Photograph by John Eastcott and Yva Momatiuk, National Geographic

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A litter of young nutria (file photo).

Photograph by John Eastcott and Yva Momatiuk, National Geographic

Five Years After Katrina, Big Alien Rodents Return

But boom in trappers keeping wetland-eating, beaver-size nutria in check.

Five years after Hurricane Katrina whacked down the population of the invasive, wetland-munching rodents in Louisiana, nutria have bounced back.

At the same time, some coastal marshes are rebounding too, because of a boom in Louisiana's nutria trappers.

The 2005 to 2006 trapping season, which runs from November 20 to March 31, yielded 168,843 nutria tails. The 2009 to 2010 season, by contrast, set a record: 445,963 nutria tails, according to state figures. Trappers hunt the rodents for money and discard their carcasses.

"The amount of animals harvested this past year is a result of economics in the area," said Edmond Mouton, who heads the Nutria Control Program with the Louisiana Department of Wildlife and Fisheries in New Iberia.

Simply put, more out-of-work residents are out trapping the rodents, which are native to South America but were introduced to the U.S. as a fur species in the late 19th century.

The impact of the hurricane—which killed many nutria outright—was short-lived, Mouton added. (Related: "Katrina Weakened, But Didn't Wipe Out, Invasive Rodents.")

"They established several populations elsewhere, and some of the populations that were decimated … slowly became re-established," Mouton said. "It is a fairly resilient species and able to handle such catastrophes."

Eroding Gulf Coasts Losing Storm Barriers

Coastal wetlands protect inland areas from intense damage by storm surges. Yet due largely to oil-and-gas development, Louisiana has the highest rate of human-induced coastal erosion in the U.S., according to the Texas-based Harte Research Institute for Gulf of Mexico Studies.

Nutria only compound the problem by eating wetland grasses, which exposes the soils to erosion from the ebb and flow of the tides, Mouton said. Marshes that get converted to open water are "unrecoverable," he said.

For every mile (1.6 kilometers) of coastal wetlands lost, storm surges increase by about a foot (0.3 meter), he noted.

Also unknown is the ultimate impact of the 2010 Gulf of Mexico oil spill on wetlands. "There is concern that [the oil spill] could exacerbate the already dire coastal-erosion issues in Louisiana," Chris Macaluso, public information director for the Coastal Protection and Restoration Authority of Louisiana, told National Geographic News in May.

Money-Making Rodents

Harvesting the 15-pound (7-kilogram) nutria—which are widespread throughout the Gulf states—is one way humans can prevent wetland damage, the wildlife-and-fisheries agency's Mouton said.

To cull the Louisiana nutria population, wildlife managers implemented a program in 2002 that paid trappers four dollars for every nutria caught. (The fee increased to five dollars after Katrina.) (Read about alien invaders in National Geographic magazine.)

Since the program started, the amount of nutria-damaged wetlands has declined from more than a hundred thousand acres (40,450 hectares) to 8,475 acres (3,430 hectares), according to program statistics. (See pictures of Louisiana's wetlands.)

"Not only has the number of acres been reduced but also the severity of damage," Mouton said.

In an average year, trappers kill about 300,000 nutria in Louisiana.

"The only year they were down was post Rita and Katrina, and that stands to reason," Mouton said. "A lot of individuals that harvest nutria live along coastal areas, and they were impacted as well by the storms."