Signal Crayfish (Pacifastacus leniusculus)

Introduced from North America, the American signal crayfish threatens native white-clawed crayfish across much of mainland Britain. Signal crayfish reproduce faster than our native species in addition to causing significant damage to ecosystems and being carriers of crayfish plague. This crayfish species is not thought to be present in the Republic of Ireland or Northern Ireland.

Individuals are most commonly found in rivers, lakes and ponds. They are bluish-brown to reddish-brown in colour with a white to pale blue-green patch near the claw hinge.

• For best results, sample during breeding or just after hatching.
• Avoid stepping into the water – this can stir up sediment, throwing up sediment DNA and any inhibitory molecules present. Sediment may clog the filter and prevent sufficient volumes of water being filtered.
• It is vital biosecurity is taken into account in survey design to reduce the spread of crayfish plague. Thoroughly disinfect all footwear/waders and equipment before entering the sampling site or moving between sites.