- Scientific name: Eriocheir sinensis
- Also know as: Hairy Crab, Shanghai Hairy Crab, Moon Crab, Woolhand Crab
- Size: Grows to 8-10 cm across carapace.
- Distribution: Natural range is in Asian waters around China, Japan and the Korean Peninsula. However, now present in major British rivers such as the Thames and Tyne as an invasive species.
The Chinese mitten crab is a species which is native to Asia, but has become present in the UK as an invasive species. It is an instantly recognisable species which spends its life in both freshwater and saltwater environments.
The Chinese mitten crab is a medium sized crab species, which can be easily identified by the bristly hairs (setae) on its claws. It has a squareish body, long spindly legs (which may also be covered in hairs) and white-tipped claws. The colour is usually a dark green, although they can also be brown or even orange. Scientists have not been able to establish why Chinese mitten crabs have developed the hairs on their claws as they do not appear to serve any purpose.
Distribution, Habitat and Behaviour
Natural range is in Asian waters where it is most common around the East China Sea, Sea of Japan, and in Russian waters in the Sea of Okhotsk. This species is now present in European and North America waters as an invasive species. In the UK is has been found in major rivers such as the Thames, Tyne, Humber and Ouse. It has also been reported in rivers and estuaries in Scotland and Yorkshire.
In its natural habitat the Chinese mitten crab spends most of its life in freshwater rivers where they will feed by scavenging for dead fish and also hunt small aquatic creatures. They are a catadromous species, meaning that when they are sexually mature at the age of around three to five years they began to migrate down rivers towards the sea, eventually spawning when they reach saltwater estuaries and shallow inshore waters. Chinese mitten crabs die soon after they have spawned.
Status as an Invasive Species
In Europe and North America the Chinese mitten crab is present as an invasive species. It is not clear how this species established a presence so far away from their natural range, although the most likely explanation is that the larva of this species has been transported from Asia in the ballast water of commercial ships. Reports of Chinese mitten crabs invading new areas go back a long way – they were first found in Europe in 1912, and in the Great Lakes in the US and Canada in the 1960s.
Chinese mitten crabs are highly damaging to environments where they are not naturally present. They outcompete native species of crustaceans for food, and can strip the bait in pots means for more commercially valuable species. In its natural environment this species burrows into riverbanks. In some areas the burrowing behaviour of mass numbers of Chinese mitten crabs has exacerbated problems with erosion causing the collapse of riverbanks in some areas, and even caused structures such as dams to become unstable. Huge downstream migrations of Chinese mitten crabs have also caused water intakes and turbines in dams to become blocked.
Attempts to remove or even just manage Chinese mitten crab numbers in areas where they have established themselves have proved very difficult. This is because this species is physically tough, able to survive in heavily polluted waters and able to move and function when it has taken on damage which would have killed or disabled other species. Its high mobility (it is able to leave water and cross dry land) and migratory patterns also make it difficult to track and trace where Chinese mitten crabs are present. Chinese mitten crab are also a species with high fecundity, releasing large numbers of eggs and propagating the species in areas where they manage to become present.
Attempts have been made to trap Chinese mitten crabs as they migrate down rivers to migrate, and attempts to collect this species as it gathers in estuaries to spawn. However, this does not appear to have made much impact on numbers in areas where Chinese mitten crabs are now established. In the USA most states have passed laws to make it illegal to store, transport, or sell Chinese mitten crab in most states. In the UK
The Chinese mitten crab is edible and widely eaten in Asian countries. In China it is possible to buy live Chinese mitten crabs (which have been refrigerated to put them into a hibernation-like state) from vending machines. Attempts to get Chinese mitten crabs accepted as a source of food in areas where they are an invasive species are yet to succeed.