Beavers: the pros and cons

Yesterday a group of fishery board and trust staff were taken on a beaver fact finding trip to Dunkeld by the Cairngorm National Park Authority. As many will know there is a rapidly expanding beaver population in the Tay catchment with beavers now present at Loch of the Lowes reserve near Dunkeld. A single male beaver turned up there in Dec 2012 followed soon after by a female. The pair setup home in the Lunan Burn, a tributary of the Lowes.

Prior to yesterdays trip I had never seen any evidence of beaver activity so it was a trip I was very much looking forward to.

The Lunan Burn is about 2-3m in width, low gradient and quite silty. The banks were well wooded although more so further upstream, at the lodge site itself there were only a few burnside alders. The main feeding area was upstream was well wooded.

The beaver lodge can be seen on the far bank of the burn. The lodge entrance is underwater for security. In the foreground is a cache of food to support the colony in the event of hard weather

The beaver lodge can be seen on the far bank of the burn. The lodge entrance is underwater for security. In the foreground is a cache of food to support the colony in the event of hard weather.

Food cache or store. It consisted of cut branches and some logs with suspiciously straight ends!

Food cache or store. It consisted of cut branches and some logs with suspiciously straight ends!

Duncan Halley a Scottish/Norwegian beaver ecologist was on hand to provide information and answer questions (Google him for more info). He reported that 99% of beaver activity occurred within 20m of water; a predator avoidance strategy as wolves prey on them where present. The lodge entrance was underwater with a food cache immediately outside. They dislike travelling through shallow water and a short distance upstream of the lodge there was a very small dam, about 6″ in height. This innocuous looking dam was built by the beavers to increase the depth of the water upstream so that they could swim underwater rather than being exposed.

Little dam to raise water levels along a transit route.

Little dam to raise water levels along a transit route.

Upstream, and above  a road bridge several other dams had been constructed. The main dam was across the burn and was about 3′ high.

The main beaver dam with water flowing around the top. The dam itself was qute water tight, testimony to the beavers dam building skills. A few of us thought that the dam would have been passable by fish such as trout by swimming up the side flow during elevated water levels.

The main beaver dam with water flowing around the top. The dam itself was quite water tight, testimony to the beavers dam building skills. A few of us thought that the dam would have been passable by fish such as trout by swimming up the side flow during elevated water levels. Photo by Lorraine Hawkins River Dee

The Beaver Salmonid Working Group are studying fish passage at this dam. 100 brown trout were electrofished from the burn and tagged with pit tags then released above and below the dam. Some of the trout were subsequently found to migrate both upstream and downstream of the dam.

Local lad Sean Dugan of the Beaver Salmonid Working Group explains the ins and outs of beaver ecology.

Local lad Sean Dugan of the Beaver Salmonid Working Group explains the ins and outs of beaver ecology.

As well as damming the main burn the beavers had also dammed a side drain in two different locations.

Very neat hosreshoe shaped dam on side drain. Apparently the drain itself was dammed with the wings added as the water level increased.

Very neat horseshoe shaped dam on side drain. Apparently the drain itself was dammed first with the wings added as the water level increased.

The net effect of the dams was to raise the water level over an extensive area flooding woodland. The woodland consisted mainly of alders/birch and willows and was a plantation rather than a natural wood. There was evidence of tree harvesting by beavers throughout the flooded area.

Impoundment above main dam.

Impoundment above main dam.

Willow of about 8" diameter felled by the beavers.

Willow of about 8″ diameter felled by the beavers.

The favoured tree is aspen followed by willow and birch with alders little used. I hadn’t realised that during the summer the main source of food is “salad” e.g. grass, herbs, crops etc with tree bark only important during the winter. The woody stems provide no sustenance but are used for building material.

This tree had been almost cut through at a higher level before the lower cut.

This tree had been almost cut through at a higher level before the lower cut. The smaller branches at the top of trees is preferred, maybe the bark there has more nutritional value.

