The Tweed Foundation

THE TWEED FOUNDATION

FAQs

These are the Frequently Asked Questions about Beavers and Fish and the answers that are already known. Click more to read more detailed answers where these exist.

1

Do Beavers eat fish?

2

Do Beavers cause problems for fish?

3

Do European Beavers make dams or is it only Canadian Beavers that do this?

4

Has the subject of Beavers and fish been well researched?

5

Beaver websites say that Beavers are beneficial for “fish”; is this true?

6

Don’t Beavers dislike the fast-flowing rivers and burns that are suitable for trout and salmon juveniles?

7

Surely Beavers and salmonids co-existed in the same rivers for thousands of years before Beaver were exterminated?

8

Salmon and Sea-trout can jump over waterfalls – surely they can jump over Beaver dams?

9

Young Atlantic salmon have been found upstream of Beaver dams, does this still mean there is a problem?

10

Salmon and trout can reach even the most remote spawning grounds so surely Beaver dams would not be a real problem for them?

11

Do Beavers cause problems in North America where there are / were a lot of Salmon?

12

Don’t Salmon and Beavers live together in Norway where there are major Salmon fisheries?

13

Isn’t the reason for the lack of studies on Beaver dams because there is not a problem to study?

14

As the Knapdale trial is in a remote location of Argyll, is there a risk to the important trout and Salmon rivers either in the rest of Scotland or in England or Wales?

15

If Beavers introduced to Britain did cause problems, could they be legally managed?

_________________________________________________________

1

Do Beavers eat fish?

No. Beavers are vegetarian. They can eat a wide variety of vegetation and are not restricted to tree bark.
 

2

Do Beavers cause problems for fish?

Yes. Beavers are interesting animals particularly because they have a great capacity to change habitat that does not suit them into habitat that does. This mainly involves changing shallow water into deeper pools by damming streams. These dams can then prevent or restrict spawning fish from getting further upstream in Autumn (see below).
 

3

Do European Beavers make dams or is it only Canadian Beavers that do this?

Yes, they do. So long as the rivers and streams in which they live are not too wide, European Beavers make dams when the water is not naturally deep enough to suit them. more
top

4

Has the subject of Beavers and fish been well researched?

No. While it has been claimed that there is a “wealth” of research on this topic, this is specifically contradicted by statements in the scientific literature. There is indeed much research on beavers themselves, however there is little on the topic of Beaver dams and their impact on migratory fish. Such research as there is shows that Beaver dams can cause significant problems for fish, particularly when autumnal rainfalls are low. more
 

5

Beaver websites say that Beavers are beneficial for “fish”; is this true?

No, Beaver dams cause problems for migratory fish for the simple reason that the more obstacles there are in a stream for fish to get over, the more difficult migration up a stream becomes for them. Beaver dams are no different from man-made obstacles such as weirs, dams, fords, bridge foundations, etc. in this respect – and no-one thinks that increasing the numbers of weirs and dams in a stream is a “good” thing for migratory fish.

It is also claimed that Beaver dams provide a richer environment and better growth for the fish living in them. However, such enrichment comes from the rotting of the vegetation submerged by a Beaver pond and is only a temporary feature of Beaver dams. Once all the vegetation has rotten away, any effect is lost. more
 

6

Don’t Beavers dislike the fast-flowing rivers and burns that are suitable for trout and salmon juveniles?

No. On smaller streams, the water velocities preferred by both Beavers and spawning Salmonids are similar. A Norwegian study actually found that Beavers preferred the Salmon spawning areas on small tributaries to colonise. This means that a map of where salmon spawn on smaller streams is also a map of where Beavers will prefer to set up home on such streams. more
top

7

Surely Beavers and salmonids co-existed in the same rivers for thousands of years before Beaver were exterminated?

Yes, but co-existence does not mean species not impacting on each other – all Predators and Prey “co-exist”, for example. Where there are fewer Salmon fry upstream of a Beaver dam than below because access by spawning adults is restricted, the species are “co-existing” but salmon are being impacted nevertheless. Of course the extent of that co-existence so long ago is not known. What we do know is that Salmon in particular are an important feature of our river ecosystems and rural economies and that they are under great pressure out at sea so require very careful management, where this is possible, which is during their fresh water phase. more
 

8

Salmon and Sea-trout can jump over waterfalls – surely they can get over Beaver dams?

