The nutria, also known as coypu, is a large, semi-aquatic rodent that has become a non-native species in many regions globally, particularly North America. Resembling a beaver or muskrat, they are large, typically two feet long with a tail adding another foot, and weigh 15 to 20 pounds.
They possess dark-brown fur, a stout body that often appears hump-backed when on land, and distinctive large, orange-yellow front teeth. Their partially webbed hind feet and high-set eyes, ears, and nostrils are adaptations for their aquatic lifestyle.
Origins and Native Habitat
The nutria’s native range spans subtropical and temperate South America, including countries like Argentina, Brazil, and Uruguay. In these environments, they naturally inhabit wetlands, swamps, and areas adjacent to slow-moving rivers.
Their characteristics, such as a thick, soft undercoat beneath coarser guard hairs, made them appealing for human use. Nutria are primarily herbivorous, feeding on aquatic and semi-aquatic vegetation like roots, rhizomes, and stems.
Reasons for Introduction
The primary reason for the nutria’s introduction outside its native range was the global fur trade, which gained significant traction in the late 19th and early 20th centuries. Nutria fur was seen as a cost-effective alternative to more expensive furs like beaver or muskrat.
Fur farms were established in various countries, including the United States, to commercially propagate these rodents for their pelts. The first recorded introduction to the United States occurred in California in 1899 for fur farming. Beyond fur production, some introductions were also for experimental purposes, such as biological control of unwanted aquatic vegetation or erosion control.
Escape and Establishment
Nutria transitioned from controlled farm environments to establishing wild populations through several mechanisms. Escapes from fur farms were common due to inadequate enclosures, particularly during natural disasters like floods or hurricanes. For instance, a hurricane in Louisiana in 1940 caused many nutria to escape and populate coastal marshes.
Additionally, deliberate releases occurred when demand for nutria fur plummeted in the 1940s, leading many ranchers to release their stock. Some individuals also intentionally released them with the belief they could thrive in the wild for hunting or to control aquatic plants. These escapes and releases led to the nutria becoming an invasive species.
Geographic Spread
Once established, nutria rapidly spread throughout new regions. Initial key introduction points in the United States included California, Louisiana, Maryland, Oregon, and Washington.
Their rapid reproduction rate, with females capable of producing multiple litters annually, and adaptability to diverse wetland habitats, facilitated their spread. Nutria breed year-round, averaging 4.5 young per litter, with young foraging within hours of birth.
The interconnectedness of waterways, such as rivers, canals, and bayous, played a significant role in facilitating their spread beyond initial release points. Today, they are found in at least 22 states across the U.S., particularly in the Gulf Coast states, the Pacific Northwest, and along the Atlantic coast.