Chronicling a problem: A research team is tracking the number, size and sex of non-native red swamp crayfish that are removed from Guion Pond. Photos by Jennifer McManamay

M’m, M’m … Bad

Louisiana crawdads make good snacks, but pose threat to Sweet Briar’s spotted salamanders

JENNIFER McMANAMAY
College relations staff writer

Juniors Sarah Doyle (from left), Doreen McVeigh and Bethany Magee sex the trapped crayfish before sorting them by approximate size while Mike Hayslett records the data.

Last March, while studying spotted salamanders on Sweet Briar’s campus during the amphibians’ annual march to Guion Pond to lay eggs, student and faculty researchers made a startling discovery.

The man-made pond is full of Procambarus clarkii, also known as red swamp crayfish or mudbugs. They’re the kind of crayfish you eat and they’re not from around here.

Biology professor Linda Fink isn’t sure how they got there, but it’s possible they were released after lab experiments many years ago. Fink said she and her colleagues have observed crayfish in the pond as long as they can remember, but they usually have been smaller in number and in size — more akin to Virginia’s native species.

While the Louisiana crawdads are tasty, it may be the mudbugs doing the feasting.

Mike Hayslett, who taught the course “Life Science by Inquiry” at SBC last spring, was one of the salamander researchers. “Crayfish were poised on sticks as mom was laying eggs,” he said.

The research team had undertaken the March study to collect data on the campus’ native salamander population, in part because Fink already was worried about non-native mosquitofish preying on the juveniles. Someone had released them a few years ago.

Alerted to the possible new threat, Fink and Hayslett didn’t yet know the crayfishes’ impact on the salamander population. In mid-summer Hayslett and biology major Doreen McVeigh ’09 attempted to count salamander tadpoles and fully developed juveniles using three different survey methods. They found none.

What they did find was a staggering number of red swamp crayfish, said Hayslett.

One late September day, Hayslett, McVeigh, biology student Bethany Magee and environmental studies student Sarah Doyle pulled a dozen minnow baskets out of the tiny pond. Each contained 10 to 15 adult crayfish — dark red, 3-inch lobster-like crustaceans, with bulging eyes, waving antennae and fully functional pincers.

The students gamely sexed each one and placed it in a bucket according to its approximate size. They recorded the numbers to report to the Virginia Game and Inland Fisheries department, which is tracking the spread of the invasive species. They are thought to be capable of crawling over land to new water sources.

Despite the crayfishes’ density, Fink isn’t drawing conclusions about what happened to the spotted salamanders. “Correlation isn’t causation,” she said.

That’s one of three “science-education-conservation” messages she wants to impress on the students working on the project and the larger SBC community.

“We know that we got zero recruitment of new salamanders from this year’s reproduction, but we don’t have data on the sources of mortality,” Fink said, noting several potential culprits, such as disease or other predators.

Research by Jennifer Summerfield, a 2007 biology graduate, provided some clues. “[Summerfield’s] lab research shows that crayfish don’t kill salamander eggs inside intact egg masses, but do kill newly hatched larvae,” Fink said.

Hayslett suggests two other hypotheses based on visual observations last spring. One, the crayfish eat the eggs as soon as they’re laid, before the protective jelly expands. The second is that the crayfish dislodge the egg masses while trying to forage on them, causing them to wash over the pond’s dam. Fink said both will be investigated next spring.

On the encouraging side, the March study showed a strong spotted salamander population in Guion Woods, where they live underground most of the year. Fink stressed that one bad reproductive year doesn’t spell their doom, but it segues to her second message: Practicing good conservation means you can’t always wait for definitive evidence.

“Suppose it takes ten years to determine that, yes, crayfish are wiping out the salamanders,” she said. “We’ll have certainty, and a diminished salamander population.”

Fink’s final point is that there are no “magic formulae” to apply to problems, so conservationists must seek creative solutions. In this case a good recipe, compliments of Elston Inn chef Glenton Goodwill, is in order.

Hayslett has harvested hundreds of mudbugs in an ongoing effort to eradicate them. Some end up as compost in the Sweet Briar Community Garden. Some landed on diners’ plates at the Elston’s Jamaican Night buffets. Others were served to participants at a wetlands restoration workshop and conference held at Sweet Briar last month.

Because, Hayslett said, “if you can’t beat ’em, eat ’em.”