Mink raft offers new hope for floundering voles

Ratty, the water vole immortalised in Kenneth Grahame's The Wind in The Willows</i>, was fond of boats. And now a raft is coming to help him in his hour of need.</p>It is a mink raft, an invention that detects and traps the American mink, which in much of Britain has pushed the water vole to the brink of extinction.</p>Utterly simple - a few bits of plywood and polystyrene - the mink raft may enable the successful reintroduction of the water vole in many areas where it would be almost certain to fail now.</p>The time and expense involved in eradicating mink - reasons the animals are flourishing - can be dramatically cut by the raft developed by the Game Conservancy Trust.</p>Developed by a team under Jonathan Reynolds, the trust's head of predation control studies, the raft has two functions - monitoring and trapping.</p>Because mink are hard to find, trapping them is haphazard. Every trap has to be checked daily, by law, with no guarantee that anything will be caught: the effort is enormous, and for smaller conservation bodies, the expense is prohibitive.</p>The mink raft is moored to the side of a river bank. It has on its flat top a wooden tunnel, which mink, inveterately curious, cannot resist entering. Inside is a pan containing a mixture of clay and sand on which their footprints will be left. Inspected once a fortnight, it shows where mink are present. If mink are found, the tunnel can be converted into a trap. Bars prevent otters from entering and mink caught inside are humanely killed. Other species found in the trap are released unharmed. The trust estimates that mink could be cleared from a river catchment for as little as £3,000.</p>Mink are found almost everywhere in Britain south of Loch Ness. Imported to fur farms from the 1930s onwards, they began escaping in the mid-1950s and started to breed in the wild. A six-year effort to eradicate them failed in 1970.</p>Their presence spelt doom for Ratty and friends for two reasons. Firstly, they fill a niche in the British ecosystem for an aquatic predator: they are fierce killers, and they swim. Stoats and weasels are no threat to water voles because they are no good in water; otters ditto, because they eat fish.</p>Secondly, mink have an instinct for "surplus killing" - the mass slaughter of any suitable animals they come across.</p>The result was that water voles declined by more than 90 per cent in Britain in less than two decades to the mid-1990s, a decline more sharp than that of tigers or rhinos.</p>Mink have also had a devastating effect on seabirds breeding in Scottish sea lochs and may be hurting other species, including water shrews, crayfish and lampreys.</p>