Exotic crabs in waterway invasion

Mitten crabs have spread as far north as the River Tyne

An exotic Chinese crab that preys on British native species is on the verge of taking over the country's major waterways, environmental experts warn.

Mitten crabs were first brought into Europe in ships' ballast water.

The UK spread has been most marked northwards to the River Tyne and on the south coast westwards to the Teign.

A study by researchers at Newcastle University compared their invasion to that of grey squirrels, which pushed native reds to the verge of extinction.

The study authors predict the mitten crab - so called because its claws are coated with small clumps of dark brown fur, or mittens - has the potential to establish itself in all major UK estuaries in several years' time.

'Drastic measures'

The crabs are already present in some waterways, including the Thames, Humber and Tyne rivers, and parts of the North Sea and Channel coasts.

They survive in both sea and fresh water, prey on protected native species, such as white-clawed crayfish and salmon eggs, and can destabilise river banks by burrowing into them.

Dr Matt Bentley, a member of the research team, said: "The pattern of the spread in the UK since the 1970s mirrors the spread in mainland Europe and in the Baltic region which experienced a major outbreak.

"This is a fairly good indication that the UK is set for a similar situation."

The study, published in the academic journal Biological Invasions, recommends that a nationwide monitoring and trapping system for the crab be introduced before it is too late to control the population.

Dr Bentley added: "With most invasive species, such as the grey squirrel, the problem is not recognised until it is too late to do anything and you cannot eliminate it without taking drastic environmental measures."