Stealthy doom floats up on mink

Voles have declined rapidly in the last 20 years

Mink, the bane of many UK river bank creatures, face a new foe in the effort to eradicate them - a floating trap.

The mink raft, developed by a British conservationist, traps the predators themselves but allows other species - like the water vole - to escape unhurt.

The raft wins the first wild animal welfare award given by the Universities Federation for Animal Welfare (Ufaw).

Mink escaping from fur farms, or set free deliberately, are implicated in the steep decline of UK water voles.

The raft contains a cartridge with a mixture of damp clay and sand inside a tunnel, in which the paw prints of any animal visiting the raft are recorded.

Focusing the trappers

When a mink is detected the raft's human controllers place a trap on board: this catches the predator, usually within about 10 days.

The raft then resumes monitoring its surroundings to see whether other mink are present.

This provides evidence on how effective the raft is proving in catching the animals, something earlier methods failed to do, and directs trapping efforts to where they can be most effective.

The UK is thought to have had about seven million water voles (Arvicola terrestris) in 1989, but that had dropped to fewer than 900,000 before the end of the century.

A vole escapes the raft: Mink are less lucky

Causes include riverside development and subsequent habitat loss, pollution, and the depredations of mink.

Voles are often mistaken for brown rats, and poisoned as pests. But while rats have protruding ears, pointed noses and almost hairless tails, voles have small ears, blunt noses and furry tails, and are shorter and rounder than rats.

Welfare gain

Slightly confusingly, the vole was immortalised in the fictional person of Ratty, the water rat in Kenneth Grahame's book The Wind In The Willows, published a century ago.

The Ufaw award was won by the raft's inventor, Dr Jonathan Reynolds, of the Game Conservancy Trust.

Dr James Kirkwood, Ufaw's scientific director, said: "We were impressed with the mink raft as it is simple, cheap and enables efficient monitoring or capture without compromising the welfare of non-target species.

"A drawback with many trapping systems is that they are often unselective and need to be used in large numbers over long periods of time to take effect.

"This results in many non-target species such as moorhen and water vole being captured which is obviously undesirable.