Blackwater National Wildlife Refuge
Northeast Region
 
2145 Key Wallace Dr
Cambridge, MD 21613
(410) 228-2677

Nutria and Blackwater Refuge

Nutria Update: On Nov. 17, 2004, the Washington Post reported that the Blackwater Refuge staff and their partners had eradicated the destructive nutria from Blackwater Refuge. With continued vigilance, Maryland wildlife authorities should be able to keep nutria out of the Refuge and allow the marshes to recover. Read the Post article for more details: Blackwater Refuge Now Nutria-Free

Visit the Friends of Blackwater Nutria Slide Show to see images showing the impact of nutria at the Refuge.


Questions About Nutria

Adult nutria. Credit: USFWS

What is a nutria?
Where are nutria found?
How fast do nutria reproduce?
What do nutria eat?
What problems are caused by nutria?
How has their population increased?
How have the nutria damaged the marsh?
What is the Nutria Exclosure Study?
What are the nutria's impacts on other species?
What are we going to do about the nutria?
What research has been done on the population?
Nutria eradication or control?
What about wetlands restoration?
How are we educating the public?
What is the Partnership?
What's the latest news concerning the eradication/control efforts?


What is a nutria?

Nutria (Myocastor coypu) are large rodents that look like beavers with long, thin tails. Nutria may weigh up to 20 lbs., but on average weight between 12-15 lbs. with males slightly larger than females. They have dense, grayish underfur overlaid by long glossy guard hairs that vary in color from dark brown to yellowish brown. Their large front teeth are yellow-orange to orange-red on the outer surface. The forepaws have four well-developed clawed toes and one non-functional toe. The hind feet have five clawed toes: four webbed and one that hangs free. Nutria have several other adaptations to help them in the water. Their eyes, ears and nostrils are set high on their heads. The nostrils and mouth have valves that seal out water while swimming, diving or feeding underwater. The female's teats are located high on her sides to allow the young to suckle while in the water. Nutria are primarily nocturnal (active at night), with peak activity occurring near midnight. When food is abundant, nutria rest and groom during the day and feed at night. When food is limited, daytime feeding increases, especially in wetlands free from disturbance.

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Where are nutria found?

Nutria inhabit fresh and brackish marshes, rivers, bayous, farm ponds, freshwater impoundments, drainage canals, swamps and various other types of wetlands. Although found in sixteen U.S. states, nutria are native to South America. Their original range includes Argentina, Chile, Bolivia, Uruguay, Paraguay and southern Brazil. After escaping from captivity in the U.S. and elsewhere, they now inhabit a much greater area. Nutria were first imported into the United States between 1899 and 1930 in an attempt to establish a fur farm industry. Many of the fur farms failed in the late 1940s because fur prices fell and nutria did not reproduce well in captivity. Many nutria were released into the wild. Nutria are now reported in every Maryland Eastern Shore county and are found from Bombay Hook National Wildlife Refuge in Delaware through the Delmarva Peninsula to Virginia's Eastern Shore. They have also been reported on the western shore of Maryland in the Potomac and Patuxent Rivers and in Virginia as far south as the Northern Neck near the Rappahanock River.

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How fast do nutria reproduce?

Nutria are highly prolific and breed all year. Reproductive peaks occur in late winter, early summer, and mid-autumn. Reproduction and survival may be influenced by extreme weather conditions. Nutria reach sexual maturity at four to six months. Sexually mature male nutria can breed throughout the year. Females are pregnant from 128 to 130 days, and are ready to breed within forty-eight hours after giving birth. Litters average four to five young; however, nutria can have up to thirteen young per litter and may have three litters per year. Young are born fully furred and active, weighing 8 oz. at birth. They can swim and eat vegetation shortly thereafter, still feeding on mother's milk for up to eight weeks. Within five days of life, nutria can survive away from the mother.

As an example of their proliferation: in 1938, twenty individual nutria were introduced into Louisiana and within twenty years, the nutria population exceed 20 million animals. By 1962, the nutria had replaced the native muskrat as the leading furbearer in Louisiana.

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What do nutria eat?

Nutria feed almost entirely on vegetation. They are opportunistic feeders with an extremely varied diet. They consume about 25% of their body weight daily. Their diet includes: Olney three-square (Schoenoplectus amercianus, formerly Scirpus olneyi), saltmarsh hay (Spartina patens), and smooth cordgrass (Spartina alterniflora), which are major components of the marshes of Dorchester County including Blackwater National Wildlife Refuge (NWR). Nutria also eat crops, lawn grasses, and ornamentals adjacent to aquatic habitats.

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What problems are caused by nutria?

As non-native species in Maryland, nutria have negative impacts on our marshes because:

  • They have high reproductive capacity.
  • They have no natural predators in Maryland.
  • They feed primarily on marsh plants, creating open water and removing habitat for native species, especially muskrat and waterfowl.

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How has their population increased?

With no natural predators to help control population growth, nutria populations in Maryland have grown rapidly. Population estimates on the inhabited 10,000 acres of Blackwater National Wildlife Refuge have grown from about 250 animals in 1968 to the most recent estimate of between 35,000 and 50,000 animals. At Tudor Farms, a 6,000-acre private wildlife management area adjacent to the refuge, population estimates between 1995 and 1998 were estimated at 17,000 to 24,000 animals. Ecologists believe that random commercial trapping has been unable to decrease the nutria population in these areas over the past decade because harvest rates have remained between 5,000 to 10,000 nutria on each area every year.

