FEATURE: Good News on Nutria

Written exclusively for Maven’s Notebook by Robin Meadows

When California Department of Fish and Wildlife biologist Greg Gerstenberg saw the first nutria caught in a duck club pond near Los Banos in 2017, he had never even heard of these water-loving South American rodents. Today, as a lead on field operations to eradicate them from the state, Gerstenberg knows these two-foot, 20-pound invaders all too well. Nutria are prolific breeders and can be astonishingly destructive, burrowing up to 150 feet deep into levees and mudbanks, and laying waste to huge swaths of wetlands. 

This unwelcome discovery of nutria five years ago raised fears that they would infiltrate the Delta, which is just 50 miles away from Los Banos and supplies water to 27 million Californians and 750,000 acres of farmland. Nutria would imperil this water system by undermining levees around the Delta’s many subsided islands, flooding the sunken land and so pulling salty water in from the San Francisco Bay. 

Once established in the Delta, the region’s maze of twisting waterways would make nutria incredibly difficult to control. “Keeping nutria out of the Delta is a priority,” Gerstenberg says. “If they go downstream along the San Joaquin River, they’d get there pretty quickly.” 

Nutria crews work the Delta and Stanislaus County year-round; the Los Banos area in the summer, when water levels are low enough to facilitate access; and the Merced River and edge populations in the winter. As of late June 2022, CDFW had live-trapped 2,990 nutria across five counties. 

The good news is that since the nutria eradication program ramped up several years ago, captures have dropped continuously — from a high of 1,230 in 2020, to 702 in 2021, and 189 for the first half of 2022 — even though the degree of effort has been steady. This suggests fewer nutria are out there. The great news is there hasn’t been a single confirmed nutria sighting in the Delta — or anywhere else in San Joaquin County — for months. 

The bad news is that the eradication team is understaffed, not for lack of funding but for lack of suitable applicants. “The work is extremely physically demanding,” Gerstenberg explains. “They’re knee-deep in mud, hot during the summer, cold during the winter, and out when it rains.” 

Other challenges include the recent rise of invasive plants like primrose, alligator weed, and water hyacinths in the San Joaquin River, which line the banks and are basically a buffet for nutria. “It’s great nutria food,”  Gerstenberg says, adding that four years ago there was almost none of this green growth along the river. 

Getting permission to check for nutria on private land can also be difficult. “We’ve had tremendous support but there are still some lands we don’t have access to,” Gerstenberg says. “If they have a pond, nutria from those lands can reinfect areas we’ve cleaned.” 

Luckily, the team is about to get some overdue additions to their detection toolbox, which currently relies on camera sightings as well as visual signs of nutria activity. Notably, the arrival of nutria-tracking dogs from Chesapeake Bay was greatly delayed by COVID, but now a contingent for field testing in California is finally on its way. These highly-specialized canines  sniff out nutria scat that people don’t even see. “Their noses find nutria that we can’t,” Gerstenberg notes. 

Also still in the works is the “Judas” program, which will use sterilized nutria that are outfitted with radio transmitters and released to the wild. These social animals will then seek out and unwittingly betray others of their own kind that have eluded detection, hence the name of the program. 

The push to eradicate nutria has already been a long haul and is far from over. That said,  Gerstenberg is cautiously optimistic. “I think we’re on the right side of the curve,” he says.

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