The nutria Myocastor coypus, also called the coypu, is a large, semi-aquatic rodent with webbed hind feet. It is indigenous to South America, but was introduced to North America, East Africa, Europe and Asia for its thick, soft fur. It has established large feral populations in some areas, and is considered a pest because of its burrowing and feeding habits.
Crop losses and structural damage
After being introduced to countries outside the speciesí natural range, nutria were either released into the wild for subsequent recapture, or raised at fur farms, from where some probably escaped. Many were also deliberately released from fur farms after the demand for fur declined. Being able to adapt to a wide variety of environmental conditions, they soon made themselves at home in local ponds, rivers, swamps and drainage canals. Nutria live in burrows that they dig in vegetated banks next to water, although sometimes they use those abandoned by other animals. They are herbivores with a huge appetite for plants, eating approximately 25 per cent of their body weight per day. At high densities their feeding can significantly impact natural plant communities. In some places they have even converted dense stands of reed to open water, destroying the habitat of wetland birds. They also increase erosion by digging up roots and underground tumours, which help to bind the soil together.
Furthermore, nutria cause considerable damage to crops such as rice, sugarcane, corn, soybean and vegetables, as well as some fruit trees. Their burrowing also weakens the banks of rivers, dams and irrigation canals, and may undermine building foundations and road beds. In the United States, nutria are most abundant along the Gulf Coast of Louisiana and Texas, where they frequently damage water-retaining levees in fields flooded for rice and crawfish production, as well as flood-prevention levees that protect low-lying areas. The animals also tend to gnaw on wooden structures with their large incisors, damaging buildings and jetties.
The most practical method of control is to encourage people to harvest nutria. During the 1970s, when nutria pelts fetched $4 to $8 each, trappers in the United States killed about 1.8 million of the animals annually, which helped to control the population. Once demand for the fur had fallen and many hunters turned to alternative livelihoods, nutria numbers increased dramatically and their negative impacts became evident. In 2002 the Louisiana authorities introduced a bounty on nutria, offering trappers US$4 for every nutria tail produced, in the hope of culling some 400 000 nutria per year.
Although nutria fur has little value today, the meat is lean in fat and high in protein, and could form an important supplementary food source. Apart from trapping, it is possible to shoot the animal at night, in areas where nocturnal hunting is permitted. Baiting is sometimes used to concentrate nutria in specific locations where they can be more easily trapped, shot, or poisoned. Poisoned bait should be placed on a floating raft in standing water where nutria are known to occur, in order to reduce the risk of affecting non-target species, and a period of pre-baiting should first take place. Once the nutria are habituated to a particular feeding site and food type, such as carrots, sweet potatoes or apples, an appropriate pesticide such as zinc phosphide can be applied to the bait. The nutria carcasses must be collected and properly disposed of, to prevent poisoning scavengers that might eat any undigested stomach material.
DID YOU KNOW?
Nutria were intentionally introduced to China, Thailand and Vietnam for fur-farming. In China they were introduced in the early 1960s, and by the mid-1980s the animals were being raised in large numbers, especially in the south. However, the quality of the fur was found to be inferiorand a market failed to establish, so in the mid-1990s many of the nutria were set free. In the meantime, other Asian countries had introduced nutria from China, including Thailand, which imported a breeding population in 1993. Today, the nutria is considered an agricultural pest in both countries.
Reference: Sue Matthews Tropical Asia invaded: The growing danger of invasive alien species Global Invasive Species Programme 2004