Crayfish pick up the wrong signals

Scientists are using the pulling power of pioneering 'sex traps' to lure invasive alien crayfish from British waters.

In an innovative research project sponsored by the Environment Agency and English Nature, alien North American signal crayfish are being tricked into thinking they'll be shown a good time if they enter the underwater baskets. But, once caught, they are only shown the door.

The first results of the research project - using pheromones, the natural chemicals produced by crayfish to attract a mate - as bait, are being presented today to an international conference on crayfish conservation. More than 120 delegates from across Europe will discuss the management of crayfish populations in a bid to share knowledge of the best ways of ensuring the survival of a unique and fascinating creature which plays an important role in the freshwater ecosystem.

The 'pheromone' trials are vital to protect the endangered native British crayfish from the more powerful North American invaders.

The Environment Agency's Peter Sibley said: "Although pheromones have been used in pest management for a number of years on land, this is one of the first attempts to use them to improve trapping success in the water."

Work began in March last year when scientist Paul Stebbing from Newcastle University began collecting female crayfish pheromones in the laboratory.

Since last August Mr Stebbing has been up to his knees in water testing the research in rivers and ponds.

He said: "Results so far suggest that using pheromones with established trapping methods could be a viable option for controlling this species.

"Female crayfish pheromones only attract the males so we are now working with male pheromones in an attempt to capture the females as well."

The native British crayfish faces an uncertain future, threatened by pollution and habitat destruction as well as competition from its trans-Atlantic rival.

The American species is bigger, more aggressive, breeds at an earlier age and produces more eggs. The 'signal' also carries a fungal disease known as 'crayfish plague' that has wiped out large numbers of native crayfish.

Peter Sibley said: "Signals really are the bullies of the crayfish world and the trouble they cause isn't confined to crayfish.

"In large numbers they can be a threat to spawning salmon by taking fish eggs. They have been known to wipe out whole areas of aquatic plants and, by burrowing into banks, they can damage the habitat of endangered species like water voles.

"The problem is, they like it here. The largest 'signal' in the world was pulled from waters in Nottinghamshire in 2000. It weighed more than 200g.

"This species is thriving well at the expense of our own species and we need to find effective ways to control them."

Project leader David Fraser from English Nature added: "Despite being afforded a highest level of protection under national and international conservation legislation, our native crayfish are acutely threatened by American signal crayfish and the future survival of native crayfish may depend on our ability to control non-natives.

"Pheromones represent the most promising means of achieving this."

The signal crayfish was introduced to Britain in the 1970s as a commercial venture to supply the restaurant trade. But some were accidentally released or escaped into the wild and their colonies are spreading.

If successful, the project could be extended to other aliens in UK waters including the narrow-clawed, noble, red swamp and spiny-cheek crayfish.

Today's conference, sponsored by the Environment Agency, English Nature, British Waterways, the Institute of Fisheries Management and the International Association of Astacology is being held at Nottingham Forest Football Club.


Vital statistics:
Native British crayfish
- breeds from the age of three-four years
- females produce up to 200 eggs
- young hatch from May to June
- adults smaller than signal crayfish

Signal crayfish
- breeds from the age of two (one in exceptional circumstances)
- females produce up to 500 eggs
- young hatch April to May
- more aggressive than native crayfish

Signal crayfish dominate in the south and east of the country. In the last decade, native crayfish strongholds have shrunk towards the north.