American Crayfish Overtaking British Cousins
March 16, 2012

American Crayfish Overtaking British Cousins

Stronger, heartier American signal crayfish are taking over populations of native white-clawed crayfish in Yorkshire.

The more aggressive signal crayfish is able to withstand disease  and is less picky about what it eats. Biologists believe these and other reasons are contributing factors in the decline of Yorkshire´s native white-clawed crayfish.

Signal crayfish can carry plague, which proves fatal in the native crayfish. Additionally, the native white-clawed crayfish suffers from porcelain disease, which makes the crayfish sluggish and suppresses their appetite. In a couple of years, this disease ultimately kills the crayfish.

Introduced in the 1970s to aid in fish farming, the American signal crayfish has taken to the British waters fantastically. However, as the population of the signal crayfish grows, the population of the white-clawed crayfish ultimately decreases. The reasons for this have not yet been understood.

Researchers from the University of Leeds Faculty of Biological Sciences are investigating why the signal crayfish is doing so well while the white-clawed crayfish is doing so poorly. The scientists hope to use this information to aid in conservation projects to restore white-claw populations.

The study compares how quickly the two species deal with their food. The American signal ate up to 83% more food a day than their British cousins. While the native crayfish are more choosy about their prey, the signal crayfish eat all types of prey.

Dr. Alison Dunn led the study and explains the eating habits this way: “The signals eat much more compared with the native crayfish. 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 bottom line, says Dr. Dunn, is that American signal crayfish simply eat too much.

According to the study, Dr. Dunn states “The huge appetites of the signal crayfish can have a massive effect on the whole ecosystem. 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.”

Dr. Dunn is also interested in the parasites that affect the native white-clawed crayfish.

“Parasites are a fascinating and vital part of any ecosystem and you have to consider their effects when looking at biological invasions,” she says. “We hope our findings will help us make predictions about how this invader might spread and help with management strategies.”

Dr. Dunn hopes fishers will help protect the population of the white-clawed crayfish. The signal crayfish is mobile and can move from place to place on its own, however, these crayfish may be inadvertently transported from place to place in fishing gear and boats.

“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,” says Dr Dunn.

The study is published the in online journal PLoS One.

Image Courtesy Martin Fowler / Shutterstock