Head of Wildlife Monitoring, Dr Vince Lea, highlights what has been achieved by the CRT’s mink eradication efforts in Cambridgeshire after joining Waterlife Recovery East’s partnership project in early 2021.

Cambridgeshire water voles are set to have their best year of the 21st Century in 2022. That’s because the CRT, in partnership with Waterlife Recovery East (WRE), had a solid year in the campaign to eradicate their invasive predator, the American mink, from East Anglia.

While I have been keeping mink at bay in the Bourn Brook on Lark Rise Farm in Cambridgeshire since 2010, it was a shoestring operation until the start of 2021 when we joined a major grant-funded operation. Waterlife Recovery East (WRE) had been established two years earlier, aiming to prove that it could achieve a 12-month period with no breeding mink in a core area covering a large part of Norfolk and Suffolk. The CRT is playing an important part in this by preventing mink from Cambridgeshire (the buffer zone) entering the core area in neighbouring counties.

The WRE received grant funding from the Government’s Green Recovery Challenge Fund in 2020. This meant we could employ Project Officer Emily Coleman to work with me for 15 months. Having two of us on the team enables us to keep our traps operating all year round.

The funding has also meant a step-change in the number of permanently operated ‘smart traps’ in the network, which now covers most of Cambridgeshire and parts of surrounding counties. We have 96 such traps compared to just five at the start of 2021.

Working together towards a mink-free GB

We have engaged with other organisations undertaking mink trapping in Cambridgeshire, such as Natural England, the Middle Level Internal Drainage Board and the RSPB. We are sharing data and obtaining specimens from them, which will contribute to the overall understanding. The aim is to prove this approach works and to expand it to eradicate mink across Great Britain. Our trial will give a good indication of the cost and logistics required to achieve this.

It would be the world’s biggest eradication attempt of a non-native species and would ensure the future for water voles, our most rapidly declining native mammal. A mink-free Great Britain would also have much better conditions for nesting water birds such as common terns, moorhens, kingfishers and black guillemots.

150 mink caught in Cambridgeshire

During 2021, with our collaborators we removed 150 mink from Cambridgeshire, three times the number we caught the year before.

Our WRE partners in the neighbouring counties of Norfolk and Suffolk also increased their efforts in 2021 but caught fewer mink than the year before. This was probably because the work they had done in the two years prior had reduced the number of mink at breeding age before they had a chance to produce many young. Plus, due to our team’s efforts, it’s likely that no mink from Cambridgeshire would have infiltrated their counties.

Preventing mink from breeding is key to the success of this project. If we can remove them at a faster rate than they are replaced, we will cause the population to decline towards extinction.

Catch rates have declined so far in 2022

As we go into our second year working with WRE, we will be monitoring closely to see how much we have reduced the mink population. If it has worked, catch rates will decline.

Our data shows that mink are up to three times rarer in Cambridgeshire now than they were last year. In WRE’s core zone, they are three times rarer still.

With fewer mink around, we are already seeing an increase in catches of their prey species such as water voles and moorhens. This is a side-effect of success as it suggests their numbers are increasing.

The trap and alert design means they are not harmed and either Emily, I or one of WRE’s volunteers get to the traps as quickly as possible to release them. We are working on modifications to deter water voles from the traps. One day we hope the traps will no longer be needed and our treasured native species can go about their day undisturbed by mink.

By Dr Vince Lea, Head of Wildlife Monitoring

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