- The Washington Times - Sunday, July 28, 2002

CROFTON, Md. As fish go, the northern snakehead is a force of nature.
The toothy, torpedo-shaped native of the Yangtze River in China grows up to 3 feet long, and when its food sources run out, it can slither to another pond or river, surviving up to three days out of water.
But it wasn't these peculiarities that got the attention of Maryland's Department of Natural Resources when the fish turned up in a soupy, 9-acre pond behind an Anne Arundel County strip mall. It was the fish's appetite.
The snakehead is a predator, devouring smaller fish and other aquatic animals. Biologists say it could adapt to Maryland's climate, so alarms went off when the DNR found dozens of juvenile snakeheads, each the size of a finger.
If the fish branches out from the original pond the nearest river is just 75 yards away it could wreak havoc on local ecosystems.
The snakehead is just one of scores of problematic plants and animals from overseas that are making new homes in the United States. Invasive species can be as big as a wild boar or as small as the West Nile virus. The elegant mute swan is an invasive species as is the trash-picking Norway rat.
They come to the United States as stowaways in transoceanic tankers. Others are discarded pets. Or maybe they're supposed to end up on someone's plate but wind up in a local stream.
Once they get established, they upset the natural order and cause damage. One study reported by the U.S. Fish and Wildlife Service estimates the total costs of invasive species in the United States at more than $100 billion a year.
Awareness of non-native species has improved over the past few decades, and steps are being taken to limit them, but many scientists believe global commerce is unintentionally spreading species to new continents.
"There's more trade with more regions," said Gregory Ruiz, a senior biologist at the Smithsonian Environmental Research Center in Edgewood, Md. "More materials that are floating back and forth" such as zebra mussels.
Zebra mussels devastated the Great Lakes after being transported in the 1980s from Eastern Europe in the ballast of commercial ships. The mussels form thick clusters of up to 700,000 per square meter, clogging pipes and turbines at hydroelectric plants.
But invasive species also hurt natural ecosystems in ways that can't be measured in dollars. To feed, zebra mussels filter tremendous amounts of water, robbing other species such as clams of the plankton they need to exist.
Conditions are ripe for zebra mussels in Maryland. They haven't made it here yet, but they have been discovered at the northernmost end of the Chesapeake Bay watershed, in New York state.
Already in the Bay is the Vietnamese nuclear worm. Over the past few years, anglers have begun using the plump pink worms, which can stretch up to 5 feet long, as bait.
Biologists fear the nuclear worms, if dumped from bait buckets into the Bay, could attack the fragile native oyster population and may carry bacteria that could cause serious even deadly illness in humans.
The oyster population, meanwhile, has been devastated by MSX, a parasite believed to have found its way into the Chesapeake in the 1960s when someone introduced an Asian breed of oyster to bolster the fishery.
The oysters didn't make it, but the disease flourished. MSX has combined with other factors to cut oyster harvests in Maryland and neighboring Virginia to roughly 1 percent of historic levels.

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