A reader in Carrick-on-Shannon glanced down from a bridge to see a mink seize a mallard drake “with a crocodile roll”; he wrote pleading for “a national cull” of the animal. Another reader, at Islandbridge in Dublin, photographed a swan on the River Liffey with nine cygnets, then returned a week later to count only four.
Mink swim in Dublin’s Dodder and Tolka rivers, and moorhens roost hopefully for safety in trees above the canals (although mink can climb, too). With half a dozen known haunts across the city, getting rid of mink is part of Dublin’s action plan against invasive alien species.
At more than half a century after its first escapes from fur farms, records of the feral American predator now cover three-quarters of the island. In 2008 there were still blank spaces on the distribution map, even in the eastern counties. Today only the highest hills remain vacant, and sightings in the west are steadily converging. For its new mammal atlas, biodiversityireland.ielists more than 1,400 reports from some 600 different 10km squares.
In the west the mink’s toll of waterbirds has been heavy at the richest lakes. At Lough Carra in Co Mayo, for example, moorhens are now startlingly few, and wintering mallard figures that regularly topped 1,500 through the 1960s and 1970s are down to a scarce 200. Thousands of gulls – black-headed and others – that used to nest on the lake islands in Carra, Corrib, Conn, Collin and Mask fell by as much as 80 per cent by the turn of the century.
At Cross Lake, a small lagoon behind the shore, just up the coast from me, I used to watch sandwich terns nesting densely and noisily on a crannog, and bringing chicks their food from the sea. By the early 1990s the first mink was seen at the lake, and the terns soon deserted, never to return.
Not protecting this lake was just one item in the litany of EU judgments against Ireland, in 2007, for failures in guarding vulnerable birds. Corncrakes, dunlin, kingfishers, red-throated divers – all potential mink victims – figure in the long roster of bird protection sites since added by the National Parks and Wildlife Service (NPWS).
Mink cannot be eradicated from Ireland. That much has been agreed since its first survey for the NPWS, in 1991. The world’s biggest example of large-scale mink eradication, in Scotland, has involved many communities and local interests working to restore wildlife and protect the raising of game birds.
A team of 186 local volunteers led by Aberdeen University scientists took three years to find, trap and shoot 376 mink over 10,570sq km of the Scottish highlands (almost twice the area of Co Mayo). They started in the headwaters of five main river catchments flowing from Cairngorms National Park and moved downhill, using mink rafts to detect and trap the animals. The project was extended to cover 20,000sq km by 2014, with long-term monitoring against reinvasion (for a PDF of a paper, search for “Turning back the tide of American mink invasion”).
In 2009 the NPWS published A Review of Mink Predation and Control for Ireland (Irish Wildlife Manuals 40, at npws.ie). It put the island's potential population of mink at up to 33,500 and estimated the options and costs of control. To tackle 800sq km of Connacht, for example, with up to 730 mink, the annual removal of three-quarters of the animals over five years would cost more than €1 million. That was roughly what Scotland spent on clearing mink from the Outer Hebrides, prime habitat for ground-nesting terns, waders and corncrakes.
At State level it has seemed more practicable to concentrate control at the most important conservation areas. Along with trapping at key lakes, the NPWS has hired trappers in Donegal, the Shannon callows, north Mayo and Connemara, last refuges for corncrakes and curlews. But eradicating mink at hot spots for their prey is a nonstop commitment, as fresh animals are constantly drawn in from outside.
The Co Donegal sites have included offshore islands, for mink can swim unexpected distances to prey on breeding seabirds. In the southwest, with its rich summer colonies of petrels and shearwaters, mink have been seen on the Great Blasket, a special protection area for the birds, and there is local concern at what is seen as an erratic pattern of NPWS trapping on the island.
The release by animal activists of 5,000 mink from a Donegal fur farm in 2010 prompted a local and effective flurry of gun-club activity. The bounty of €3 per furry mink tail, introduced in 2012 by Jimmy Deenihan, as minister for arts and heritage, has brought a wide if marginal control on the growing density of mink, at least in the west. In east Galway, for example, where rivers run slow, Killimer gun club trapped the most animals in the county last year, earning itself €300.
Michael Viney's Reflections on Another Life, a selection of columns from the past four decades, is available from irishtimes.com/irishtimesbooks