Hundreds of invasive crayfish killed by disease

Paul Eccleston, The Telegraph 8 Aug 08;

A deadly plague is thought to have wiped out hundreds of crayfish in a river system.

All the creatures killed so far have been from an invasive species - the Turkish crayfish - but there are fears the disease could spread to the native white-clawed crayfish.

The dead crayfish were found by a ranger in the lower River Colne in Colchester, Essex and samples have now been sent for analysis to the Centre for Environment, Fisheries & Aquaculture Science (CEFAS) in Weymouth.

But the crustaceans are thought to have been killed by the highly-virulent fungal disease Aphanomyces astaci, commonly known as crayfish plague.

A similar outbreak on the River Waveney in nearby Suffolk last October killed thousands of crayfish

The risk of the disease spreading piles further pressure on the native crayfish which has already been driven to local extinction on many of the waterways in southern England by the relentless advance of another invasive species the American Signal crayfish.

Larger than the native crayfish it was introduced to be farmed for the restaurant trade but many escaped and quickly became established in rivers and lakes. The voracious Signal eats almost anything in its path including plants, snails and fish and has quickly displaced the native crayfish. It also carries a variation of the plague which is harmless to itself but which is fatal to its English cousin.

The Turkish crayfish was also brought into the UK as a food source but has not spread as quickly as the Signal.

The population in the Colchester area has not been big enough to cause problems and the loss of significant numbers to the plague may even help native river wildlife.

"It is usually found at the bottom of the river and tends only to appear when other species of crayfish have moved on," said Environment Agency Fisheries, Recreation and Biodiversity officer Julia Stansfield.

"Although only Turkish crayfish have been affected so far we think it will be only a matter of time before it spreads to the native species and that would be a disaster. There are no native crayfish left in the Colne but there are still some remnants in the River Stour and the River Chelmer."

The Environment Agency is asking anglers and other river users to be aware of the dangers of spreading the disease and is urging them to clean and disinfect equipment such as keep-nets.

Ironically it may be people who are trapping bigger invasive crayfish for food - at the same time helping cut numbers in the river - who are spreading the disease.

Julia Stansfield explained: "One possible route for the spread of this disease is use of unlicenced crayfish traps. The idea of this 'wild food' is much in vogue.

"While this is safe to do in parts of the country where native crayfish have already been wiped out, in the east of England we are trying to protect one of the last strongholds.

'If members of the public notice dead crayfish in any other rivers, please let the Environment Agency know as soon as possible.'