Myocastor coypus (Kerr, 1792)

Features
Simular Species
Biology
Maximum Size
Distribution
Interest to Fisheries
Current Status
Impacts
Recommendations
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Scientific Name: Myocastor coypus

Integrated Taxonomic Information System (ITIS): 180402

Other scientific names appearing in the literature of this species:

Myopotamus bonariensis (Lowery, 1974).

Common Name: Nutria, coypu, coypu rat, swamp beaver, nutria rat

Distinguishing Features:

Nutria are brown in color. They have a long tail which is rounded, scaly and sparsely haired. The muzzle and chin are white and the ears and eyes are small. The incisors are large and dark orange, protruding beyond the lips. The four inner toes of the hind feet are webbed (Whitaker, 1988). The dental formula is I1/1, C0/0, P1/1, M3/3=20 (Lowery, 1974).

Similar Species:

The muskrat, Odantara zibethicus which is smaller and has a vertically flattened tail, higher than it is wide. The beaver, Castor canadensis which is larger and has a large horizontally flattened tail (Whitaker, 1988

Biology:

Nutria are aquatic South American rodents active primarily at night (Chabreck, 1962). Over their native range they are extensively trapped for their fur (Gorostiague and Regidor, 1993). Although they are generally found in freshwater habitats, populations inhabiting brackish and salt waters are known (Nowak, 1991). They generally live in pairs, however, the presence of many animals in a favorable habitat may give the impression of colonial living (Nowak, 1991). Gosling (1994) reported nutria to be polygynous. Wild individuals rarely live more than 3 years, captive individuals may live 6 - 7 years with reports of some captive individuals living as many as 10 years (Nowak, 1991).

Reproduction and Fecundity: Males are larger than females. Gosling in Doncaster and Micol (1988) reported full grown males to be 15% heavier than females. Breeding occurs throughout the year (Whitaker, 1988; Dagault and Saboureau, 1990; Gosling, 1994). Nutria may reach sexual maturity as young as four months of age, but typically they mature at eight months of age (Lowery, 1974). Nests are made with plant materials and consist of burrows dug into the river bank, or alternatively nests are made in the burrows of other animals, such as in the lodges of beavers and muskrats. Courtship includes a good deal of chasing, fighting and biting. Males use specialized anal scent glands, which become more developed from October through December, to mark their territories (Gosling, 1994). Gestation lasts approximately 130 days, after which 1 to 11 (typically 4-6) young are born fully haired and with their eyes open (Lowery, 1974; O'Neil and Linscombe, 1977; Doncaster and Micol, 1989). Young weigh approximately 225 grams at birth (Nowak, 1991). They swim with their mother and feed on plant matter within 24 hours of birth (Whitaker, 1988). Female nutria have 4-5 pairs of nipples located on the side of their torso, which allow them to suckle their young while swimming or to stand up and watch for predators (Gingerich, 1994). The young are weaned in five to seven weeks (Lowery, 1974; O'Neil and Linscombe, 1977). Females enter estrous in as little as 24 hours after giving birth, otherwise they come into heat every 24 to 26 days, and remain in that state for 1 to 4 days (Lowery, 1974).

Trophic Interactions: Nutria feed on almost any terrestrial or aquatic green plants, occassionally also consuming grains (Whitaker, 1988). Preferred plants in marsh areas include three-cornered grass, cattail, bullwhip, and alligator weed, whereas duck-weed appears to be a preferred item in swamp areas (O'Neil and Linscombe, 1977). Roots are another preferred item (Nowak, 1991). Like other rodents, their teeth are continuosly formed from the adjoining tissue throughout their life. Nutria can eat up to 25% of their body weight in plants per day (Gingerich, 1994). Where abundant they may cause severe damage to the vegetation. They often venture into crop fields, also causing considerable damage. Nutria may occupy feeding platforms (5 to 6 feet across) to rest and avoid predation (O'Neil and Linscombe, 1977; Whitaker, 1988). In a manner reminiscent of lagomorphs, nutria re-ingest their fecal pellets to digest food more completely while at rest (Whitaker, 1988).

Alligators are the main predator of adult nutria. Juveniles are prey to a wide variety of swamp animals, including turtles, gars, large snakes, and birds of prey (Lowery, 1974).

Maximum Size:

Nutria grow to a total length (including tail) of 140 cm, attaining a weight of 11.4 kg (25 lb) (Whitetaker, 1988). A maximum weight of 17 kg has been reported for the species (Nowak, 1991).

Distribution:

Nutria are native to southern Brazil, Bolivia, Paraguay, Uruguay, Argentina, and Chile (Nowak, 1991).

In the Gulf of Mexico ecosystem, they are established along coastal areas of all five Gulf states (Whitaker, 1988; Hollander et al., 1992).

