White-clawed crayfish - Austropotamobius pallipes - is our only native freshwater crayfish. Once common and widespread in streams, ponds and lakes, it is under threat from alien crayfish. Many populations of White-clawed Crayfish have already been lost and most of those remaining are at risk of extinction.
General information: Like a small lobster, the White-clawed Crayfish
grows to about 10–12 cm in length whereas the invasive American Signal Crayfish grows to about 16 -18 cm. The smaller native species is dark greenish brown with pale undersides to its claws.
Crayfish live in both flowing and still water, and are usually found in streams with stony beds. They can live in water with some sediment.
Crayfish are active mainly at night, hiding by day under stones or in crevices in the riverbank.
They take about six years to reach full size, but breed after three or four years. They mate in October/November, with eggs hatching the following May or June.
White-clawed Crayfish require good water quality to support their prey species – insect larvae and fish. They also feed on larger plants and detritus.
They benefit from gravel-bottomed or pebbled stream beds. They live under larger stones, in undermined, overhanging banks, amongst stonework, roots of woody vegetation, saturated logs and accumulations of fallen leaves.
In Barnsley, White-clawed Crayfish are still found in Cawthorne dyke / Daykin brook, a tributary to the river Dearne, although they are threatened by Signal Crayfish populations extending their range.
The decline in numbers.
Numbers of white-clawed crayfish are now significantly reduced, with up to a 50% decline in numbers and range in the UK in the last 25 years.
The White-clawed crayfish has suffered a decline of 50 – 80% across its European range in the last ten years.
Local surveys have shown a continued decline in the numbers of White-clawed Crayfish and loss from streams where they were previously. Whereas Signal Crayfish continue to extend their range.
Factors causing loss or decline
There are a number of reasons for the significant drop in the numbers of White-clawed Crayfish and their absence now from streams and water courses where they were previously.
The invasive Signal Crayfish predate and compete with White-clawed Crayfish. Signal Crayfish are the most widespread non-native crayfish, grow much larger than our native crayfish, are much more aggressive, and are able to produce more young.
Crayfish plague has significantly reduced the numbers of White-clawed Crayfish. It is a disease caused by a fungus which is carried and spread by the Signal Crayfish although it does not affect them. Spores from the fungus can also be spread by water and fish.*
Habitat modification and management of water courses can also affect White-clawed Crayfish.
Pollution, particularly incidents involving pesticides and sewage leakages into water courses, can wipe out entire populations of White-clawed Crayfish from local streams.
Good practice in helping to conserve crayfish populations
What we can do - local action
Maintaining and possibly increasing White-clawed Crayfish populations in the Barnsley area will be difficult but local actions include:
White-clawed crayfish Austropotamobius pallipes is ‘endangered’ on the IUCN red list of threatened species and is at risk of global extinction
It is a Priority Species in the 2007 UK Biodiversity Action Plan.
It is a species of principal importance under Section 41 of the NERC Act (2006).
As such it is a national priority species in Biodiversity 2020.
It is a local priority species for Barnsley because of its national status, its severe decline and the risk of its loss to Barnsley.
The white-clawed crayfish is listed in Appendix III of the Bern Convention and Annexes II and V of the ECD Habitats Directive. It is classed as globally threatened by IUCN/WCMC.
It is protected under Schedule 5 of the Wildlife and Countryside Act 1981 in respect of taking from the wild and sale. Updated in the Countryside and Rights of Way Act 2000.
The Salmon and Freshwater Fisheries Act 1975 prohibits the taking of this species by certain methods and requires consent for proposed introductions.
It is illegal to catch or handle native or non-native crayfish without a licence.
As a Section 41 species under the NERC Act (2006), White-clawed Crayfish need to be taken into consideration by any public body in managing their estate.
What is being done:
Annual surveys of tributaries to the river Dearne to the west of Barnsley are carried out by Trevor Mayne.
Daykin brook is scheduled as a Local Wildlife site but is not under positive cosnervation management.
An attempt to create an ark pond to house White-clawed Crayfish away from Signal Crayfish has not been successful thus far
Links for further information
Buglife, supported by the Environment Agency, has a comprehensive information hub for the public and professionals.