( Myocaster coypus )
DESCRIPTION: At first glance, a casual observer may misidentify a nutria as either a beaver (Castor canadensis) or a muskrat (Ondatra zibethicus), especially when it is swimming. This superficial resemblance ends upon a more detailed study of the animal. Nutria are approximately 2 feet long, and have a robust, highly-arched body. Males are slightly larger than females; the average weight for each is about 12 pounds. Males and females may grow to 20 pounds and 18 pounds, respectively. They have short legs and a round tail that ranges from 13 to 16 inches long. The dense grayish underfur is overlaid by long, glossy guard hairs that vary in color from dark brown to yellowish brown. Like beavers, nutria have large incisors that are yellow-orange to orange-red on the outer surface. Because nutria spend much of their time in the water, they are highly adapted for a semi-aquatic existence. Their hind feet are webbed for swimming, and their eyes, ears, and nostrils are set high on their heads so they can stay above the waterline when swimming. Additionally, the nostrils and mouth have valves that seal out water while swimming, diving, or feeding underwater. When moving on land, nutria may drag their chests and appear to hunch their backs.
PATHWAYS/HISTORY: The original range of nutria was south of the equator in temperate South America, including Argentina, Bolivia, southern Brazil, Chile, Paraguay, and Uruguay. Nutria were first imported into the United States between 1899 and 1930 in an attempt to establish a fur farm industry. When the nutria fur market collapsed in the 1940s, thousands of nutria were released into the wild. Wildlife agencies further expanded the range of the nutria by introducing the species into new areas of the United States with the intent that nutria would control undesirable vegetation and enhance trapping opportunities. A hurricane in the late 1940s aided dispersal by scattering nutria over wide areas of coastal southwest Louisiana and southeast Texas. Accidental and intentional releases have led to the establishment of widespread and localized populations of nutria in various wetlands throughout the United States. Feral nutria have been reported in at least 40 states and three Canadian provinces in North America since their introduction. About one-third of these states still have viable populations that are stable or increasing in number. Adverse climatic conditions, particularly extreme cold, are probably the main factors limiting range expansion of nutria in North America. Nutria are most abundant in the states along the Gulf of Mexico coast, but they are also a problem in other southeastern states and along the Atlantic coast.
RISKS/IMPACTS: Burrowing is the most commonly reported damage caused by nutria. Nutria dig into soils to eat the basal and root portions of wetland plants. The roots of marsh vegetation bind the soft organic marsh soils together. When this root fabric dies, the soils become susceptible to erosion, which ultimately results in stream bank instability, added sedimentation, and reduced water quality. Nutria burrows can also damage flood control levees that protect low-lying areas; weaken the foundations of reservoir dams, buildings, and roadbeds; and erode the banks of streams, lakes, and ditches. Nutria damage, however, is not limited to burrowing. Depredation on crops is well documented. In the United States, sugarcane and rice are the primary crops damaged by the nutria. Other crops damaged by the nutria, include corn, milo, sugar and table beets, alfalfa, wheat, barley, oats, peanuts, various melons, and a variety of vegetables. This depredation can lead to significant losses, especially for small farmers. The nutria alone is thought to be responsible for amount $6 million of damage to crops alone. However, the extensive damage that they do is often hard to put a dollar value on, because of the immense ecological value of the ecosystems that they destroy. Nutria feed on wetland plants and invertebrates and may compete with native species such as muskrats. These actions may result in loss of vegetation and wildlife habitat. Marsh loss removes habitat for native wildlife species, such as waterfowl, wading birds, and muskrats. Loss of native plants often leads to invasion of non-native species such as reed canarygrass, which offers little habitat value for wildlife. The rodents can also serve as hosts for several pathogens, including tuberculosis and septicemia, which are transmittable to people, pets, and livestock. In addition, nutria can carry parasites, such as nematodes, blood flukes, tapeworms, and liver flukes. Many of these organisms are found in nutria feces and urine and can contaminate drinking water supplies and swimming areas.
MANAGEMENT: Due to the damage that nutria are capable of inflicting on the environment, much research has gone into methods of controlling this pest. Other communities and countries have successfully controlled nutria with live removal, including the United Kingdom, which has fully eradicated nutria. Nutria are mainly controlled by trapping, usually live spring traps and sometimes nets. A fence with buried pipelines may also be put around populations to contain them. In some states they are hunted, but since they are mostly active at night, this often causes a problem for hunters. At times it is possible to stress populations by regulating water levels and installing bulkheads to deter them from burrowing and reproducing.
WHAT YOU CAN DO: Do not feed ducks, geese, nutria or other wildlife. It attracts non-native species, such as nutria. Individuals can help control the nutria population by alerting their local division of the Department of Natural Resources. When officials are alerted early they can stop the problem before it gets out of hand. In some states or localities, nutria are protected as furbearers because they are economically important; thus permits may be necessary to control animals that are damaging property. In other areas, nutria have no legal protection and can be taken at any time by any legal means. Consequently, citizens experiencing problems with nutria should be familiar with local wildlife laws and regulations. General aquatic nuisance species prevention: Do not release aquarium pets or live food into the environment. Never dump live fish, e.g. baitbuckets, from one body of water into another body of water. Always drain water from your boat, livewell, and bilge before leaving any water access.
PROFILE CREDIT: Susan Pasko, NOAA and Anne Marie Eich, USFWS - IMAGE CREDIT: USGS