AN invasive foreign crab found in a Scottish river could have a "devastating impact" on salmon and trout if the species spreads, scientists have warned.
The Chinese Mitten Crab was recorded in Scotland for the first time when it was found in the River Clyde in recent months.
It is classed as one of the top 100 worst alien species in the world and threatens biodiversity by competing for food, preying on native species and causing severe damage to riverbanks through burrowing.
The crab could pose a threat to native salmon and trout if it spreads to parts of the river where they spawn, as the crabs will eat fish eggs.
The crustaceans, native to East Asia, were first recorded in the River Thames in 1935 and one has now been spotted north of the border.
The remains of the crab were found in the Clyde on June 23.
Dr David Morritt and Jessica Webster, from the School of Biological Sciences at Royal Holloway, University of London, have been studying the crabs in collaboration with Dr Paul Clark at the Natural History Museum.
They are concerned about the environmental risk to Scotland.
Dr Morritt said: "Our laboratory feeding trials with sub-adult Chinese mitten crabs reveal that the crabs apparently show a preference for larger [fish] eggs.
"The occurrence of these Chinese mitten crabs in a Scottish river could have a devastating impact on the famous salmon and trout fishing rivers should they manage to reach parts of the catchments where these fish spawn."
Dr Willie Yeomans, of the Clyde River Foundation, added: "The chance discovery by an angler poses a potentially significant ecological threat to the Clyde system, the ecology of which is recovering from centuries of poor water quality and structural modification."
Chinese mitten crabs, which travel well on land, spend most of their life in freshwater but return to salt water to breed.
Under water, the "setal mat" on the crab's claws spreads out and looks like furry mittens, the function of which is not known.
One of their other colloquial names, especially in Asia, is "hairy crab" while the scientific name - Eriocheir sinensis - means "Wool hand, the Chinese".
It is thought the species was probably accidentally introduced to the River Thames by shipping.
In the late 1980s the mitten crab began to disperse westwards along the Thames and there are now well-established populations of them in a number of Welsh and English rivers, as well as a single sighting in Ireland in 2006.
Their presence is being tracked by the Mitten Crab Recording Project.
The International Maritime Organisation has set out standards for the control and management of ships' ballast water in an effort to control the transport of species to non-native waters.
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