The first ever Chinese mitten crab trap in Britain has been installed, amid the growing population of the invasive species.
Mitten crabs, which first appeared in the UK in 1935, have recently been seen scuttling around London and Cambridgeshire, including at a park in the south-west of the capital, a dyke in Whittlesey and a country park in Peterborough.
The species – named after its furry claws – is thought to have travelled from eastern China to Europe and north America in the sediment found on the bottom of ships ballast tanks.
The crab can be identified by its grey-green to dark brown body and dense brown ‘fur’ on their white-tipped claws.
Dr Paul Clark is a researcher at the department of life sciences for the Natural History Museum, who specialises in Chinese mitten crabs.
A mitten crab is pictured climbing over the weir at Pode Hole before the trap was installed
The Chinese mitten crab that a dog walker came across in Bushy Park in Richmond upon Thames
The first ever permanent Chinese mitten crab trap has been installed at Pode Hole, in Lincolnshire
He has worked with them since 1976, after he was asked to retrieve the second mitten crab found in Britain.
In an interview with MailOnline, Dr Clark said: ‘Numbers are rising because they have a very unusual life history. After the migration downstream, adult females may be able to produce three spawings of eggs.
‘The number of eggs in each spawing can produce between 500,000 and one million. So that’s how many larvae they are hatching into the estuary. Of course, not all those larvae will develop through to become a juvenile crab to go back up stream again.
‘But once this species has become established, it’s very difficult to get rid of it.’
Now the first ever permanent Chinese mitten crab trap has been installed at Pode Hole, in Lincolnshire, in collaboration with Lincolnshire Wildlife Trust, the Welland and Deepings Internal Drainage Board and the Natural History Museum.
They are hoping that this trap will catch trap downstream and upstream migrating mitten crabs.
Dr Paul Clark is a researcher at the department of life sciences for the Natural History Museum, who specialises in Chinese mitten crabs
They installed the trap on the 31st August this year but have not manged to catch a Chinese mitten crab as of yet. Dr Clark says it might be delayed because of the warm weather, but he is unsure.
Mick Henfrey, who is employed by the Welland and Deepings Internal Drainage Board, built the trap. The Welland Board also donated around £8,000 to build the device.
The trap works as a letterbox, trapping the mitten crab inside until they are extracted and taken away for analysis.
Dr Clark believes that if he were to walk down to the Chelsea embankment, within the hour he could pick up around 50 to 100 small crabs.
He added that Chinese mitten crabs ‘have very few predators,’ perhaps the odd pike, and birds, but he believes that they would not decrease their population.
The crustaceans were seen at waterways in Cambridgeshire, including a dyke in Whittlesea (pictured)
The crabs erode riverbanks by burrowing into them and also affect the fishing industry by feeding on fish stocks and damaging nets
‘I imagine off the top of my head that if otters were to come back in any numbers, they could probably deplete the population but at this moment in time, the population especially in the Thames for example, is not being depleted at all.’
When asked if the Chinese mitten crabs threaten our native species, Dr Clark said: ‘Yes, they’re eating us out of house and home.’
‘We were very concerned because we think they eat fish eggs. We fed them some fish eggs and they devoured everything.
‘The biodiversity in the Thames has probably gone down dramatically and the same in other areas, but it is difficult to monitor that.’
At this point in time, it is unknown what Chinese mitten crabs primarily feed on. Dr Clark said that they are going to freeze and preserve the crabs that have been caught in the trap and may even investigate what they have been eating.
He stresses that no mitten crabs will be released back into the area. The expert added: ‘There is a possibility over a number of years that we could deplete that population in that catchment.’
‘The issue with this crab is it has this unusual life history and spends most of its time in freshwater. It’s not a true freshwater crab,’ Dr Clark said.
‘In Africa, for example, you have true freshwater crabs, that live in rivers and they don’t migrate backwards and forwards and that’s how they are. We don’t have any freshwater crabs.
‘This crab is filling a niche that wasn’t occupied before in our country and probably on the continent as well.
‘And this is why it’s causing problems because our native animals have not evolved with this crab. As an invasive, it’s 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 mitten crab in his laboratory that had a body which spanned 85mm in width (8.5cm).
Since 2016, the species – named for its furry claws – have been classed as being ‘widely spread’ across the UK
Chinese mitten crabs were considered to be established in the River Thames in 1973 and have spread further afield since then, including in the Tyne, Humber, Medway, Wharfe, Ouse, Tamar, and Dee rivers.
Since 2016, the species – named for its furry claws – have been classed as being ‘widely spread’ across the UK.
According to the Natural History Museum’s ‘Mitten Crab Watch,’ more than 800 records have been submitted so far – which confirms that the creature is spreading across the UK.
Their interactive map shows that there have been confirmed sightings of the crab across Britain – including London, Newcastle, Manchester, Swansea, Glasgow and Brighton.
Andy Litchfield said he had been 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 the 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 that it was a crab.’
He took a video of the encounter which saw the crab get defensive and put its claws in the air.
At the end of 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 to the car park when he saw the creature. He told The Hunts Post: ‘It was alive and had quite large pincers, I’ve never seen anything like that at Fen Drayton before.
‘I took photos, but I didn’t want to touch it.’
Defra said that it had received reports of the crab on the Cambridgeshire Fens and they encouraged people to report sightings to stop the movement of their eggs and urged people to take photos.
Map shows sightings of Chinese mitten crabs across the UK: Experts say population is growing