Species checklist - animals

American mink by John McAvoyAmerican mink by John McAvoy

American mink
Mustela vison/Neovison vison

The American mink (pictured above) was imported for its fur, but after escapes and deliberate releases it has now become established in the wild. Mink prey on freshwater fish, birds and the native water vole. Mink predation has had a devastating impact on water vole numbers, which saw a dramatic decline during the 20th century.


Carnivorous semi-aquatic member of the weasel family with rich, usually dark brown fur. There is often a white patch on the chin. It is a generalist and opportunist predator with a variable diet including aquatic, semi-aquatic and terrestrial prey. Mink habitually follow waterways, lake edges and coasts, but cross other habitats regularly. They can often spend time feeding away from water.

Signal Crayfish

Pacifastacus leniusculus

Another American escapee. The signal crayfish is posing major threats to the wildlife of our rivers. It was introduced in the 1970s and bred on farms for the restaurant trade, many escaped or were released and they are now present in almost every river catchment in England. They are voracious predators, eating plants, inverterates, snails, asmll fish and eggs. Their burowing can undermine riverbanks and destabilise structures built on the edges of rivers. They also carry a fungus, known as crayfish plague, which causes them no harm but is fatal to our native white-clawed crayfish and has had a detrimental impact on their numbers.

Signal crayifsh copyright Trevor Renals


Lobster-like in appearance and reaches a maximum size of 16-18cm. It is much larger than the native white-clawed crayfish and its claws have red undersides with a small turquoise/white blotch on the upper surface at the claw hinge. Found in streams, canals, rivers, lakes and ponds, and is also able to survive in brackish water. 

Photo: Signal crayfish by Trevor Reynolds