Nutria (Myocastor coypus)

DESCRIPTION

The Nutria, a member of the rodent family, is native to South America, and it was introduced both accidentally and purposely in the waterways in several American states.  The species has proved to be overly destructive of habitat in some areas, creating problems for muskrats and waterfowl.  This species can tolerate winters in temperate areas only.  An important fur bearer in Louisiana and Texas coastal area, nutria are viewed as detrimental in most other areas. 

Adult nutria are about 14 inches long from the nose to the base of the tail.  The tail itself is 12 to 17 inches long, round, and hairless.  Coloration is brownish, and both sexes are similar in appearance and weight. The nutria is unique in that it has 3 sets or lengths of fur.  Primary guard hairs are about 3 inches in length.  Beneath this layer is the secondary  guard hairs, which are more numerous and give the species its overall coloration. The underfur is short, and less dense than either a muskrat or beaver underfur.

The whiskers on a nutria are obvious.  These whiskers are about 4 inches in length, and very numerous.  Teeth number 20, and include 4 large incisors, and allows the nutria to cut off underwater plants without getting water into its mouth.  The mouth also has glands located near the corners which produce oils that the nutria uses to comb and waterproof its fur.  Nutria average 16 to 18 pounds in weight. Occasionally, individuals may weigh 25 pounds or more.  Also unique is the location of the mammary glands on the females.  The teats are located high on the sides of the nutria, which allows young nutria to nurse as the mother swims in the water. 

Front feet have five toes, including a small toe corresponding to our thumb. Hind feet are much larger, and unique in that all toes are connected by a skin web except for the toe corresponding to our little toe. 

Nutria are apt to breed in any month of the year in North America.  One male usually has 2 or 3 mates which share the same burrow. Female nutria mature at about 5 1/2 months of age, and female nutria usually have two litters per year.  Many females breed within two days after giving birth to a litter. 

Litter sizes vary according to a cycle.  The first litter is small, with 2 to 4 being born.  The second litter is larger with 4 to 6 offspring. The third litter is smaller than the second, and the fourth again increases in size.  For one reason or another, each litter is either larger or smaller than the litter previous preceding it, and according to a pattern.  If nutria litter sizes were averaged, five would probably be the average size.  Female nutria are capable of producing only 6 litters as a rule. Females who produce seven litters in their lifetime are rare. 

At birth the young are fully furred, and their eyes are open; they are able to move about and feed upon green vegetation within a few hours. At that time they weigh approximately 200 g. They mature rapidly, increasing at the rate of about 400 g per month during the first year, and reach sexual maturity at the age of 4 or 5 months.  The maximum length of life for nutria kept in captivity is 12 years, but the life span in the wild probably is considerably less.

Nutria spend most of their time in or near the water.  Although they are awkward and vulnerable on land the species will travel inland to feed upon preferred foods, including crops.  Nutria are vegetarians and they do have large appetites. Primarily a surface feeder, nutria often over harvest favored foods, causing the production of less favored foods for themselves and other wildlife species. Nutria destroy marshlands in a unique manner, beginning their feeding pattern from the inside of a marsh area and moving outward, thus causing a swifter disintegration of large section of marsh. Nutria feed on the roots and stems of marsh vegetation, digging underneath and overturning the plants to feed on the root mat. This feeding behavior does not allow a plant to survive after it is fed upon. Nutria commonly cut off a preferred food near the waterline and swim or carry it to a feeding platform for eating.  These platforms are used most often during the trapping seasons, possibly because they are warmer on the nutria's hairless feet. Favored foods for nutria include rushes, reeds, cattails, arrowhead, square-stem spike rush and sawgrass.  Sugarcane, alfalfa, corn and rice are also eaten if available.

Nutria are thought of as colonial because the same den is shared by the dominant male with two or three females and their offspring.  Den entrances are often a foot or two beneath the water's surface, and the den entrance is often as much as two feet in diameter.  The inner chamber of the den is above the waterline, and lined with grasses brought in to serve for bedding. 

Nutria do not remain underwater for long periods of time.  Research shows that they are capable of holding their breath while submerged for about five minutes. 

A shy and retiring species, nutria are not usually seen unless there is a deliberate attempt to find them. Nutria burrow into banks of ponds and lakes, and these holes are usually larger and more destructive than muskrat burrows. 

A large rodent, nearly as large as a beaver but with long, rounded, scaly, ratlike tail; hind feet webbed; incisors orange-colored; female with mammae along each side of back, not on belly; upperparts reddish brown; the underfur dark slaty; tip of muzzle and chin white. External measurements of adults average: total length, 800-900 mm; tail, 350-400 mm; hind foot, 130-140 mm. Total length may reach 1.4 m. Weight, normally 8-10 kg.

