By Vicky Boyd

When a Roberts Island farmer brought a dead nutria into the San Joaquin Ag Commissioner’s office in April, California Department of Fish and Wildlife officials had hoped the rodent was just a young male dispersing into new territory.

But with the recent trapping of 17 additional young and adults around Walthall Slough near Lathrop, Fish and Wildlife representatives now fear nutria have established a breeding population in the Sacramento-San Joaquin Delta, said Peter Tira, California Department of Fish & Wildlife spokesman.

Although new trap catches complicate eradication, state wildlife leaders still believe it can be accomplished.

“We do believe eradication is still possible,” he said. “We do believe we’re early enough to eradicate the population. However, we keep finding more and more. And the job becomes longer, more involved and more of a challenge the more we find.”

18 trapped in San Joaquin County

As of Oct. 18, state and federal wildlife biologists had trapped a total of 310 nutria in six Central Valley counties, Tira said. Of those, 18 were in San Joaquin County.

“We’ve got males and females,” he said. “We’ve got young – that’s how we determined there’s a breeding population in the Delta. We had hoped they were just a couple of rogue males about to disperse, but we found females and we found young. It’s a breeding population unfortunately, and we’re going to go after them aggressively.”

Nutria, which some have dubbed “giant swamp rats,” can weigh up to 20 pounds. Females reach sexual maturity as young as four month old, and they can have up to three litters ranging from four to 13 young per year.

These semi-aquatic rodents pose a triple threat to the state. They can burrow into levees, undermining the water-system infrastructure. Just by their lawn-mower-like feeding habits, they can quickly denude an area of vegetation and open it up to erosion.

In addition, they can cause direct crop damage, such as was reported by a Lathrop-area bean grower who lost part of his crop to nutria feeding.

Joe Bacchetti, who farms with his cousin and brother near Tracy, said the recent discovery of nutrias so close to the Delta is definitely concerning.

At a summer board meeting of Reclamation District 773 – Fabian Tract, the rodent was a topic of discussion, said Bacchetti, also district president.

“It was still down south back then,” he said. “Now two months later, you’re telling me it’s up here. We were told they had it under control – don’t worry about it. Now look at what happened.”

The reclamation district already has to control ground squirrels that burrow into Fabian Tract levees, weakening them, as well as beavers that build errant dams. Now Bacchetti said district maintenance personnel will have to be on the lookout for nutria, which can make much larger burrows into levees than ground squirrels.

David Strecker, who farms on Roberts Island, said he also is worried about the nutria catches not far from his family’s operation.

“It’s a concern because we know they’re already here,” said Strecker, San Joaquin Farm Bureau first vice president. “I know we’ll continue to see them, and it’s going to be a long fight for someone to eradicate them.”

At the same time, he said the catches are a positive sign that trappers are able to detect the pest where it’s present.

When Strecker is in his fields or near levees, he said he keeps his eyes peeled for anything that might signal nutria presence.

“I’m always looking for signs, not only on the levees but also along my drainage ditches or evidence in my crops,” he said.

Surveyors focus on the Delta

With the latest discoveries in the Delta, Tira said Fish and Wildlife is retrenching and will be moving a team of two to six biologists from Merced County to join an existing team based in Stockton. The two groups will survey the lower Delta.

The California Department of Agriculture is training an additional team, which will focus on surveying the northern Delta around Highway 12, he said.

The San Joaquin County Ag Commissioner’s Office won’t be actively involved in the state eradication efforts, said Ag Commissioner Tim Pelican. Instead, his office will have more of a support role, such as helping state biologists obtain permission from private land owners to enter their property.

But he nevertheless remains concerned about the new invasive pest. “The biggest issue is we don’t want them to get into the levees,” he said. “With winter coming, they could put giant holes in the levees, and that’s not good for anybody.”

Since this summer, Fish and Wildlife has sent out more than 20,000 letters to private property owners in the Central Valley seeking permission to enter their property to survey for nutria. So far, the response has been overwhelmingly positive.

“We’ve been incredibly grateful for the responses,” Tira said. “Farmers, ranchers and landowners – they get it. Most of them love the wildlife on their land. They certainly don’t want another ag pest to have to deal with. And they want to preserve the integrity of the water-delivery system.”

Once the state receives permission for entry, biologists survey the property to determine whether it is even suitable nutria habitat. If not, they move on. If it has waterways or other swampy areas, they then look for nutria sign. 

“These are incredibly dense, heavily vegetated wetlands,” Tira said of nutria habitat. “It’s not easy walking. There’s noting quick or easy about this work – it’s painstaking.”

State surveyors also may ask the landowner’s permission to install game cameras.

Nutria are elusive and mostly nocturnal, so crews typically don’t see the rodents out and about during daylight. Game cameras can capture nighttime activity if nutria are present. Should the surveys be positive for nutria or nutria sign, the information is turned over to the U.S. Department of Agriculture’s Wildlife Services, which does the actual trapping under contract with the state.

Currently, 40 state employees are working on the nutria eradication program, although only one is dedicated full time to the effort. The others split their time with other programs. Eradication funding continues to be a challenge, Tira said. Currently, the state budget contains no dollars dedicated specifically to nutria eradication.

Instead, Fish and Wildlife and CDFA pull money from other programs. In addition, he said, Fish and Wildlife has applied for and received several grants, including a three-year, $1.2 million one from the Proposition 1 water bond; a three-year, $600,000 one from the California Wildlife Conservation Board; and a three-year, $1.2 million State Wildlife Grant.