A serious threat to the native wildlife of the Western Isles, the North American mink is the subject of a long-running management scheme. But those responsible for its control have a certain respect for this tenacious predator, writes Fergus MacNeill from Scottish Natural Heritage
Originally published in Autumn 2009
Photograph: John MacAvoy
It has been described as a hard-wired predator that uses an overkill strategy just to survive and been likened to a fox that gains entry to the hen coop and kills everything inside. The truth may be somewhere in between, but what is clear is that the North American mink, or Neovison vison, has no place in the Western Isles. It is simply the wrong predator in the wrong location.
Mink first started to spread through the islands following the failure of fur farming ventures on Lewis in the 1950s. Some mink escaped, while the suspicion is that many of the animals were simply cut loose when the farms folded. Either way, the mink took readily to an island chain that, with its many miles of coastline, plus countless lochans, burns and rivers, provides a near-perfect habitat for this semi-aquatic animal. Within little more than 40 years, the animals had spread from Lewis into Harris and across to the Uists, giving the islands the dubious honour of having one of the highest densities of non-native mink anywhere in the world.
But the spread of mink has taken a toll on the islands’ internationally-important populations of ground-nesting wader birds, as well as once vibrant seabird colonies and vulnerable moorland species. Highly efficient predators, mink take not just the eggs of nesting birds, but also young and even adult birds. Not used to facing ground-dwelling predators â€“ the islands have no fox, stoats or weasels â€“ the native wildlife has few natural defences and so provide easy pickings for the mink.
Species such as terns, black- and red-throated divers, corncrake, dunlin and ringed plover have all shown worrying signs of decline. Some, such as the seabirds, have been hit hard by dwindling food supplies, but predation by mink has also played its part. Largely nocturnal hunters, they have been known to decimate entire colonies of terns in a single night.
And such is the mink’s voracious appetite that they have also begun to impinge on key rural economies on the islands. The animals’ liking for parr and smolts in winter has obvious implications for trout and salmon numbers, while their keen taste for fresh meat (rather than carrion) has also impacted on game shooting and poultry farming. In some areas, the threat of mink is such that crofters have simply given up keeping hens and ducks.
Given such impact, the decision was taken to launch an ambitious mink eradication programme â€“ by far the largest project of its kind in the world. Launched by Scottish Natural Heritage (SNH) in 2001, the Hebridean Mink Project (HMP) was formed in partnership with the then Scottish Executive, the RSPB, Comhairle nan Eilean Siar, the Central Science Laboratory in York and Western Isles Enterprise. Much of the funding for the programme â€“ which cost Â£1.65 million in the first phase â€“ came from the EU Life Nature Fund, a European programme designed to help protect internationally important sites designated under the EC Habitats and Wild Birds Directives.
The initial five-year pilot aimed to determine if an eradication project could be carried out on such a scale, with a focus on removing the mink from North Uist and Benbecula and reducing the population on South Harris to prevent the animals returning to North Uist. However, the project area soon increased by a third when it was discovered that mink were also on South Uist.
Early successes on the Uists and Benbecula led to the current second phase that concentrates efforts on the much larger Lewis and Harris, and will run through to March 2011. This time, with EU Life funding turned down, the bulk of the Â£1.9 million cost is being met by SNH, with support from the Esmee Fairbairn Foundation, Comhairle nan Eilean Siar and Highland and Islands Enterprise.
I recently spent a day with a trapper in the Lewis Peatlands Special Protection Area to see just what is involved in capturing these wary predators. In addition to impressive field skills and an encyclopaedic knowledge of native flora and fauna, I can testify that the trappers are also exceptionally fit. After more than 10 miles of hiking through tough terrain, I was on my knees.
A major problem with mink is their tendency for a killing spree approach, rather than just taking single prey items. “Mink kill en masse here as they do in their native range of the US and Canada,” explains Bob Chaffer, foreman trapper for the HMP. “There, they stash the food in caches where it remains fresh because, in winter, it’s freezing.”
But that’s just not the case in the damp, mild climate of the Western Isles. “Here, meat goes off after a couple of days, so the mink go out and kill again and again. That’s where you get the comparison with the fox in the chicken coop.”
Understanding this and other behavioural characteristics has enabled trappers to focus on the most effective way to tackle an estimated 1,500 mink on Lewis and Harris and a further 500 on the Uists. Trapping techniques have been refined since the first phase, with trappers now settled on a winning formula. One key to success has been the use of anal gland lures as an attractant â€“ at first, every bit as unpleasant as it sounds. Iain Macleod, HMP Project Manager, recalls having to open the carcasses of dead mink and extract the anal gland secretions by hand. “It was a messy business,” he says with some understatement.
