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Discovery of invasive nutria in California

Landowners, we need your help...

CDFW has deployed nutria survey teams from the Delta through the San Joaquin Valley. CDFW needs written access permissions to enter or cross private properties for the purposes of conducting nutria surveys and, where detected, implementing trapping efforts. Landowners and tenants, we need your help; so CDFW can survey for and remove destructive nutria from your properties, complete and submit the new-window-iconNutria Project Temporary Entry Permit.

General Information

For general information on nutria biology and ecology please see the nutria species profile page.

A large, male nutria captured in Merced County in 2017
Large, male nutria trapped in a private wetland in Merced County, June 2017. CDFA photo.

Nutria Impacts

Through their extensive herbivory and burrowing habits, nutria have devastating impacts on wetland habitats, agriculture, and water conveyance/flood protection infrastructure. Nutria consume up to 25% of their body weight in above- and below-ground plant material each day. Due to their feeding habits, up to 10 times the amount of plant material consumed is destroyed, causing extensive damage to the native plant community, soil structure, and nearby agricultural crops. The loss of plant cover and soil organic matter results in severe erosion of soils, in some cases converting marsh to open water. Further, nutria burrow into banks and levees, creating complex dens that span as far as 6 meters deep and 50 meters into the bank and often cause severe streambank erosion, increased sedimentation, levee failures, and roadbed collapses.

Normal and damaged wetlands
Wetland loss caused by nutria damage in Blackwater National Wildlife Refuge, Delmarva Peninsula, Chesapeake Bay. Left, normal marsh in 1939 before nutria introduction in the 1940s. Right, by 1989, over 50% of the Refuge's marshes had been converted to open water due to the destructive feeding habits of nutria. Photos courtesy of USFWS.

Aerial photo of normal and damaged marsh
An exclosure experiment in a Louisiana marsh demonstrating the severe ecological damages caused by nutria herbivory in wetland habitats. Photo courtesy of Louisiana Dept. of Wildlife and Fisheries.

Burrow in bank of waterway
Nutria burrows in ground

Nutria burrowing causes extensive damage to water infrastructure, banks, and levees, and creates a hazard for people, livestock, and machine operators. Potential levee and dike failures due to nutria burrowing have serious implications for flood protection, water delivery, and agricultural irrigation in California. Left, nutria burrow in Tualatin National Wildlife Refuge in Oregon. Photo courtesy of USFWS. Right, extensive burrowing damage by nutria in Oregon. Photo courtesy of Trevor Sheffels, PSU.

Discovery in California

Confirmed detections of nutria in California can be viewed in the link opens in new windownutria detection map (PDF). As of May 15, 2018, 65 nutria have been taken in California, with several additional animals confirmed present, across Merced, Stanislaus, San Joaquin, Fresno, Tuolumne, and Mariposa Counties.

Map of nutria detections in California, as of May 15, 2018.

Eradication Effort

CDFW is collaborating with other agencies and local partners to develop the most effective strategy for eradicating nutria from California. As depicted in the "Invasion Curve" figure below, invasive species infestations typically experience a lag phase, while population size and area infested are relatively small, successful eradication is most feasible, and control efforts are most cost-efficient. As time progresses, the population size, area infested, and costs required for control increase exponentially, and the probability of successful eradication is lost. Conceptually, (1) represents where we believe the current extent of the nutria population is in California; eradication is feasible with rapid response; (2) represents the nutria population in the Chesapeake Bay (Delmarva Peninsula) prior to implementation of the link opens in new windowChesapeake Bay Nutria Eradication Project (CBNEP). The CBNEP strategically removed over 14,000 nutria from 2000-2015 and has not detected a nutria since early 2015. (3) represents the link opens in new windownutria population in Louisiana, where population control costs up to $2 million dollars each year for bounty harvests alone.

Exponential growth curve graphic showing area infested and cost increasing over time

Currently, there is a small window of opportunity to successfully eradicate the population of nutria from California. As time progresses, the population size and geographic area of infestation are increasing, along with the effort, resources, and funds required for successful eradication. Over time, the probability of successful eradication decreases, and California would be left to manage and mitigate the devastating impacts of nutria on wetlands, agriculture, and water conveyance/flood control infrastructure.

The interagency Nutria Response Team includes representatives from CDFW, the California Departments of Food and Agriculture, Parks and Recreation, and Water Resources, the U.S. Department of Agriculture, the U.S. Fish and Wildlife Service and local county agricultural commissioner offices. The team is currently preparing an eradication plan, the first stage of which is determining the full extent of the infestation. Assistance from local landowners and the public throughout the Central Valley, Sacramento-San Joaquin Delta, and beyond is critical to successfully delineating the population.

Take by Landowners/Hunters

CDFW has classified nutria as a nongame mammal. link opens in new windowFish and Game Code §4152 specifies property owners or their agents (who possess written permission from the owner or tenant) may take nutria at any time by any legal means to address damage to crops or property. Restrictions apply to the use of traps and types of traps. Given their very similar appearances, particularly in overlapping size classes, citizens should take extra precaution to link opens in new windowdistinguish nutria from other aquatic mammals (PDF); the majority of nutria reports received by CDFW have been muskrats, as have been some "nutria" featured in the media.

Any nutria taken on private or public land should be reported to CDFW as soon as possible for purposes of delineating the extent of the infestation. At minimum, CDFW needs photos to confirm identification; preferably, CDFW needs the carcass to determine sex, age, and reproductive status.

