Invasive "Walking" Fish Not Wreaking Havoc Yet, Scientists Say

Brian Handwerk
for National Geographic News

October 3, 2006

The infamous snakehead, once dubbed the "Frankenfish," is in the U.S. to
stay, experts say. Fortunately, the Asian import seems to be coexisting
peacefully with native species—for now.

The Potomac River, which runs through West Virginia, Virginia, Maryland, and Washington, D.C., on its way to the Atlantic, has seen a thriving population of snakeheads arise after several of the fish were released into Virginia's Dogue Creek in Fairfax County (map of Virginia).

But so far the snakeheads appear to have had little discernable impact on the native ecosystem, to the relief of scientists and anglers alike.

"We have not seen any adverse effects," said fisheries biologist Steve Owens, with Virginia's Department of Game and Inland Fisheries in Fredericksburg.

But surveys also show that northern snakehead populations are booming in the Potomac.

The aggressive predators are appearing in more locations and in far greater densities than they did just last year.

Snakeheads now occupy at least 15 miles (24 kilometers) of the Potomac River and its tributaries.

The fish frequent large swaths of weedy shallows—making eradication efforts almost impossible. (Related: "Maryland Wages War on Invasive Walking Fish" [July 2002].)

Steve Minkkinen coordinates the U.S. Fish and Wildlife Service's snakehead control and management plan from Annapolis, Maryland.

"In places where they've had an introduction and they've established a beachhead, like snakeheads in the Potomac, we don't have any track record for being able to eradicate aquatic species like that," he said.

Worrying for Nothing?

Alien species can wreak havoc in ecosystems that evolved without them by outcompeting—or outright eating—native inhabitants.

Early reports, which suggested that snakeheads could cover significant overland distances and spread from one body of water to the next, were especially worrisome.

But fears of the "walking fish" appear unfounded, experts say. Although snakeheads do breathe air and can survive several days out of the water, the species present in the U.S. cannot travel overland.

"They are either going to swim to where they are going to get to, or, unfortunately, people can end up putting them in other places. That's the only way they could have gotten into the Potomac," Minkkinen said.

Fears for the safety of the river's bass populations have also, so far, been unrealized.

Anglers prize Potomac bass (which are also a non-native species). The fish are top predators that scientists fear could suffer from direct conflict with snakeheads.

But fishers and scientists alike report no noticeable decline in bass numbers to this point.

Opportunity to Learn

Though snakeheads may be in the Potomac to stay, wildlife managers still hope to prevent the spread of the fish to other watersheds.

The key, they say, is understanding their quarry.

Much snakehead behavior and biology remains unknown, at least in the Western world, so the Potomac population serves as a live laboratory for research.

"I think we'd better use [the Potomac] as a place to learn what [the snakeheads'] impacts are going to be and learn about their general biology and behavior," Minkkinen said.

"Once we understand what their impacts are on the Potomac, we'll better understand what their impacts might be in other parts of the United States," he continued.

"Unfortunately they've been released in a huge watershed with thousands of acres of what looks like perfect habitat. I don't think we've begun to understand how well they are going to do.

"It will really be decades before we know the full impact."

Across the Ocean

Those control efforts appear to be too late for at least two other states.

Snakeheads, also known as mudfish, are an Asian delicacy. Live specimens, though banned in the U.S. since 2002, are treasured by customers at North American Chinese markets.

The fish that gave rise to the Potomac snakeheads, for example, may have been released after purchase from nearby Washington, D.C.'s Chinatown.

And similar acts may have spawned other snakehead footholds in the U.S.

A South Florida population of a different species of snakehead appeared during much the same time period as the Potomac invasion.

"The first bullseye snakehead showed up in a suburb of Fort Lauderdale in the year 2000," said Walter Courtenay Jr., a biologist and snakehead expert with the U.S. Geological Survey in Gainesville, Florida.

"They are in the canals and ponds—which spread all over Southeast Florida like a road map."

Courtenay reports that Florida populations, like their northern counterparts, appear to be growing in number, and their impact on native species remains unknown.

And the northern snakehead may be establishing another beachhead in Pennsylvania.

The fish are known to inhabit two south Philadelphia ponds that drain into the Schuylkill River near its confluence with the Delaware River.

One fisher has already reported a confirmed snakehead catch in the Delaware.

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