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Nutria (Myocastor coypus), also called coypu in other parts of the world, are non-native rodents from South America that destroy large acres of wetland habitat by chewing the above-ground biomass as well as the roots of vegetation. Due to nutria influence, especially in Louisiana, there has been a substantial loss of coastal wetlands, turning a productive, diverse landscape into open water. Many agencies such as CWPPRA, CTRCL, LDWF, USFWS, and USACE are involved in trying to diminish populations throughout coastal Louisiana. One program is the Coastwide Nutria Control Program which pays $5 per nutria tail when delivered to collection centers. 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 all the money and effort put into restoration would be pointless without proper nutria control.

Brief Background

According to the U.S. Geological Survey they were first introduced to Louisiana in the early 1930's, but the population was kept in check, or at a small population size, because of trapping pressure from the fur industry. The earliest account of nutria spreading freely into Louisiana wetlands from their enclosures was in the early 1940's; 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 transplanted from Port Arthur, TX to the Mississippi River in 1941 and then spread due to a hurricane later that year .

Life History Strategy

Nutria are capable of destroying large acres of wetlands due to their life history strategy or life history theory. Nutria 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 nutria die within the first year and less than 15% of a wild population include individuals over three years old. Male nutria sexually mature as early as 4 months and females as early as 3 months, however both can have a prolonged adolescence up to 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 13 young. Baby nutria can eat vegetation with their parents within hours of birth; they are born fully furred and with open eyes. Also, the mother may be able to 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 nutria will nurse for 7-8 weeks at which time they will leave their mother.

In addition to a relatively quick reproduction cycle, nutria consume large amount of vegetation. They are found most commonly in freshwater marshes but also inhabit brackish marshes and rarely salt marshes. 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. Creating ‘eat-outs’, areas where 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.
This semi-aquatic rodent consumes about 25% of its body weight daily and feeds year round. On average a mature, healthy nutria weighs 12 lbs, but they can reach as much as 20 lbs. Dr. Andy Nyman of Louisiana State University School of Renewable Natural Resources has stated in conversation that nutria congregate at areas with high nutrient input such as near freshwater and sediment diversions (more sources on this to follow). So, an average 12 lb nutria can consume 3 lbs of vegetation everyday in typical habitat, but with more nutrients, particularly nitrogen for plant growth, a nutria now may ingest more resources thereby promoting growth. More information about freshwater and sediment diversions can be found at the CWPPRA page. These life strategies for survival have enabled this rodent to reproduce often and consume large amounts of plant material for much of its' life.

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 scale of negatively impacted land by herbivory increased to about 105,000 acres. The Louisiana Department of Wildlife and Fisheries has determined that nutria impacts to wetlands decreased from an estimated 80,000+ acres of Louisiana wetlands in 2002-2003 season to about 6,296 acres impacted during 2010-2011 season . The LDWF stresses that without effective, sustainable nutria population control, coastal wetland restoration projects will be greatly hindered.

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 impact 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 1.4 times 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

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." China and Korea consider nutria, or coypu as it is called outside of the U.S., a delicacy. For nutria recipes visit this site.

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.