Marek Warszawski

The giant rodent invasion is here. We're not doing enough to stop it

Large rodents invading the San Joaquin Valley

Large invasive rodents may be invading California's Delta. A small team of Fish & Wildlife field biologists is assessing the danger nutria pose for wreaking havoc on the Delta.
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Large invasive rodents may be invading California's Delta. A small team of Fish & Wildlife field biologists is assessing the danger nutria pose for wreaking havoc on the Delta.

To the untrained eye, it looked like an ordinary stand of cattails growing alongside a pond in a managed wetlands. Ordinary, except for several that lie toppled in the mud.

Which is why Greg Gerstenberg chose this particular spot to park his Ford Expedition and amble over for a closer look.

The senior wildlife biologist for the California Department of Fish and Wildlife bent down and picked up one of the fallen cattails. With his index finger, Gerstenberg traced bite marks made by tiny teeth that severed the stalk at a 45-degree angle.

From the angle of the bite marks, and the fact that this cattail and others lying nearby still have their roots intact, Gerstenberg can be certain what kind of animal caused this damage.

"Definitely a nutria," he said. "You're looking for a track in the mud. You're looking for a cattail that has been nibbled on."

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A nutria with its distinctive white whiskers found trapped by California Department of Fish & Wildlife Wednesday, June 13, 2018 near Los Banos. Eric Paul Zamora ezamora@fresnobee.com

Those subtle but telling signs are vital clues in California's incipient effort to eradicate an invasive, voracious swamp rodent that threatens to wreak havoc on our wetlands and water conveyance systems. Since March 2017, when the first confirmed nutria specimen seen in the state since the 1970s turned up in his driveway after it got snared in a beaver trap at a nearby duck club, Gerstenberg has been out here on the frontline.

Initially, that effort was a one-man operation. Gerstenberg set up cameras and left bait, typically a few sweet potatoes, in areas where he thought nutria might be present. If he got a sighting, he returned with traps. Today he supervises a team of six rotating wildlife biologists, reassigned from their normal duties, who spend their days doing assessments and checking traps. Which typically involves wading through waist-deep swamp water under the broiling sun.

It's a laborious process, and the search area is vast. Inside the hunter check station that serves as home base, six large maps hang from an office wall. Three of them depict cross sections of the San Joaquin Valley from the Delta to Tulare County. The other three are of the Merced, Tuolumne and Stanislaus river drainages.

Portions of each map have been divided into numbered units, either wetlands or riparian zones that could contain nutria. Each unit represents a 40-square-mile area. Total up the units, and you get 1.8 million acres.

Those numbers illustrate the daunting task facing Gerstenberg and his team. How can six field biologists (and one supervisor) be expected to assess 1.8 million acres, an area larger than the state of Delaware?

"We can't," Gerstenberg replied plainly. "We need help. We cannot do this with six people."

Let's hope someone in Sacramento is listening.

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California Department of Fish & Wildlife senior field biologist Greg Gerstenberg points out newly re-discovered nutria sightings on a map at the North Grasslands Wildlife Area's Salt Slough Unit Wednesday, June 13, 2018 near Los Banos. Eric Paul Zamora ezamora@fresnobee.com

Since February, when the CDFW issued a warning that invasive rodents up to 3 feet long (including their rat-like tails) and 25 pounds have taken a foothold in the San Joaquin Valley, the resources and manpower devoted to the eradication effort have been grossly insufficient.

Nutria are voracious eaters that devour up to 25 percent of their body weight in plant matter per day. In places like Louisiana and Chesapeake Bay, Maryland, they've turned lush wetlands into barren mudflats that no longer offer protection to fish, birds or other native wildlife.

If unchecked, the same devastation will happen here. And if allowed to spread into the Delta, the toll will be even higher.

Nutria are furious burrowers. A colony of them could easily dig into our vast network of irrigation canals and levees, exposing crops and even homes to floodwaters.

"They're incredibly destructive," said Julie Vance, regional manager for the CDFW Region 4 headquartered in Fresno.

Nutria are also incredibly reproductive. If we don't act with conviction now to control the population, it'll be a lost cause. They'll be here for good.

Females reach sexual maturity at three months, give birth to up to 13 babies at one time and can produce two to three litters annually. Meaning in any given year, one female and her progeny can give rise to 200 offspring.

The mathematical term is "exponential."

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California Department of Fish & Wildlife field biologist Greg Gerstenberg, left, and environmemtal scientist Evan King, check traps that have been set in a pond featuring ideal habitat for the newly re-discovered nutria Wednesday, June 13, 2018 near Stevinson. Eric Paul Zamora ezamora@fresnobee.com

Making matters more complicated, we have no way of knowing how many nutria are out there. Did we detect them early, before they began to multiply? Or are their numbers already in the tens of thousands? Officials can't be sure, since they don't have the manpower, or permission in many cases, to check out every area where nutria may have spread.

"We don't really know where on the bell curve we are or how long these animals have been here," said Terry Palmisano, the state incident commander in charge of nutria eradication. "Are they still at a point where we can beat them back? We're not sure, but we're hopeful. And we've got to go out there and make the effort."

