Planet Earth Online

Isotopes - weapons of mink destruction

4 January 2010, by Sara Coelho

The team collected whiskers from American mink (Neovison vison) killed during the eradication programme and analysed the ratios of carbon and nitrogen isotopes.

Isotopes are different forms of the same chemical element, and the proportion between light and heavy isotopes is a 'chemical fingerprint that can tell us about what animals have been eating and where they have been feeding,' explains Dr Thomas Bodey from the Queen's University Belfast.

'This is because the ratios of heavy to light isotopes vary according to a range of biological and physicochemical processes,' he adds. Whiskers collected from mink feeding inland will have a higher proportion of the lighter carbon-12 isotope than those removed from animals living near the coast on a seafood diet.

Bodey and his colleagues found that as the cull proceeded, the mink living inland moved towards the vacated territories on the coast. Mink are semi-aquatic mammals that in the Outer Hebrides find productive coastal habitats attractive, as they offer access to marine food.

This means that 'if trapping can be focussed on coastal areas, then inland areas on larger islands do not become an increasingly difficult logistical challenge requiring more and more traps and man hours to cover,' says Bodey.

The results, published this month in the Journal of Applied Ecology suggest that the eradication campaign will get better value for money if traps are concentrated in the coastal areas, 'to ensure the maximum number of animals are caught as rapidly as possible.'

American invader

American mink are not native to the Hebrides and became a problem after animals that escaped or were released from fur farms adapted well to the islands and quickly multiplied.

'The Hebrides are a very important breeding area for many sea and shorebird species, with internationally important numbers of several species,' says Bodey.

'The breeding birds are under threat now because mink eat eggs, nestlings, and adults if they get the chance,' he says. 'They have been implicated in the extirpation of many small seabird colonies on the west coast of Scotland.'

Eradicating mink is a logistical challenge because they are spread over a wide area and on many islands. As semi-aquatic animals mink can easily swim between rocky islets and spread havoc in otherwise isolated bird colonies.

But the main difficulty 'is trapping the final few individuals as, without this, the entire effort is likely to fail and the population will gradually recover.'

'Isotopes allow us to identify the types of places in which most mink are feeding and thus target the trapping campaign more efficiently.'

'We have shown that the same techniques can be used to quantify which food types are important, and how the diets change in response to removal of other individuals during an eradication campaign,' says Bodey.

'This is relevant not only for mink management, but for other eradication campaigns of other species as it adds another technique to the eradication toolkit.'

The isotope analyses were carried out at the NERC Life Sciences Mass Spectrometry Facility at East Kilbride. The Food and Environment Research Agency (FERA) and the University of Exeter also the supported the research.

Keywords: Biodiversity, Europe,

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