Derbyshire Wildlife Trust is working on a clever new way of tracking water vole and the main cause of their loss in the UK, the American Mink. Along with the University of Derby, we are looking for traces of their DNA in the environment to see if either species is present in the Dove catchment and to help us focus our habitat improvement work to where it is needed.

Largely considered Britain's fastest declining mammal, with populations plummeting by up to 90% in last century, the water vole is both an indicator and engineer of a healthy wetland ecosystem. Through digging, burrowing and grazing actions, this small but mighty keystone species helps improve wetland habitat by redistributing nutrients, diversifying vegetation growth and ultimately benefitting a host of other organisms such as insects, birds and other small mammals. Unfortunately, water vole populations have faced a rapid decline due to habitat loss and fragmentation, inadequate river management and intense predation by the invasive, non-native American mink.

What is eDNA? 

DNA is unique in all species, and provides the code to make all living things. Some of this DNA is shed into the environment while a water vole is going about its daily activities. This environmental DNA (eDNA) can be detected in water, soil and even air. Simply collecting a water sample provides enough material to analyse and reveal which species were recently present in an area, a technique particularly crucial for monitoring a species as elusive and increasingly scarce as our charming water vole. Sequencing of eDNA has quickly become a popular and cost-effective method to survey species in a non-invasive manner and will be vital to continue monitoring changes in biodiversity with shifting environmental conditions.

During Spring this year, staff and volunteers collected water samples from 30 sites at 1km intervals, along the Bentley and Henmore Brooks, near Ashbourne – a key area where water vole populations are still clinging on against environmental pressures. Water was pumped through syringes and specialised filters that trap any suspended material, including eDNA. The filtering process quickly takes its toll on the arm muscles of all those involved, although made substantially easier by the use of a rather non-technical piece of equipment – a sealant gun.

Samples will be analysed by the University of Derby later this year, providing a current picture of water vole activity, as well as detecting the presence of American mink. The eDNA analysis only tells us about the presence or absence of water voles (and mink) rather than revealing abundance. However, a negative result is equally important in highlighting where water voles should and could be present.

Along with visual surveys carried out at each site to determine habitat quality, these results will help guide future work to recover water voles in Derbyshire, including targeted mink control and habitat management.

What makes good water vole habitat? 

As herbivores consuming up to 80% of their body weight every day and known to feast on over 250 different plant species, water voles rely on wide margins of lush, dense vegetation for foraging, as well as cover from predators. Soft, penetrable banks alongside slow-flowing water are also essential for the creation of their extensive burrowing systems connecting land and water.

An array of management tasks will be undertaken over the next 2 years to maximise these desirable habitat characteristics. For example, fencing will be installed on suitable banks to reduce disturbance by livestock and dogs and provide buffered zones of refuge. Removal of Himalayan balsam - another invasive, non-native species in the UK that spreads rapidly and dominates other vegetation – will encourage more diversified banks of native flora. Selected tree works will also create a more beneficial balance of sunlight along the watercourse, promoting denser growth of ground vegetation. Collectively, the enhancement of these banks will increase the availability of suitable habitat, allowing remaining water voles to disperse and repopulate areas they once thrived in Derbyshire.

This forms part of the wider Dove Catchment Water Vole Recovery Project, a joint effort between Derbyshire and Staffordshire Wildlife Trusts to boost water vole numbers in the Dove catchment through targeted enhancement of available habitat and strategic mink control.