So far, Gerstenberg and his team have trapped and killed 159 nutria. About one-third of them came out of a single pond, located on private property, near the confluence of the Merced and San Joaquin rivers outside Newman.

Each kill undergoes a necropsy where various measurements are recorded and logged. The largest specimen was a 24-pound pregnant female containing 11 fetuses.

"They're nothing but intestines," Gerstenberg said. "They're built to eat, digest and reproduce."

Nutria have been detected as far north as Roberts Island in the south Delta outside Lathrop, when a dog turned up with a dead animal in its mouth, as far south as Tulare County and as far upstream as Don Pedro Reservoir.

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California Department of Fish & Wildlife senior field biologist Greg Gerstenberg, right, carries a small nutria that was trapped and killed as field biologists assess the invasive rodent population near Los Banos Wednesday, June 13, 2018. Eric Paul Zamora ezamora@fresnobee.com

So far, assessments have been limited to state wildlife areas, national wildlife refuges and a few areas owned by irrigation districts. That does not include state parks, where an agreement over how to handle nutria kills has yet to be worked out. (Firearms are not permitted on state parks, and Gerstenberg uses a .22 to put down captured animals.)

In order to access private lands along the San Joaquin River and other riparian areas, officials mailed more than 7,000 letters to landowners requesting permission.

"Thankfully we have been getting a good response," Vance said, "perhaps because people are quite alarmed at having giant rodents on their property."

A glaring question that needs asking is why CDFW has been stuck with such a difficult and odious task, one that isn't in its job description. Wildlife biologists are trained and devoted to protect animals and enhance habitat. With rare exceptions (Gerstenberg grew up trapping muskrats in Dinuba), they have no experience in trapping and killing swamp rodents.

Where is the California Department of Food and Agriculture, which lists "protect against the invasion of exotic pests and diseases" as part of its mission statement? Where is the state Division of Boating and Waterways, which protects against aquatic invasive species like quagga and zebra mussels?

Those agencies have joined the effort, somewhat. ("We are working to identify funding for personnel and equipment to more intensively survey farmland in the valley," CDFA spokesman Jay Van Rein said.) But the heavy lifting, along with the scraping together of funds, has been left solely up to the CDFW. A $1.2 million grant from Proposition 1, along with budget reallocations, is the primary money pot.

An infestation of nutria, an invasive swamp rodent, was recently found in the Sacramento-San Joaquin Delta. See how to identify them and report sightings.

Fortunately, some help is on the way. Starting in July, three trappers employed by the U.S. Department of Agriculture's Wildlife Services will begin a five-month contract. That agency is known for its effectiveness in dealing with nuisance animals – so much so that if often gets criticized for its success by animal-rights groups.

In addition, the CFDW is hiring a full-time nutria biologist and will soon have the use of two scent-trained dogs. And if more nutria turn up in the Delta, more wildlife biologists based in those regions will join up on a rotational basis.

But, honestly, it's not enough. Maryland spent $21 million to eradicate nearly 14,000 animals across a 400-square mile area and employed up to 19 biologists at any given time. That effort appears to have worked. No nutria have been spotted in Chesapeake Bay since 2014.

The situation here will be even harder to manage. The search area is larger as well as less defined and contained. And unlike Maryland, the San Joaquin Valley lacks harsh winters that slow nutria's reproductive roll.

In addition, California laws prevent the use of certain traps that might be more effective in killing nutria but could also ensnare native wildlife like beavers, muskrats and otters.

Gerstenberg's crew is using mainly cage and clamshell-type traps that keep the trapped animals enclosed and alive. In areas of heavy infestation, where non-target animals aren't present, more lethal body-vise traps are being utilized.

"We want to get the nutria, but we also don't want to leave a trail of death of other animals," Vance said.

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Evan King, environmental scientist with the California Department of Fish and Wildlife, sets free a muskrat caught in a trap June 13, 2018, near Stevinson. Eric Paul Zamora ezamora@fresnobee.com

Opening nutria to legal hunting like in Louisiana is not an option. Officials are concerned, and rightfully so, that people would transport the invasive rodents to other areas in order to increase hunting opportunities. Which is the last thing they want to happen.

Furthermore, nutria are nocturnal and nearly impossible to distinguish from beavers or muskrats while swimming. So hunting isn't the answer.

The only remedy is putting more people in the field to set up detection stations with bait and cameras and hiring full-time trappers who aren't taking time away from their normal duties. And sole responsibility, and money, can't be placed on agencies like the CDFW that are already underfunded.

A state with a reported $8.8 million budget surplus should be able to chip off a few million to fight off a destructive, invasive pest.

"We can't sustain this long-term," Gerstenberg said. "I keep looking behind me wondering when the troops are going to arrive."

They'd better arrive soon, or nutria will destroy what's left of our wetlands and we'll be spending a lot more money to repair the damage they cause.

Marek Warszawski: 559-441-6218, @MarekTheBee
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