Dams, specifically aimed at preventing the spread of North American signal crayfish have been installed between two Scottish river systems to prevent the threat this invasive non-native species poses to the River Annan, one of the best salmon and sea trout rivers in Britain.

North American signal crayfish feed on salmon eggs and freshly hatched salmon are already found in the River Clyde catchment. Scientists have installed a £50,000 barrier, consisting of two dams set 30 yards apart, close to where the headwaters of the rivers Clyde and Annan meet, in South Lanarkshire.

Both rivers will now be checked regularly to monitor the spread of crayfish.

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Scotsman (1 Jul 2011)

Herald (1 Jul 2011)