Chinese Mitten Crab (Eriocheir sinensis)

Introduced to Europe over the last 200 years, the Chinese mitten crab was first recorded in the UK in 1935 in the Thames estuary and the species is now well established in the River Thames, Humber, Medway, Tyne, Wharfe and Ouse.

Adult crabs can be identified by their large size and the dark, mitten-like growths that they develop on their claws. They live in freshwater streams and rivers but migrate to saltwater to breed as they are unable to lay eggs at low salinities. Adults migrate down rivers in autumn and eggs hatch in spring, when juveniles and adults migrate back up the river. They are also able to cross dry land and have been found in isolated freshwater ponds.

This ability to travel large distances and cross dry land means that all water bodies in Britain are at risk of invasion from this species. Chinese mitten crabs threaten native species through predation, erosion and siltation of river banks and damaging flood defenses. In Ireland, individuals have been recorded on three occasions in Waterford harbour; one individual in 2006, 16 in 2009 and 2 crabs in 2021, one of which was a berried (reproducing) female.

• Avoid stepping into the water – this can stir up sediment, throwing up sediment DNA and any inhibitory molecules present. Sediment may clog the filter and prevent sufficient volumes of water being filtered.
• Any suspected sightings or positive eDNA results should be reported to the relevant monitoring programme. UK-based sightings/positive eDNA results should be reported to the Marine Biological Association using the email [email protected] or via relevant recording apps (e.g., iRecord or iNaturalist).Ireland: Records Biodiversity