Katrina Weakened, But Didn't Wipe Out, Invasive Rodents

John Roach
for National Geographic News
September 9, 2005
Hurricane Katrina's path of destruction dealt at least a temporary setback to the nutria, the South American rodent species that is devouring wetlands along the Gulf of Mexico, according to experts.

Scientists believe decades of wetlands loss in the Gulf region—due in part to the voracious appetites of the rodents—made Hurricane Katrina's destruction worse.

"Some of the storm protection that nature provides from wetlands, especially in southeast Louisiana, that flood protection, it just wasn't there," said Justin Baker, a biologist with the Louisiana Department of Wildlife and Fisheries in New Iberia.

Baker heads up a program to reduce the numbers of the invasive rodents with an incentive program: Registered trappers are paid four dollars (U.S.) for every nutria tail they deliver to collection agencies. The target is to kill 400,000 nutria each year.

Baker's department encourages trappers by touting the virtues of nutria fur, which is similar to that of beaver, and by circulating recipes for nutria meat.

Adult nutria weigh about 15 pounds (7 kilograms), falling in size between a muskrat and beaver. Their prolific nature—a female can produce two litters of five or six young a year—and insatiable appetite for wetland vegetation are wreaking havoc along the U.S. Gulf Coast.

In April 2005, an aerial survey found 53,475 acres (21,641 hectares) of nutria-caused wetland damage in Louisiana. That figure is nearly half the damaged acreage surveyed when the control program started in 1998.

Jacoby Carter is an ecologist who studies nutria at the U.S. Geological Survey National Wetlands Research Center in Lafayette. He said Katrina's impact on the rodent was likely significant but temporary.

"It most likely greatly reduced the populations in the affected areas, [but] it probably did not wipe them out," he wrote in an e-mail to National Geographic News. "Since nutria do swim, some probably found refuge on floating items."

Given the rodents' prolific nature, their recovery is certain, Carter added.

Wetland Destruction

Baker said that nutria damage to wetlands stems from their feeding habits: Unlike muskrats, they eat everything in sight before moving on. "They literally eat themselves out of house and home," he said.

With the vegetation removed, fragile organic soils are exposed to erosion through the action of the tides. Unless the damaged areas are quickly revegetated, the eroded soils sink below sea level and the area becomes open water.

The degree to which nutria-caused wetland loss heightened the affects of Hurricane Katrina is unknown, but it's something the USGS's Carter plans to investigate.

"The state flew flights to assess nutria impacts along the coast," the ecologist said. "It would be interesting to see if the areas they marked as heavily impacted by nutria suffered more storm damage than areas that were nearby but not noted as heavily impacted by nutria."

Meanwhile, Baker said the control program will continue. The trapping season runs from November 20 through March 31, and applications for trappers are currently available from the Louisiana Department of Wildlife and Fisheries.

The control program demonstrates the ability of wetlands to recover, already halving the damaged acreage since 1998. Baker hopes participation will remain steady, allowing more wetlands to recover.

"As long as the wetland is not totally destroyed and converted to open water, which is the most severe case of wetland damage here, the wetland can come back," he said.

New Threats

While Hurricane Katrina likely reduced nutria populations in Louisiana, Mississippi, and Alabama, the storm also brought new threats, Carter said.

Exotic pets were "more than likely" left behind in evacuated homes and may have escaped into the environment. As an example, Carter pointed to the Cuban treefrog (Osteopilus septentrionalis).

"This has become an important pest in Florida," he said. "It looks similar to our native green treefrog and occupies similar habitats. However, it is larger, poisonous, and it eats native treefrog species with abandon."

If the invasive frogs become established in the wild, they could have a devastating impact on frog populations in New Orleans as well as the nearby Jean Lafitte National Historical Park and Preserve.

"The Cuban treefrog is just one example," Carter said. "This is a situation that bears close monitoring and perhaps action, if resources allow."

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