U.S. targets marsh-wrecking rodents

Nutria under study at Blackwater refuge

February 02, 2002|By Joel McCord | Joel McCord,SUN STAFF

BLACKWATER NATIONAL WILDLIFE REFUGE -- They're preparing an assault here. Nothing on the order of the Allied landing on the beaches at Normandy, but an attack nonetheless, on the orange-toothed South American rodents that have ravaged these marshes for the past 60 years.

The plans aren't as secretive as those surrounding the D-Day invasion -- Mike Slattery of the U.S. Fish and Wildlife Service says they'll launch in March and will tell you what methods they'll use to capture and kill nutria -- but the planning has been as intense and complex as a military campaign.

The first step is to reconnoiter the enemy. Government biologists and local trappers have joined forces in a $3.1 million pilot project to find the best way to rid the vast but shrinking marsh of the pests that threaten its existence. Then comes the attack and finally an effort to restore the lost grasses and shrubs.

Nutria, known to scientists as Myocaster coypus, look like a cross between a rat and a muskrat, with long tails and dark brown fur on their backs shading to orange and beige across their shoulders.

Native to Argentina and Chile, they were exported to the United States and Europe in the late 1930s in a futile effort to shore up failing fur industries. Some escaped, and with no natural predators, their populations mushroomed until they became an ecological problem in 22 states in the United States, and in England and North Africa.

Nutria fragment the marsh by creating deep swimming channels through the grasses. Unlike other animals, which graze on the tops of grasses, nutria eat the roots, exposing the fragile marsh sediments that supported the plants to erosion from wave action. The level of sediment falls below the water, preventing the establishment of new plants.

Soon, there are scattered hummocks of grass surrounded by mudflats and after that, nothing but mud flats covered at high tide with shallow, lifeless water and nutria tracks at low tide.

"It's like a cancer eating the marsh from the inside out," says John Morton, a wildlife biologist with the fish and wildlife service.

8,000 acres of marsh gone

In the past 50 years, the Blackwater refuge has lost an estimated 8,000 of its 23,000 acres of marsh, and more than half the remaining marsh is in danger.

Aerial photos of the refuge area from the late 1930s show the Blackwater and Little Blackwater rivers slicing through vast expanses of grasses, then joining together to flow into Fishing Bay. Photos of the same area today show a stretch of water so broad it is all but impossible to pick out the original river courses.

The losses are critical because Blackwater is a haven for tens of thousands of migrating geese and ducks, and home to reptiles, amphibians, the endangered Delmarva fox squirrel and more than 250 species of birds. The refuge contains the largest concentration of American bald eagles in the Eastern United Sates north of Florida.

Destruction of the marsh works its way up the food chain. The fish that feed the wading birds disappear, as do the rodents and reptiles that feed the falcons and bald eagles that have made this marsh their home. Because the grasses are gone, there is no seed for the geese and ducks and other migrating birds to feed on.

Without grasses, the marsh also ceases to perform its ecological function of filtering runoff and capturing sediment, which contributes to the deterioration of Chesapeake Bay's water quality.

The nutria aren't entirely to blame for the marsh loss, Slattery says. A combination of rising sea level -- believed to be linked to global climate change -- and sinking land also figures in. But the South American rodents exacerbate the problem.

Hunters and trappers take as many as 8,500 nutria a year, "but it doesn't make a dent," Slattery says.

While nutria have few enemies in the natural world, they have few friends among humans. Even the Humane Society of the United States is reluctant to take the animals' side.

"This is something we struggle with," says Bette Stallman, a wildlife scientist with the society. "We understand that introduced species can cause problems, and we haven't come up with a good solution. But we prefer they target the long-term causes of wetland degradation ... climate change and rising sea level."

In preparation for the assault, biologists from the University of Maryland, Eastern Shore, aided by a team of local trappers, have spent the past two years capturing, tagging and releasing the furry creatures here and in two other nearby locations to study their movements in the wild.

On a cold, gray winter morning, nutria tracks are easily visible from a flat-bottomed aluminum boat plying the narrow creeks and guts of Swan Pond Marsh. "You can see the mashed grass and the droppings," says Dean Hopkins, a waterman and trapper from Nanticoke hired to help with the study.

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