This Friday the National Trust are set to release 100 water voles onto a Yorskhire estate as part of a reintroduction plan. The voles have been bred specifically for release and are part of wider, landscape management plan that hopes to make the environment healthier and return it to a more natural state.
Water voles are locally extinct in many places due to changes in river use, pollution and predation by mink. Out of the three key factors, mink predation is thought to be the main issue after mink escaped from fur farms or were released by animal rights groups in the 80’s and 90’s. Water vole populations are thought to have dropped from tens of millions to less than 1 million over a period of around 40 years. They were so abundant that there is very little data on their populations as no one thought to study them. The fact that voles can be released is an indication that rivers are becoming healthier and more natural places which benefits the entire ecosystem.
The voles are being released into a place called Malham tarn, which is the highest freshwater lake in England. The National Trust made a statement saying that this is the highest altitude release ever done and a lot of the media has turned the “high altitude release” into some sort of special achievement. The lake is 377 metres above sea level, it is not quite Everest. The feature of the height is that it means the voles are being released into an upland lake which allows them to colonise tributaries and streams and move downstream over time. It is easier to monitor a population in this way and it is easier to implement river management strategies at the beginning of the river, which is high up. Also, Malham Tarn has not had any reports of mink for around 10 years and historically had a high water vole population, making it a good choice for a release site.
Voles are a good indicator of the health of a river, not just showing the absence of mink but also showing that there is a plentiful food supply and that the river is clean and stable. Rivers that fluctuate or change rapidly can result in voles being flooded out of their burrows. If this release proves successful it would certainly validate what the National Trust has done to improve the health of water systems. Voles themselves are part of the ecosystem and their addition helps with seed dispersal and vegetation control and so they are not just a trophy animal, they are important additions.
The problem with voles, other than being the most rapidly declining animal in Britain, is that very little is known about them and their interactions with otters and mink. Mink eat voles, we know for sure. But anecdotal evidence says that otters will eat voles and that otters will attack mink, a claim that is hotly disputed as mink and otters cohabit a vast number of rivers around the world. The issue is that choosing a release site is very difficult without knowing the predation rates. It is thought that otter predation on voles is low and so if otters push out the mink then the voles could probably survive with otters. If both otters and mink are present together the voles will struggle and possibly die out again. This release will be closely monitored and so it will provide a lot of information which can be used for future releases. If this release is successfully the National Trust has said they will release a further 100 voles next year which could possibly mean the return of the water vole.