Nutria pose ‘triple threat,’ officials warn

Issue Date: July 4, 2018
By Kevin Hecteman
Wildlife biologist Evan King records data while checking nutria traps in a private farm pond in Merced County.
Photo/California Department of Fish and Wildlife
Among other destructive habits, nutria burrow into the ground, which can undermine levees and lead to flooding.
Photo/California Department of Fish and Wildlife
Department of Fish and Wildlife senior wildlife biologist Greg Gerstenberg resets a trap on the China Island Unit of the North Grasslands Wildlife Area outside of Gustine.
Photo/California Department of Fish and Wildlife

Could a 20-pound swamp rodent ruin California's water delivery system and farmers' crops up and down the Central Valley?

Left unchecked, nutria could well do exactly that, wildlife officials say.

Nutria are semi-aquatic rodents that the California Department of Fish and Wildlife has described as a "triple threat": They can damage crops, undermine levees and other water infrastructure, and wreak havoc on wetlands.

"If they weaken a levee enough, you're going to have that localized flooding," said David Strecker, who farms hay and row crops on Roberts Island near Stockton. "But that does impact the state on a much greater perspective. If one of these islands floods, that affects how much water is available for export. That affects how much water is available for the local farmers and even for the local municipalities that rely on the delta."

Strecker said he's aware of two nutria sightings the past two months: one on a ranch a mile from his and another in Lathrop. Since then, the San Joaquin Farm Bureau has been working to spread the word.

"We've been distributing that information out to the entire county, but mostly to the people that are located in the delta, where this would be the biggest problem," Strecker said.

David Passadori, who grows almonds and walnuts in northern Merced County, found about four nutria at an irrigation pond on his property last fall.

"I have berry bushes around the pond," Passadori said. "They were living in there."

He thought they were muskrats at first, but after working with his county agricultural commissioner, he trapped them—and hasn't seen any since.

A nutria has also shown up in Tuolumne County. Gary Stockel, the county agricultural commissioner, said a photo of a nutria was taken near Don Pedro Reservoir in January 2017.

"The community has been notified of the sighting, and we are encouraging folks to either contact us or contact (state Fish and Wildlife) directly," Stockel said.

Peter Tira, an information officer for the California Department of Fish and Wildlife, said evidence of nutria damage can be hard to spot.

"What's tricky about nutria is that they burrow by coming up underwater," Tira said. "It's not obvious to the eyes that nutria are damaging a levee or farm canal, because you don't see the damage until it collapses."

Besides burrowing, nutria also eat vegetation—as much as a quarter of their body weight each day, according to CDFW—and leave a large swath of destruction in their wake. They'll almost always be found near waterways, which Tira describes as nutria freeways.

Strecker said those areas will bear close vigilance.

"We're going to have to watch closely in the smaller sloughs and smaller waterways where the land adjacent is below sea level, and you have a lot of the shallow and tule areas on those waterways, which seems to be a prime location for these to set hold and move in," he said.

CDFW reports that nutria have been confirmed in six counties—Fresno, Merced, Mariposa, Stanislaus, Tuolumne and San Joaquin. It's not known yet how many are in the state, and efforts are underway to survey the extent of the problem, Tira said.

If a survey finds potential nutria presence, cameras and hair-snare traps will be set to catch images and samples of fur. If the hair tests positive for nutria, traps will be set.

Tira said some 200 nutria have been trapped so far, with efforts focused on the northern San Joaquin Valley in hopes of keeping the rodents out of the delta.

"The goal is complete eradication—removal from the landscape," Tira said. "They pose a real threat to our agricultural economy, especially if they get up into the rice country, which is perfect nutria habitat. We haven't found them that far north yet."

One of Strecker's concerns is the animal's rapid breeding habits.

"The rate at which these can reproduce is staggering," he said.

Nutria can reach sexual maturity at the age of 4 to 6 months, according to CDFW, and produce their first litter by 8 months. They can have as many as three litters per year, with anywhere from one to 13 baby nutria. Tira said nearly every female nutria trapped so far has turned out to be pregnant.

CDFW wants to know about all potential nutria sightings, and is sending 7,000 letters to property owners along the San Joaquin River, from Merced County to the delta, requesting access to survey for nutria.

"If we're going to be successful in eradication, we're going to have to get the cooperation of landowners (and) farmers to assess their property and trap any nutria they may have," Tira said, noting that CDFW has received a lot of support from farmers, including one in Merced County who donated sweet potatoes used to bait traps.

The recently enacted 2018-19 state budget includes $400,000 allocated to the Department of Food and Agriculture to survey the extent of the problem and help CDFW with eradication efforts.

Noelle Cremers, who works on wildlife and environmental issues for the California Farm Bureau Federation, said it will be helpful to have CDFA involved.

"Farm Bureau would like to ensure that there is a coordinated effort to eradicate nutria before they become established," Cremers said.

Bruce Blodgett, executive director of the San Joaquin Farm Bureau, said he would like to see federal funding directed to the U.S. Department of Agriculture Wildlife Services program.

"They're the ones that are the most trained, and appropriately trained, to address the issue," he said.

Nutria often are mistaken for muskrats, beavers or river otters. CDFW has a spotters' guide and more information on its website at

Anyone who believes they've seen a nutria or evidence of its presence should take photos and report the sighting at; email; or call 866-440-9530. CDFW advises that if a nutria is captured, it should not be turned loose, and CDFW or the county agricultural commissioner should be contacted as soon as possible.

Nutria are already established in 30 states, including Oregon and Washington. They've shown up in California before but were eradicated by the 1970s. It's not known how the rodent made its way to the San Joaquin Valley this time.

(Kevin Hecteman is an assistant editor of Ag Alert. He may be reached at

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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