THE only species of crab that can be found in UK freshwaters has been found in the  Conwy Estuary.

The Chinese mitten crab, an invasive non-native species (INNS) which poses a threat to biodiversity, is also already established in the Dee Estuary.

This Invasive Species Week (May 20-26), Natural Resources Wales (NRW) is asking people across Wales to help stop the spread of the species.

Rare sightings have also been recorded in the Severn estuary, and NRW is encouraging people to record any sightings on the iRecord app or online so they can better understand their impact and spread.

The species are known to eat rare salmon eggs, large quantities of mussels and so much river vegetation that they can cause major damage to river courses.

They can carry diseases such as lung fluke and crayfish plague, and will outcompete and predate on the protected, white-clawed crayfish, as well as damage flood assets by burrowing.

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Adult Chinese mitten crabs spend four to five years in freshwater and move down to estuaries to breed and spawn before they die.

Their plankton develop in the estuary, and then juveniles move back upstream.

Jennie Jones, specialist advisor for INNS at NRW, said: “Protecting biodiversity is so vital in tackling the climate and nature emergencies.

“It is important to take action to tackle INNS that pose a threat to native wildlife.

“Most non-native species are harmless, but about 10-15 per cent can become invasive and cause harm.

“These types of invasive non-native species, like the Chinese mitten crab, outcompete some of our native biodiversity and cause damage to the environment.

“There are ways we can all help to prevent the spread of these species, including carrying out biosecurity, recording your sightings and joining a local action group. 

“We really encourage people to get to know what these invasive species are, and record their sightings through the iRecord app or through its online space that collects information about where these non-native invasive species are being seen.”

INNS are one of the top threats to global biodiversity; 86 per cent of extinctions that have happened on islands were contributed to by them.

It costs Great Britain’s economy more than £2billion a year to deal with the issue, and INNS can even harm human health. 

Once a INNS has been introduced it can be difficult to manage, particularly in the marine environment.

To help stop the spread of the Chinese mitten crab and other INNS, there are three things everyone can do to help:

  • Ensure you do not accidently move this species to a new area by checking, cleaning and drying any equipment, clothing or shoes before travelling to a new site.
  • Learn how to identify mitten crab and keep an eye out for this species.
  • Record any mitten crab sightings via iRecord.