The nutria, also known as the coypu, is a large, semi-aquatic rodent native to South America. Females are highly reproductive, capable of giving birth multiple times each year, enabling rapid population growth in new environments. The species is recognized as a destructive invasive species in North America and globally due to its voracious appetite for vegetation and extensive burrowing habits. The nutria was primarily introduced as a result of the fur trade, leading to significant ecological and economic problems.
The Nutria’s Journey
The nutria is native to the southern half of South America, including countries like Argentina, Bolivia, Chile, Paraguay, and Uruguay. It was first imported into the United States around 1899 to establish a fur and meat market, though the initial population in California failed to establish long-term.
The primary mechanism for their widespread establishment was the collapse of the nutria fur market in the 1940s. As demand plummeted, many ranchers intentionally released their stock or could no longer afford to contain them, leading to accidental escapes. Some releases also occurred with the misguided goal of controlling unwanted aquatic vegetation.
Outside of their native range, nutria populations thrived due to a lack of natural predators. This absence, coupled with favorable climates in areas like the Gulf Coast, allowed the nutria to rapidly spread and establish high-density populations. Today, the species is established in at least 16 to 22 states across the United States.
Ecological Destruction of Wetlands
The primary threat posed by the nutria stems from its destructive feeding behavior in wetland ecosystems. Nutria are voracious herbivores, capable of consuming up to 25% of their body weight in vegetation daily. Their diet is problematic because they prefer the roots, rhizomes, and tubers of marsh plants, such as Spartina and bulrush, rather than the leafy above-ground parts.
This habit of consuming the root mat causes “eat-outs,” which are patches of marsh where vegetation is completely destroyed. Since the roots bind the soil together, their removal leads to severe erosion. The marsh loses its structural integrity and eventually converts into open water, permanently losing habitat.
The loss of coastal marshes has significant consequences for native species and human communities. The destruction removes habitat for native fish, birds, and crustaceans. Furthermore, the loss of these wetlands eliminates the natural storm protection they provide to inland areas, increasing vulnerability to flooding and storm surge.
Damage to Infrastructure and Agriculture
Nutria cause significant economic and structural damage to infrastructure and agricultural systems. Their burrowing habits are particularly destructive along water conveyance systems and flood control features. They excavate den systems into banks, which can extend up to 16 feet deep and 160 feet into the bank.
These extensive burrows compromise the structural integrity of levees, dikes, and irrigation canals. When the soil structure is undermined, it can lead to bank slumping, levee failure, and roadbed collapse, increasing the risk of flooding. The damage is especially pronounced in areas that rely on earthen structures for flood protection and water management.
Nutria also inflict substantial losses on the agricultural sector through heavy grazing and consumption of root crops. They damage commercially important crops like sugarcane and rice, and feeding on rice plants can significantly reduce crop yields. Other crops, including corn, alfalfa, and various vegetables, are also affected.
Controlling the Population
Control programs are necessary once nutria populations are established in non-native areas due to the extensive damage they cause. The most effective management strategy for removal is trapping. Various types of traps are employed, often baited with attractive food items like sweet potatoes or carrots. These include cage traps, foothold traps, and body-gripping traps.
Incentive programs, such as bounty systems, have also been implemented in some regions to encourage trappers to control the population. Chemical control methods, primarily using baits treated with zinc phosphide, are sometimes used for large-scale elimination, although this method carries the risk of affecting non-target species.
Non-lethal methods, such as exclusion fencing, can protect small, sensitive areas like home gardens, but they are generally too costly and impractical for large wetland areas. Complete eradication is extremely difficult once the species is widespread, necessitating sustained, long-term control measures to mitigate ongoing environmental and structural damage.