White-clawed Crayfish Austropotamobius pallipes
The white-clawed crayfish is the largest native freshwater crustacean species. It is being severely affected by the non-native signal crayfish. They have pinkish-white claws and a pitted appearance ranging in colour from brown to olive. Being predominantly nocturnal and partial to hiding in crevices, this species is particularly hard to find.
Conservation status in Norfolk
White clawed crayfish are protected by the Wildlife and Countryside Act and the Countryside Rights of Way (CROW) Act. This means that a special licence is required from Natural England to survey for crayfish or to use crayfish traps. A Norfolk Biodiversity Action Plan has been drafted by the Environment Agency.
Our native crayfish have been severely affected by the introduction of the non-native signal crayfish. The signal crayfish was introduced to this country in the early 1980’s for farming and commercial aquaculture, but unfortunately many escaped and entered our water courses. Signal crayfish grow up to twice the size of white-clawed crayfish and are highly aggressive, therefore outcompeting the smaller and retiring native species by predation and direct competition for food.
Some non-native crayfish can carry a fungus (Aphanomyces astaci) commonly known as crayfish plague, which does not affect them but can be lethal for our native crayfish. Local warnings have been given to all water users in the River Waveney area regarding this crayfish plague following a recent outbreak. The Environment Agency is advising the public to clean any equipment with disinfectant, bleach or anti-fungicidal products
How to help
With the aid of the Biodiversity Action Plan, careful monitoring of water systems and protection of suitable habitat sites we can help conserve this species.
Martin Pugh
Information on the White-clawed Crayfish
How to recognise
This species of crayfish is the only native UK species. As the name suggests, the white-clawed crayfish has pinky-white claws; the body (carapace) is smooth but with a pitted appearance and a brown to olive colour. Their claws can feel rough on the upper side and can be a dirty white, almost pink colour on the underside, thus distinguishing white-clawed crayfish from their main threat; the introduced American signal crayfish (Pacifastacus leniusculus). Signal crayfish grow to much larger sizes and have distinctive red claw-undersides, although immature crayfish can be difficult to tell apart. The Turkish crayfish is another potential confusion species and is becoming more widespread in eastern England. The shape of the rostrum (tip of head) and presence of a row of spines on the carapace are the safest features for a positive ID for white-clawed crayfish. (Photos can be sent to NWT for identification).
Adult white-clawed crayfish moult once or twice a year and can grow up to 12cm in length from the tip of the head (rostrum) to the end of the tail (telson). Crayfish have many predators from dragonfly larvae to large fish such as Pike, Trout and Eels. Herons and bitterns are also amongst their predators as well as the otter, mink and rat.
Where to see
The white-clawed crayfish is Britain’s largest native freshwater crustacean. It is sensitive to pollution and is generally found in clean calcareous rivers and streams, being an indicator of good water quality. It may also be found in clean standing waters such as water filled quarries. White-clawed crayfish prefer to hide in crevices of rocks, bankside burrows or in submerged tree roots, therefore making them hard to find.
When to see
Crayfish are mostly nocturnal and are active between the months of July and September. During winter months they will hide along riverbanks in a state of inertia. Breeding will start in the autumn when water temperatures drop below 10˚C. Females carry the eggs (up to 100) under her tail, when hatched they still remain attached to the female, until June when they will start to disperse.
Did you know?
This species was once widespread in Europe, but many populations have been wiped out by habitat modification, pollution and, most importantly, by the introduction of non-native species such as signal crayfish. Ireland and the UK still provide some important strongholds for the white-clawed crayfish, although they have disappeared from much of southern England and the species is now only found in small pockets of the UK. In Norfolk, white-clawed crayfish have been recently spotted in the River Wissey, River Glaven and River Wensum (an SAC site for native crayfish).
Related questions
There are no questions regarding this species, perhaps you should ask us one?