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Last Updated: Tuesday, 10 February, 2004, 09:40 GMT
Danger to river from crabs
Chinese Mitten Crab. Image copyright: Natural History Museum
The crabs have hit coastal defences
Image: Natural History Museum
Marine experts are warning there is a danger that a north Devon river could be infested by a freshwater crab from China.

A Chinese Mitten Crab was found in the River Torridge in January and experts suggest that the fact she was bearing eggs means there are likely to be more.

With no natural predators, there are fears the crab could take hold on the river where its habit of burrowing into riverbanks can make them unstable leading to potential flooding, as well as damaging salmon and trout eggs.

The crab is believed to have arrived in the ballast tanks of a large ship which are emptied in British waters before travelling on to the Far East.

Ballast treatment

The practice has had a devastating effect on marine life in places such as the Great Lakes, the Baltic Sea and the Black Sea by bringing in non-native species which overrun indigenous animals.

Douglas Hurdston from the National Marine Aquarium in Plymouth said the crabs' burrowing can have potentially devastating effects for a habitat and its inhabitants.

He said: "The obvious problems with this is the potential for flooding.

"But it can also cause problems for the river itself, because a lot of sediment and soil can go into the river.

"If it is a salmon-breeding area, it can cover over nests and kill all the eggs in them. It will also swamp the food of the salmon and trout."

The International Maritime Organisation is calling for all ballast water to be treated before its discharged from vessels.

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