Following the trip to see the beaver site we were given a few presentations in the afternoon. Some interesting statistics: the mean width of streams at dam sites = 2.5m and the maximum width dammed = 6m. The maximum gradient of streams at dam site was 2%. So all the main Spey salmon spawning tributaries should remain dam free but there is still likely to be a large overlap in the potential range of beaver and salmonid habitat within the Spey catchment. I have mentioned the importance of gradient several times before on this blog before. The best spawning gravels in burns occur between 0.5 and 1% gradients, so there is an obvious overlap there. Burns under 3m in width also tend to be dominated by trout although also used by salmon; it is possible that there would be greater overlap between trout and beaver habitat. Another interesting fact about beaver recolonisation is that they rapidly spread along the full length of catchments before filling in the gaps. Movement into neigbouring catchments is a much slower process, assuming no assistance of course. A copy of Duncan Halley’s presentation can be viewed here.

The Government will be deliberating on the fate of official beaver reintroductions in 2015 after considering evidence from the official beaver introducton trial in Knapdale in Argyll plus the report currently underway on the Tayside population. It is pretty clear how the decision will go but  with the Tayside population expanding at 20% per annum the 2015 decison may be an irrelevence. Many are already present along the Tay mainstem. In such locations they don’t build dams rather they burrow into the banks grazing in surrounding areas.

The appearance of beavers in Speyside is only a matter of time, whether they arrive via official introduction or out the back of a white van will be interesting. The Insh Marsh area is considered prime beaver habitat but there are other areas where they would do very well.

The fact finding, or softening-up trip was very informative, Duncan Halley was convincing but there are alternative views on the impact of beavers see http://www.tweedfoundation.org.uk/Tweed_Management/Beavers___Fish_-_the_facts/FAQs/faqs.html. We were told many times yesterday that dam building is not a mainstream activity by beavers but we saw several dams within 150m of each other. The implementation of flexible and responsive control measures will be key in persuading the fisheries sector to adopt a relaxed view on beaver introductions but we are not good at managing wildlife in this country. In Norway they are a game animal and they are hunted for food and sport. Duncan Halley even turned up wearing a beaver skin waistcoat; suprised he got through customs!

I know that where beavers are present they are regarded as an integral part of river and salmonid ecology; will we develop the same understanding here?

 

There are 13 comments for this article
  1. Doug Powell at 12:03 pm

    Hi Brian

    Interesting discussion – can’t help but think there could be a parallel with the SNR ponds being used in the Wye catchment. Early days for the WSA and the Wye but hopes are high.

    Doug

    • Brian Shaw Author at 10:24 pm

      Thanks Doug,

      Are you thinking the beaver ponds would make good smolt release ponds!!

      Brian

      • Doug Powell at 12:51 pm

        Can’t see any reason why not – Beavers are allegedly 99% vegetarian so presumably would not eat the parr which would have to be stocked into the ponds. It is my understanding that the survival rate to Smolt is many many times that obtained “in river”.

  2. Rick Lanman at 1:29 am

    Although some beaver dams may be barriers to migration, most winter storms of any size make them passable for our trout and salmon here in California. As has been mentioned above, C. fiber and your salmonids were historically sympatric and likely co-evolved to benefit from one another. The key benefit of our C. canadensis to Coho salmon is the beaver ponds increase young salmon survival about 2,000-fold. The ponds are important winter refugia packed to the gills with salmon food. Since a fish can lay thousands of eggs, smolt survival may be a much more positive factor than the possible negative of beaver dams being passage barriers.

    • Brian Shaw Author at 9:24 am

      Hi Rick,

      Thanks for the comment. The ecology of our salmon species is probably quite different to Coho, Atlantics are considered to be primarily stream dwellers, although there is probably a lack of knowledge about how important ponds/small lochans are for juvenile salmon, especially overwintering habitat. Looking at a typical 3m wide spawning burn a beaver dam may drown out 150m of stream habitat, turning it into pond/with associated wetland. Certainly that would be good trout habitat and the productivity of that stream for trout would increase, assumming the dam wasn’t a barrier. In the 150m of what used to be stream you might only expect the atlantic salmon smolt production to be around 25, not a lot granted in its own right, although if replicated 100 times it starts to become more significant. Any spawning habitat within the former stream will have been lost (downstream impact) and depending on fish passage there might be an impact further upstream.
      I can see benefits for lot of other flora and fauna including tree regeneration and in the same way as the sight of an otter makes your day, so I’m sure would a beaver. But if we become overrun with them attitudes will change. We need to be able to manage them.
      Best regards

