BBC News is reporting that signal crayfish (Pacifastacus leniusculus) have been found in the River Tweed in Scotland. The North American crayfish have been in the U.K. for decades, but the presence of physical barriers was thought to have been enough to prevent them from getting into the Tweed. The Tweed is home to a major salmon fishery, and officials are greatly concerned about the crayfish displacing the salmon. One biologist, noting that there are no native crayfish species in the tweed, is calling for a crayfish-targeted biological control to be introduced to combat the invader. For more details about the story, and to see two kids who caught one of the signal crayfish (Scottish accent translation not provided), check out this video.