AMERICAN SIGNAL CRAYFISH
What’s the problem? Invasive crayfish are one of the greatest threats to freshwater ecosystems worldwide. They were introduced to English fish farms in 1975, spreading widely, and were first recorded in Scotland in 1995. In the UK, signal crayfish are driving native whiteclawed crayfish into extinction – if not by transmitting crayfish plague, which is lethal to white-clawed crayfish, then by out-competing them with their larger size and faster growth. Signal crayfish also devastate the wider environment, reducing overall invertebrate biomass in infested waters by more than 40 per cent. By undermining banks with half-moon-shaped tunnels up to 2m long, they increase erosion and dump silt into gravels, which inhibits successful spawning by native fish. Research by the Ribble Rivers Trust shows that they drive trout and other fish out of streambed refuges into areas where they’re more vulnerable to predation. Signal crayfish may also be responsible for the decline of many amphibians.
What you can do
Take careful biosecurity measures when you leave an area where signal crayfish are known or suspected to be present. Apart from stringent biosecurity, no effective means of control are currently known. NB: Trapping signal crayfish usually requires a licence. If you catch an alien crayfish, it’s illegal to release it or allow it to escape: crushing is usually the most humane means of dispatch.