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Review of mink predation and control

Invasive American mink Neovison vison populations are well established in Ireland as a result of escapes from fur farms, some of which still operate. They are important predators of globally threatened seabirds and waders. As a member state of the EU and signatory to a number of international agreements, Ireland has a legal obligation to conserve biodiversity, and species such as mink need to be managed through control or eradication.

Won under competitive tender from the National Parks and Wildlife Service (NPWS), Department of Environment, Heritage and Local Government (DOEHLG), Republic of Ireland, was a collaboration between The Food and Environment Research Agency (FERA) and Quercus.

The current known distribution of mink in Ireland suggests that the species is highly prevalent in the east but less widespread in the west. Our habitat favourability modelling suggests that the mink still has considerable potential to increase its range and population in western areas, areas that hold internationally important bird populations in designated sites. It has been estimated that the mink population in Ireland is potentially between 20,500 and 33,500 individuals based on the carrying capacity of available habitats. An 800-km2 area holding an estimated population of 300-730 mink was modelled under varying levels of population control. It was found that the population could be eradicated, at a cost of € 1,062,425, by annualremoval of 75% of the population over a five-year period. Other approaches are also discussed.

A review of the capture, monitoring and euthanasing techniques currently used for mink was carried out drawing on information in the literature, from ongoing or recently completed projects and from a questionnaire survey of mink control practitioners across Europe. The review also explored the different strategies used in mink control, focussing on eradications, control over large areas, and intensive control at sites specifically for bird conservation. Recommendations for techniques and strategies have been made for potential mink control projects in Ireland. Finally, the review looked at the likely cost of a mink control operation in a 800km² area in the west of Ireland.

Live capture trapping is the most common technique currently used for mink control in Europe and traps are most commonly either baited with fish or left unbaited, though a small number of projects make extensive use of mink scent glands. Air weapons and to a lesser extent, firearms are the most common means of euthanasing mink. Air weapons are the recommended technique as they are safer to operate at close quarters. Large projects that are run throughout the year by formally employed staff, use either bankside cage traps, raft traps or a combination of the two. Searching for spraints is a commonly used technique for monitoring populations, especially in projects that cover a large area. Rafts are also used as a monitoring tool as they provide a medium for recording footprints which, when confirmed allow operators to trap reactively using the rafts themselves. Thus raft trapping is the main technique used by smaller projects, especially those that run seasonally, as it allows volunteers or a smaller number of staff to carry out mink control.

Where mink eradication from a geographically well-defined area, such as an island, is possible, or where long-term mink control over a large area is the main aim, projects need to be run through the year with techniques adapted to vary with the seasonal changes in mink behaviour. Where eradication is possible, projects are run for defined periods of time until extinction. In areas where long-term control is the desired goal, mink control is carried out intensively until populations fall to virtual extinction, and is then replaced by monitoring to inform reactionary control as the presence of immigrant individuals is recorded. In small-scale projects where the aim is to reduce the impacts of mink on species of conservation concern, intensive mink control is carried out annually for a short period prior to the breeding season of the vulnerable species in question.

The 1100km² Hebridean mink project, where the preliminary goal was to eradicate mink from a well defined large area, was well-resourced, professional staffed and used several seasonal capture techniques adapted to mink behaviour. The smaller scale, Thames Valley project, was more resource limited, and the primary goal was to safeguard reintroduced water vole populations. Consequently, volunteers carried out reactive trapping using mink rafts that were important both as a means of monitoring and capture.

The lessons learned in the management of predators in New Zealand, and in particular on the mainland through a scheme known as the “mainland islands” project is also discussed to explore any strategies and techniques not covered by the formal case studies, that may be applicable to the management of mink in Ireland.