Date of this Version
Biology and Natural History of the Nutria, With Special Reference to Nutria in Louisiana
The nutria or coypu (Myocastor coypus) is a rodent native to South America that has been introduced almost worldwide since the early 1900’s, originally with the intent of fur farming in many cases. The nutria is a large (over 6 kg), semi-aquatic rodent with a voracious appetite and high reproductive potential. Nutria became established in the Louisiana wetlands in the 1930’s. The habitat proved to be ideal and populations exploded, reaching an estimated 20 million animals in less than 20 years. Trapping of nutria for their pelts formed the backbone of the Louisiana trapping industry from the 1960’s until the early 1980’s when prices for furs on the world market and in Louisiana fell drastically. Since then the annual trapping harvest, which was over one million animals per year for many years, has dwindled to 29,544 in the 2000-2001 season. Since the virtual cessation of the annual harvest, nutria numbers have increased dramatically. Reports of damage to wetland habitats emerged in the late 1980’s. Numerous studies of the wetland environments of Louisiana since then have documented the deleterious effects nutria grazing is having on the habitat. While nutria serve as an important prey item for the alligator, effects of nutria activity on other animals are primarily negative. Their most important impact is habitat modification and in many cases, habitat destruction. When impacts of intense nutria herbivory are added to the abiotic forces that are degrading the Louisiana coastal marshes the potential for lasting loss of wetland area is magnified. This report reviews the general biology and natural history of nutria; the chronology of nutria establishment in Louisiana and historic population fluctuations; interaction of nutria with other animals in Louisiana, and impacts of nutria herbivory on the wetland plant communities.
Socioeconomic and Cultural Analysis of Nutria in Louisiana
Louisiana’s coastal wetlands represent a very significant proportion (at least 40%) of the Nation’s wetland resources. These wetlands represent an invaluable resource to the state and Nation, a resource whose wetland losses alone have been valued in the billions of dollars. Coastal storms and many factors contribute to wetlands loss. However, a major concern that is greatly accelerating the loss of coastal wetlands in Southeastern Louisiana is the overabundant population of nutria. Louisiana has a proud tradition of resource utilization. At one time it was the leading producer of fur pelts in North America and led all states in the production of muskrats and mink. The state still has a significant number of residents who utilize the land and coastal resources—trapping and fishing (including shrimping and oystering), to earn a living or supplement their livelihood. But this number is decreasing, in large part because fur prices have dropped so low in recent years that trapping isn’t worth the trapper’s time and effort. In 2000-2001, less than 1,000 trapping licenses were sold statewide in Louisiana. Many of these coastal resource users have been forced to seek employment in the oil and gas industry and elsewhere. It is questionable whether many will ever return to the traditional coastal resource uses. In an attempt to deal with nutria overpopulations, the Department of Wildlife and Fisheries, Fur and Refuge Division, has requested federal funds for an incentive program for trapping or shooting nutria. It is anticipated that such funds, if approved, would allow the payment of up to $4.00 per nutria taken. Our analysis of past trapping participation and pelts compared to pelt price suggests that $4.00 is a sufficient incentive to bring about the desired harvest of nutria. However, interviews of knowledgeable local people suggest that the specifics of program implementation could lead to significant problems if they are not thought through and implemented very carefully. The concerns include primarily trespass and poaching by trappers and hunters, and potential water quality problems if the harvested nutria are just left in the marsh and are not utilized. Thus, within the regulatory authority available to the Department and the Fur and Refuge Division, it should strive for procedures that protect against these concerns as much as possible.
Nutria Control in Louisiana
The nutria (Myocastor coypus) is a large semi-aquatic rodent that was introduced throughout much of the world as a means of increasing the fur market in the first half of the twentieth century. Although not considered a pest in their native range of South America, nutria presence in areas has often met with greater detriment than benefit. Nutria have damaged crops, marsh vegetation, and water control structures. The damage caused from the nutria has been described for decades, yet science is adding value to the marshes that provide prime habitat for many mammalian, avian, reptilian, and amphibian species as well as floral species. The uniqueness of the marsh and coastal habitats is in jeopardy of being damaged to an extent that the cost of repair would be astronomical. Current re-vegetation projects are often met with failure due to nutria foraging unless labor-intensive exclosures are constructed. It is the purpose of this document to review and discuss the methods to control the nutria in the state of Louisiana to a level that damage is more manageable. Techniques that are addressed in this document include: incentive payment, chemical control (toxicants), incentive-bonus, induced infertility, trapping, controlled hunting, and chemical repellents. These techniques are ranked by feasibility of implementation and the probability of obtaining the expected result--control to a manageable level.