
Photo credit: iStock

The University of Southampton is looking at the effect beavers have on other species, including migratory fish such as salmon and trout. In their initial findings, researchers found that in addition to boosting fish populations that beaver dams do have a positive impact on wetland ecosystems and could also help prevent flooding.

While there are still many questions about the impact of beavers on fish migration to be answered, working with Scottish Natural Heritage, the Game and Wildlife Conservation Trust, and the Salmon and Trout Association, the reseachers aim to close this knowledge gap.

Speaking to BBC Countryfile Magazine, Principal Investigator of the study, Professor Paul Kemp said that the key findings had so far shown that beavers offer a positive impact for fish and other forms of wildlife.

Professor Kemp said: “Beavers have created a series of dams on the modified river, which has increased the amount and diversity of habitat for the local trout. 

“As a result the abundance of trout is substantially higher in the beaver modified stream, and what is more the trout in the ponds tend to be much larger than in the control stream.  We are also seeing a greater number of other species, such as stickleback.”

However, concerns have also been raised that beavers, and the dams they construct could have a negative impact on fish, particularly salmon and trout, as the dams hinder fish migration and affect the natural habitat.

Mark Lloyd, Chief Executive of the Angling Trust & Fish said: “We remain opposed to beaver re-introductions for the time being because there are great risks involved and many fish species in our rivers are under severe threat.

“One of the key problems fish face is the 26,000 man-made barriers to fish migration which cumulatively, can prevent fish moving up and down rivers to complete their lifecycles.

“Nearly all fish need to migrate within rivers to enable them to thrive.  Until these barriers are removed and made passable to fish, we feel that introducing many new dams into rivers is too risky.”

While the research found that beaver dams impede the upstream movements of the trout under low flow conditions, they found this to be a temporary obstruction.

Professor Kemp said: “The dams can create quite a significant impediment under low flow conditions.  However, this appeared to be only temporary, and when the rains came the waters rose and many more fish were observed to pass the dams.

“In reality, dams are more porous than they might at first appear, with temporary channels around the side, and if the difference in water levels are not too great the trout can jump over them.”

Devon Wildlife Trust (DWT), which is running the River Otter Beaver Trial and working with Professor Kemp’s team to understand how these impacts might translate in a lowland English river said that they anticipate that beavers will help wetlands and fish populations. 

Mark Elliott, the Beaver Project Lead for DWT said" “Many fish populations are under enormous pressure and we anticipate that beavers will help alleviate some of these issues, providing a greater range of habitats, regulating flows and improving water quality which should benefit the whole river ecosystem.

"In the event that we see any beaver dams on the river Otter we will be monitoring their impacts on the water environment including fish and their invertebrate prey in great detail.”

Read both side of the debate: Mark Lloyd of the Angling Trust's five reasons why beavers should not be reintroduced in Britain and Mark Elliott of the Devon Wildlife Trust's five reasons why beavers should be introduced into Britain's rivers. 

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