Maryland Wages War on Invasive Walking Fish

Hillary Mayell
for National Geographic News
July 2, 2002

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An angler caught an air-breathing, land-crawling, voracious predator this past weekend in a pond in Crofton, Maryland.

The good news is that the fish, a northern snakehead that has been targeted by biologists for the last several weeks, was caught. The bad news is that it was 26 inches (66 centimeters) long; the fish caught in mid-May that alerted wildlife officers to the possibility of an invasion by an alien species was only 20 inches (51 centimeters) long.

"Either the fish grew six inches in a few weeks or we have more than one in the pond," said Bob Lunsford, a biologist with the Maryland Department of Natural Resources.

The knowledge, with the weekend catch, that there is more than one fish in the Crofton pond is what is keeping biologists awake at night.

"Our biggest fear is that there are more than one and they'll reproduce," said Lunsford.

A second fear, based on the fish's ability to breathe out of water and travel across land, is that the snakehead could leave the pond and travel the 75 feet (23 meters) or so to the Little Patuxent River, and from there invade the state's river system.

Battling Alien Species

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

Alien species—plants and animals that have become established outside of their natural range as the result of human activity—pose a huge threat to the biodiversity and health of an ecosystem. Once established, the alien species can eat the native species or compete with them for habitat, food, or both. Lacking natural predators in their new environment, the invaders can drive natives to extinction, drastically degrade ecosystems, and cost billions of dollars a year in eradication efforts.

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