August 9, 2012
Do Beavers Benefit Wild Salmon In Scotland?
redOrbit Staff & Wire Reports - Your Universe Online
According to a study by the University of Southampton, reintroduced European beavers could have an encouraging impact on wild salmon populations in Scotland.
Due to their dam building activities and potential to block migratory life phases, representatives from recreational fisheries north and south of the border are concerned that beavers can harm economically important fish stocks. However, results of a study conducted by scientists at the University of Southampton, funded by Scottish Natural Heritage, have indicated that the substantial beneficial effects from the beaver might outweigh the negative ones.
According to the study, "While the activities of beavers can result in localised and often temporary negative impacts on fish, primarily due to dams impeding their movements and reducing the availability of suitable spawning habitat, these can be at least off-set by the benefits of increased habitat diversity and resulting abundance and productivity of fish, including salmon."
"The positive findings were more frequently based on quantitative evidence, while discussion of negative impacts was often speculative," commented Dr. Paul Kemp, a researcher in freshwater fish ecology and fisheries management from the University's International Centre for Ecohydraulics Research who led the study.
Considering the background of those who participated in the survey, Dr. Kemp and his colleagues were surprised that the "weight of evidence" tended to indicate an overall positive effect. "Most participants were from a fisheries background and whom you might expect would tend to side with the fish, but based on their experience of beaver and fish interactions tended to be positive towards beaver," he says.
Ever since a total of 16 beavers from Norway were released in Argyll in 2009 and 2010, beaver reintroduction has been a contentious issue in Scotland. This was part of a scientific trial conducted by the Scottish Wildlife Trust, The Royal Zoological Society of Scotland, and the host partners, the Forestry Commission Scotland.
An establishment of a breeding population of escaped beavers on the River Tay is surrounded by more controversy. This has caused problems south of the border as the Angling Trust has written to Richard Benyon, the UK minister for Fisheries and the Natural Environment, asking that trapping and destruction of the beavers be urgently undertaken to prevent their spread to England where it is claimed they could damage fisheries.
A critical view of over 100 sources of peer-reviewed information in which benefits were cited 184 times compared to 119 for the negative effects was carried out by researchers. Beaver activity can have both positive and negative effects on fish according to the analysis of existing literature. Siltation causing loss of spawning habitat immediately upstream of dams and the construction of beaver dams which can temporarily impede the movement of some fish, particularly in narrow rivers and streams, are some negative effects.
Beavers can also have beneficial effects on fish by increasing the variety and area of habitats in streams. Also the presence of dams and ponds increases the amount of invertebrates, which are the main source of food for many stream-dwelling fish, and provide refuge during periods of high or low water flows.
The study also reports the findings of an expert opinion survey of 49 fisheries managers, scientists, and beaver ecology experts, from Europe and North America, where most of the research has been conducted. 58 percent (more than half) of those who responded think that the overall impact of beavers on fish populations was positive. The study was published in the leading international fisheries journal Fish and Fisheries.
Professor Roger Wheater, the Chair of the Beaver-Salmonid Working Group, says: "I would be very surprised if biodiversity were not increased but our concern continues to be the impact on salmonid spawning areas and the management required to deal with situations where salmonids in any particular system are at risk."