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The first Chinese crab trap has been installed in Britain, amid the growing population of the invasive species.
Mitten crabs, which first appeared in the UK in 1935, have recently been spotted scurrying around London and Cambridgeshire, including in a park in the capital’s south-west, a dyke in Whittlesey and a country park in Peterborough.
The species, named for its hairy claws, is believed to have traveled from eastern China to Europe and North America in sediments found at the bottom of ships’ ballast tanks.
The crab can be identified by its greenish-gray to dark brown body and its dense brown “fur” on its white-tipped claws.
Dr. Paul Clark is a researcher in the biological sciences department at the Natural History Museum and specializes in Chinese crabs.
A mitten crab is shown climbing the dam at Pode Hole before the trap was set.
The Chinese crab that a dog walker found in Bushy Park in Richmond upon Thames
First permanent Chinese mitten crab trap installed at Pode Hole in Lincolnshire
He has worked with them since 1976, after they asked him to recover the second crab found in Britain.
In an interview with MailOnline, Dr Clark said: ‘The numbers are rising because they have a very unusual life history. After downstream migration, adult females can produce three spawns of eggs.
‘The number of eggs in each spawning can produce between 500,000 and one million. So that’s the number of larvae that are hatching in the estuary. Of course, not all of those larvae will develop into juvenile crabs that will go upstream again.
“But once this species has become established, it is very difficult to get rid of.”
The first permanent Chinese mitten crab trap has now been installed at Pode Hole in Lincolnshire, in partnership with Lincolnshire Wildlife Trust, the Welland and Deepings Inland Drainage Board and the Natural History Museum.
They hope this trap will catch migrating crabs downstream and upstream.
Dr. Paul Clark is a researcher in the biological sciences department at the Natural History Museum and specializes in Chinese crabs.
They installed the trap on August 31 of this year, but so far they have not managed to catch a single Chinese crab. Dr. Clark says it could be delayed due to warm weather, but he’s not sure.
Mick Henfrey, an employee of the Welland and Deepings Internal Drainage Board, built the trap. Welland Board also donated around £8,000 to build the device.
The trap works like a mailbox, trapping the crab inside until it is removed and taken for analysis.
Dr Clark believes that if he walked up Chelsea Embankment, in an hour he could pick up between 50 and 100 small crabs.
He added that Chinese crabs “have very few predators,” perhaps the occasional pike, and birds, but he believes this would not decrease their population.
The crustaceans were spotted in Cambridgeshire waterways, including a dam at Whittlesea (pictured).
Crabs erode river banks by burrowing into them and also affect the fishing industry by feeding on fish stocks and damaging nets.
“I imagine that if otters came back in large numbers they could probably deplete the population, but at the moment the population, especially in the Thames for example, is not depleting at all.”
When asked if Chinese crabs threaten our native species, Dr Clark said: “Yes, they are eating us out.”
‘We were very worried because we think they eat fish eggs. We fed them fish eggs and they devoured it all.
“Biodiversity in the Thames has probably decreased dramatically and the same in other areas, but it is difficult to monitor that.”
At this time, it is unknown what Chinese crabs primarily feed on. Dr. Clark said they will freeze and preserve the crabs that were caught in the trap and even investigate what they have been eating.
It emphasizes that no crabs will be returned to the area. The expert added: “There is a possibility that within several years we could deplete that population in that basin.”
‘The problem with this crab is that it has an unusual life history and spends most of its time in fresh water. “It’s not a true freshwater crab,” Dr. Clark said.
‘In Africa, for example, there are true freshwater crabs, which live in rivers and do not migrate back and forth, and that’s how they are. We don’t have freshwater crabs.
‘This crab is filling a niche that was not occupied before in our country and probably also on the continent.
‘And that’s why it’s causing problems because our native animals haven’t evolved with this crab. As invasive, it is something new.”
The Natural History Museum has said the invasive crabs could grow to the size of dinner plates. Dr. Clark said he once had a crab in his laboratory whose body measured 85 mm across.
Since 2016, the species, named for its hairy claws, has been classed as “widespread” across the UK.
Chinese crabs were considered established in the River Thames in 1973 and have since spread further afield, including into the Tyne, Humber, Medway, Wharfe, Ouse, Tamar and Dee rivers.
Since 2016, the species, named for its hairy claws, has been classed as “widespread” across the UK.
According to the Natural History Museum’s ‘Mitten Crab Watch’, more than 800 records have been submitted so far, confirming that the creature is spreading across the UK.
Its interactive map shows confirmed sightings of the crab across Britain, including London, Newcastle, Manchester, Swansea, Glasgow and Brighton.
Andy Litchfield said he was walking his dog in Bushy Park, south-west London, when he saw a crab last Friday.
He told the Woking News and Mail that he had seen crabs before but “never on land.”
He added: “I was walking my Labrador in Bushy Park on Friday morning when he stopped to sniff something on the ground and I was surprised to see it was a crab.”
He took a video of the encounter in which the crab was seen getting defensive and raising its claws in the air.
Late last month, one of the creatures was spotted at the Royal Society for the Protection of Birds’ (RSPB) Fen Drayton Nature Reserve, near Huntingdon.
Simon Passey was walking towards the parking lot when he saw the creature. He said The hunting post: ‘It was alive and had quite large pincers, I’d never seen anything like it at Fen Drayton before.
“I took pictures, but I didn’t want to touch it.”
Defra said it had received reports of the crab in the Cambridgeshire Fens and encouraged people to report sightings to stop the movement of its eggs and urged people to take photographs.
Map shows Chinese crab sightings across UK – experts say population is growing