|Coypu or Nutria
Temporal range: Late Pliocene–Recent
The coypu (from the Mapudungun, koypu), (Myocastor coypus), also known as the river rat,  and nutria, is a large, herbivorous, semiaquatic rodent and the only member of the family Myocastoridae. Originally native to subtropical and temperate South America, it has since been introduced to North America, Europe, Asia, and Africa, primarily by fur ranchers. Although it is still valued for its fur in some regions, its destructive feeding and burrowing behaviors make this invasive species a pest throughout most of its range.
There are two commonly used names in the English language for Myocastor coypus. The name "nutria" (or local derivatives such as "nutria- or nutra- rat") is generally used in North America, Asia and throughout countries of the former Soviet Union; however, in Spanish-speaking countries, the word "nutria" refers to the otter. To avoid this ambiguity, the name "coypu" (derived from the Mapudungun language) is used in Latin America and Europe. In France, the coypu is known as a ragondin. In Dutch it is known as beverrat (beaver rat). In Italy, instead, the popular name is, as in North America and Asia, "nutria", but it is also called castorino ("little beaver"), by which its fur is known in Italy.
Coypus live in burrows alongside stretches of water. They feed on river plants, and waste close to 90% of the plant material while feeding on the stems.
The coypu was first described by Juan Ignacio Molina in 1782 as Mus coypus, a member of the mouse genus. The genus Myocastor, assigned in 1792 by Robert Kerr, is derived from the Greek mys and kastor, or "mouse-beaver". Geoffroy, independently of Kerr, named the species Myopotamus coypus, and it is occasionally referred to by this name.
Four subspecies are generally recognized:
- M. c. bonariensis: northern Argentina, Bolivia, Paraguay, Uruguay, southern Brazil
- M. c. coypus: central Chile, Bolivia
- M. c. melanops: Chiloé Island
- M. c. santacruzae: Patagonia
M. c. bonariensis, the subspecies present in the northernmost (subtropical) part of the coypu's range, is believed to be the type of coypu most commonly introduced to other continents.
The coypu somewhat resembles a very large rat, or a beaver with a small tail. Adults are typically 5–9 kg (11–20 lb) in weight, and 40–60 cm (16–24 in) in body length, with a 30–45 cm (12–18 in) tail. They have a coarse, darkish brown outer fur with a soft dense grey under-fur, also called the nutria. Three distinguishing features are a white patch on the muzzle, webbed hind feet and large bright orange-yellow incisors. The nipples of female coypu are high on her flanks. This allows their young to feed while the female is in the water.
Coypu may be mistaken for the muskrat, another widely dispersed semi-aquatic rodent that occupies the same wetland habitats. The muskrat, however, is smaller, more tolerant of cold climates, and has a laterally flattened tail that it uses to assist in swimming whereas the tail of a coypu is round. It can also be mistaken for a small beaver, as beavers and coypus have very similar anatomies. However, beavers' tails are flat and paddle-like, as opposed to the round rat-like tails of coypu.
Life history strategy 
Coypus can live up to six years in captivity, but it is uncommon for individuals to live past three years old; according to one study, 80% of coypus die within the first year, and less than 15% of a wild population is over three years old. Male coypus reach sexual maturity as early as 4 months, and females as early as 3 months; however both can have a prolonged adolescence, up to the age of 9 months. Once a female is pregnant gestation lasts 130 days and she may give birth to as few as one offspring or as many as thirteen. Baby coypus are born fully furred and with open eyes; they can eat vegetation with their parents within hours of birth. A female coypu can become impregnated again the day after she gives birth to her young. If timed properly, a female can become pregnant three times within a year. Newborn coypus nurse for seven to eight weeks, after which they leave their mother.
Beside breeding quickly, each coypu consumes large amounts of vegetation. An individual consumes about 25% of its body weight daily, and feeds year-round. Being one of the world's larger extant rodents, a mature, healthy coypu averages in weight at 5.4 kg (12 lb), but they can reach as much as 10 kg (22 lb). They eat the base of the above-ground stems of plants and often will dig through the organic soil for roots and rhizomes to eat. Their creation of "eat-outs", areas where a majority of the above- and below-ground biomass has been removed, produces patches in the environment, which in turn disrupts the habitat for other animals and humans dependent on marshes.
Commercial and environmental issues 
Local extinction in their native range due to overharvesting led to the development of coypu fur farms in the late 19th and early 20th centuries. The first farms were in Argentina and then later in Europe, North America, and Asia. These farms have generally not been successful long term investments and farmed coypu often are released or escape as operations become unprofitable.
As demand for coypu fur declined, coypu have since become pests in many areas, destroying aquatic vegetation, marshes, irrigation systems, chewing through human-made items, such as tires and wooden house panelling in Louisiana, eroding river banks, and displacing native animals. Coypu were introduced to the Louisiana ecosystem in the 1930s when they escaped from fur farms that had imported them from South America. Nutria damage in Louisiana became so severe that in 2005, a bounty program was in effect to aid in controlling the animal. In the Chesapeake Bay region in Maryland, where they were introduced in the 1940s, coypu are believed to have destroyed 7,000 to 8,000 acres (2,800 to 3,200 ha) of marshland in the Blackwater National Wildlife Refuge. In response, by 2003, a multi-million dollar eradication program was underway.