However, with trappers often checking 20 to 30 traps per day, it was just not possible to extract enough of the scent, so the team started to use a commercially available lure from the US. Easy to use and incredibly effective, the lure convinces the mink that another animal â€“ perhaps a potential mate or rival â€“ is on its patch and so it will enter the trap to check it out. Mink are highly territorial in winter and spring, so the lures target the animals’ own territorial behaviour and use that against them.
Tactics change, however, during the summer when mink activity slows down and mothers are committed to den sites. At this time, the traps are instead baited with fresh food, such as oily fish. “Mink are good mothers and a female with young will not want to spend hours chasing live prey,” explains Macleod. “So, a ready supply of freshly caught fish is often enough to do the job during the summer months.”
The traps themselves are set carefully in tunnels, usually close to water. Trappers, many of whom come from game-keeping or professional trapping backgrounds, open a group of traps on a rotational basis. Once a trap is opened for use, it is checked every 24 hours.
Professional standards are high and animal welfare is an important part of the project: caught minks are invariably unhappy, but in good condition. Meanwhile, the use of lures for much of the year also means that the capture of non-target animals is uncommon â€“ after all, most steer clear of such a predator’s scent.
Mink, plus any rats or ferrets that are caught, are dispatched using a single shot from an air pistol or rifle. The carcasses are then tagged, frozen and sent to what is now the Food and Environment Research Agency in York for analysis. There, the carcasses are checked for age, sex, health and breeding patterns, with placental scars an indication of how many kits a female might have had. “There is a lot of science behind the project that is then fed back to us on the ground,” says Macleod.
A huge amount of technology â€“ as well as legwork â€“ is involved in the project. The strategy on Lewis and Harris has been to trap heavily, with 7,500 individual traps currently in use. The area covered may be vast â€“ roughly 2,000 square miles â€“ but trapping is on such a scale that islanders are said to be never more than 500 metres from a trap.
The whole task has received strong support from estates and local communities, although people are sometimes a little too keen to help. There have been instances of individuals opening traps thinking they are helping, but this can actually lead to animals suffering. “Once a trap is opened by us, it is checked daily, but if we don’t know that a trap is open, we can’t check it,” says Macleod.
GPS technology is used to keep track of the traps, while satellite tracking is also used to ensure the safety of the actual trappers, who work alone and â€“ as I discovered â€“ cover vast distances. “We use hand-held spot trackers, so, from our offices in Stornoway, I know the position of every tracker. The system is backed up three times a day to ensure that everyone is safely off the hill.”
Such technology also highlights not just the sheer scale of the
project, but also the level of physical effort needed to make it a success. Between them, the 18 or so trappers cover more than 25,000 miles a year in their pursuit of the mink. It is a remarkable statistic made even more impressive by the challenging terrain involved. “Fitness levels are high â€“ it is hard graft if you are covering 10 to 15 miles a day. You can have all the field skills in the world, but if you can’t be bothered getting out of bed in the morning, it’s no use to anyone,” remarks Macleod.
But despite all the hard work involved and the mink’s own efficiency as a predator, the project team stresses the importance of not demonising the animal. “We have to be rational and scientific. This work is about determining and then analysing the behaviour of the animal so that we can find an Achilles heel,” comments Macleod.
“Ours is not the only project in Scotland attempting to solve the mink problem and our solutions are often different, but the basic fact remains that we now recognise that there are possible answers to the problem of invasive mink predation.”
To date, trappers have removed about 70â€“80% of the mink population on the islands. “Our best week was when we trapped 51 animals, although we tend to average around 25. If you take that out of a population of roughly 2,000, then you can see that we are making good progress.”
Crucially, the trappers are aided by the mink’s own life-cycle. In the Western Isles, the animals only live for three or four years. They breed in the first year, but only three or four kits tend to survive each winter, so they are not as productive as other species, such as rabbits or rats.
Recent anecdotal evidence suggests that the reduction in mink numbers is already paying dividends, with several new tern colonies springing up and gulls now more accepting of nesting and roosting on rocky coastlines rather than outlying skerries. More and more crofters have even taken to keeping poultry once again.
Now entering the final 18 months of the project, the goals have changed and not catching many mink will soon become the new measure of progress. “We have caught 970 mink on Harris and Lewis and would expect that total to reach 1,200 before we can say that the population has gone,” believes MacLeod.
Once the project is complete, monitoring will still be needed and isolated incidents dealt with in future years. However, after all the hard work, the hope is that the islands and their wildlife will gradually begin to return to a life unthreatened by this small but extremely destructive interloper.
The Hebridean Mink Project has seen significant success in the time since this feature was first published with catches declining steadily. For more information see the Hebridean Mink Project page.
For information on the work being done elsewhere in Scotland, see theÂ Scottish Mink Initiative