Maryland Suffers Setback in War on Invasive Walking Fish

Hillary Mayell
for National Geographic News
July 12, 2002
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The news keeps getting worse for Maryland wildlife officials. Biologists sampling the lake captured more than 100 juvenile northern snakeheads, confirming their worst fears: The air-breathing, land-crawling, voracious predator found in a pond in Crofton, Maryland, is multiplying.

Finding that many doesn't provide scientists with enough information to estimate the overall number of northern snakeheads now living in the pond.

"You only expect to get a small percentage of the fish when you're sampling," said Steve Early, Maryland's freshwater fisheries manager, who conducted the survey. "But I'm worried if I have 100 or if I have 1,000 in the pond; I've still got too many."

Finding the juveniles means the northern snakehead is now an established population in the Crofton pond, said Walter Courtenay, professor emeritus of zoology at Florida Atlantic University. "All it takes is the ability to successfully reproduce to be defined as an established population," he said.

Courtenay, who has been preparing a risk assessment on the snakehead for the U.S. Geological Survey since September, estimates that the juveniles are about five months old.

State fisheries managers were first alerted to the possibility of an invasion by an alien species when an angler caught, photographed, and threw back an unusual looking fish in mid-May.

Plans to rid the pond of the fish were put into motion as soon as it was identified as a northern snakehead.

The proximity of the Little Patuxent River and the fish's ability to breathe out of water and travel across land has increased the sense of urgency among wildlife officials.

A scientific panel of federal and state officials representing a number of disciplines will be convened, perhaps as early as next week.

"The panel will be looking at a number of strategies for containment and control of this population, as well as long-term recommendations on how to better prevent similar invasions," Early said.

Fears of Expansion

Besides figuring out a way to eliminate the snakeheads from the Crofton pond, the group is likely to recommend searching for snakeheads in other freshwater bodies.

State officials don't believe the fish has moved yet, said Early, but at the moment, the Little Patuxent River, which is about 75 feet (23 meters) from the pond, can't be sampled.

"Rains in the upper watershed have raised the water level, making the water too fast and too muddy to be conducive to sampling," said Early.

The lower end of the pond has been sandbagged to prevent the alien fish from reaching the Little Patuxent should there be heavy rains.

Battling an Alien Species

The sooner wildlife officials come up with a solution for ridding the pond of the fish, the better.

Ninety percent of the northern snakehead's diet consists of other fish. They can grow to more than three feet (one meter) long and can live in waters that are covered in ice, so there's no hope of a dieback over the winter.

Worse, northern snakeheads are extremely fertile; females can lay as many as 100,000 eggs a year.

Options for eliminating the fish in the Crofton pond are somewhat limited. They can't be fished or trapped out because there is no way of knowing whether all of them have been captured.

The panel is likely to consider draining the pond, but there are problems with that approach. The water can't be flushed into the Little Patuxent, so "there would have to be some kind of engineering solution for working through a filter," said Early. Even then, because the snakehead can bury itself in the mud for several months, some could survive the draining.

Electroshock hasn't worked so far and can't be tried again until winter, when the dense vegetation in the pond has died back, allowing the use of large equipment. Even then, some snakeheads could survive.

The discovery of the juvenile fish may force wildlife officials to employ the most drastic option: poisoning the pond using Rotenone, a plant-derived toxin.

"None of the other methods guarantee that you'll get every fish in the pond," said Courtenay.

Bigger Problem

The northern snakehead's arrival in Maryland is only the latest in a long list of invasions by alien species around the world [see sidebar].

Alien species—plants and animals that have become established outside their natural range as the result of human activity—pose a huge threat to the biodiversity and health of an ecosystem.

Once established, an alien species can eat native species or compete with them for habitat and food. Lacking natural predators in their new environment, the invaders can drive natives to extinction, drastically degrade ecosystems and cost millions of dollars a year in eradication efforts.

Once an alien species establishes itself, it's nearly impossible to eradicate. "The folks in Maryland are not overreacting one little bit," said Courtenay.

A snakehead species introduced in Uzbekistan in the early 1960s, he said, spread so fast and with such devastating effect on native fish populations that local fishers were able to establish a commercial fishery. "They turned a negative into a positive, but that doesn't mean it wasn't an ecological disaster," he said.

Educating the Public

The northern snakehead invasion in Maryland highlights one of the most frustrating problems wildlife specialists face—the ignorance of the general public about the catastrophic consequences that can occur when non-native species are released into the wild.

Snakeheads are native to Asia and equatorial Africa, and are imported into the United States as part of the aquarium trade, or to be sold as food.

According to the Maryland Department of Natural Resources police, the Crofton invasion was born sometime in 2000 when a man purchased two live snakeheads in New York City's Chinatown district intending to make soup for his sick sister; the soup was postponed, the fish put in a tank. When they outgrew the tank, he dumped the by then foot-long fish in the pond.

Because of their potential invasiveness, possessing a live snakehead is illegal in 13 states. Maryland, Virginia, and the District of Columbia are not among them, although it is illegal to release non-native fish into Maryland waters.

Charges won't be filed against the Maryland culprit because of a two-year statute of limitations that bars prosecution.

Courtenay expects the U.S. Fish and Wildlife Service to issue a federal regulation totally banning the importation of live snakeheads before the summer is out.

If there is a silver lining to the alien species invasion in Maryland, it's the publicity surrounding the situation.

"The news on television and in print has reached more people with the message that, number one, we have a bad fish out there, and number two, don't release non-native fish into the wild, than any public education program the USGS, Fish and Wildlife Service, or anyone else has been able to do," said Courtenay.

"And," he added, "that's an important message to get across."

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