Nutria Identification

Nutria are large, semi-aquatic rodents that reach up to 2.5 feet in body length, 12- to 18-inch tail length and +20 pounds in weight. Nutria strongly resemble native beaver and muskrat, but are distinguished by their round, sparsely haired tails and white whiskers (see CDFW’s link opens in new windownutria ID guide (PDF)). Both nutria and muskrat often have white muzzles, but muskrats have dark whiskers, nearly triangular (laterally compressed) tails and reach a maximum size of five pounds. Beavers have wide, flattened tails and dark whiskers and reach up to 60 pounds. Other small mammals can sometimes be mistaken for nutria if seen briefly or in low light conditions, including river otters and mink. 

Adult nutria in Tuolumne County, 2017. Photo courtesy of Peggy Sells.
Adult nutria discovered in a private pond in Tuolumne County, east of Don Pedro Reservoir. Though muskrats may have a white muzzle, both muskrats and beaver have dark whiskers. Nutria have characteristic white whiskers, and most often have conspicuous, darks ears with light-colored fur underneath, as seen in this image. Photo courtesy of Peggy Sells.

Muskrat on grass
Beaver sitting on snowy bank
 

Dark brown weasel-like mink
California has several aquatic mammals that occur in the same habitats and may be confused with nutria. Top left, muskrat, note the nearly triangular tail and dark whiskers that distinguish muskrats from small nutria, photo courtesy of Missouri Dept. of Conservation. Top right, American beaver, note the broad, flat tail that, along with dark whiskers, distinguishes small beavers from nutria, CDFW photo. Bottom, American mink, note the fully furred tail, dark whiskers, and weasel-like body form, photo courtesy of Alaska Dept. of Fish and Game.

Juvenile river otters in cattails
River otter on ice
 
Left, juvenile river otters, pictured here in a cattail marsh, may also be mistaken for nutria. Note the long body and thick, fully-furred tail, CDFW photo. Right, adult river otter, photo courtesy of National Park Service.
The dark ear and lighter fur underneath help distinguish nutria from other mammals, particularly in night photos. CDFW photo.
Nutria have dark ears with lighter fur below. CDFW photo.
 
Nutria often have a dark undercoat, with lighter-colored guard hairs. Their dark, conspicuous ears, with lighter fur underneath, are helpful in distinguishing nutria from other aquatic mammals when their round tail is not clearly visible. CDFW photos.
Nutria front foot showing the 5th residual toe, which is not visible in nutria tracks. CDFW photo.
Nutria hind foot showing the webbing betwen the four inner toes, and outer, fifth toe free from webbing. CDFW Photo.
 

Left, nutria front foot, showing the four toes visible in tracks and the barely visible fifth, residual toe on the inner, lower area of the foot. Right, nutria hind foot, showing the webbing between the inner four toes and outer, fifth toe free from webbing. CDFW photos.

Habitat

Nutria can be found anywhere in or near freshwater or estuaries. Thus far, they have been found in cattail and tule marshes, ponds, canals, sloughs, and rivers. All currently known locations are upstream of the Sacramento-San Joaquin Delta, which provides a vast amount of ideal and interconnected habitat for nutria.

Look for nutria and signs of nutria presence in wetlands, canals, rivers, and creeks, along levees and riparian areas, in flooded agricultural fields adjacent to waterways, and in the transition zone between wetland and terrestrial habitat.

Sign

Because nutria are wasteful feeders, signs of presence typically include cut, emergent vegetation (e.g. cattails and bulrushes), with only the basal portions eaten and the cut stems left floating, or grazed tops of new growth. Nutria create runs between feeding sites and burrows. Nutria often pile cuttings to create feeding/grooming platforms. Nutria construct burrows with entrances typically below the water line, though changing water levels may reveal openings. 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. 

Nutria cutting showing characteristic 45 degree angle and residual sliver. CDFW photo.
Nutria cutting showing characteristic 45 degree angle cut and residual slivers. CDFW photo.

Nutria cuttings have a 45 degree angle bite and often have a residual strip attached to the stem. CDFW photos.

Cut and dried cattails piled in marsh
Large amounts of vegetation cuttings left floating or piled into beds are characteristic of nutria presence

Vegetation clearing and cuttings characteristic of nutria damage. CDFW photo.
Top left, nutria often pile their vegetation cuttings into feeding/grooming beds. Top right, cattails cut by nutria and left lying in the marsh, a characteristic sign of nutria presence. Bottom, a vegetation clearing or "eat out" with cuttings floating throughout the area, characteristic signs of nutria herbivory damage. CDFW photos.

Nutria runs in grass of wetland
Nutria create "runs" in the vegetation between feeding areas and near entry/exit points along the water's edge. CDFW photo.

Nutria scat is distinctly grooved and floats on water. CDFW photo.
Scat floating on water
 

Nutria scat is distinctly grooved and floats on the water's surface. CDFW photos.

Closeup of nutria tracks in mud
Nutria tracks and tail drag in mud
 

Left, closeup of nutria tracks showing webbing between 4 of 5 toes on the hind foot. CDFW photo. Right, nutria tracks and tail drag. Photo courtesy of USDA.

What You Can Do

Suspected observations or potential signs of nutria should be photographed and immediately reported to CDFW’s Invasive Species Program online, by e-mail to invasives@wildlife.ca.gov, or by phone at (866) 440-9530. Observations on state or federal lands should be immediately reported to local agency staff on the property. Reports will be followed up on by the interagency nutria response team and will help in their eradication effort.

Nutria are a Restricted Species in California under the California Code of Regulations, Title 14, Section 671, and cannot be imported, transported, or possessed live in the state of California.

Outreach Materials and Resources



Habitat Conservation Planning Branch
1700 9th Street, 2nd Floor, Sacramento, CA 95811
Mailing: P.O. Box 944209, Sacramento, CA 94244-2090
(916) 653-4875