(Source: 1. National Trappers Association, http://www.nationaltrappers.com/nutria.html, 
2. U.S. Fish and Wildlife Service, Chesapeake Bay Nutria Control, http://invasives.fws.gov/Indexhottop.NU.html, 3. The Mammals of Texas - Online Edition, http://www.nsrl.ttu.edu/tmot1/myoccoyp.htm).

IMPACTS

The introduction of nutria to many different places have had many adverse affects.  Most of the states in which the animals was introduced, are facing the same types of problems.

TEXAS
They have been widely introduced in Texas as a "cure-all" for ponds choked with vegetation. They do reduce many kinds of aquatic plants, but they will not eat "moss" (algae) and many of the submerged plants. At times they do the job too well. The trouble is that once nutrias get established in a lake, their high reproductive capacity soon results in overpopulation. There are so many nutrias that the available food supply will not satisfy them, and then trouble begins. The animals move into places where they are not wanted or where they destroy vegetation that is valuable for such wildlife as waterfowl and muskrats. A case in point is Eagle Lake in Colorado County. There, a stocking of nutrias increased to the point where the animals seriously damaged the waterfowl values of the lake. Hundreds of dollars were spent in attempts to eradicate the pests.

Currently, nutria populations in Texas are moderately high and on the increase. Unless the market for nutria improves, a serious and costly overpopulation problem is likely in the very near future

(Source from The Mammals of Texas - Online Edition, http://www.nsrl.ttu.edu/tmot1/myoccoyp.htm)

CHESAPEAKE BAY AREA
The drop in demand for Nutria coats, in part a result of the anti fur movement, has triggered a population explosion. Nutria released by breeders who could no longer afford to feed them have moved into 40 states. Marsh loss is the biggest direct impact of the nutria due to their feeding and digging behaviors. The resulting losses of marsh vegetation is staggering, totaling thousands of acres loss each year due to nutria damage and the associate saltwater intrusion that occurs. It is estimated that 65% of Chesapeake Bay coastal wetlands have been lost since the 1700's and the impacts from nutria add unwelcome pressures on an already fragile system. Blackwater National Wildlife Refuge is losing approximately 500-1000 acres/year from nutria damage and several times that amount over the entire Blackwater/Fishing Bay estuary. These losses drastically affect the refuge's ability to meet its wildlife management objectives and maintain a healthy ecosystem. 

(Source: 1. U.S. Fish and Wildlife Service Chesapeake Bay Nutria Control, http://invasives.fws.gov/Indexhottop.NU.html; 2. Nutria On The Munch, Popular Mechanics, July 1997,
http://popularmechanics.com/popmech/sci/tech/9707TUANQM.html)

GULF STATES
In many coastal marshes, massive numbers of the animals have become a severe problem because they eat vegetation, including the roots that hold the marsh together. Often communities of nutria eat away at a section of marsh until it disappears to open water. Then they move to an adjacent area and begin the process again, according to wildlife officials.  "They eat the vegetation right down to the mud line," and then the mud flats erode, Mr. Windom said. Where there's no new marsh to move to, large numbers of nutria sometimes freeze to death in winter because they've eaten away all of their cover, Mr. Windom said.  A 1996 survey showed that 100,000 acres of Louisiana's marsh had been damaged by nutria. In other areas of the state, the holes nutrias dig in levees have caused expensive problems. Ironically, the reduced demand for fur, which was influenced by animal rights groups, has sometimes resulted in nutria not being trapped, but exterminated.

Nutria often invade crop areas and cause considerable damage especially to rice and sugar cane fields, with reports of damage to soybean plantations near Mississippi's coast. There was 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 hurricane Audrey. Many invaded sugar cane fields, where they reeked havoc, damaging innumerable plants many of which they did not even consume. Nutria have also been attributed with the decline of muskrat populations in Louisiana. They have been reported to compete with muskrats and water fowl for trophic resources. 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. 

Nutria carry a number of parasites and diseases. Disease agents Louisiana nutria carry include Toxoplasma gondii, Clamidia psittaci, Francisella tularensis, Leptospira sp., and encephalomyocarditis virus. 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. 

(Source: 1. Dallas Morning News, "Louisianians urged to eat nutria, save the coast", 
http://twri.tamu.edu/watertalk/archive/1997-Jul/Jul-15.18.html; 2. Nonindiginous Species in the Gulf of Mexico Ecosystem, Species Summary, http://lionfish.ims.usm.edu/~musweb/nis/Myocastor_coypus.html).