      Brian

  3. Sean Dugan at 6:33 pm

    Hi Brian,

    Thanks for posting this excellent summary of the day and for the pictures also. Yes I agree with your penultimate paragraph in that the implementation of an adaptive management approach is important as we learn how beavers interact with Scottish salmonid systems (if they are allowed to remain in 2015).

    There are many unknowns in the Scottish situation and much of these are tied to the density and character of dams which may be created in future. The question you raised on Monday about trout dominance over salmon in lentic habitats is an area the BSWG is currently looking into. As is the issue raised by David Summers regarding high/low flow conditions in the Spring smolt run. -Literature suggests that although most dams are passable, impacts are exacerbated in low flow conditions.

    Cheers, Sean

  4. Iain Ogden at 8:20 pm

    An interesting article Brian,
    We have limited beaver [I assume the same species as those in Scotland] activity close to our house in a forest SE Oslo. The dam is a significant construction some 6-7m wide and >1.5m in height. 100m downhill the stream is 1.5-2.5 wide. The resulting flooded area above the dam is approx. 2 acres of unknown depth with many standing trees now dead. The lodge is a huge structure several metres in height and width. While I have little doubt there is increased biodiversity [different newt spp, various duck spp, waders, bats] I suspect neither salmon nor trout could ascend the dam. Salmon are not a prevalent spp in SW Norway and I’ve seen no sign of them in the key salmon areas of Trondelag and Finnmark but I think salmon in low land areas [e.g. Scotland] would be particularly vulnerable if populated by beavers.

    • Brian Shaw Author at 9:26 am

      Thanks Iain, always good to hear from people with direct experience of european beavers, and with knowledge of salmon ecology.
      Brian

    • Hugh Chalmers at 9:53 pm

      Please ask Duncan re beaver in the Trondelag, I am sure this is where I filmed beaver with Duncan in 1998

  5. Heidi Perryman at 4:35 pm

    Here in Martinez California we have lived with a family of beavers in our creek for 6 years. We control the height of the main dam with a flow device, and there are four more which help increase stream complexity and wish fish pass easily. Because these dams trap silt and organic matter they create a more complex invertebrate community. This feeds an ever-diversifying population of fish. Hyporheic exchange cools the temperatures when underground waters pass through the bank, creating ideal conditions for fish.

    In fact, we have documented three new species of fish in the creek since the beavers came. We can tell the overall fish population is growing because the number of egrets, woodducks and otters that come to eat it every day is growing also.

    Martinez and Scotland used to have millions more beavers, and coincidentally millions more salmon and trout. These species co-evolved for a reason.

    Heidi Perryman

    • Brian Shaw Author at 12:02 am

      Interesting Heidi. Here we have a limited range of fish species, only about 6 common native species, with a few introduced species currently restricted to limited localities within the catchment. Salmon and trout are the economically valuable species with eels the only other species of concern which utilises the smaller tributaries. I have read some papers today which do mention (American) beaver dams restricting salmon distribution. We were told to consider the catchment scale positive benefits of beavers, a statement which in itself is an acknowledgment of local negative impacts? It is not yet clear to many that the potential positive benefits outweigh the negatives. Effective management measures are likely to be essential if we are to enjoy the positives.
      Brian

  6. stuart milner at 3:11 am

    we all would like to get back to nature but some times i think we do it wrong (soon i may have to apply for firearms certificate to include wolf and bears

  7. Henry Spence at 8:07 pm

    Hi Brian,

    This must be a real worry, how can creating more dams/obstacles in a river system be anything other than detrimental to migratory fish stocks? As if the salmon/sea trout don’t have enough problems as it is.

    This I am sure will be yet another problem that our kids/grandkids will have to try and sort out in 40 years time….it’ll make the culling of badgers seem like childsplay!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.