Interest to Fisheries:

Current Status of this Species in the Gulf of Mexico Ecosystem:

Nutria were intentionally introduced into North America, for their fur. They were extensively marketed as the next "mink" to gullible buyers. At one point, breeding pairs were sold for up to $2,500 a pair (Jackson, 1994). However, for various reasons, nutria fur never caught on in the United States.

Nutria were first introduced into the Gulf of Mexico near New Orleans in the early 1930's. It's believed that all the individuals released during this first introduction were recaptured by trappers. In 1938, between 12 and 20 nutria imported from Argentina were introduced into Avery Island, Louisiana by tabasco tycoon E.A. McIlhenny (Griffo, 1957; Lowery, 1974; Jackson, 1994; Trillin, 1995). These reproduced prolifically. Many escaped from captivity or were released, and rapidly multiplied in the wild. The first specimens of nutria appeared in the Louisiana fur market during the 1943-44 season. In the 1945-46 season the number of nutria trapped reached 8,784. Griffo (1957) reported the number of nutria present in Louisiana to have reached 1,000,000 by 1957. By the 1969-70 season 1,604,175 nutria were trapped in Louisiana alone (Lowery, 1974). Presently, they are more important than the muskrat in Louisiana's trapping industry (Whitaker, 1988; Choate et al., 1994).

Nutria have expanded their range throughout the Gulf states at an alarming rate (Wolfe, 1981; Hollander et al., 1992). There is a healthy population established along the north and central parts of the western coast of Florida. As is the case with most other populations, this population originated from individuals which migrated from Louisiana, and individuals that were intentionally or accidentally released from nutria fur farms within the state (Griffo, 1957). Additionally, Nutria have been introduced throughout the Gulf of Mexico ecosystem to control aquatic vegetation in lakes and ponds (King, 1968). However, where introduced for this purpose, nutria have failed miserably because they will readily consume all types of vegetation, and frequently prefer native plants and crop plants to the species they were intended to control (Griffo, 1957; Conniff, 1989; Jackson, 1994).

Nutria numbers peaked in the 1970's, and then began to decline. Weather extremes including hurricanes, droughts, and freezes, as well as increased trapping, habitat degradation and increases in alligator populations have been attributed the decline (Jackson, 1994). However, trapping efforts declined in the mid 1980's because of a fall in fur prices, and nutria numbers have since been steadily increasing. Recent attempts to control nutria populations include efforts to commercialize nutria meat (Trillin, 1995).

Potential Impacts:

Where abundant, nutria may deplete wild vegetation in coastal areas, severely damaging wetlands (Trillin, 1995). Nutria often invade crop areas and cause considerable damage especially to rice and sugar cane fields (Ensminger, 1955; Lowery, 1974; O'Neil and Linscombe, 1977; Whitaker, 1988; Gingerich, 1994; Trillin, 1995), with reports of damage to soybean plantations near Mississippi's coast (Wolfe, 1981). Ensminger (1955) summarized extensive damage caused to rice plantations both by direct predation of the rice and by extensive damage to the levees surrounding rice ponds caused by the nutrias burrow digging. In 1957, thousands of nutria were pushed inland by huricane Audrey. Many invaded sugar cane fields, where they reeked havoc, damaging innumerable plants many of which they did not even consume (Lowery, 1974; Jackson, 1994). Nutria have also been attributed with the decline of muskrat populations in Louisiana (Lowery, 1974; O'Neil and Linscombe, 1977). They have been reported to compete with muskrats and water fowl for trophic resources (Griffo, 1957; Lowery, 1974). Concern has been raised over the abundance of nutria present on some of Mississippi's barrier islands. There, nutria apparently dig up and eat the roots and rhizomes of sea oats, which are of critical importance in stabilizing beach dunes (Wolfe, 1981).

Nutria carry a number of parasites and diseases (Lowery, 1974; Howerth et al., 1994). Disease agents Louisiana nutria carry include Toxoplasma gondii, Clamidia psittaci, Francisella tularensis, Leptospira sp., and encephalomyocarditis virus (Howerth et al., 1994). Parasites recorded from this species include trematodes such as Heterobilharzia americana, Echinostoma revolutum, and Psilostomum sp., cestodes such as Anoplocephala sp., acanthocephalans such as Neoechinorhynchus sp., and nematodes such as Trichostrongylus sigmodontis, Logistriata maldonadoi, and Trichuris myocastoris. In addition, they carry the nematode Strongyloides myopotami, which causes a condition known as "marsh itch" or "nutria itch" in people. This is a severe rash often affecting trappers when they handle nutria. It is caused by the larval form of this nematode which penetrates the skin of human beings (Lowery, 1974).

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* Current site content modified from original content developed by the University of Southern Mississippi/College of Marine Sciences/Gulf Coast Research Laboratory through a grant administered by the Gulf of Mexico Program.