From Department of Housing, Local Government and Heritage
Published on
Last updated on
All water users are being urged to take precautions after confirmation of an outbreak of crayfish plague on the River Blackwater and the detection of crayfish plague causative agent in the River Awbeg and Spa Glen Stream which are within the extensive Blackwater River catchment. This worrying situation is being monitored by the National Parks and Wildlife Service (NPWS), Inland Fisheries Ireland (IFI), the Marine Institute and independent ecologists.
Crayfish plague was first discovered in Ireland in 2015 in Co Cavan, and has spread to several other rivers across the country. However, this is the first recorded outbreak of the deadly crayfish plague in Co Cork.
In response to the outbreaks of crayfish plague, a National Crayfish Surveillance Programme was established in 2018 as a Memorandum of Understanding between NPWS and the Marine Institute. This programme uses environmental DNA (eDNA) a novel, non-invasive method of detection of the DNA of crayfish and the disease from water samples. It monitors the spread and persistence of crayfish plague throughout Ireland and the distribution of the White-clawed Crayfish.
The White-clawed Crayfish is a globally threatened species and Ireland holds one of the largest surviving populations. The crayfish plague is devastating, causing 100% mortality of White-clawed Crayfish. Given the experience of outbreaks elsewhere, a total kill of the crayfish population is expected which will have major consequences for the ecology of the Blackwater, Awbeg and the whole of Munster Blackwater catchment.
There is no indication of how crayfish plague reached the catchment but the disease is easily transmitted in water or via contaminated equipment (for example: kayaks, waders or nets). It is completely harmless to people, pets, livestock and all other freshwater organisms.
This outbreak is of great concern as it is within the Blackwater River (Cork/Waterford) Special Area of Conservation (SAC) which contains an internationally important population of White-clawed Crayfish.
The Blackwater catchment is popular with anglers, kayakers and other recreational users. NPWS and IFI are urging all users of any river to implement the Check, Clean and Dry protocol which involves routine checking, cleaning and drying of equipment after leaving a river and before entering another waterbody.
Cleaning everything that has been in contact with the water using hot water (above 45oC) or a high pressure spray if possible followed by a drying period where all equipment and wet gear is dry for at least 48 hours, should be adopted as standard practice in all freshwaters. Disinfect everything if complete drying is not possible.
Containment of the outbreak is essential to prevent spread to other as yet unaffected populations in Ireland. If the crayfish plague continues to spread, there is a high probability that the White-clawed Crayfish will become extinct from most rivers in Ireland.
White-clawed Crayfish is the only native freshwater crayfish species found in Ireland and is present in lakes, rivers and streams over much of the island. Throughout its European range, this species has been decimated by the impact of crayfish plague which spread to Europe with the introduction of North American species of crayfish, especially Signal Crayfish. Many American crayfish species are resistant to crayfish plague, but can act as carriers of the disease which is rapidly fatal when passed to the White-clawed Crayfish. To date there has been no record of American crayfish species in Ireland, suggesting that the spread of the crayfish plague is solely due to human activities and lack of biosecurity.
White-clawed Crayfish are protected under Irish Law and the EU Habitats Directive and it is illegal to introduce any non-native species of crayfish to Ireland.
The combined impact of the introduced crayfish species (which may out-compete the smaller native crayfish) and crayfish plague have completely eliminated the White-clawed Crayfish from much of its European range, leaving Ireland as the last stronghold of the species.
Check, Clean and Dry protocol: Check, clean and thoroughly dry equipment and clothing that comes in contact with the water before using again. If everything cannot be dry for at least 48 hours before re-entering the water, then disinfect it.
CHECK your gear, footwear and watercraft after leaving the water for mud, aquatic animals, or plant material. Remove anything you find and leave it at the site.
CLEAN everything thoroughly as soon as you can. Pay particular attention to nets, waders, and areas that are damp and hard to inspect. If possible, use hot water (at least 45oC) or a high-pressure spray.
DRY all equipment and clothing until dry for at least 48 hours – some species can live for many days or weeks in moist conditions.
Disinfect cleaned items if complete drying is not possible. Items can be soaked, thoroughly sprayed or wiped down with disinfectant. Extreme care should be taken when using disinfectants and the manufacturer’s guidelines should always be followed.
Further information on the Check, Clean and Dry Protocol: Check Clean Dry - Invasives.ie.
Members of the public who suspect they have seen a non-native species of crayfish are asked to take a picture of it showing the underside of the claws and submit this through this web page http://records.biodiversityireland.ie/record/invasives or the Biodiversity Data Capture app.
White-clawed Crayfish Austropotamobius pallipes occurs throughout Ireland mainly, but not exclusively, in areas of limestone geology. It lives in a very broad range of freshwater habitats from tiny streams and ditches to many small, medium and large lakes. The species is a generalist feeder and it in turn is a significant prey item of the Otter.
Crayfish plague is caused by a fungus-like organism Aphanomyces astaci which is of North American origin but now occurs throughout Europe. The crayfish plague organism (technically an Oomycete and often called water moulds) normally grows on the outer shell of crayfish and as North American crayfish are generally immune to it, as they can prevent any infection reaching their body tissues. However, when the water mould infects White-clawed and other European crayfish, it rapidly, and fatally, spreads into the body tissues. Infected animals become distressed and behave abnormally and may survive several weeks before dying.
Non-indigenous Crayfish are any species which are not native to the country. Many crayfish species have been moved within Europe and into Europe from North America and Australia. The most significant of these is the North American Signal Crayfish Pacifastacus leniusculus which is one of the main carriers of crayfish plague. This species is much larger than the White-clawed Crayfish and with distinctive red coloration on the underside of the claws. Background information on the native and non-native crayfish and the crayfish plague is available to view and print from these web pages: