Battle of the otter and the mink

WHEN MINK first started to spread around the country, there were a lot of worries about what the impact of a new species of carnivore would be on other wildlife.

One big worry was that they might have a bad effect on our otter population.

Mink are much smaller than otters but they are closely related and they eat many of the same things. The fear was they might win out in the competition for limited food resources. This was particularly worrying because Irish otter populations are of international importance.

The species is extinct in many western European countries and regarded as vulnerable over all its range. Ireland has the highest density of otters of any country in Europe and is regarded, along with western Scotland, as about their last stronghold.

A careful eye was kept on the situation here and about 25 years ago a research project was set up in eastern England to see if there was any correlation between the spread of mink and a decline in otter numbers.

The research seemed to indicate that the otter populations remained the same after the mink arrived and everybody breathed a sigh of relief.

But new evidence in the past couple of years has added a twist to the story of the relationship between the two species. It seems that otters kill mink and even eat them. This is based on observations from several countries and recently our own wildlife rangers have collected otter droppings, or spraints, with mink bones in them.

This is even better news and could be a factor in the reduction in mink numbers in recent years, particularly in Leinster, where they’ve been established for longer. The first American mink arrived in this country in 1951 as captive animals on fur farms that were concentrated in the south east.

WITHIN 10 years, there were several reports of animals escaping into the wild. Then fur prices crashed due to changes in fashion in the early 1970s and it’s widely believed that some bankrupt fur farmers deliberately released their animals. They spread and multiplied and by 2000 had covered the whole country, even such apparently unsuitable places as the Burren, which has very little open water.

The ecological catastrophe that some people predicted never happened. Mink populations are stabilising and reducing and there is evidence that prey species are developing defensive strategies. Water birds that nest in reed beds like coots, water hens and grebes, were initially hit hard by mink taking their eggs and young. But they have learned to change their nesting habits. Some water hens have been nesting in trees.

The greatest damage done by mink has probably been to our vulnerable stocks of freshwater crayfish. In some midland streams and lakes mink live almost exclusively on them because they find them easy to catch. However, it must be admitted that otters eat quite a lot of crayfish too.

The fact of the matter is that we have to learn to live with mink, just as their prey species have done. It’s not possible to eradicate them or even to control their numbers.

Hayden and Harrington in Exploring Irish Mammals write: “Mink populations have a self-regulating mechanism relating to their territorial behaviour.” What this means is that if you shoot or trap a mink another will almost instantly fill its place. In fact if you kill a big, strong mink you could actually increase the number of animals in the area as its territory may well be divided between two weaker mink.

No, when it comes to controlling the numbers of mink we’d be much better off encouraging otters to do the job rather than trying to take on the task ourselves.

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