Establishing new populations of European mink in Hiiumaa and Saaremaa Island, Estonia

Summary

The European mink (Mustela lutreola), Critically Endangered since 2011 and lacking any known viable wild population, was the subject of island reintroductions on Hiiumaa and Saaremaa in Estonia, drawing on a captive-breeding colony of about 100 animals at Tallinn Zoo under the EAZA breeding program, aimed at establishing self-sustaining populations after removing feral invasive American mink from Hiiumaa. Since 2000, 475 mink had been released on Hiiumaa by 2012 through a sequence of trialed methods, hard release with preconditioning (too high mortality), releasing pregnant females (survived, but litters vanished), and eventually only yearlings born in release enclosures; research found mortality peaked in the first six weeks, mainly from fox, stray dog and raptor predation, and released mink shifted to a typical wild diet within about a month. Public awareness on Hiiumaa proved very high after sustained media coverage, supported by amphibian-pond and stream-habitat improvements, but the wild population there has stabilized around only 30-35 post-winter animals with breeding occurring at unclear and possibly insufficient rates, skewed toward older or released individuals. A 2012 pilot release of 11 radio-collared mink on Saaremaa fared far worse, with seven dying within a month, 71% to fox predation, leading researchers to judge the release site suboptimal and further Saaremaa releases potentially infeasible given high fox density. Difficulties included unstable funding, an EU-mandated rabies-vaccination campaign that appeared to boost competing carnivore numbers, fragmented habitat lacking a strong source area, and inflexible state conservation procedures. The project rates itself partially successful, crediting close in-situ/ex-situ team coordination as its key strength.