Boffins are plotting a honey trap to snare "plague-carrying" giant crayfish - invaders from North America - which have wiped out our native species in parts of the River Wharfe.

The pioneering project designed to lure the American signal crayfish, pictured, into specially-developed sex traps could help bring back the native fish, last seen in the Wharfe near Grassington six years ago.

Thousands of the invaders - more than twice the size of the native crayfish - have taken over a stretch from Conistone to Burnsall.

They are more voracious and have out-competed the native crayfish for food, driving them from their natural habitat.

Our own more delicate types are just managing to hang on in some of the Wharfe's small tributaries

The signal also carries a fungal disease known as crayfish plague, which has wiped out many native-born types. So scientists at Newcastle University are devising a plot to use pheromones of both male and female signal crayfish to trick them into entering an underwater basket. Once caught they will be dispatched.

Details have been presented to 120 delegates at an international conference on crayfish conservation.

The scientists believe the trials are vital to protect our endangered fish from the invaders which were brought in to feed the demands of the restaurant trade.

Environment Agency experts believe the signal crayfish taking over the Wharfe escaped from a nearby fish farm where they were being bred for the restaurant trade.

Simon Williams, an EA ecologist, said: "The last recorded native was seen in 1996.

The first recorded signal was in 1990. When we can solve the problem of removing the signal crayfish - that needs to be done first - then we can look at ways of reintroducing our native fish."

He said signal crayfish were adaptable and were known to have crawled across land to reach other habitat areas.

Newcastle University scientist Paul Stebbing, who has been leading the project, said: "Results so far suggest that using pheromones with established trapping methods could be a viable option for controlling the species."

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

If the sex trap project was a success, it could be extended to target other invaders such as the narrow-clawed, noble, red swamp and spiny-cheek crayfish, he added.