Invasive Species in the Chesapeake Watershed
What is Myocastor coypus?
Nutria are semi-aquatic rodents that exhibit rat-like features and are intermediate in general appearance and size, between muskrat and beaver. Adult nutria weigh about 15 to 20 pounds and are 2 to 25 inches in length. They have a round and scaly tail sparsely covered with bristles that comprises up to approximately 35% of their length. Nutria have webs between the inner four toes of their hind feet, but not between the fourth and fifth (outer toes). Their small, black, unwebbed front feet are much smaller than their hind feet. They have large front teeth which range from yellow to dark orange. Their pelage consists of long, coarse guard hairs which nearly conceal a thick, dense underfur. The general coloration of the upper parts is dark yellowish brown or reddish brown, masking the dark slate underfur (Burt and Grossheider 1976). Nutria are native to Brazil, Bolivia, Paraguay, Uraguay, Argentina and Chile (Nowak 1991).
Sexual maturity occurs at about four to six months of age and is dependent upon food supply and availability. Nutria reproduce throughout the year, having two to three litters annually (Brown 1975; Willner et al. 1979). The gestation period of nutria is approximately 130 days after which 1 to 11 (typically four to six) young are born fully haired and with their eyes open (Nowak 1991). However, the rate of miscarriages is 45% and only 65% of the embryos survive to be born.
Nests are made with plant materials and consist of burrows dug into the river bank, or alternatively they are made in the burrows of other animals, such as in lodges of beavers and muskrats. Courtship includes a good deal of chasing, fighting and biting. Once the female is in heat, courtship is discontinued and breeding is prompt. Nutria do not mate for life. A female may breed with one or several males each time she comes in heat. Nutria will breed both in and out of the water.
Female nutria usually come in estrus every 24 to 26 days and stay in heat for one to four days. Estrus begins within a day or two after giving birth or after miscarriage. Males are fertile and capable of breeding all year long. 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 four to five 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).
Nutria prefer a semi-aquatic habitat in swamps and marshes and along the shores of rivers and lakes. They generally live in pairs; however, the presence of many animals in a favorable habitat may give the impression of colonial living (Nowak 1991). Wild individuals rarely live more than three years; captive individuals may live six to seven years with some reports of captive individuals living as many as 10 years. Predation, disease and parasitism, water level fluctuations, habitat quality, highway traffic, and weather extremes affect mortality. Annual mortality of mortality is between 60 to 80% (Willner 1982).
Nutria feed on almost any terrestrial or aquatic green plants and occasionally consume grains (Whitaker 1988). Important food plants in the United States include cordgrasses (Spartina spp.), bulrushes (Scirpus spp.), spikerushes (Eleocharis spp.), chafflower (Alternanthera spp.), pickerelweeds (Pontederia spp.), cattails (Typha spp.), arrowheads (Sagittaria spp.) and flatsedges (Cyperus spp.). Nutria can eat up to 25% of their body weight in plants per day (Gingerich 1994). Where abundant, they may cause severe damage to vegetation. Feeding habits of nutria vary considerably. They feed while in the water, on floating objects or on land. Nutria commonly cut off a preferred food near the waterline and swim it or carry it to a feeding platform (five to six feet across) for eating. They seem to prefer the soft, succulent parts near the bases of plants, especially when eating course plants such as cattail, cord grass and reeds.
Nutria were intentionally introduced into North America for their fur. The first nutria for fur farming in North America were imported in 1899 from South America to Elizabeth Lake, California; these nutria apparently were not successful in reproducing, and very little information is available on their eventual fate. The 1930s are generally considered the boom years for establishing nutria ranches in the United States, though between 1899 and 1940 ranches were established in California, Washington, Oregon, Michigan, New Mexico, Louisiana, Ohio, Utah and elsewhere (Evans 1970).
Shortly after the boom years, World War II came and nutria farming virtually collapsed, a collapse that can be attributed to poor reproduction, low fur prices and competition with beaver pelts (also bringing low prices). Some ranchers released their nutria or did nothing to recapture those that escaped because of inadequate holding facilities, storms or floods (Evans 1970). State and federal agencies and individuals translocated nutria into Alabama, Arkansas, Georgia, Kentucky, Maryland, Mississippi, Oklahoma, Louisianna and Texas, with the intent that nutria would control undesirable vegetation and enhance trapping opportunities. Nutria were also sold as "weed cutters" to an unknowing public throughout the Southeast. A hurricane in the late 1940s aided dispersal by scattering nutria over wide areas of coastal southwest Louisiana and southeast Texas (Evans 1983).
