A shipping container within earshot of roaring lions, with a nearby rollercoaster twisting through the sky, is perhaps not the location you’d expect for a crustacean conservation project. But then these are not normal times for the white-clawed crayfish (Austropotamobius pallipes), the UK’s only native crayfish species.
It’s an invertebrate under severe pressure, with its plight very much a tale of the age. There’s the familiar story of a threat to native wildlife from an invasive species, but also a vast mobilisation of experts and laypeople to come up with creative solutions against steep odds – enough to warm the heart a little amid gloomy biodiversity narratives.
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“It’s a bit crazy, the amount of people working on one animal, but I think that’s because it’s such an important part of the ecosystem,” says Jen Nightingale from Bristol Zoo, who pivoted from studying Amazonian manatees to native crayfish after a zoo visitor highlighted its struggles to her more than 15 years ago.
Why is the white-clawed crayfish important?
The UK has a globally important population of white-clawed crayfish, an elusive keystone species that promotes waterway health through its feeding and burrowing behaviour. It’s the densest population in Europe, mainly concentrated in central and northern England, where chalk-bedded watercourses, the species’ preferred habitat, are most common.
What threats is the white-clawed crayfish facing?
The problem is, its existential threats are on a continental scale, meaning that being the best-preserved isn’t the boast it used to be. There has been a 70 per cent decline in numbers since the 1970s, with populations now falling almost everywhere.
While the much-publicised deterioration of the UK’s rivers and streams and increasing drought due to climate change are certainly part of the reason why the species is listed as Endangered by the IUCN and protected by UK law, the biggest threat is that posed by the invasive American signal crayfish (Pacifastacus leniusculus).
By far the most common of four crayfish invaders in UK waters, it was introduced to the country around 50 years ago as part of an attempt to diversify aquaculture. But it found its way into our waterways and thrived – similarly to grey squirrels – at the great expense of a vulnerable native.
The American rival is bigger, hardier, produces more offspring and can outcompete the white-clawed for hiding places and food. It even increases in size as natives shrink when they are found in the same locations.
Unfortunately, these are not the limits of its impact. The signal brings with it ‘crayfish plague’, a fungal-type disease that spreads rapidly through waterborne spores and can kill entire white-clawed crayfish populations within two weeks.
If all that wasn’t bad enough, in late 2024, white-clawed crayfish were found dead in Northumberland’s River Wansbeck of an as-yet-unknown disease. Quickly classed as a category 1 incident by the Environment Agency – the most serious level – it has prompted a mission to move those unaffected to safety. It seems this crustacean just can’t catch a break.
While the future does appear at best uncertain for our beleaguered, pincered friend, there’s no sign of a white flag from anyone fighting its corner. After all, nothing inspires the British like an underdog story.
What's being done to save native crayfish?
And so, back to that shipping container near the lions and the rollercoasters. Flamingo Land, a North Yorkshire resort, has just established a modular facility to house crayfish, with strictly controlled biosecurity and water quality. The aim is to receive females with eggs from the wild – probably from nearby watercourses, where they are under threat – then rear juveniles through to adulthood and potential release. Before that, 37 captive-reared ‘practice crayfish’ are currently under the watchful eye of Kieran Holliday, Flamingo Land’s science, research and conservation officer, ahead of full licensing to handle wild-caught specimens.
“We can maintain the tanks to a level where there’s no stresses and improve the survivability of the young from around five to 90 per cent,” says Holliday. “From 20 females, there’s a possibility we can get 800 crayfish back into the wild, compared to only 80, or even fewer, if they’d bred in natural conditions. Boosting numbers is the best thing we can do.”
The numbers game is one part of why captive breeding is so important. The other is that it’s the only sure-fire way to guarantee ‘new blood’ free of pathogens that can be moved elsewhere. While it’s the newest, Flamingo Land is far from the only such facility in the UK, with five hatcheries and six other holding and quarantine centres elsewhere, and plans for many more.
With wild release the aim of such initiatives, it begs the question: what constitutes a suitable release location, when many of our waterways are teeming with signal crayfish and awash with microscopic threat?
Where can native crayfish populations be moved?
One solution is simply to move white-clawed crayfish populations to locations where that competition and source of disease simply isn’t there – known as ‘ark sites’. These are habitats such as headwater streams with natural barriers against the invader, ponds or pits. To date, around 100 such sites have been established.
Since making the shift from huge marine mammals to diminutive invertebrates, Nightingale has done enough to be considered the Noah of the ark, leading a strategy that has inspired nationwide approaches. It began with the zoo’s breeding and research programme, evolving to supply numerous ark sites, from nearby locations to more northerly refuges. The efforts have seen 3,500 juveniles reared in captivity and a further 4,500 wild individuals relocated. If that wasn’t enough, Nightingale even has her own hatchery at home.
