British crawfish falling victim to US rival

It appears Britain’s only native species of crawfish is tad more snobbish than its American cousin, and it’s proving a definite hindrance to its survival.

American signal crawfish are not only less fussy about what they eat than Britain’s white-clawed crawfish but it’s also are more resistant to parasites.

Researchers from the University of Leeds in England have published a study in the online journal PLoS One that looks at why signal crawfish – or “crayfish,” as non-Southerners like to refer to the crustacean – have been gaining the upper hand over white-clawed crawfish in Great Britain since the former’s introduction from the US in the 1970s.

Among other things, the study compares how the two species deal with food.

“The American signal crayfish ate up to 83 per cent more food per day than did their native cousins,” according to

“The research also showed that white-clawed crayfish are much more choosy about what they eat, preferring particular types of prey, while the signals eat equal amounts of all prey,” it added.

The English publication This is Bristol recently noted the biological differences between the species:

“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.

“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.”

In addition to the above, white-clawed crawfish are also affected by a common parasite, porcelain disease, which affects their ability to catch prey, leading affected crawfish to eat 30 percent less.

The parasite doesn’t seem to affect the signal crawfish, however.

“The signals eat much more compared with the native crayfish,” said Dr. Alison Dunn of the Faculty of Biological Sciences at the University of Leeds. “But the situation is exacerbated by a parasite which essentially changes the native’s behavior – the white-clawed crayfish can’t eat or handle as much food as the signal, because the parasite weakens its muscles.

“The huge appetites of the signal crayfish can have a massive effect on the whole ecosystem,” added Dunn, who led the study.

“In particular it affects biodiversity because there is a reduction in the numbers of prey. In some Yorkshire rivers, for example, the fish population has declined because signal crayfish are eating large numbers of fish eggs.”

The signal crawfish was introduced to Britain for fish farming.

Dunn said that humans can play a part in protecting the white-clawed crawfish by understanding how invading species spread. For example, the signal crawfish is able to move overland of its own accord, but may also be inadvertently moved around through such items as damp fishing gear.

“We need to be much more careful about how we move animals and plants around from habitat to habitat, and raise public awareness about these issues,” she said.

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