A rare species of crayfish has been released into rivers to promote the growth of its population across the UK.
The white-clawed crayfish is the only native freshwater crayfish in the UK but is now considered to be endangered, due to the risk posed by non-native crustaceans.
Since the 1970s there has been more than a 70% decline in this species in southwest England. In response, conservationists at Bristol Zoological Society have bred more than 4000 white-clawed crayfish at their hatchery at Bristol Zoo Gardens. When they reach adulthood, the crayfish are released into safe rivers and lakes in secret sites around the UK. This last release has seen the introduction of over 200 white-clawed crayfish into rivers in Somerset and Hampshire.
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The American signal crayfish is one of the most significant threats to the species, carrying a fungal disease known as ‘crayfish plague’. The populations of other invertebrates and fish have been significantly affected by the introduction of these crayfish. But it’s not only damaging to other species – the American signal crayfish’s extensive burrows destabilise surrounding riverbanks, which can cause erosion and collapse. This, in turn, increases the chance of flooding.
“Just one non-native crayfish in a river system is enough to spread the crayfish plague and wipe out the native populations within a year,” says Paul Hetherington, director of communications for Buglife, an organisation centred around the conservation of invertebrates.
“Signal and several other non-native species carry – but are unaffected by – the plague, but our native crayfish are wiped out by it.”
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Originating from America, the signal crayfish was introduced to the UK in the 1970s to be farmed for food for the restaurant trade, but has since overwhelmed the country’s lakes and rivers, particularly in the south. They breed faster than native species and out-compete with them for food. ‘Crayfish plague’ can be spread via river equipment such as fishing tackle, canoes or wet footwear, so people are advised to disinfect or wash anything that has been in contact with rivers or lakes to limit the spread.
Chefs and conservation charities have previously promoted trapping American signal crayfish to eat, as a way of controlling its population. However, a 2020 study found this system to do more harm than good, due to the fact that the trapping process may inadvertently spread the crayfish plague.
“Control of signal and other invasive crayfish is extremely difficult and mainly revolves around trapping,’ explains Hetherington. ‘In some closed systems, poisons have been use, but these will kill much more than just the crayfish.”