Invasion of 20-pound rodents wreaking havoc on California may have been intentional
California is facing a renewed problem with nutria, large semi-aquatic rodents weighing around 20 pounds that were previously believed to have been eliminated from the state decades ago. Wildlife officials now say evidence points to people as the source of their return.
The California Department of Fish and Wildlife reports that genetic testing shows the animals currently found in the state are most closely related to nutria populations in Oregon. That finding contradicts earlier theories that they might be survivors of a small, undetected group that remained in California after eradication efforts in the 1970s.
According to state biologists, the results strongly suggest the animals were brought back into California rather than naturally expanding from any leftover local population. One wildlife official involved in the investigation noted that the distances involved, combined with the lack of sightings between Oregon and California, make natural migration extremely unlikely and point instead to human involvement.
Researchers say the exact reason for the reintroduction is unclear. Possible explanations range from people mistakenly releasing the animals in hopes they could help manage aquatic plants, to individuals keeping them as unusual animals, or even intentional release intended to cause environmental harm.
The investigation gained momentum after pregnant nutria were discovered in Merced County in 2017, marking the first confirmed presence in the state in many years. That discovery triggered a broader genetic study in which scientists compared modern samples with preserved museum specimens from across California and other regions.
The analysis ultimately showed that the current population matches nutria from central Oregon, supporting the conclusion that they were transported and released rather than originating from a hidden remnant group in California. Nutria were originally spread widely around the world during the fur trade era in the late 1800s and early 1900s. After fur demand declined, many were released into the wild, including in parts of the United States. California later declared the species eradicated by the late 1970s.
Since their reappearance was confirmed, state officials have launched an extensive eradication campaign due to the damage nutria cause. The rodents dig extensive burrows that can weaken riverbanks, levees, and other flood-control structures, and they also harm wetlands and agricultural areas. They are considered a high-priority invasive pest.
So far, efforts to remove them have led to the elimination of 7,841 animals across the Sacramento–San Joaquin Delta and the Central Valley as of the end of March. Officials continue working to prevent the population from spreading further while investigating how the animals were introduced in the first place.
About Post Author
