River Reflector February 2019

The White clawed crayfish (Austropotamobius pallipes) is the UK’s only native species of crayfish and is one of our largest freshwater invertebrates. It is currently facing a number of threats including habitat fragmentation, water pollution and crayfish plague all contributing to its rapid decline in the last 30 years.

Crayfish, often referred to as freshwater lobsters, are one of the most amazing and unworldly creatures found in our rivers, lakes and ponds. There are over 600 species of crayfish worldwide with only the white clawed crayfish being native to the UK.

Found in the Balkan Peninsula, this European freshwater crayfish reaches its northerly limit in the UK where it has the greatest population densities. Although difficult to tell apart from other crayfish, these gentle giants are olive-green to brown in colour and can reach up to 15 centimetres in length. The common name refers to the fact that the undersides of the claws are off-white to pinkish in colour.

Crayfish are mostly nocturnal and are more active and visible during the spring and summer. They mature after 3-4 years and can live up to 12 years in well oxygenated, calcium- rich water. This alone makes them a key indicator species of high water quality. Their ideal habitat is shallow streams and rivers with rocks and crevices that they hide under to avoid predation. Tree roots and vegetation offer shade in hot summers and provide coverage for the day before venturing out at night to feed on plants, small animals and detritus. They live alongside other key invertebrates such as caddis fly larvae, mayfly’s and mollusc species like otters and water vole. Trout and stickleback also occur in the same habitat. 

River Reflector

White Clawed Crayfish 

White clawed crayfish are found in scattered locations across England and Wales, but are almost entirely absent from Scotland. It is estimated that populations have declined by 70%  since the 1970 and this decline continues almost everywhere. Pollution, habitat destruction and introduction of non native crayfish have all been important factors into their decline. Out of the 7 invasive species of crayfish in the UK the signal crayfish (Pacifastacus leniusculus) is by far the biggest threat. A more aggressive crayfish, it has successfully outcompeted our native for food and habitat. Signal crayfish are more tolerant to pollution and able to produce more eggs. However, the sudden diminish in white clawed crayfish is primarily due to a lethal infectious fungal disease carried by the signal crayfish called crayfish plague.

 

River Reflector

Signal Crayfish (Left) White clawed Crayfish (Right)

What you can do?

It is estimated that white clawed crayfish could face extinction in the UK within 30 years if current populations are not protected. By simply cleaning and disinfecting wellies, waterproof clothes, fishing tackle and water sports equipment you can reduce the spread of crayfish plague, one of their biggest threats. Click on the link to find out more: http://www.nonnativespecies.org/checkcleandry/

There are other conservation projects now being set up to try and reverse the trend. A major recent initiative is the 'Ark Site programme', which aims to identify isolated self-contained sites that can support a healthy, self-sustaining population of white-clawed crayfish. Setting up Ark sites can be straightforward and inexpensive and can provide a sustainable future for the white clawed crayfish in the UK. If you have a potential Ark site on your land contact rivershub@shropshirewildlifetrust.org.ukfor more information.

rivers

Always remember to check-clean-dry before entering and leaving a watercourse

Where to find them in Shropshire

In Shropshire, populations have declined dramatically, the River Corve in South Shropshire did once have strong numbers of Crayfish, but we are unsure how many can now be found here. There have also been reports of white clawed crayfish within the River Clun also in south Shropshire.

White clawed crayfish are currently endangered and are now legally protected. A license must be held in order to survey them otherwise it is illegal. If you are interested in learning more about white clawed crayfish and want to be involved in surveying and learning the importance of keeping waterways clean for wildlife contact rivershub@shropshirewildlifetrust.org.uk to join a organised survey group this summer.

River Reflector

River Clun at Clun bridge