American Mink – non-native species

American Mink

Light coloured American mink

Light coated American Mink photo Lan_keven

Another American alien species is the American mink.  Thoughtlessly introduced into the wild it now appears over most of the UK except for the very north of Scotland.  It’s a lively, bold predator; much more likely to be spotted than the shyer otter.  It’s not even that perturbed by humans. It ravages the banks of the rivers where water voles live and the females, particularly, are small enough to slither into the voles’ nesting holes.  Like foxes taking poultry, they kill prolifically and continue until the entire group of birds or animals are dead; they will raid a hen house too, given the opportunity.  They carry away some of the kill but leave a great deal behind.


American Mink Phil Lanoue

Portrait of an inquisitive American mink. Photo by Phil Lanoue

Obviously American mink are great swimmers, having partially webbed feet, but they also climb trees and raid nests for eggs and chicks.  It’s frustrating that the American Mink don’t have a much greater impact on American signal crayfish.  They do take crayfish as a regular part of their diets; however, the native crayfish is far more vulnerable.   They also take advantage of ground nesting birds and moorhens are particularly suffering a decline from the predation by American mink.

American mink are smaller and slighter than otters; they are brown with a white chin/throat and under parts.   Breeding light coloured specimens selectively for the fur trade rendered the British feral mink a lighter brown than the true American Mink. They have somewhat fluffier tails than otters and more pointed faces.  Although there are reports that the species is diminishing more needs to be done by way of trapping and removing mink from sensitive areas where water voles are established and breeding.

The reintroduction of the otter in many areas will hopefully help stop the catastrophic crash in water vole numbers that has happened over the last 6 decades – up to 95% loss.   Otters prey on mink and, by reducing numbers, allow water vole numbers to improve.  Although otters eat water voles the otter is too large to enter the water vole burrow so the whole family is at less risk of obliteration.

Welsh otters Photo by JC Roberts

Welsh otters Photo by JC Roberts

The above photo shows the difference between a mink and an otter.  If nothing else the foot print of an otter has the webbing visible and is an appreciable size, the footprint of an American mink is as dainty as a kitten’s and the webbing is not visible, in size no bigger than a 2 pence piece.

It is essential to remember that if you catch an American mink in the UK you may not then release it back into the wild, nor may you keep it.  It must be humanely dispatched with a suitable firearm.  If you are unable to do this you should contact a game keeper, a ranger or the RSPCA.  

American Signal Crayfish – non-native species

Crayfish are freshwater crustaceans, and there are two main species in UK – the native white-clawed crayfish (Austropotamobius pallipes), and the non-native American signal crayfish (Pacifastacus leniusculus), which was introduced to Britain in the 1970s by crayfish farmers.

The American signal crayfish is bigger, breeds earlier and more prolifically and carries a fungal disease that affects the white-clawed crayfish very badly.  They can cross dry land to move to ponds and rivers and will survive a long time out of the water completely.  They can be 25cm long; flip one over and the bright red claws signal that you have found the alien.

Its legal to catch American signal crayfish for food but there are bylaws covering the trapping of crayfish, and what you can do depends on local circumstances – especially if there are native crayfish in your area.

Contact the Environment Agency to ask about your local circumstances, or you can get a crayfish trapping advice pack from the National Fisheries Laboratory on 01480 483968. You will need Environment Agency tags on your trap for it to be legal.

Don’t put any crayfish you’ve caught into ponds or other bodies of water temporarily, as they could escape and colonise an area that doesn’t have them.

Depending on whether the Environment Agency allow it in your area, you can make your own trap. You could make a cylinder with chicken wire, up to a metre long, and bend the ends over forming a cone that crayfish can climb into but not out of. The trap shouldn’t have an entrance of more than 95mm, because if there are otters in the area, they could get caught.  Bait your trap with something attractive to crayfish (a fish-head would do), and a stone to weigh it down, then put it into the water.