Nutria were introduced in Maryland in the 1950s to promote the fur industry. Earlier, in 1943, the federal government brought nutria to Dorchester County, Maryland. This location on Maryland's lower Eastern Shore was part of an experimental fur station at Blackwater National Wildlife Refuge (Blackwater NWR). In a relatively short period of time, captive rearing proved unprofitable and the remaining project nutria either escaped and/or were inadvertently released; in addition, a limited number of nutria were reportedly released by adjacent landowners. These animals functioned as the origin of the now overwhelming populations in the state (Robert Colona, pers. comm.). Currently, there is virtually no commercial fur market and only a very small meat market for nutria. This situation combined with the animal's reproductive success has led to a population boom: for example, estimates on a 10,000 acre parcel of land located in Dorchester County have expanded from less than 150 nutria in 1968 to 35,000 to 50,000 animals today (Robert Colona, pers. comm.).
Because of its high rate of productivity, aggressive nature and similar habitat needs, nutria compete with and displace native muskrats. Although foxes, owls and racoons prey upon young nutria, humans are the only predators to take adults in this region. Nutria feeding habits can also be extremely destructive to marsh vegetation: the animal forages directly on the vegetative root mat causing what is called an "eat out." This type of feeding loosens the plant's hold on the soil; without this binding mechanism, the soil washes away. Animals start the process by grazing; wind, waves and tides then remove any remaining soil and plants. "Eat-outs" can turn productive wetlands into barren mud flats that often cannot be re-vegetated.
Where Are Nuria Found in the Chesapeake Bay Watershed?
There are confirmed reports of nutria from the Chesapeake Bay Bridge to Ocean City, Maryland, and south to the Virginia border (see attached distribution map). Nutria are also on the western shore of Maryland in the Patuxent and Potomac rivers, and to the northeast in Delaware (Bounds 1998). There are established populations in at least eight counties on the eastern shore of Maryland, with the densest populations in Dorchester County (Robert Colona, pers.comm.).
Are There Existing Management Efforts for Nutria in the Chesapeake Bay Watershed?
There have been sightings of nutria along the Nanticoke River but population numbers and distribution are limited. There are no research or management activities associated with nutria at this time.
Rapidly increasing numbers of nutria, coupled with resultant marsh loss, prompted the formation of a nutria control partnership in Maryland. This partnership, which includes over 27 state and federal agencies and private organizations, produced a comprehensive pilot project proposal in 1998 entitled, "Marsh Restoration: Nutria Control in Maryland." The project focused on development of techniques for both removing nutria and reversing marshland degradation (Robert Colona, pers. comm.).
On October 30, 1998, President Clinton signed PL 105-322, which authorized the Department of the Interior to expend up to $2.9 million for the three-year pilot project. The Pilot Project began in January 1, 2000, and will end in December 2004. The project's management team includes the Maryland Cooperative Fish and Wildlife Research Unit, Maryland Department of Natural Resources, University of Maryland Eastern Shore, and U.S. Fish and Wildlife Service. Its three phases include: (1) conducting public outreach and education; (2) collecting baseline data on nutria behavior and reproductive physiology; and (3) testing various control methods for the purpose of eradicating nutria in the study sites.
For the third objective, there will be a brief three month period (January to April 2002) of trapping to assemble pre-intensive harvest baseline data. Intensive harvest will then be implemented in March 2002 on three discrete areas in Dorchester County (Blackwater NWR, Tudor Farms, and Fishing Bay Wildlife Management Area). These harvested areas will be paired with three equal size areas where limited harvest will occur, and three equal size areas where no harvest will occur. Harvest will initially be focused on 1,500 acres of marsh, though this area may expand if eradication occurs quickly. Effects of intensive harvest on home range and movement, health and reproductive behavior and performance of nutria will be examined and compared to baseline data collected in 2000 and 2001. The management team will also examine how intensive harvest affects temporal patterns of gonadal steroid secretion during their reproductive cycle. This information will be used to formulate effective strategies for controlling nutria.
