DNA Study Links California's Nutria Invasion to Oregon Population

CDFW researchers trace origins of destructive rodent pest through genetic analysis of historical and current samples.

Apr. 13, 2026 at 5:10pm

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A highly structured abstract painting in earthy tones, featuring sweeping geometric arcs, concentric circles, and precise botanical spirals, conceptually representing the complex genetic relationships and invasion pathways of the nutria rodent.A genetic analysis of invasive nutria populations provides critical insights to help wildlife managers combat the spread of this destructive rodent across California.San Pablo Today

Scientists with the California Department of Fish and Wildlife (CDFW) have completed a genomic study of the invasive South American nutria rodent, linking the 2017 discovery of nutria in Merced County to a population in central Oregon. This was the first comprehensive genetic analysis of the semi-aquatic pest, which has challenged control efforts worldwide for decades.

Why it matters

Nutria are highly destructive to wetland habitats and agriculture, and their rapid reproduction and spread pose a major threat to California's ecosystems. Understanding the origins and pathways of nutria invasions is critical for informing eradication efforts and developing effective management strategies.

The details

To identify the origins of nutria in California, CDFW researchers compared DNA from invasive nutria populations around the world, building a global genetic dataset. This allowed them to trace the California nutria back to a population in central Oregon. The genetic data also provided insights into how nutria spread across landscapes, information that will guide future eradication and management plans.

  • Nutria were first discovered in Merced County, California in 2017.
  • Nutria were previously declared eradicated from California by the late 1970s.

The players

California Department of Fish and Wildlife (CDFW)

The state agency responsible for managing and protecting California's wildlife and natural resources.

Mike Buchalski

Lead of the CDFW Wildlife Genetics Research Unit, who oversaw the nutria genetic study.

Kristen Ahrens

CDFW Research Scientist who helped create a global genetic reference dataset for nutria populations.

Valerie Cook

Manager of CDFW's Nutria Eradication Program, which has removed over 7,800 nutria from California since 2017.

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What they’re saying

“CDFW conducts sophisticated genetics research to improve management outcomes for California's wildlife populations.”

— Mike Buchalski, Wildlife Genetics Research Lead, CDFW

“Genetics allowed us to narrow down the most likely source of California's nutria population and provide land and wildlife managers with information about how these animals are spreading across the landscape.”

— Kristen Ahrens, Research Scientist, CDFW

“This study supports our long-held belief that the current invasion is the result of reintroduction rather than explosive growth of a remnant, undetected population.”

— Valerie Cook, Nutria Eradication Program Manager, CDFW

What’s next

CDFW's Nutria Eradication Program will continue its efforts to remove nutria from hundreds of thousands of acres of wetland and riparian habitat across California's Sacramento-San Joaquin Delta and Central Valley.

The takeaway

This genetic study provides critical insights that will inform future nutria eradication and management strategies, helping protect California's vulnerable ecosystems from the destructive impacts of this invasive rodent species.