Chinese mitten crab
- Habitat: It spends most of its life in rivers, but must migrate to the sea to breed. Once the crabs have mated the males are thought to die, leaving the females to brood the eggs. In the spring the eggs hatch into larvae and after about six to seven weeks these metamorphose into juvenile crabs, which then migrate back up the river into freshwater to complete the life cycle.
- Description: The Chinese Mitten Crab is very distinctive crab, light brown in colour, with hair growing on equal sized claws that are often referred to as ‘mittens’. It is currently the only crab to live in freshwater in Ireland and Britain and therefore may have significant impacts on the functioning of this environment. This species is also able to migrate across land unlike all other crab species in Ireland. Mitten Crab are an intermediate host for the mammalian lung fluke Paragonimus ringer, known to infect humans. They burrow into river banks causing holes about 3 cm in diameter. Dead bodies (carapaces) may be found though positive identification would require the mittens to be present.
- Origin and Distribution: The species is originally from Asia where it is considered a delicacy in local cuisine. Now found in Europe, where it invaded nearly a century ago, Mitten crabs have now spread to North America. For reasons that are not understood, the populations of mitten crabs in England and North America did not at first expand like those in mainland Europe, but numbers are currently rising, prompting concern.
- Impacts: When population densities are high, the species causes considerable damage to soft sediment banks through burrowing which increases erosion and might affect flood defences. This has been documented in Europe and North America. In Ireland there is concern that the species may impact on the native and endangered White Clawed Crayfish as well as fish species such as the protected Twaite Shad fish. Additional negative impacts, such as loss of biodiversity and recruitment of commercial species are expected. There are economic impacts associated with introduction of this species. To date, in Germany, the species is known to have cost at least 80 million Euro in monetary value. The Mitten Crab is also an intermediate host for the mammalian lung fluke Paragonimus ringer, known to infect humans.
- How did it get here? It is unclear at present how exactly the Chinese Mitten Crab arrived in Ireland. Likely vectors for introduction include ship ballast water and hull fouling. Other human mediated vectors such as the live food trade and smuggling may be possible as the mitten crab is a delicacy.
Where is it found in Ireland? Chinese Mitten Crab was first found in Waterford Estuary by fishermen catching them in their net.
To Date Not found in Northern Ireland
See the National Invasive Species Database for more information on the distribution of this species in Ireland.
Do not introduce to new sites.
Clean all equipment before moving between waterbodies.
Do not move water from one body to another.
Current Legislative Position (Listed on 03 August 2016)
This species must not intentionally be brought into the Union; kept; bred; transported to, from or within the United Kingdom, unless for the transportation to facilities in the context of eradication; placed on the market; used or exchanged; permitted to reproduce, grown or cultivated; or released into the environment.
For further queries, you can contact the Non Native Invasive Species Team in the Northern Ireland Environment Agency on 028 9056 9558.