In April 2002, a pilot eradication effort will begin in Maryland on Blackwater NWR, Fishing Bay Wildlife Management Area (WMA) and Tudor Farms. The pilot will test two prospective eradication methods, perimeter trapping and saturation trapping using both foothold and conibear type traps, to determine the most efficient eradication method. A sustained trapping effort based on the average daily movements of nutria (about 40 acres) and landscape habitat features will proceed in a strategic and directional manner across the marshes on these properties in order to compare the two methods. Follow-up trapping efforts will be conducted in already trapped areas, and trapping parameters correlating to a reasonable conclusion of successful eradication will be developed. A monitoring protocol to determine ultimate success or failure of eradication efforts at already trapped sites will be implemented. It is hoped that the two-year effort will answer the elemental questions of whether or not nutria can indeed be eradicated from the Chesapeake Bay ecosystem, and what level of effort is required to do so.
At this time, there are no research or management activities associated with nutria in Virginia. Population numbers and distribution are limited. Individuals have been sighted and trapped at Saxis WMA and Back Bay NWR. There has been no evidence of marsh damage or "eat outs" by the nutria in these two areas.
Legal Status of Nutria
Nutria are regulated as a furbearer species.
Nutria are listed as "unprotected"; therefore the Maryland Department of Natural Resources does not have the authority to regulate them, though they can be controlled or eradicated within the Department's authority to control wildlife populations that cause damage to other resources or economic interests.
Nutria are considered a "nuisance" species in Virginia. It is unlawful to take, possess, transport or sell all other wildlife species not classified as game, furbearer, or nuisance, or otherwise specifically permitted by law or regulation. There is a continuous open season for trapping nuisance species.
Bounds, D. 1998. Marsh Restoration: Nutria Control in Maryland. Pilot Program Proposal.
Brown, L.N. 1975. Ecological relationships and breeding of the nutria (Myocastor coypus) in the Tampa, Florida area. J. Mamm. 56:928-930.
Burt, W.H. and R.P. Grossenheider. 1964. A Field Guide to the Mammals. Houghton Mifflin Co., Boston, 284 pp.
Colona, R. Maryland Department of Natural Resources, Furbearer biologist.
Colona, R. Nutria, an Exotic Dilemma, Combating an Ecological Catastrophe. Marsh Restoration/Nutria Control Partnership.
Evans, J. 1970. About Nutria and their Control. U.S. Department of Interior Bureau of Sport Fisheries and Wildlife. Denver, 65 pp.
Evans, J. 1983. Nutria. In R.M. Timm, ed. Prevention and cCntrol of Wildlife Damage, Coop. Ext. Serv., University of Nebraska, Lincoln.
Gingerich, J.L. 1994. Florida's Fabulous Mammals. World Publications. Tampa Bay, 128 pp.
Griffo, J.V., Jr. 1957. The status of nutria in Florida. Quarterly Journal of the Florida Academy of Sciences 20(3):209-215.
Jackson, D.D. 1990. Orangetooth is here to stay. Audubon 92(4):88-94.
Lowery, G.H., Jr. 1974. The Mammals of Louisiana and its Adjacent Waters. Louisiana State University Press. 565 pp.
Nowak, R.M. 1991. Walker's Mammal's of the World. Fifth edition. John Hopkins University Press, Baltimore, MD. 1,629 pp.
O'Neil, T., and G. Linscombe. 1977. The Fur Animals, the Alligator, and the Fur industry in Louisiana. Louisiana Department of Wildlife and Fisheries. Wildlife Education Bulletin No. 109. 68 pp.
Trillen, C. 1995. The nutria problem. Atlantic Monthly 27 (2):30-32; 40-42.
Whitaker, J.O., Jr. 1988. The Audubon Society Field Guide to North American Mammals. Alfred A. Knopf, Inc., New York. 745 pp.
Willner, G.R., J.A. Chapman and D. Pursley. 1979. Reproduction, physiological responses, food habits, and abundance of nutria on Maryland marshes. Wildl. Monogr. No. 65. 43 pp.
Willner, G.R. 1982. Nutria. In J. A. Chapman and G.A. Feldhamer, eds. Wild Mammals of North America: Biology, Management, and Economics, pp.1059-1076. The Johns Hopkins University Press, Baltimore, Maryland.
Species summary for Myocaster coypus Kerr, 1972
Nutria and Trade
"The effect of nutria (Myocastor coypus) on marsh loss in the lower eastern shore of Maryland: an exclosure study"
USGS Nonindigenous Species Mammal Distribution Information
United States Fish and Wildlife Service Chesapeake Bay Nutria Control
Proud Partners in the Watershed-Wide
Last modified October 10, 2012