In 2025, California DNA analysis suggested Oregon may be linked to the state’s renewed nutria invasion after the rodents reappeared in 2017

A genomic study of 267 California nutria points to central Oregon and a recent introduction rather than a long-hidden group. In 2017, a pregnant female nutria was captured in a private wetland near Gustine in Merced County, California. The California Department of Fish and Wildlife says nutria had been declared eradicated from the state by 1978, with no reported detections between then and their rediscovery. During the summer of 2017, officials captured 19 additional nutria in the Grasslands Ecological Area.California’s nutria threaten wetlands, waterways, and agricultural land. A genetic study points to central Oregon as the population’s closest match and suggests waterways aid their spread. Eradication teams have removed 7,841 animals since 2017, at an estimated annual cost of $5 million. (Representational/Unsplash)A 2025 study published in Evolutionary Applications found that California’s current nutria population was genetically most similar to invasive nutria in central Oregon. The findings suggest a recent introduction followed by rapid spread, although the genetic evidence cannot establish the precise route by which the animals reached California.The invasion threatens wetlands and agricultural land in the Central Valley, where nutria can damage vegetation, undermine streambanks and levees, and contribute to soil erosion. To investigate the animals’ origins, researchers analyzed 6,809 genetic markers from 267 California nutria sampled between 2020 and 2022. They compared the results with genetic data from populations in Oregon, Washington, Louisiana, Texas, Maryland, and Virginia. The study also examined historical museum specimens to assess whether the current population might descend from earlier nutria populations in California.DNA resultsThe California nutria formed a distinct genetic cluster, but their closest relatives came from central Oregon, while nutria from northern Oregon were genetically linked to Washington. Scientists also examined maternally inherited DNA and found that all California nutria shared the same marker, which also appeared in nutria from Oregon and Washington.Historical specimens provided a way to compare the current population with nutria from earlier decades. Researchers sequenced pelts, skulls, and bones from California fur farm animals, with most specimens dating from 1930 to 1960. The older specimens had four variants of the maternal DNA marker, indicating greater diversity than the single variant found in the current population. One of the historical variants matched the marker found in modern California nutria.However, this genetic overlap does not establish that the present population descended from animals that survived undetected in the state. Because the historical and current populations shared a maternal marker, the evidence alone cannot determine whether the earlier population persisted or whether nutria were introduced again. The authors considered a recent introduction followed by rapid spread more likely, given California’s favorable climate and the animals’ reproductive potential.Researchers comparing genetic samples from California and other states found California nutria form a distinct cluster most closely related to central Oregon populations. Historical specimens shared one maternal marker with modern animals, but cannot show whether the population persisted or was reintroduced. (Representational/Unsplash)What do officials think about it?In an April 7, 2026, news release, the California Department of Fish and Wildlife said the genetic findings suggest that the current invasion resulted from an intentional reintroduction, with the animals likely transported from central Oregon. Transporting nutria is prohibited under California Fish and Game Code Section 2118 and Title 14, Section 671, of the California Code of Regulations. The genetic analysis supports the hypothesis of a recent introduction, but it does not identify who transported the animals or establish the circumstances behind their release.Since 2017, California’s Nutria Eradication Program has removed 7,841 nutria, the department reported. Officials estimated that eradication efforts cost the state about $5 million annually. Teams search hundreds of thousands of acres of wetland and riparian habitat from San Pablo Bay to Kings County, using direct observation, motion-detection cameras, and fecal-detection dogs to locate animals for trapping.The study also offers guidance for eradication efforts. Because researchers found little genetic differentiation across the invaded range, they argued that managers could treat the Central Valley as a single eradication unit. River distance appeared to matter more than straight-line distance in explaining gene flow, suggesting that waterways help nutria move through the landscape. Access to affected areas also poses a challenge because much of the invaded range is privately owned, and some wetlands cannot be trapped during hunting and nesting seasons.To trace the population’s origins, researcher Kristen Ahrens contacted museums and universities across California to obtain historical specimens. One unusual contribution came from the Butte County Weights and Measures Department, which provided a taxidermied nutria. Ahrens also reported that the research team had developed a global genetic reference database to help other scientists compare nutria populations and investigate invasion routes. The project received funding from the California Department of Water Resources in cooperation with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service.The Hindustan Times US Desk brings you the latest news and developments from across the United States. 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