The threat of the North American signal crayfish to the native white-clawed crayfish is well-known but what about the other non-native crayfish species in the UK? What are they and do they pose a threat to the white-clawed crayfish?
The native white-clawed crayfish, Austropotamobius pallipes, can be found in aquatic environments, such as rivers and lakes, in areas of England, Wales and Northern Ireland. They have however been subject to a significant population reduction in the last decade due to problems such as river pollution, habitat destruction and the ‘crayfish plague’ disease, which is spread via non-native species. White-clawed crayfish are now listed as endangered by the IUCN (Buglife 2016). The crayfish themselves are around 10cm in length and are brown with the underside of their claws being pale in colour (H&IWWT and EA, 2009).
Introduced non-native crayfish species are often invasive and can outcompete the native species for resources, as some are of a larger size and can produce a greater number of offspring, as well as spread disease. The crayfish plague causes soft tissue to be damaged, and it is actually caused by a water mould, Aphanomyces astaci (Buglife, n.d.a). However the plague is not just carried by the invasive signal crayfish.
Non-native species of crayfish found in the UK include:
Signal crayfish, Pacifastacus leniusculus
Originating from North America this species is the most well-known non-native crayfish in the UK. Thought to have started colonising around the 1970s, they are around 12-16cm in length (Buglife, n.d.b), and are recognised by the white coloured blotch on the top of their claws and red colouration underneath. They are now widespread across Britain and are not only aggressive but carry the crayfish plague, although are unaffected by the disease themselves.
Narrow-clawed or Turkish crayfish, Astacus leptodactylus
Initially from Eastern Europe, this crayfish species was introduced or escaped due to the European food trade around the 1970s and can now be found in England. These crayfish are around 15cm in length (Buglife, n.d.b), and have narrow bodies, with distinctive thin, straight claws. Although more competitive than the native white-clawed crayfish, they too are susceptible to the crayfish plague.
Spiny-cheek crayfish, Orconectes limosus
Although not the largest crayfish species, growing to around 12cm (Buglife, n.d.b), populations can expand quickly. This species was originally from Eastern areas of the USA (Buglife, n.d.b), and they were found in England at the beginning of this century (Ellis, 2014). Red-brown stripes across their tail give away their identity. This species unfortunately is a vector for the crayfish plague and they may also damage river banks by burrowing.
Noble crayfish, Astacus astacus
A European species they are not however native to the UK but were introduced in the 1980s due to aquaculture and are now found in a few sites in South West England (Ellis, 2014). Their colouring varies but they may be confused with signal crayfish due to the red colour on the underside of their claw. However they are less of a threat as they are vulnerable to the crayfish plague.
Red swamp crayfish, Procambarus clarkii
Currently found in London, this crayfish is from southern USA and northern Mexico (Buglife, n.d.b). However it was introduced at the beginning of the 1990s to England (Ellis, 2014). Adult crayfish are reddish in colour, with red warty claws and are around 10cm in length (Buglife, n.d.b). Another species which carries the crayfish plague they are also prolific burrowers and can adapt to different environments, such as surviving in wetlands which are seasonal.
Virile crayfish, Orconectes virilis
Originating from Canada and North America this species is able to breed quickly, facilitating rapid population growth. Banks of rivers can also be damaged by their burrowing behaviour and they carry the crayfish plague. Discovered in 2004 they are currently found in London (Ellis, 2014). Although smaller than 10cm (Buglife, n.d.b), this crayfish could threaten our native species.
White river crayfish, Procambarus acutus
White river crayfish were thought to have been introduced in 2012 in southern England (Ellis, 2014), however much less is known about this species.
What is being done to help native crayfish?
There are various ark sites around Britain, which are isolated areas where white-clawed crayfish have been relocated to because they are unlikely to become populated by non-native species and the sites are also managed favourably for the native species. Controlling invasive crayfish is difficult but conducted in some areas, for example by trapping. Ecological surveys and further research continue to help towards an understanding of population dynamics and the spread of the crayfish plague.
How to help prevent the spread of crayfish plague
Crayfish plague spores can remain active for around one to three weeks (H&IOWWT and EA, 2009), therefore when visiting watercourses it is important to look at your equipment and clothing (such as fishing rods or shoes) for any signs of activity; always wash your equipment and then allow it to dry. Don’t spread water from different watercourses, such as when planting vegetation, or use crayfish as fishing bait. If you see a crayfish you can report it to the appropriate local wildlife organisation or the Environment Agency.
- More information about crayfish in the UK can be found at the Crayfish Hub, a joint venture between Buglife and the Environment Agency. buglife.org.uk/uk-crayfish-hub
- For more tips on distinguishing crayfish by appearance visit buglife.org.uk/sites/default/files/Final%20Crayfish%20ID%20distribution%20and%20Legislation%2023%2006%2015_JG.pdf
Buglife. (2016) Crayfish for Everyone [www document].www.buglife.org.uk/crayfish-for-everyone (Accessed 2016).
Buglife. (n.d.a) Crayfish in Crisis [www document]. www.buglife.org.uk/sites/default/files/Crayfish%20in%20crisis%20FinalDoc2.pdf (Accessed 2016).
Buglife. (n.d.b) Invasive Crayfish Species [www document]. www.buglife.org.uk/sites/default/files/Invasive%20crayfish%20species%20-%20Profiles_0.pdf (Accessed 2016).
Ellis, A. (2014) ‘Claws for thought – Invasive non-native crayfish in the UK’, CIEEM In Practice: Freshwater ecology, 84, 34-36.
H&IWWT and EA. (2009). Crayfish and River Users. Hampshire: H&IWWT and EA.