In the United Kingdom, Coypu were introduced to East Anglia, for fur, in 1929; many escaped and damaged the drainage works, and a concerted programme by MAFF eradicated them by 1989. However, in 2012 a 'giant rat' was killed in County Durham, with authorities suspecting that the animal was, in fact, a coypu.
Coypu meat is lean and low in cholesterol. While there have been many attempts to establish markets for coypu meat, all documented cases have generally been unsuccessful. Unscrupulous entrepreneurs have promoted coypu and coypu farms for their value as "meat", "fur", or "aquatic weed control". In recent years they have done so in countries such as the United States, China, Taiwan and Thailand. In every documented case the entrepreneurs sell coypu "breeding stock" at very high prices. Would-be coypu farmers find that the markets for their products disappear after the promoter has dropped out of the picture.
In the former Soviet republics of Central Asia, specifically Kyrgyzstan and Uzbekistan, Nutria (Russian and local languages Нутрия) are farmed on private plots and sold in local markets as a poor man's meat.
In addition to direct environmental damage, coypu are the host for a nematode parasite (Strongyloides myopotami) that can infect the skin of humans causing dermatitis similar to strongyloidiasis. The condition is also called "nutria itch".
The distribution of coypu tends to expand and contract with successive cold or mild winters. During cold winters, coypu often suffer frostbite on their tails leading to infection or death. As a result, populations of coypu often contract and even become locally or regionally extinct as in the Scandinavian countries and such USA states as Idaho, Montana and Nebraska during the 1980s (Carter and Leonard 2002). During mild winters, their ranges tend to expand northward. For example in recent years range expansions have been noted in Washington State and Oregon (Sheffels and Sytsma 2007), as well as Delaware.
According to the U.S. Geological Survey nutria were first introduced the United States in California, 1899. They were first brought to Louisiana, USA in the early 1930s for the fur industry, and the population was kept in check, or at a small population size, because of trapping pressure from the fur traders. The earliest account of nutria spreading freely into Louisiana wetlands from their enclosures was in the early 1940s; a hurricane hit the Louisiana coast that many people were unprepared for and the storm destroyed the enclosures, enabling the nutria to escape into the wild. According to the Louisiana Dept. of Wildlife and Fisheries, nutria were also transplanted from Port Arthur, TX to the Mississippi River in 1941 and then spread due to a hurricane later that year.
Herbivory damage to wetlands 
Wetlands in general are a valuable resource both economically and environmentally. For instance, the U.S. Fish and Wildlife Service determined that wetlands covered only 5% of the land surface of the contingent 48 United States, however they produce 31% of the nation's plant species. These are very biodiverse systems and provide resources, shelter, nesting sites, and resting sites (particularly Louisiana’s coastal wetlands such as Grand Isle for migratory birds) to a wide array of wildlife. Human users also receive many benefits from wetlands such as cleaner water, storm surge protection, oil and gas resources (especially on the Gulf coast), reduced flooding, and chemical and biological waste reduction just to name a few. More information about wetlands values and services can be found on the wetland page. In Louisiana there is rapid wetland loss due to a variety of reasons; it is estimated that this state loses area about the size of a football field every hour. According to the U.S. Geological Survey, from 1932 to 2010 Louisiana lost enough acres of wetland to total the size of Delaware.
In 1998 the LDWF conducted the first Louisiana coast-wide survey, which was funded by the Coastal Wetlands Planning, Protection, and Restoration Act and titled the Nutria Harvest and Wetland Demonstration Program, to evaluate the condition of the marshlands. The survey revealed through aerial surveys of transects that herbivory damage to wetlands totaled roughly 90,000 acres. The next year LDWF performed the same survey and found that the area damaged by herbivory increased to about 105,000 acres. The Louisiana Department of Wildlife and Fisheries has determined that wetlands affected by nutria decreased from an estimated 80,000+ acres of Louisiana wetlands in 2002-2003 season to about 6,296 acres during 2010-2011 season. The LDWF stresses that coastal wetland restoration projects will be greatly hindered without effective, sustainable nutria population control.
As stated by Tiffany McFalls, a biologist from Southeastern Louisiana University, and her colleagues in the article "Hurricanes, Floods, Levees, and Nutria: Vegetation Responses to Interacting Disturbance and Fertility Regimes with Implications for Coastal Wetland Restoration", nutria herbivory "severely reduces overall wetland biomass and can lead to the conversion of wetland to open water." Unlike other common disturbances in marshlands, such as fire and tropical storms, which are a once or few times a year occurrence, nutria feed year round and so their effect on the marsh is constant. Also nutria are typically more destructive in the winter than in the growing season. This is due largely to the scarcity of above-ground vegetation; as nutria search of food they will dig up root networks and rhizomes for nutrition. While nutria are the most common herbivores in Louisiana marshes, they are not the only ones. Feral hog, also known as wild boar (Sus scrofa), swamp rabbit (Sylvilagus aquaticus), and muskrat (Ondatra zibethicus) are less common, however feral hogs are increasing in number in Louisiana wetlands. Through experimentation, McFalls and her colleagues discovered that on plots open to nutria herbivory there was 40% less vegetation than in plots guarded against nutria by a fence. For this study above-ground biomass was measured for a year. This number may seem insignificant, and indeed herbivory alone is not a serious cause of land loss, but also noted in the study is that when herbivory was combined with an additional disturbance, such as fire, single vegetation removal or double vegetation removal to simulate a tropical storm, the effect of the disturbances on the vegetation were greatly amplified." Essentially this means that as different factors were added together the result was less overall vegetation. Adding fertilizer to open plots did not promote plant growth in this study, instead nutria fed more in the fertilized areas. This led McFalls and her colleagues to infer that increasing fertilizer inputs in marshes will only increase nutria biomass instead of the intended vegetation, therefore increasing nutrient input is not recommended.
