Nutria Response Team looks to stop spread of destructive rodent in inland waters of Central California

By on February 24, 2018

The semi-aquatic nutria – native to South America and reaching up to 20 pounds and 2.5 feet in body length with a 12-inch tail – are wreaking havoc in in the wetlands, rivers, canals and other freshwater habitats in Fresno, Merced and Stanislaus Counties. Consequently, a Nutria Response Team, with representatives from California Department of Fish and Wildlife (CDFW); the California Departments of Food and Agriculture, Parks and Recreation, and Water Resources; the U.S. Department of Agriculture; and the U.S. Fish and Wildlife Service along with staff from local county agricultural commissioner offices, has convened with the goal of eradicating nutria from the state.

Nutria, also known scientifically as Myocastor coypus, are destructive, wasteful feeders capable of destroying up to ten times the vegetation they consume. Signs of presence typically include cut, emergent vegetation such as cattails and bulrushes, with only the base portions eaten and the stems left floating, destroyed by the rodent’s long, orange teeth. Nutria construct burrows with entrances typically below the water line, though changing water levels may reveal openings.

Much like other aquatic mammals, nutria often create runs, or paths in and out of the water or between aquatic sites. Nutria tracks have four visible front toes and, on their hind feet, webbing between four of five toes. Tracks are often accompanied by narrow tail drags.

“This is a very significant threat in terms of the environmental damage and our agriculture industry,” said Peter Tira with the California Department of Fish and Wildlife in a recent National Geographic article. It’s a very frightening situation in terms of impact.”

But the CDFW believes early intervention actions could be successful in eradicating nutria from the area and is asking the public’s help in looking for and reporting nutria sightings in order to determine the extent of the infestation. Since March 30, 2017, more than 20 nutria, including males, pregnant females and juveniles, have been documented within private wetlands near Gustine, duck clubs, the Merced River near Cressey, adjacent to the San Joaquin River near Grayson, south of Dos Palos, the San Luis National Wildlife Refuge, and Salt Slough on the San Joaquin River.

Greg Gerstenberg, a state biologist in Los Banos is trapping nutria on a few acres of a private duck hunting marsh in Gustine, Merced County, where they were first discovered according to the Sacramento Bee. “This animal needs to be controlled now,” he said. “We have a limited window of opportunity here.”

The nutria are prolific swamp rodents. Females nutria can reproduce by six months of age, breed year-round, and can produce three litters in 13 months. Within approximately one year of reaching reproductive maturity, one female nutria can result in more than 200 offspring, which can disperse as far as 50 miles.

If the South American native rodent gains a foothold in California’s waterways, the CDFW claims it will severely impact California’s resources, causing the loss of wetlands, severe soil erosion, damage to agricultural crops and levees and reduced stability of banks, dikes and roadbeds, as they have done in Louisiana, Chesapeake Bay and the Pacific Northwest. Nutria are also capable of degrading water quality and contaminating drinking supplies with parasites and diseases transmissible to humans, livestock and pets.

The new Nutria Response Team is currently preparing an eradication plan, the first stage of which is determining the full extent of the infestation. The assistance they receive from local landowners and the public throughout the Central Valley, Sacramento-San Joaquin Delta and beyond is critical to successfully delineating the population.

Suspected observations or potential signs of nutria should be photographed and immediately reported to CDFW’s Invasive Species Program online, by e-mail to or by phone at 866- 440-9530.