Irish crayfish are at high risk that someone may accidentally or even deliberately introduce a different species, which carry a lethal disease, into Ireland or bring in crayfish plague on boats, wet angling equipment and wet clothes.
One of the major reasons for the decline in White-clawed crayfish is the spread of ‘Crayfish Plague’ Aphanomyces astaci – a water mould that infects and kills white-clawed crayfish. Crayfish plague first arrived in Europe in Italy in 1859, either with imported crayfish from North America or in ballast water. There was an outbreak in Ireland in 1987. American crayfish are not affected. However after 150 years of contact, no resistance has been discovered in native European crayfish.
This fungus-like disease is carried mostly by Signal crayfish Pacifasticus leniusculus, which are unaffected by it. However other introduced crayfish species do carry plague, including the Red swamp crayfish Procambarus clarkii and the Spiny-cheeked crayfish Orconectes limosus. Each American crayfish species carries a different strain of the plague.
The White-clawed crayfish are not immune to plague and once introduced it quickly kills off this species in a short time.The ‘Pacifastacus’ strain appears completely lethal and eradicates all native crayfish. It is not even necessary for the American crayfish to be present – the plague fungus produces spores which can be transferred on wet nets and boots, on boats, and even on fish for restocking.