Saving the British crayfish
Though nobody realised it at the time, back in the 1970s the Americans secretly invaded Britain.
A small group of heavily armed, armour-protected warriors swept through much of the nation following the rivers and streams and leaving death and destruction in their wake.
Ever since they appeared in our waterways more than 30 years ago, the American signal crayfish has threatened the very existence of our native white-clawed crayfish.
The American specimens are considerably larger, more aggressive and more heavily armed then the native British creatures – with lobster-like pincers able to offer a nasty nip.
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The white-clawed crayfish, in comparison, are terribly English. They have lived a gentle, peaceful life in their watery homes for countless generations. When it came to out-competing their British cousins, the Yankee crustaceans soon won a claws-down victory. But they posed an even greater threat to our timid little beasties.
"The American signal crayfish were carriers of a fungus, which was usually harmless to them but which rapidly swept through the native population like a plague," explains ecologist Lydia Robbins of Avon Wildlife Trust.
"Signal crayfish first entered our waterways in the 1970s when they either escaped from aquaculture enclosures, were illegally released – perhaps viewed as a possible source of food – or escaped while being used as bait by anglers."
Lydia is at the forefront of a major new conservation project which aims to conserve and reintroduce our native species to the River Avon and its tributaries.
The scheme – which is being organised jointly between the Environment Agency, Avon Wildlife Trust and Bristol Water – heralds the start of a concerted effort in the next few years to curb the dramatic decline of native crayfish across the region, by moving them from threatened areas to specially selected refuge streams.
The first rescues took place at the end of October when a population near Bristol was transported in cooled tanks to its new habitat.
Earlier this month, the Government agency Natural England presented Bristol Zoo with a grant of £105,000 to establish a captive breeding programme to support the reintroduction scheme.
"It's essential to have up-to-date facts about where native and non-native crayfish occur in the South West by collating existing information and carrying out surveys," Lydia explains.
"This way, we can prioritise the most threatened populations and look accordingly for refuge streams away from non-indigenous crayfish.
"Once we have identified a possible refuge site, we then need to assess a wide range of other factors so a number of scientific tests are carried out. For example, we need to know what other species are present, understand the water chemistry, assess the threat of pollution and of course we need to make sure the site offers the habitat characteristics crayfish like such as enough stones under which they can seek refuge."
The scheme couldn't come at a better time. As a result of crayfish "plague", the Bristol and old Avon area has lost three of its four most abundant native populations recently.
"Last year, we lost the entire population of native crayfish in the River Frome, which had been one of the few remaining strongholds for the white claw in the South West," says Lydia.
"But once the fungal spore had found its way into the river, it eradicated the native species within weeks.
"We had lots of calls from people who had discovered large numbers of dead crayfish in the river. Sadly, when the 'plague' strikes a watercourse, it does so in dramatic fashion.
"We've also recently lost one of the few remaining populations of native crayfish in the Tetbury Avon. Once again, they were wiped out within a month of the 'plague' arriving."
Unfortunately, research into fully eradicating signal crayfish from river systems, including by intensive trapping, has to date proved unsuccessful.
"Once the American signal crayfish is there, I'm afraid there's no realistic way of getting rid of it," Lydia says.
And there's no guarantee that the imperious aggressors won't move in on the refuge streams in the future.
"Unfortunately, they can travel easily over land," Lydia explains. "I recently read about a guy who bought a signal crayfish for the pot but couldn't bring himself to cook it, so he put it outside on the doormat.
"By the next morning, it was found two miles away, marching along the road."
And Lydia is sceptical about TV chefs' calls to eat the American signal crayfish out of existence.
"Eating American signal crayfish would not make any kind of a significant difference in ecological terms," she says. "I'm afraid that's a great myth that's been propagated by celebrity chefs on the television.
"And there's a real danger, of course, that if people don't know what they're doing they will either catch the protected native species instead or unwittingly transfer the fungal spores from the signal crayfish to other parts of the watercourse."
The alien invaders were imported for food in the 1970s originally, but have escaped or been released illegally into the wild.
They also threaten more than our crayfish. Research which is currently being compiled shows their extensive impact on other species such as trout and salmon numbers.
"Translocating white-clawed Crayfish to refuge sites mitigates the threat from American signal crayfish by actively conserving populations," says Peter Sibley from the Environment Agency.
"It's hoped by introductions to more isolated areas they will re-establish because they are an important part of river ecosystems in the South West.
"As Britain's largest freshwater invertebrate, they are a natural component of other animals' diet including trout, otters and herons.
"To avoid predation, crayfish are nocturnal, hiding in refuges during the day. As omnivores, their diet of plant and animal matter varies widely, from fallen leaves to small invertebrates and fish. It was important not to harm the resident ecology when transferring crayfish to new sites so scientific tests examining water quality have been undertaken."
Peter says that the public can help the ecologists' efforts in avoiding the spread of "plague" by drying out and disinfecting angling equipment between sites.
"We would stress that white-clawed crayfish are protected by law and a licence is required to catch any kind of crayfish in Britain," he adds.
For Lydia, the project does not end with reintroducing the native species.
"The work needs to go on for years," she says. "We need to carefully monitor the populations, because if their decline is not addressed, the native species could be extinct within 30 years."
For more information about the project, or to volunteer your services to the Avon Wildlife Trust, log on to www.avonwildlifetrust.org.uk