Warning mink are vicious do not try to touch them
The American mink, mustela vision, is a recent introduction to Great Britain, having been released from fur farms into the wild by animal rights protestors during the 1950s. This proved to be a bad move on their part as a great many of the mink where then destroyed by farmers, and the ones that survived devastated local wildlife populations. In recent years these feral populations have been very successful, and the mink is now well established across most of England and Wales. Mink are often first mistaken for otters but although very similar in looks they are much smaller 30-45cm in body length (plus a tail of 13-26cm).
Mink will normally make a den within ten metres of water and have a large diet including fish, frogs, invertebrates (such as snails), mammals (rats, mice and even rabbits) and waterfowl.
A mink will dive into a pond freely swimming underwater and easily catching whatever food it wants, often taking extra to save for later.
I have actually seen a Mink taking a 14 inch koi from my own pond in a built up part of Ipswich. They are about so don’t disregard them as a very serious threat to your pond (and other pets).
To protect your pond from mink you must ensure that it cannot get to your pond in the first place, this means sealing off any gaps in or under fences, gates or hedges.
Mink droppings (mink scat) look like curled up earthworms and may smell of fish due to their diet. Their paw prints are around 2.5cm across with five toes, other than these tell tale signs a mink leaves no signs of its visit apart from the rapid disappearance of fish.
Live Traps are available and cost around £30 locally, these do not harm any animal inadvertently caught (such as hedgehogs) and are too small to cause a problem for domestic cats. But be warned that it is illegal to release a mink into the wild and as such it will most likely need to be humanely destroyed if caught. Traps should be baited with fresh fish or shellfish and set to be very sensitive.