American exports

Fast links to two articles about North American crayfish causing problems elsewhere.

One is in National Geographic, and looks at Africa:

The 6-inch-long (15-centimeter-long) invader is already widely distributed in lakes and other bodies of water throughout Kenya, as well as in Rwanda, Uganda, Egypt, Zambia, the Seychelles, Mauritius, and South Africa.

Conservationists are now concerned the crayfish will reach the East African lakes of Malawi, Tanganyika, and Victoria, which are home to hundreds—and probably thousands—of species found nowhere else.

My understanding is that one solution to the invasion, fishing crayfish for food, may be a particularly tough sell in Africa. Apparently, many of the locals view eating crayfish in much the same way that North Americans view eating insects.

Another is in Scientific American:

Virile crayfish were first spotted in East London’s waterways in 2004, probably after being dumped into a pond from a home aquarium. Since then, they have colonized 17 kilometers of the River Lee and surrounding waterways. River Lee has no native white-clawed crayfish left—they were all wiped out by the signal crayfish invasion in the 1980s.

“500 meters a month”

500 meters a month is how fast invasive crayfish can spread through an ecosystem, according to a report in The Guardian.

The Environment Agency said virile crayfish (Orconectes virilis), which are non-native, prey on native wildlife and spread crayfish plague, a disease deadly to native white clawed crayfish. The north American predators have recently been seen in waterways in east London after first being found on the river Lea near Enfield in 2004.

They have since colonised more than 10 miles of the river and linked waterways, spreading into Hertfordshire.

The agency has fitted small radio transmitters on the backs of the unwelcome guests, with preliminary results showing that virile crayfish are moving upstream at a rate of 500 metres a month.

This is substantially faster than their cousin, the signal crayfish, which is also non-native.

The Environment Agency report shows not only the two crayfish pictured above, but also notes that Lousiana red swamp crayfish (Procambarus clarkii) and Turkish crayfish (Astacus leptodactylus) are also present in the London area.

Hat tip to Kevin Zelnio.

The Loch Ken monster

The Craywatch project focuses on North America (for now), but other countries provide good examples of why we need to keep an eye on crayfish.


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This news article tells of the economic costs of invasive signal crayfish (Pacifastacus leniusculus) in Loch Ken, Scotland (emphasis added):

Susan O’Hare, who runs the Cross Keys Hotel in the town, said: “We have had fishermen who came last year who are now booking trips in Ireland. We can lose between £3,000 and £4,000 a weekend. My fishermen have been catching crayfish after crayfish.”

One million of the creatures were removed from the loch by a cull carried out in 2009.

Just a few weeks before that, another report from Scotland described a new fence that had been put in place to try to contain the signal crayfish:

"Unfortunately there are no techniques available that will allow us to get rid of signal crayfish from rivers and streams," said Dr Colin Bean, a freshwater adviser with SNH.

"So taking the radical step of developing and installing a physical barrier may offer us the best hope of stopping the species from moving into new catchments."

Two dams have now been installed 20 metres apart at a cost of £50,000.

I wish them luck. But the Australian experience with fences suggests that invaders are very good at getting past them. It’s not clear to me how fences will stop little larval crayfish.

And finally, this story isn’t so much about the economic cost, but the loss of biodiversity and native heritage:

More than 50 dead white clawed crayfish were found in Chad Brook, Long Melford.

The Environment Agency confirmed the deaths were caused by the disease, rather than pollution, and it expects the rest of the colony to perish. ...

Only two colonies of native crayfish remain in the East of England in their natural setting.

Keep watching the streams!

Crayfish picture by shimgray on Flickr; used under a Creative Commons license.