GULF 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. 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.  The number of nutria present in Louisiana were reported to have reached 1,000,000 by 1957. By the 1969-70 season 1,604,175 nutria were trapped in Louisiana alone. Presently, they are more important than the muskrat in Louisiana's trapping industry. 

Nutria have expanded their range throughout the Gulf states at an alarming rate. 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. Additionally, Nutria have been introduced throughout the Gulf of Mexico ecosystem to control aquatic vegetation in lakes and ponds. 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. 

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. 

MARYLAND & CHESAPEAKE BAY AREA
Introduced in the 1940's to bolster Maryland's Eastern Shore fur industry, the South American nutria (Myocastor coypus) has been implicated in the loss of emergent marsh, especially that dominated by Olney 3-square (Scirpus olneyi) along the Blackwater River in Dorchester County. 

Nutria infestation of the Chesapeake Bay began as early as 1943 with attempts to stimulate the local economy by importing nutria to provide an alternative source of fur for trapping and fur farming. This effort included the establishment of an experimental fur production facility on Blackwater National Wildlife Refuge in Dorchester county, Maryland. The nutria population expanded in Dorchester county from less than 150 in 1968, to an estimated 50,000 animals currently. Every Maryland county along the eastern shore of the Chesapeake Bay have reported nutria populations and the range of this invasive rodent is expanding. 

(Source: 1. Maryland Department of Natural Resources, (Myocastor coypus) On Marsh Loss In The Lower Eastern Shore Of Maryland: An Exclosure Study, http://159.189.24.10/resshow/nutria.htm; 2. Nonindiginous Species in the Gulf of Mexico Ecosystem, Species Summary, 
http://lionfish.ims.usm.edu/~musweb/nis/Myocastor_coypus.html; 3. Nutria Harvest and Wetland Demonstration Project, http://www.nwrc.usgs.gov/special/nutquest.html; 4. U.S. Fish and Wildlife Service, Chesapeake Bay Nutria Control, http://invasives.fws.gov/Indexhottop.NU.html)

Since these animals are regarded as highly destructive, nuisance animals, many plans have been developed to help control the increasing populations. 

LOUISIANA
Nutria are managed as a fur bearer, and the harvest is regulated by the establishment of an annual trapping season (November 20 through March 20).  During the trapping season you can harvest nutria if you are properly licensed ($25 trapping license and have permission from the landowner).  Since 1987, the LDWF (through the Louisiana Fur and Alligator Advisory Council) has conducted various marketing and education projects in an attempt to increase the demand for nutria pelts.  In 1995 LDWF, the Louisiana Department of Health and Human Resources (LDHHR) and the Louisiana Department of Agriculture and Forestry (LDAF) established rules and regulations to allow nutria meat to be processed for human consumption.  The goal of these endeavors is to increase the value of nutria to facilitate a sufficient economic incentive to encourage trappers to harvest more nutria.

Officials from the Louisiana Department of Wildlife and Fisheries are trying to reduce the nutria population by increasing the demand for nutria fur as well as nutria meat. Wildlife and Fisheries biologist Mike Windom said nutria are eating away huge areas of coastal marsh. So, by eating nutria and creating a market for them, people can help save Louisiana's coastal wetlands, he and others said.  For the residents of south Louisiana, who often refer to the animals as "nutria rats," that may take a major attitude adjustment. Eating nutria, for most people, would mean taking a first taste. But that's all it takes, according to wildlife official Greg Linscombe, who said that every time he can get someone to try a nutria's meat, they like it.  "A young nutria tastes a lot like rabbit," Mr. Windom said, adding that they can be fried, barbecued or cooked numerous other ways. 

Developing and publicizing recipes is part of the new $2.1 million project. The new coastal project calls for a demonstration that nutria meat can be good to eat. Then, it calls for the development of a plan to market the meat of the animals. The project also requires a study of the impact nutria are having on the coast and on monitoring of selected coastal marshes to assess the amount of nutria damage. The project is being financed through the Breaux-Johnston Act, which provides about $30 million a year to Louisiana to deal with the state's 35 square miles of annual coastal wetland loss. Meat processing companies have agreed to put up the 25 percent local funding required under the federal act, which will pay for the other 75 percent of the project. One of the requirements of the project is to determine if a meat processing
system can be developed to harvest nutria and increase demand for their meat, according to a summary of the two-year project. The project's bottom line: Eat a nutria. Save the coast.

