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.

Bad bait

The sale of crayfish is a completely grey market, as I found trying to track down pet ownership of Marmorkrebs. Trying to gather good information about the sale of crayfish for bait is hard, and as far as I can find, Bob DiStefano and colleagues have done probably one of the only systematic studies to examine this.

DiStefano and colleagues surveyed all the American state and Canadian provincial agencies in detail. They found that about half of the jurisdictions responding reported problems caused by crayfish used as bait. Yet of those, only a few had banned the use of crayfish as bait outright. The other states and provinces had some other legislation intended to prevent the introduction of exotic crayfish, such as limiting how far they could be transported. This tremendous hodgepodge of rules and regulations doesn’t lend itself to easy enforcement.

The team also did extensive surveys of bait shops in Missouri. Missouri is one of the jurisdictions that has a series of regulations designed to prevent the spread of crayfish across watersheds rather than an outright ban. The state is trying to do the right thing. But not surprisingly, the authors turned up a lot of illegal crayfish; in their brief surveys, 27% of the bait shops had illegal crayfish.

Some shops had legal crayfish species that were gotten by an illegal means (e.g., from out of state).

Almost none of the shop owners had a clue about what species of crayfish they had.

Even if the bait shops were following all the laws (which were few and far between), there’s no way of knowing what the fishermen they sold the bait to did.

It’s difficult to know how many introductions have been caused by a combination of careless bait shop owners and fishermen, but this paper provides some hints of past introductions that could have been cause by crayfish being released as bait. Procambarus acutus is mainly distributed in the south-eastern corner of the state, but there are pockets further north that are probably the result of bait sales.

In short, using any crayfish as live bait is a problem! About the only exception would be a crayfish you catch at the bank of the river or lake you intend to fish in.

Reference

DiStefano RJ, Litvan ME, Horner PT. 2009. The bait industry as a potential vector for alien crayfish introductions: problem recognition by fisheries agencies and a Missouri evaluation. Fisheries 34(12): 567-597. DOI: 10.1577/1548-8446-34.12.586

Crossposted from the Marmorkrebs blog.