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Geo-Joint: Keeping the Nutria from Getting Dug In

Posted on June 25 2019

Lots of mammals like water. Humans, for one, although we don’t generally use it as a habitat. Beaver are more integrally involved with the water, damming it, swimming in it, slapping their tails on it. Beaver are important to their natural habitat and have been reintroduced at some effort in places where they had been hunted out by trappers. Their dams have positive effects on water movement and improve habitat for a host of other species. Each biome of the world has its own suite of water mammals that work in harmony with the plant life and other animals to keep a healthy balance in the local ecology. Problems crop up, however, when a member of one region gets transplanted to another.

The nutria. Kinda cute, but quite a nuisance. Note the round tail, unlike a beaver’s

The nutria, also known as the coypu, is an animal that many might confuse with a beaver, especially because it inhabits some of the same kinds of neighborhoods. There are, though, some significant differences between them, notably that full-sized adults are only a third as large as a grown beaver, and the nutria has a face full of white whiskers, while beaver sport a smaller, dark mustache. And the beaver’s well known, wide, flat tail contrasts with the nutria’s longer, thin, rounded tail. Nutria have large, orange incisors like a beaver, but don’t use them to gnaw down trees, nor do they construct dams. They live in burrows dug into the earthen banks along water bodies, going as deep as 20 feet and sometimes extending half the length of a football field. So there are a number of qualities that separate the two species, but most important is where they came from. Beaver are native to North America, while nutria come from southern South America, where conditions are different. Whether there are more predators, or pathogens, or less optimal habitat, nutria numbers are regulated by nature in their original home. Those living in a new environment are less constrained, and causing problems.

California’s Central Valley is seeing an invasion of nutria, a threat to the safety of its extensive levee system.

To be sure, none of the headaches brought by nutria are the little animal’s fault. They didn’t ask to be carried north. As is often the case, somebody with a seemingly bright idea did a dumb thing. Back in the late 19th century, nutria were brought to Lake Elizabeth, just west of Lancaster in Southern California. The intent was to establish a fur-trapping trade in the area. The effort fizzled, due somewhat amazingly to their failure to reproduce. If the nutria does one thing well, it is reproduction. Sexually mature at four to seven months, they can give birth to as many as 13 offspring at a time, and can be re-impregnated a mere 48 hours after giving birth. This they can do in any season of the year, resulting in two to three litters per year per female. Their numbers add up. Nutria were also introduced in the southeastern US in the 1930s for fur farms, with the inevitable escapes and perhaps even purposeful releases. They provided a rich source of furry material for the fashions of the ‘40s, ‘50s and ‘60s, but economic downturns, oversupply of fur in Europe, and the rising objections of animal rights activists stymied the industry. Nutria populations had ebbed and flowed with fluctuating markets for decades, and when the pressure was off, nutria were found to be having ill effects on the marshlands and croplands of the Mississippi Delta. Nutria are voracious eaters of vegetation, consuming 25 percent of their body weight in plants daily. In that process, and in their burrowing, they waste and destroy ten times as much plant volume as they eat. Their appetite showed clearly in the denuded wetlands when their numbers were large. Their burrowing habits also weakened parts of the delta most vulnerable to the ravages of hurricanes and storm surge. During one large hurricane in 1957, the storm surge not only did great damage to the swampy land, but also washed thousands of the little creatures upstream to new habitats. With trapping declining, nutria populations continue to grow, and they have become an existential problem for the margins of coastal states, and in water-rich areas inland.

The nutria’s big orange incisors help it chew through as much as quarter of its body weight in aquatic plants daily.

The plague has spread to areas far from the Delta, as evidenced by their appearance in 30 states, and their establishment in 18. They have also spread around the world to 5 out of 7 continents—Australia has avoided them, and Antarctica’s too cold. But everybody loves to visit California, and many come to stay. Though they fouled out in their first sojourn to the state 130 years ago, and subsequent invaders were eradicated by 1978, a new wave of nutria has landed. How they got to the state this time isn’t known for sure. Their development on fur farms in other states, and crazy as it now sounds, their introduction in various places as helpful consumers of pesky non-native aquatic overgrowth may have given them a route in. In California, though, it’s not the coastline that is threatened. A reproducing population was found well inland in a San Joaquin Valley location in 2017, and since then they have been captured or observed in Stanislaus, Tuolumne, Merced, Mariposa, San Joaquin, and Fresno counties. Almost all the females caught were pregnant, so the Central Valley is primed for a population explosion.

Nutria are social animals, and quite prolific.

Burrows like this in a stream bank can be disastrous when dug into a levee system.

Beyond their decimation of native aquatic plant species in sensitive wetlands habitats, and of crops like rice in farmland, nutria also carry pathogens for tuberculosis and septicemia, and harbor tapeworms and other unsavory internal organisms passable to humans and farm animals though water. But that’s not the scariest part. The activities of nutria endanger California’s most vital commodity—its water supply. Burrowing into levees and earthen dams weakens these structures, making them vulnerable in periods of high water flow or during the shaking of an earthquake. Water officials in California are desperate to keep nutria from becoming a presence in the Sacramento Delta, where the failure of levees could inundate farmland and rural communities, hamstring commerce, and interrupt the very ability to keep vast urban areas sufficiently hydrated should any of the state’s extensive canals collapse. To this end, Fish and Wildlife workers are scrambling to trap and eradicate all the nutria they can find. But it isn’t easy. It’s not effective to try and shoot small animals obscured by thick vegetation. And because the animals are nocturnal, that would also have to happen in the dark. In addition, a lot of their preferred habitat happens to be on private land. The effort to determine ownership, locate the owner, and secure permission to enter and set traps wastes time and money.

Trapping nutria is the most effective way of controlling or eradicating their population.

Those involved feel the tide of nutria in California can still be turned, though it will take a number of well funded years and increased staffing to achieve it. For all the sophistication and massive scale of the Golden State’s waterworks, it is humbling that a lowly rodent could throw the system into chaos if it is allowed to expand its range and population unchecked. Ideas for how to accomplish that are varied. Beyond simple trapping and disposal to cut their numbers, some suggest promoting of the little troublemakers as a good meaty protein source for people or pets. So….nutria cordon bleu, anyone? Fido?

Tour the Central Valley and go nutria hunting! This road map of California by Benchmark Maps will help you find your way in that vast agricultural region. Available from



caption: The nutria. Kinda cute, but quite a nuisance. Note the round tail, unlike a beaver’s
source: (CC by 4.0 International)

caption: The nutria’s big orange incisors help it chew through as much as quarter of its body weight in aquatic plants daily.
source: Flickr: Bédarieux, Hérault, FRANCE (CC by SA 2.0 Generic)

caption: Nutria are social animals, and quite prolific.
source: Wikimedia Commons: Rolf Dietrich Brecher from Germany (CC by SA2.0)

caption: Burrows like this in a stream bank can be disastrous when dug into a levee system.
source: Flickr: born1945 (CC by 2.0)

caption: Trapping nutria is the most effective way of controlling or eradicating their population.
source: Pixnio: Tess McBride, USFWS (Public domain)

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