Argyll Fisheries Trust
"To promote and improve the health of aquatic ecosystems and self sustaining fish populations. To understand the biology and ecology of all freshwater fish species, including those that migrate between fresh and marine waters, their environment and factors that affect them"
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Argyll Fisheries Trust News

Friday, 8 February 2008

The Scottish Beaver Trial 2007 / 2008

The proposed trial re-introduction of the European beaver (Castor fiber) to Knapdale by the Scottish Wildlife Trust (SWT) and the Royal Zoological Society of Scotland (RZSS) as gone through a two month public consultation process. This consultation found around 70% of respondents to be in favour of the proposed trial and an application has now been made to the Scottish government to release up to 20 beavers to the area.


The European or Eurasian beaver is a large, semi-aquatic rodent which was hunted to extinction in Britain in the 16th century. The European beaver is a ‘keystone’ species and its re-introduction is thought to be beneficial to a wide range of species. The European beaver inhabits riparian broadleaved woodland bordering freshwater and is totally herbivorous, and will feed on a wide verity of herbaceous and woody species.
Unlike its American counterpart European Beavers favor burrowing in to banks as opposed to building lodges. Where ground is unsuitable for burrowing the European beaver will build lodges or use a combination of both burrow and lodge. European Beavers will dam streams when conditions are unfavorable to maintain water levels and create large areas of slow moving water. Beavers will also construct canals which allow them to travel away from the main body of water.

The Argyll Fisheries Trust’s comments to the Scottish Wildlife Trust

The AFT is supportive of a vision of attaining healthy aquatic wildlife communities in Argyll, which historically may have included European Beaver. The proposed trial re-introduction of the beaver raises some major concerns for freshwater fish populations, particularly at a time when native Atlantic salmon, sea trout and European eel populations are at low abundance relative to known records in Argyll. Atlantic salmon and River lamprey are afforded protection under the European habitats Directive and both Atlantic salmon and brown trout (including the migratory form, the sea trout) and are also noted as important species in the Argyll & Bute Local Biodiversity Action Plan. On this basis, we urge that the concerns of fishery management groups over the proposed trial are given due consideration.

Our concerns are both specific to the proposed trial release site, which has limited potential for interaction with migratory fish, which may not provide a representative view of the potential impact on fish populations upon which to assess the proposed trial and also the further distribution of beaver outside this site both during and post the trial period. The main reasons for our concerns are based on two characteristics of beaver behaviour;

Distribution of salmonid and other native fish

Research from Sweden, Norway and Baltic states indicate that beaver are likely to construct dams in certain habitat types, which have a known potential to restrict salmon, trout, eel and lamprey distribution, restricting access to habitats they require to complete their life-cycles. For example, in the Lithuanian National Report of the 31st May 2006 to the Baltic Sea Trout workshop, “Beaver activity” was listed as a threat to Sea trout stocks in four rivers. This proven potential to reduce the productivity of native fish populations and associated fisheries will require both strict supervision of the beaver during the trial and significant resources employed to predict likely beaver colonisation patterns and management of post-trial colonisation of new habitats. This management is likely to require considerable resources, which are not currently available within the fishery management sector.

Changes in riverine habitat characteristics

While the beaver is understood to ‘manage’ riparian woodland habitats, which may be beneficial to a range of aquatic wildlife, there is also potential for significant changes in the distribution and abundance of habitats suitable for salmonid and other native fish recruitment. Construction of dams are understood to increase the abundance of open and relatively slow flowing deep water habitats and decrease the availability of fast flowing shallow water habitats that are suitable for salmonid fish spawning and early juvenile fish life-stages. Significant changes in the distribution of habitats favourable to early life-stages of salmonid fish have potential to reduce productivity of salmon and trout populations and possibly promote habitat characteristics preferred by non-native species, such as minnow and other coarse fish species. While the increased amount of deeper water produced in smaller streams by Beaver dams is often stated to be an advantage in that adult trout can inhabit such ponds, this is of no benefit to migratory Sea-trout populations as the resident “Brown-trout” element of such populations is largely (and in some cases, wholly) male. In such populations it is much more important that the females from the sea get as far up their spawning burns as quickly and easily as possible compared to providing relatively few resident, male brown-trout with some deeper water in which to live.

The longer-term potential for beaver to change the distribution and productivity of a number of native fish species (and related fisheries) requires further research and monitoring to be undertaken at a local (Argyll) and national level. Experience from Bavaria is that Beaver are not much limited by lack of their prime habitat, as the effect of their dam-building is to modify sub-prime habitat to suit their needs - even agricultural drainage ditches have been utilised by Beaver there. Beaver released into the wild are therefore, on Bavarian experience, likely to spread widely throughout Scotland, colonising a very wide range of watercourses and living in urban as well as rural areas. Given the current modelling information of beaver distribution in Scotland predicts relatively low numbers of families to become established, it will be necessary to re-evaluate this information in light of what has been experienced in other countries where re-introductions have taken place.

As the beaver’s effects on the physical form and hydrology of streams is so profound, their introduction is likely to have very significant impacts on fisheries (and flood prevention) throughout the country, so very great care needs to be taken in setting up and assessing any trial. Improved modelling techniques will be required to provide a realistic estimate of the resources required to manage beaver populations in relation to maintaining productive fisheries.

It should also be noted that there is evidence from Estonia is that the ponding back of water behind Beaver dams would eliminate any populations of Pearl Mussel (Margaratifera margaratifera) covered by such deepened water. Given the fragile conservation status of this iconic Scottish freshwater species the effect of Beaver ponds on them should be given particular attention.

Therefore, we recommend that within the proposed trial period there are sufficient resources made available by the project at a local and national level to fully investigate the likely distribution of beaver at these scales and predict likely affects on freshwater habitats and associated fish populations. A list of questions to be answered by such a trial can be provided by RAFTS (Rivers and Fisheries Trusts of Scotland). It will also be necessary for project managers to provide the criteria upon which the trial will be assessed prior to introduction so that all factors are given fair consideration at the end of the trial period. Further to this, it will be important to provide a realistic guide to the likely management activities and their associated costs required to avoid significant impact on migratory fish and other aquatic wildlife before the end of the project.

Further details on the re-introduction of the European beaver and a copy of the consultation report can be found at