Declaring war on pesky nutria Destruction: Maryland researchers want to eradicate the orange-toothed rodents that are chewing up Eastern Shore marshlands.


BLACKWATER NATIONAL WILDLIFE REFUGE -- There's a war going on here, and the bad guys are winning.

To look at this peaceful scene, where late autumn sunlight shimmers on the wings of a soaring bald eagle and turns the still waters mirror-bright, you would not know that the marsh's heart is literally being eaten alive.

But a South American rodent called nutria is rapidly helping to destroy one of the East Coast's loveliest and most productive wetlands. Lacking natural enemies in North America, the nutria chews up marsh grasses at the root, turning the dappled mosaic of rushes and shrubs into miles-wide swaths of shallow, lifeless water.

The creatures have contributed to the destruction of about 7,000 of the refuge's 23,000 acres, along with other Eastern Shore marshes from Delaware to Virginia. Wildlife managers say the damage affects anyone who swims or sails on the Chesapeake Bay, makes a living fishing its waters or dines on its bounty.

To fight back, Congress last month authorized spending $2.9 million of taxpayers' money on a three-year research project unlike any other:

"The reason we're researching them is to know how best to kill them, OK," said refuge biologist Keith M. Weaver. "I hate to put it so crassly, but it's true."

Nutria, said Weaver, are "a cancer on the marsh. Economically, ecologically and, in my opinion, just morally, we have a right and a responsibility to protect these areas."

It will be at least a year before the federal money becomes available, biologists say. When it does, the refuge is expected to become ground zero in Maryland's effort to eradicate the voracious, orange-toothed rodents, which number 40,000 to 50,000 statewide.

Since nutria were first imported into the U.S. in the 1930s in an ill-advised attempt to raise them for the fur trade, they have spread to 22 states. Louisiana has spent tens of millions of dollars fighting them, and still has a population of at least 1.5 million nutria.

The Bayou State has given up on eradication; Louisiana officials now speak of "nutria control." They're trying a $1 million publicity campaign to encourage hunting, in which celebrity chefs tout nutria gumbo, nutria a la moutarde and other culinary delights.

In Maryland, where cold winters help keep the pests in check, "We believe we can be successful in completely eliminating nutria," Weaver said.

In the 1940s, when fur-trapping was one of the few ways to earn cash in Dorchester County, nutria were imported to a federal government fur experiment station in the heart of the refuge. Wildlife managers hoped to supplement the trade in native muskrat furs.

But the nutria's fur turned out to be -- well, ratty, uneven in color and quick to wear out. A few escaped from pens about 50 years ago, Weaver said, and they've been unstoppable since.

Unlike muskrats, which graze on grasses that later re-grow, nutrias destroy the places where they dine. They dig up marsh plants by the roots with their sharp claws, shearing them off below ground level with their long, curved, bright-orange teeth. The result: Sea water seeps in to turn the brackish marshes into open water. Erosion hastens the damage.

Aerial photos from the 1930s show a miles-wide expanse of marsh grasses at the center of the refuge, where the slender channels of the Blackwater and Little Blackwater rivers once met. Today, that spot is a three-mile stretch of open water, roughly six inches deep and stripped bare of grasses.

Nutria aren't entirely to blame; erosion and rising sea levels are natural processes. But the rodents speed up the destruction and set off what Weaver calls "a chain reaction."

As the marsh disappears, so do the young fish that should have ended up in fishermen's nets or in wading birds' craws. Gone are the frogs that feed the refuge's resident population of threatened bald eagles and peregrine falcons. Gone too are the seeds and insects that feed the huge flocks of migrating ducks and geese that have made the refuge an internationally recognized haven for waterfowl.

"What most people don't understand is the significance of those marshes," said Josh Sandt, the deputy director of the state's Department of Natural Resources. "If I was a sailor, would I rather sail on muddy water or clear blue water? With a healthy marsh acting as a filter, you would sail on clear blue water."

Since 1989, managers have offered local trappers a "nutria rebate" on the refuge's 18 winter trapping leases. For every nutria killed, trappers get a $1.50 deduction in their $500 to $600 lease fees. Most pay off their leases in nutria tails rather than cash, Weaver said. Still, at least 35,000 nutria remain, managers estimate.

To find a way to eliminate them, Maryland and refuge officials turned to the St. Patrick of nutria, Morris Gosling, director of the research arm of the Zoological Society of London. Gosling spearheaded the world's only successful nutria eradication campaign -- a 6-year, 2.6 million pound effort that drove the animals out of England.

"You have to keep trapping them everywhere and all the time," said Gosling. "You've got to maintain it for years to make sure they don't come back."

The Britons' early efforts failed, until they studied the animals' behavior and learned better trapping methods. They discovered nutria are not the brightest members of the rodent family.

"In fact, nutria are easy to catch," Gosling said from his London office. "Often they walk right into the trap even if there's no bait." The British used traps baited with carrots or beets set along the nutrias' watery trails, and on floating rafts where they liked to sun in the open marsh.

"The last animals were killed in 1989, and none have been seen since," Gosling said. Meanwhile, the recovery of the damaged English marshes has been "spectacular." After visiting the Maryland refuge, he thinks similar methods could work here.

Beginning in 2000, refuge managers hope to use the federal money, along with nearly $1 million in state or private matching funds, to test methods of trapping nutria. On another site, the creatures will be radio-collared so their movements can be tracked, but otherwise left alone.

Scientists will compare the two sites to see whether the grasses recover when nutria are removed. Researchers also will try to restore damaged areas, using specially rigged sprayers to replace the sediments torn away by the creatures' claws and replanting them with native grasses.

"We're starting to get the impression that once it gets to be open water it's lost marsh, irreversible," said Weaver. "We can see areas disappearing right before our eyes. When it gets to this stage, it's almost too late."

Pub Date: 11/10/98

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