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