(Source: 1. Nutria Harvest and Wetland Demonstration Project,
http://www.nwrc.usgs.gov/special/nutquest.html; 2. Dallas Morning News, "Louisianians urged to eat nutria, save the coast" http://twri.tamu.edu/watertalk/archive/1997-Jul/Jul-15.18.html; 3. Louisiana Environmentalist, July - August, 1994, http://www.leeric.lsu.edu/le/cover/lead074.htm)

Similar methods have been utilized by the other Gulf States.  Louisiana is one of the only states that has made the consumption of nutria a major control method.

MARYLAND & CHESAPEAKE BAY AREA
The overabundance of nutria and the alarming loss of marsh in this region has prompted state legislation proposing a 10 year nutria eradication program. The relationship between nutria foraging activity and marsh loss, however, remains unclear and a long-term eradication effort has been postponed until evidence of cause and effect can be obtained. To address this issue, a collaborative partnership between the Maryland Department of Natural Resources and the Patuxent Wildlife Research Center was established in 1995. A formal peer-reviewed study plan was developed outlining the use of exclosures to isolate the effect of nutria foraging activity on marsh loss. The objective of the study is to demonstrate whether exclusion of nutria from emergent marsh habitats can stabilize or recover marsh vegetation. We predict that exclusion of nutria within these habitats will result in expanded vegetative cover or decelerated vegetative loss, while marsh loss will continue on unprotected sites. Use of exclosures in this study implies certain assumptions: 1) that nutria are the primary herbivore in this habitat and that muskrats, deer, waterfowl and other possible grazers have negligible effect on vegetation (or will be controlled), and 2) that the physical influence of fenced enclosure will have negligible effect on the measured vegetative response.

Research investigating the role of nutria in marsh loss is of major concern to the State of Maryland and the Blackwater National Wildlife Refuge. It is also of special interest to the Chesapeake Bay Program's Wetland Workgroup whose major goal is to achieve "no net loss" of wetlands within the Chesapeake Bay watershed. In 1994, the workgroup recognized the potential adverse effects of exotic species on Bay wetlands and importantly has adopted an objective to address the problem of exotic species management.

At present, 2,160 m (7,000 ft) of heavy gauge vinyl-coated wire has been entrenched in the marsh at Blackwater NWR to establish 18 30m x30m randomly selected exclosures. A set of 18 paired as well as 18 randomly selected control plots (unfenced) also have been established to control for site variation, especially differences in nutria density. Measures of vegetative cover and species compositional changes will be monitored by aerial photography and ground plot measurements over time. The study will monitor vegetative changes through two annual cycles with projected completion in 1998.

(Source from Maryland Department of Natural Resources, (Myocastor coypus) On Marsh Loss In The Lower Eastern Shore Of Maryland: An Exclosure Study, http://159.189.24.10/resshow/nutria.htm)

Nutria Meat Nutritional Analysis
    http://www.nwrc.usgs.gov/special/nutrnutr.html
This site provides a graph of the nutritional value of nutria as a food source.

Skulls Unlimited
    http://www.skullsunlimited.com/Capromyidae.htm
Here you can order skulls of various animals.  There is a good picture of the skull of the nutria.

National Biological Information Infrastructure
    http://www.invasivespecies.gov/profiles/nutria.shtml
This site provides numerous links to articles and journals found in their invasive species database.

Nonindigenous Aquatic Mammals in Freshwater Systems
    http://aquat1.ifas.ufl.edu/mcmasys.html
This site provides additional information on the introduction and impacts of the nutria in the United States.

Myocastor coypus Skull
    http://members.aol.com/rnorv/Coypu/coypu.htm
Here at this site is an excellent photo of a nutria skull showing characteristic teeth. 

Department of Land Resources and Environmental Sciences Montana State University-Bozeman
   http://agadsrv.msu.montana.edu/lresclasses/LRES110/Nutria_Beaver_hook.htm
This site provides lecture material from a course at Montana State University on nutria, beaver, and wetlands.

Committee On Resources House Of Representatives
    http://commdocs.house.gov/committees/resources/hii50341.000/hii50341_0.HTM
This site provides the minutes from an oversight hearing on pilot program to control nutria at the Blackwater National Wildlife Refuge in Maryland.

Woodlands Executive Conference Center and Resort
    http://www.flex.net/~lonestar/nutria.htm
Provides information on the description of the nutria and gives a little information on the introduction of the species.

Nutria Links
    http://www.mapfish.com/nutria.html
This site provides numerous links to many different sites.

ABC News.com
    http://www.abcnews.go.com/sections/science/DailyNews/invaders990927.html
This site provides and article titled "Some Species Aren’t Welcome", concerning the nutria.