Most Unwanted:
Non native crayfish species
Habitat: Freshwater
Threat: Threatens the endangered white-clawed crayfish
Status: Potential
All non native crayfish pose a threat to Irish ecosystems. Crayfish are small crustaceans that resemble small lobsters. They are found in freshwater aquatic systems and some species are known to be able to travel over land to new areas. Some species of crayfish have become invasive in many parts of the world. In Britain new species of crayfish have become established and these species have caused widespread ecological damage. Their presence endangers the already threatened white clawed crayfish.
In contrast to the situation in Britain, the island of Ireland has remained free from non native crayfish to date. This is good news for the white-clawed crayfish. This species is considered globally threatened with extinction by the IUCN and the island of Ireland is one of the last few remaining refuges.
What is it
The North American Signal Crayfish, Pacifastacus leniusculus is considered the most likely non-native crayfish species to be introduced to Ireland. Nevertheless, due to potential impacts and the possible loss of the endangered white-clawed crayfish the following species also ranked as high risk and threat to Ireland:
Marble Crayfish (Procambarus sp), Louisiana Crayfish (Procambarus clarkii), Spiny cheeked crayfish (Orconectes limosus), Noble Crayfish (Astacus astacus).
Impact
Invasive non native crayfish are known to have a detrimental effect on populations of white clawed crayfish. American crayfish species can be carriers of the so-called 'crayfish plague' - a disease caused by a fungus (Aphanomyces astaci). The 'plague' does the American crayfish little apparent harm but is lethal to European species such as the white-clawed crayfish (http://www.lbap.org.uk/bap/species/crayfish.htm). Crayfish plague carried by signal crayfish is one of the main reasons for the collapse and extinction of native white-clawed crayfish across Europe, including in Britain.
Some species of invasive crayfish can cause additional damage to river systems by constructing burrows in the banks leaving them prone to collapse. This presents a hazard to human health and safety by weakening walkways and of the river side and impacts on the flood defence of the areas affected.
Where are they now
Due to the rapid expansion and colonisation of European water bodies, signal crayfish are now widespread across many parts of Europe, but are not present in Ireland. The nearest neighbour populations to Ireland are present in England, Wales and parts of southern Scotland. Due to trade and travel links, Britain is considered the most likely source of non-native crayfish, but they are present across Europe, so there are a number of pathways that would bring non-native crayfish into Ireland.
Since signal crayfish are acid intolerant, it is believed that if introduced to Ireland, they would quickly establish themselves in the lime-rich midlands, which is the core area of white-clawed crayfish. Such a scenario would likely prove catastrophic for white-clawed crayfish.
How can they get here
Intentional introduction or escape from aquaria is considered the most likely route into Ireland for each of these species.
What you can do if they are found in Ireland
Report all sightings
To maximise the effectiveness of any control measures, and thereby protect the endangered white-clawed crayfish and other aquatic organisms, early detection of any introduced populations is crucial. Everyone is encouraged to report all potential sightings of the species of crayfish highlighted here. If you see some of these animals on sale in your local areas, or suspect some have escaped into a river system near you, please report your sighting and include a photograph if you can. Remember the native white-clawed crayfish is an endangered species so please try not to disturb this species.
Additional reading
Habitas Invasive Alien Species in Northern Ireland
