Outbreak of crayfish plague in Co Cavan

There has been an outbreak of ‘Crayfish Plague’ Aphanomyces astaci  – a water mould that infects and kills white-clawed crayfish – in the Bruskey River near Ballinagh, Co Cavan. The National Parks and Wildlife Service (NPWS) has described the outbreak as a serious concern and warned it could have a potentially irreversible ecological impact. It is particularly worrying as the outbreak is in the expansive Erne catchment, which is also connected to the Shannon catchment via navigable canals. White-clawed crayfish Austropotamobius pallipes are listed under Annex II of the EU Habitats Directive. Ireland is a stronghold for the species in Europe as the island has been free of crayfish plague and does not have non-native crayfish species present.

It has long been known that Irish crayfish are at high risk from this disease. The risk has been there that someone may accidentally or even deliberately introduce a different species, which carry a lethal disease, into Ireland. Similarly the risk was there that crayfish plague could be introduced on boats, wet angling equipment and wet clothes. Until now, Ireland has been free of crayfish plague and is the only European country without any established non-native crayfish species. The circumstances around the current outbreak of crayfish plague are unknown.

One of the major reasons for the decline in White-clawed crayfish is the spread of crayfish plague. 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, but the disease has not been recorded since.

American crayfish are resistant to the disease. 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 non-native crayfish species also 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 highly susceptible to crayfish 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. This current outbreak of crayfish plague is therefore of serious concern. For further information please see these links:-

Anglers and the public are being urged to take precautions such as thoroughly disinfecting fishing gear to stop the plague spreading and to report mass mortalities, sightings of large red-clawed crayfish. For further information contact NPWS and the contacts are Brian Nelson (01 888 3294; brian.nelson@ahg.gov.ie) or Ciaran O’Keeffe (087 2646416; ciaran.okeeffe@ahg.gov.ie).