Genomic Study Indicates Human Reintroduction of Nutria to California After 1970s Eradication

A genomic study released by the California Department of Fish and Wildlife on Tuesday indicates that nutria discovered in Merced County in 2017 are genetically connected to a population in central Oregon. This finding suggests that the invasive rodents were reintroduced to California by humans after the species was eradicated from the state in the 1970s.

Nutria are large semi-aquatic rodents native to South America that can weigh up to 20 pounds and consume large quantities of vegetation.

The study represents the first of its kind for tracking nutria genetics in the region. Officials stated that the distance between the Oregon population and Merced County makes natural migration unlikely, as no nutria have been found in the intervening areas.

The motive for the reintroduction remains unclear, according to state officials.

Some possibilities include attempts to control vegetation on private property or other human actions. The introduction and transport of nutria into California is illegal under state law. Nutria feed aggressively on aquatic plants, consuming up to a quarter of their body weight daily.

This behavior can damage marsh ecosystems and habitats for native species. Their burrowing also weakens levees and irrigation systems, raising risks of flooding and infrastructure damage.

Since the 2017 discovery, the state has removed thousands of nutria from affected areas.

Annual control efforts cost about $5 million, including the establishment of inspection stations at key entry points to prevent further introductions. Officials emphasize the need for continued vigilance to protect California's wetlands and ecosystems. The study results are expected to support future genetic research on nutria at national and global levels.

Wetlands in California, which are already fragile, face ongoing threats from invasive species. Affected stakeholders include wildlife managers, agricultural operations near waterways, and communities reliant on stable infrastructure.