“Having worked with them for 15-plus years, I know that you can’t stand still,” she says. “What’s really nice is this second wave of interest, with people setting up ark sites. Crayfish maintaining waterway health is turning into an ecosystem service, and I think that a lot of rewilding estates will end up creating ponds.”
Creating a bespoke ark site for white-clawed crayfish is not always straightforward, with conservationists having to consider the likes of predator risk and micro-habitat niches required for the species to thrive. In Wallington, Northumberland, the local National Trust team has just finished its second ark site, in a pond on farmland. It includes habitat modifications such as dead wood, stone-filled containers and willow bundles.
“Crayfish usually have a lot to eat in terms of foraging for leaf litter, mosses and other plant matter,” says Nick Allen, a National Trust ranger at Wallington. “Usually, when you create an ark site, you have to give them a few more places to live.” Biosecurity is also key, with the recent mystery disease outbreak in the area only serving to underline the point. “What we’re realising with biosecurity is this illness is not just spread through the water. It’s spread on hands. It’s spread on boots. It’s spread on feet. It’s potentially spread by livestock as well.”
In practice, this means that sites should either be in isolated spots or, when in more public locations, used as an opportunity to educate passers-by about their role in the species’ survival using signage and outreach work. Once a site is ready, successful establishment is generally a matter of leaving the crayfish to it. The first ark in the area, a man-made cattle watering hole near Wallington Hall, has proved the ‘hands-off’ approach works, with recent surveys showing evidence of breeding.
And what about the signal crayfish?
It’s hard to discuss saving the white-clawed crayfish in its native habitat without addressing what exactly should be done about its prolific rival. “Not very much has gone on nationally. I think basically because we haven’t really found a solution,” says Nicky Green, who runs a specialist crayfish conservation and control consultancy.
Eradication is no longer feasible, with the UK split into what are known as containment and exclusion zones. In containment zones, which are mostly in the south, it is legal to trap signal crayfish with a licence, while exclusion zones forbid this.
Despite well-meaning interventions over the years from commentators advocating the trapping and eating of signal crayfish, the expert view is that it’s a bad idea. “I would say, don’t do it. It is now illegal to transport live signal crayfish, as you’re risking the spread of crayfish themselves as well as plague. It’s just not worth it, as they’re so good at escaping,” says Green.
Aside from this risk, trapping alone doesn’t make inroads into invader populations. Males are often the key target in measures to reduce breeding populations, including of signal crayfish. Trapping the crustaceans only removes the largest 10 per cent of males, leaving smaller individuals to thrive without more aggressive competitors.
With a gourmet solution off the menu, researchers are striving to find better restraints. One option is installing barriers on waterways, which has been tested in mainland Europe. Another is trapping the large males and introducing predators such as large fish to tackle those left behind. Studies at Prior Park in Bath, where signal crayfish burrowing was undermining a 17th-century bridge, are showing potential.
The most promising option of all may well be using gene-editing technologies to blunt signal crayfish breeding. Though years away from application, scientists are optimistic that targeted manipulation could render all the young of the species one sex or infertile, causing populations to crash. “If that ever gets off the ground, that would be our silver bullet,” says Green – though she warns that more funding is needed to make such ideas a reality.
Another avenue to explore is the white-clawed crayfish’s resistance to plague. This is a tantalising possibility, with certain populations evolving resistance in Italy and Spain. Unfortunately, it’s not as simple as shipping them over for breeding programmes as, while the Mediterranean cousins may be resistant, they’re still likely to be disease carriers. But the recent rediscovery of what are known as ‘relic populations’ at spots in the UK ravaged by plague offer hope that a local breakthrough could be on the horizon. “We can have them screened, and look at them physiologically and genetically, because they’re populations where you think, ‘How can they still be there?’” says Nightingale. “The quest is to find those populations with resistance and start breeding them – that’s a powerful tool. In my lifetime, I definitely want to do that.”
What does the future hold for the white-clawed crayfish?
Stable conditions for a wholesale native crayfish revival are certainly not imminent, meaning that, for now, any efforts form part of a waiting game. A sustainable future for this secretive crustacean requires not only financial support but a significant investment of both time and expertise from an array of partners – government agencies, national parks, river custodians and, of course, volunteers.
Despite spending well over a decade working to protect the white-clawed crayfish, including removing populations to safety during the recent disease outbreak in Northumberland, Ian Marshall, a technical specialist from the Environment Agency, is undeterred. “The passion of conservation organisations and volunteers is only increasing. People want to get things done,” he says. “We’ve seen the loss of many populations over the years but it is amazing how some of them hang on. Nature finds a way of surviving. We’d be foolish to write them off this early.”
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Main image: white clawed crayfish in France/Credit: Getty