The Tweed Foundation

While Beaver are still to colonise major salmon areas in Europe, the control of Beavers is a major fisheries management issue in North America, where there is a large overlap between Beaver and Salmon. Many reports of the work needed to remove Beaver dams or discourage Beavers from building in particularly sensitive areas can be found online:- search for “Beaver” and “Fish Passage” for example.

The  North Atlantic Salmon Conservation Organisation (NASCO) Plan of Action for the Application of the Precautionary Approach to the Protection and Restoration of Atlantic Salmon Habitat CNL(01)51 includes the inventorying of  “A range of factors/activities that may adversely affect the productive capacity of a river”. These factors / activities are listed in a Table that includes:-

Impact on Salmon Habitat

Activities That Could Cause These Impacts

Physical

Injury to fish, impaired access to spawning habitat and production areas, impaired outmigration to marine environment.

    Man-made dams,
    culverts,
    Beaver and debris dams    ,
    bridges,
    weirs,
    turbines,
    screens.

Beaver dams are therefore regarded by NASCO as having the same sort of potential to impact on Salmon as any other instream structure. All the member states of NASCO, including Norway and Sweden, should follow this advice.

In Sweden Beaver dams are not generally considered a problem. However when hydro dams were built on their main rivers in the early 20th century, fish passes were not generally built at dams, blocked nursery areas being “replaced” by hatcheries. This greatly reduced the extent of wild salmon populations.

A web search for “Beavers” and “Fish Passage” gives thousands of results and turns up many reports on work that has had to be done to ensure fish passage past Beaver dams. It is clear from these that problems are so common that such work is routine rather than a matter for research – to the extent that there are commercial companies offering the equipment needed for the various techniques that have been developed to  try and solve such problems. It is not just fish passage, of course, that requires work at Beaver dams – road culverts are regarded as being useful, narrow, points in streams for dam building by Beavers, leading to the flooding of roads and property. Judging the issue by the number of studies on Beaver dams and fish passage in the scientific research literature is therefore misleading.  Similarly, if a web search for “Weirs” and “Fish Passage” is carried out, thousands of results are again found, showing problems to be widespread, but few papers on weirs and fish passage are published in the research literature, again because the issue is a routine fisheries management issue rather than a research one.

Whilst this paper has been prepared by The Tweed Foundation on the basis of information that it believes is accurate, any party seeking to implement or otherwise act on any part or parts of this paper is recommended to obtain specialist advice. The Tweed Foundation does not accept responsibility under any circumstances for the actions or omissions of other parties occasioned by their reading of this paper.