Check the next day. Anything other than American signal crayfish, let go, and don’t leave a trap in a watercourse for more than 24 hours, in case something other than a crayfish gets trapped in it. Let any native crayfish go.

But if you catch any American signal crayfish even small ones,don’t put them back because it is illegal.

American signal crayfish are cannibals, and if you remove only big ones, there will be nothing to keep the numbers of small ones down. The Environment Agency in Scotland have urged fishermen to kill American signal crayfish on sight.

Take them out of the trap, and keep them in lidded buckets of tap water for a couple of days to purge their intestines of any food.  If you just put them in a bucket they will get out and be roaming round the garage and climbing into the car engine.



American Signal Crayfish

How to use American Signal Crayfish after you have caught a few.

Whatever your thoughts on non-native species there’s no disputing that the Americans are over here and they’re thriving.  The only patriotically British thing to do is eat the blighters!  So I started browsing the net for a recipe… and came across this one from a chap called James Graham.  And it features another non-native – the zander, well what can you say?  You just have to eat your way through the aliens! 

American Signal Crayfish

American Signal Crayfish signalling!

Fillets of Gloucestershire zander with duck egg, asparagus and crayfish


For the zander
For the crayfish stock and crayfish jellies
For the duck eggs
  • 3 duck eggs, yolks only (reserve the egg whites for another recipe)
For the almond foam
  • 50g/2oz almond paste
  • 100ml/3½fl oz chicken stock
  • 70ml/2½fl oz semi-skimmed milk
  • asparagus spears, trimmed and peeled, to serve

Preparation method

  1. For the zander cheeks, sprinkle the flour onto a plate. Coat the zander cheeks in the flour, then dip into the beaten egg, then into breadcrumbs. Dip again into the egg and again into the breadcrumbs, until the fish cheeks are well coated. Set the coated cheeks aside and reserve with the zander fillets.
  2. For the crayfish stock and jellies, heat the olive oil in a saucepan over a medium-high heat, then add the crayfish heads and fry for 1-2 minutes, until they turn red.
  3. Add the onion, leek and carrots and fry for 3-4 minutes. Add the chopped tomatoes and the water, to cover (you may not need all the water).
  4. Bring the liquid to a boil, then turn the heat down and simmer for 50 minutes. Strain the liquid into a clean pan (discard the solids) and reduce the stock until the volume of liquid is about 400ml/14½fl oz.
  5. Remove 200ml/7fl oz of the stock, place in a bowl and, while still hot, whisk in the agar-agar powder.
  6. Pour the liquid into an ice cube tray to make eight large ice cubes. Add one crayfish tail to each cube compartment and set aside for the jelly to set.
  7. Whisk the butter into the remaining crayfish stock until it is glossy and has a sauce consistency. Set aside.
  8. For the duck egg, place the duck egg yolks in a bowl set over a pan of simmering water (do not allow the water to touch the base of the bowl). Whisk the yolks until they thicken and register 60C on a sugar thermometer, then remove from the heat immediately, cover and keep warm.
  9. For the almond foam, bring the almond paste, chicken stock and milk to a simmer in a saucepan, whisking continuously, until well combined. When combined set aside and keep warm.
  10. Just before serving reheat gently (do not boil) and blend with a hand blender to create a foam.
  11. For the zander, heat the oil and butter in a frying pan until the butter is foaming. Add the zander fillets, skin-side down and fry for about three minutes. Carefully turn over, then cook on the other side for 2-3 minutes or until cooked through. Set aside and keep warm.
  12. Just before serving, cook the asparagus until tender in boiling salted water, drain and season.
  13. Heat the vegetable oil to 180C (check the temperature with a digital thermometer) or use a deep-fat fryer (CAUTION: Hot oil can be dangerous. Do not leave unattended.) When hot, add the breaded zander cheeks and deep-fry until until golden-brown. Remove with a slotted spoon and drain on kitchen paper.
  14. To serve, spoon half of the duck egg yolk onto both plates. Place four cubes of crayfish jelly on top, then top with the asparagus and a zander cheek. Place a zander fillet to one side and drizzle with crayfish sauce. Spoon the frothed almond foam over the zander cheek.