No. Both Salmon and trout are good at jumping over obstacles but only if these have a good flow of water over the top of them and a deep pool below them. Beaver dams generally have neither. Although Sea-trout are actually better than Salmon at getting over barriers that require more of a “scramble” than a clean jump and there are places in Scotland where Sea-trout can pass and Salmon cannot, Beaver dams are a major problem for them in the Baltic countries. more
 

9

Young Atlantic salmon have been found upstream of Beaver dams, does this still mean there is a problem?

Yes. All types of instream structure - fords, weirs, bridge foundations, etc. are more often partial barriers than total, i.e. they restrict fish passage rather than stop it altogether. This needs quantitative sampling to show – quantities of fish upstream and downstream of an obstacle need to be compared for a valid assessment to be made. Making such comparisons is standard fisheries management practice in Scotland – if survey work finds an average of 10 salmon fry per minute’s sampling downstream of a weir and an average of 1 salmon per minute upstream of it, then it is clear that there is a problem even if there are salmon fry upstream of it every year. Over the years, the cumulative loss of breeding upstream of such a weir will increase in significance. The simple presence of young Salmon upstream of a Beaver dam can not therefore show that there is no problem. more
top

10

Salmon and trout can reach even the most remote spawning grounds so surely Beaver dams would not be a real problem for them?

No. Despite their extreme agility both Salmon and trout often have difficulty reaching spawning grounds in smaller streams unless they get high enough spates at the right time in the Autumn; beaver dams would make such situations much worse. more
 

11

Do Beavers cause problems in North America where there are / were a lot of Salmon?

Yes. Some benefits have been recorded for Coho Salmon, a Pacific Salmon species which lives on the west coast of North America and has different habitat requirements to the Atlantic Salmon which is Britain’s native salmon. Beaver dams have been shown to restrict the migration of Atlantic Salmon in eastern Canada. more
 

12

Don’t Salmon and Beavers live together in Norway where there are major Salmon fisheries?

No. The main Beaver and Salmon areas of Norway are in different parts of the country. The main Salmon rivers are in the west and north of Norway whilst Beavers are in the centre and east. In the south where Salmon have been wiped out of many rivers by acid rain, there is obviously little scope for interaction between the species. When Beavers do cause a problem in Norway they can be removed by hunting which was a prime reason for their introduction.

The physical differences between the Norwegian and Scottish landscapes must also be remembered. In steep, mountainous areas, Salmon spawning is largely confined to the main channels of rivers, which are too wide for Beavers to dam. Tributaries in such areas are generally too steep for Salmon to use or are blocked by waterfalls. In flatter landscapes however, tributaries are much more accessible to Salmon allowing them to spread through the landscape into streams only a couple of metres wide. more
top

13

Isn’t the reason for the lack of studies on Beaver dams because there is not a problem to study?

No. Beaver dams are recognised as a problem for salmonids by many sources and specifically by The North Atlantic Salmon Conservation Organisation (NASCO). As said above, Beaver dams, from a fisheries management point of view, are simply a class of instream structure, like weirs, fords, dams, etc. and need to be assessed in the same, quantitative, way (see 11 above) good fisheries management cannot therefore dismiss them without investigation. more
 

14

As the Knapdale trial is in a remote location of Argyll, is there a risk to the important Trout and Salmon rivers either in the rest of Scotland or in England or Wales?

Yes. There may be few migratory fisheries at Knapdale so it is unlikely that the effects on them can be monitored in the trial. However Beavers are good parents and have the capacity to breed well and to spread rapidly if they are introduced. For example, in Sweden they have increased from 50 to 100,000 in 40 years. There are groups that want to make introductions in several places on the Island of Great Britain and wherever they start, beavers are likely to spread throughout the land mass where they will be protected by European legislation. more
 

15

If Beavers introduced to Britain did cause problems, could they be legally managed?

No. Wild Beavers are protected by European legislation. However once Beavers require “managing” then there is, by definition, a problem and any management of the problem will require funding; there can be no clear idea who will pay for this 50 years hence. Moreover some countries (Latvia, Estonia, Poland) have found that Beavers are actually rather difficult to control especially if lethal methods are not used. It is very unlikely that the British public would accept either hunting or shooting as acceptable, whatever the official position might be. Therefore it is unlikely that management could be an effective or economic solution to problems caused by Beavers. more
top

[Beavers] [FAQs] [Questions] [References]