Signal Crayfish

(Pacifastacus leniusculus)

Signal crayfish

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, damp fishing gear or equipment. Freshwater crayfish look like small brownish lobsters. There are about 650 different crayfish species worldwide, but only six species in Europe and only one species in Ireland.

The six European crayfish species are or were widely caught for food, but all are now threatened, chiefly by a fatal disease, the ‘crayfish plague’ carried by crayfish introduced from North America. There are now ten species of American crayfish across Europe. Many of these alien crayfish now live wild in the UK.

However, Ireland is in the fortunate situation of being the last European country having no alien crayfish and we have one widespread native species, the White-clawed Crayfish, Austropotamobius pallipes. It can be found in Ireland, Britain, France, Spain, Italy and Croatia.

Crayfish plague

The fungus-like Aphanomyces astacithat causes the lethal crayfish plague is related to potato blight and grape disease, which also crossed the Atlantic to Europe. Each American crayfish species carries a different strain of the plague. 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. Crayfish and trout should therefore never be farmed together.

Download the National Parks and Wildlife Service leaflet: default Protect Irish Crayfish (1.17 MB)