Control efforts 
As stated by CWPPRA, nutria herbivory "is perhaps the least studied or quantified aspect of wetland loss." Many coastal restoration projects involve planting vegetation to stabilize marsh land, however, if nutria are in the area then without proper nutria control all the money and effort put into restoration would be pointless. The most recent program instituted to provide incentives for harvesting nutria is the Coastwide Nutria Control Program and it has proven to be the most successful in minimizing the nutria population. Starting in 2002, LDWF has performed aerial surveys just as they had done for the Nutria Harvest and Wetland Demonstration Program (mentioned previously), only it is now under a different program title. Under the Coastwide Nutria Control Program, which also receives funds from CWPPRA, 308,160 nutria were harvested the first year (2002–2003), revealing 82,080 acres damaged and totaling $1,232,640 in incentive payments paid out to those legally participating in the program. Essentially once a person receives a license to hunt or trap nutria then that person is able to capture an unlimited number. When a nutria is captured simply cut off the tail and turn it in to a Coastal Environments Inc. (CEI) official at an approved site. Each nutria tail is worth $5, which is an increase from $4 before the 2006-2007 season. Nutria harvesting increased drastically during the 2009-2010 year with 445,963 nutria tails turned in worth $2,229,815 in incentive payments. Each CEI official keeps record of how many tails have been turned in by each individual per parish, method used in capture of the nutria, and the location of capture. All of this information is transferred to a database that calculates the density of nutria across the Louisiana coast and the LDWF combines this data with the results from the aerial surveys to determine the number of nutria remaining in the marshes and the amount of damage they are inflicting on the ecosystem.
Another program executed by LDWF involves creating a market of nutria meat for human consumption, though it is still trying to gain public notice. Nutria is a very lean, fibrous, protein-rich meat; in certain ways it is much better than beef, chicken and turkey for the human body. It is low in fat and cholesterol with the taste, texture, and appearance of rabbit or dark turkey meat according to a study published in the Journal of Food Science. This same study tested the meat, before and after processing, and came to the conclusion that it is in fact safe for human consumption. There are few pathogens associated with the meat but proper heating when cooking should kill all microbes. The quality of the meat and the minimal harmful microorganisms associated with it make nutria meat an "excellent food product for export markets."
There are several control methods that are desired but are currently ineffective to use for various reasons. Zinc phosphide is the only rodenticide currently registered to control nutria, but it is expensive, remains toxic for months, detoxifies in high humidity and rain, and requires construction of floating rafts (expensive) for placement of the chemical. It is not yet sure how many non-target species are susceptible to zinc phosphide, but birds and rabbits have been known to die from ingestion. Therefore this chemical is rarely used, especially not in large-scale projects. Other potential chemicals would be required by the U.S. Environmental Protection Agency to undergo vigorous testing before it would be acceptable to use on nutria. The LDWF has estimated costs for new chemicals to be $300,000 for laboratory, chemistry, and field studies and $500,000 for a mandatory Environmental Impact Statement. Contraception is not a common form of control, but to some wildlife managers it is preferred. It also is expensive to operate; an estimated $6 million to drop bait pre-laced with birth control chemicals annually. Testing of other potential contraceptives would take about 5–8 years and $10 million with no guarantee of FDA approval. Also an intensive environmental assessment would have to be filled out to confirm or deny that any non-target organisms were impacted by the contraception chemicals. It is unlikely that either of these control methods will be utilized in the near future.
Coypu are classed as a "prohibited new organism" under New Zealand's Hazardous Substances and New Organisms Act 1996 preventing it from being imported into the country. In the United States an eradication program on the Delmarva Peninsula, between Chesapeake Bay and the Atlantic coast, where they once numbered in the tens of thousands and had destroyed thousands of acres of marshland, had nearly succeeded by 2012.
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|Wikimedia Commons has media related to: Myocastor coypus|
|Look up coypu in Wiktionary, the free dictionary.|
- History, distribution and spread of coypu introductions worldwide; efforts to eradicate with links to other nutria sites
- The Effect of Nutria on Marsh Loss in the Lower Eastern Shore of Maryland undated USGS report
- Portland State University Report on coypus in the Pacific Northwest of North America.
- Species Profile- Nutria (Myocastor coypus), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Nutria.