The signal crayfish, (Pacifastacus leniusculus), is an aggressive invasive species of crayfish from North America. Its distribution within Scotland is largely restricted to rivers and streams in the southwest, though it has also been recorded in the River Nairn catchment.
Signal Crayfish can prey on small fish and fish eggs, and also compete for food and cover with some species.
For further information, please download the Freshwater Research Services information sheet:
Signal Crayfish - an unwanted addition to Scottish streams (pdf 884KB)