ALIEN INVADERS - The Signal Crayfish
By Paul Orford

The Signal Crayfish, introduced into the UK in 1970 have become an unwelcome and destructive invader of the rivers, canals and lakes in the South West.

Signal crayfish have had a major impact on our own native crayfish species, the white clawed crayfish. The American invaders are more efficient feeders making them grow and reproduce more quickly. They also carry a nasty fungal disease that they are immune to but which has wiped out whole populations of our native species. They can also burrow into banksides causing them to collapse.

Concerns over the domination of Signal Crayfish have been raised for many years but the problem only seems to be getting worse. In the past the Environment Agency has concentrated research projects on how to eliminate the Signal Crayfish although more recently it has become excepted that completely removing them from our waters could have serious impacts on our natural ecosystem. Phil Bolton from the EA explains: "We're looking at the real effects these crayfish are having on the fish, invertebrates and plant life in our water courses. We need to limit these impacts even if we can't yet find a solution to get rid of the alien species altogether."

Since the 1970s a byelaw in the Thames Region has allowed fishery managers and anglers to use traps for Signal Crayfish, with written permission from the EA. This will soon be extended to include the whole of England and Wales. However there are concerns about how successful trapping is in controlling crayfish levels. It could actually help boost their levels in the long term. Large Signal Crayfish eat smaller ones and as trapping tends to catch the larger crayfish, more smaller ones survive increasing the population and causing more damage to the environment.

The EA recognises the problem that Signal Crayfish cause to anglers [stealing their bates] and more importantly to the environment. They have commissioned crayfish research which will not only estimate crayfish populations but will also provide detail on methods to investigate the effects of trapping and the impact of different crayfish population sizes on the environment.

How to keep crayfish away from your bait.
check baits regularly to enure they haven't been stolen
use hard or fake baits
wrap and tie soft baits
divert crayfish away from your hook baits by loose feeding a stong smelling bait away from where you are fishing.

If you want to provide information on Signal Crayfish and the problems they cause, please contact Fish South West or thamesfisheriesfeedback@environment-agency.gov.uk

October 2005 - Fisheries with crayfish problems can now have them removed by a professional company as the fight against the foreign invaders gathers pace. With more rivers, lakes and canals than ever before now infected with the American Signal Crayfish, one man has equipped himself to remove the menace. Comtinental Crayfish boss Alan Mitchell will come to your fishery and remove the crayfish free of charge. Call Alan on 01865 377499.

Source: Newscast - The magazine for anglers in the Thames Region - produced by the Environment Agency