Zander ... caught by Nick Horton - Jan 2013

Zander … caught by Nick Horton – Jan 2013

Water Shrews – UK native species

Water Shrews –  Neomys fodiens

 Protected in the UK under the Wildlife and Countryside Act, 1981.

 Water shrews are the largest British shrew. They are busy little mammals who are well adapted to an aquatic lifestyle. They have a dark black-grey coat of short fur that has a white underside and which is waterproof.  They have hidden ears, only visible as white tufts, which are closed when they are in the water. They have a stiff fringe of hair beneath their tail, which they use as a rudder when swimming and they can dive to depths of over  70cm. Although they don’t have webbed feet,   they have large hind feet with a row of stiff hairs and are the only shrew likely to be seen in the water.

Small picture of water shrew

Water shrew; dense fur and hidden ears.

Water shrews are mostly active at night, particularly just before dawn. They need to eat 50% of their body weight every day to stay alive and can travel up to 160 metres along the water’s edge to find food and shelter. Water shrews do not hibernate but remain active throughout the winter when their dense fur protects them from the cold and wet.

Pregnancy lasts roughly 20 days and 3-15 young are born per litter between April and September, with a peak of activity in May and June. Females have between one and three litters in a season. The juveniles usually leave the nest at six weeks old.  Water shrews are generally solitary, each maintaining its own territory, although they frequently live in close proximity to each other in a favoured area of stream-bank.  Females produce their young in a nest woven from dry grass, usually in a burrow or under a log. After breeding the adults die-off and the young shrews carry the population through the winter before becoming sexually mature the following spring, ready to breed in the summer following their birth.

small picture of water shrew on water

Water shrew, they can leap out of the water to catch prey in the air.

They spend their time hunting for invertebrate prey, even swimming underwater to catch caddisfly and mayfly larvae. Their main food source is freshwater shrimps, small snails, water skaters and caddis larvae which they obtain by diving and hunting underwater. Occasionally frogs, newts and small fish are eaten. They also feed on many terrestrial invertebrates such as earthworms, snails and beetles.

Occasionally water shrews are killed by birds of prey, foxes, large fish and cats but most water shrews die from exhaustion after the breeding season.

Water shrews are widely distributed throughout mainland Britain, but generally uncommon. They are scarce in the Scottish highlands and absent from Ireland and most of the small islands including for the Channel Islands, the Isles of Scilly, Scottish islands and the Isle of Man.  They are found on some of our larger islands, including the Isle of Wight, Anglesey, Arran, Skye and Mull.  Occasionally the species is found far from water in rough grasslands, scrub, woodlands and hedgerows, usually as young are dispersing. They have low populations densities compared with most small mammals.

Unlike other shrew species found in Britain, the water shrew has venomous saliva that stuns its prey. Over the centuries, this has led to many myths surrounding them. In Ancient Egypt, they were worshipped and mummified, whilst the Greeks and Romans believed that these little creatures were a source of evil!  Even though the shrew’s bite rarely punctures the skin, a red rash appears at the site of the bite which is sore to touch for several days.  Water shrews have red tipped teeth, caused by iron pigment deposits; this wears away with time.

Because water shrews are never very abundant, it is difficult to tell if their populations are under threat. They are still numerous in many sites where long-term studies have been conducted. The likely reasons for any decline in their numbers are habitat loss and water pollution. While they can tolerate a good deal of disturbance from human activities, drainage schemes and river-bank clearance may adversely affect them by altering the water supply, reducing their food supplies, destroying their burrows and the vegetation cover. They are very vulnerable to pollutants and pesticides in the water which they ingest indirectly via their prey and directly through their grooming activities.

Thanks to Lev Dahl at Wiltshire Wildlife Trust who inspired this article.