September 2020 BBC Wildlife 41
BEAVERS
Otterhada dampresent,mainlyonthe
tributaries.“Thenumberofterritories
is a keymeasureofsuccess,”saysMark.
Thoughthecurrentestimated 17 is a good
number,theRiverOttercould,ecologically
speaking,supportupto179.However,
reachingtheriver’scarryingcapacity
ofbeaversis notrealistic.“Thewaywe
intensivelymanagethislandscape,and
theharmonythat’srequired‘mammal-to-
mammal’placesa naturalsocialcaponthe
beaverpopulationhere.”Thebenefitofbeavers
Duringtheirfive-yeartenancy,thebeavers
havealreadyhada profoundimpactin
theOtterValley,notleastinbolstering
otherwisedwindlingnumbersofa fellow
riparianmammal.“We’vegotnewareasthat are being re-colonised by water voles
as a result of the beavers,” says Mark,
“and we’ve had some lovely responses
from wetland birds – teal, snipe, even
woodcock have all benefitted. We’ve seen
kingfishers in new areas, herons feeding
on a thriving population of amphibians –
even otters are clearly benefitting.”
Such findings shouldn’t come as a
surprise. Beavers have ‘British waterways’
etched into their DNA. Naturally, many
other creatures would have evolved
alongside them.
But it’s the impact on local fish
populations that has been particularly
interesting. Many anglers have been
concerned that beaver dams will
prevent salmon migration upstream,
despite very few dams coinciding with
known salmon runs. And nature
continues to surprise. A 37 per cent
increase in fish populations has been
measured in the beaver pools, and
footage shows sea trout defiantly leaping
the dams during high flows. If dams
are buffered by scrubby margins, Mark
explains, the resulting overflow creates
multiple channels – migrating salmonids
can swim around the dams.Top left: grazing on
aquatic vegetation.
Above, left: by
damming a stream,
the beavers created a
pond within a large, wet
woodland enclosure.
Above: the RiverOtter has become a
permanent home
to beavers. Left:
these mammals leave
distinct toothmarks on
bark. Bottom left: what
remains of a heavily
gnawed willow tree.