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Exposed marsh. Credit: USFWS

How have the nutria damaged the marsh?

Nutria feed primarily on marsh vegetation that extends above the waterline. Nutria use their beaver-sized incisors and powerful forefeet to dig under the marsh surface to feed directly on the root mat, leaving the marsh pitted with holes and deep swim canals. Areas devoid of vegetation are called "eat outs" and the swim canals are called "runs." Blackwater National Wildlife Refuge has lost about 8,000 acres of Olney three-square bulrush, a preferred food choice of nutria, since 1938; 53% of the remaining marsh is considered to be in unhealthy condition and is likely to be lost in the future. Nutria are a primary force in accelerating marsh loss in the Blackwater basin by attacking the very structure that holds the marsh together, the vegetative root mat. The root mat is especially critical because much of the marsh in the Blackwater basin is a type of floating marsh above a layer of fluid mud. Once the nutria chew through the mat and expose the mud, tidal currents and wave action lead to erosion. The marsh surface sinks and the vegetation is lost to flooding. These areas destroyed by nutria become permanent, open water ponds.

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Nutria exclosure Credit: USFWS

What is the Nutria Exclosure Study?

The objective of the Study, conducted in the early 1990s, was to demonstrate the specific impact of nutria on the marsh in and around the refuge by creating quarter-acre fenced areas that excluded nutria but allowed other animals to enter. These were located randomly in the marsh. After several growing seasons, the vegetation within the exclosures recovered, but vegetation in unfenced control plots continued to decline. This finding provides scientific evidence that nutria are directly instrumental in marsh loss in and around the refuge, and it establishes that the marsh has some limited capability to recover in the absence of nutria. The preliminary conclusion is that areas heavily damaged by nutria are also highly vulnerable to tidal erosion which lowers the marsh surface and prevents new vegetation from growing.

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What are the nutria's impacts on other species?

Marsh loss removes habitat for native wildlife species, such as waterfowl, wading birds, and muskrats. Healthy marshes also function as sediment/nutrient filters, contributing to the maintenance of clean water, and serve as nurseries for young crabs and fish. Three-square bulrush (Scirpus olneyi) is an especially valuable food resource for wintering waterfowl. The loss of this plant removes it as food for these birds and reduces invertebrate populations, which migrating waterfowl also feed on. The swim channels through the marsh also permit the saltwater tidal flooding of many isolated, interior ponds that support submerged aquatic vegetation. The increase in salinity and turbidity limits the growth of submerged aquatic vegetation, important for making dissolved oxygen and serving as food and shelter for many native species. Submerged aquatic vegetation is an important food source for migrating and wintering waterfowl, especially American Black ducks, a species of priority concern in the Atlantic Flyway. Some investigators reported that nutria have negatively affected native muskrat populations. Where the larger, more aggressive nutria have become abundant, the muskrat have declined due to competitive displacement. Maryland has lost over 73% of its original wetlands, making the remaining wetlands vital to maintaining the health of the Chesapeake Bay ecosystem. Unfortunately, large expanses of Maryland's marshes are being degraded by nutria.

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What are we going to do about the nutria?

Maryland has a team of federal, state and private agencies and organizations working on the Maryland Nutria Project, which has two phases. In 1998, a proposal for a pilot project (Phase I) to study Maryland's Eastern Shore population of nutria and test trapping strategies was submitted to Congress for funds by a partnership of federal and state agencies and private partners working together. Funds were received and Phase I was conducted from 1999 through mid-2002.

Key components of the pilot program were:

  • Research to determine population size, physiological status, and behavior
  • Restoration of wetlands
  • Public education and outreach
  • Testing of trapping strategies¬†

In Phase II of the Nutria Project, begun in mid-2002, experience and data from Phase I is being applied to the greatest extent possible to a systematic eradication effort across the entire acreage of the study sites: Blackwater National Wildlife Refuge and adjacent Fishing Bay Wildlife Management Area (state) and Tudor Farms (private). Phase II is designed to test the hypothesis that nutria can be eradicated on the Delmarva Peninsula.

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What research has been done on the population?

In Phase I, six experimental areas were chosen on these study sites. All trapping at this stage was live and all animals, except those used to study the population's overall health and reproductive status of individuals, were released with either tags for recapture to estimate populations or radio collars or transmitters to study their behavior. Nutria were marked to generate population estimates. Radio-telemetry was used to obtain data on nutria movements, behavior, and life history information essential in developing a successful eradication program. Reproductive physiology has been and will continue to be studied to assist biologists in control efforts.

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Nutria eradication or control?

In Phase II of the project, a combination of different traps and trapping strategies are being used to control nutria. A variety of trapping methods will be compared to determine trap effectiveness and to maximize the number of nutria captured. Progressive and systematic trapping will be used to cover the entire area under study. Forty-acre grids have been measured across the entire refuge and adjacent lands and trapping specialists from the U.S. Department of Agriculture's Wildlife Services are systematically setting and checking traps in one sweep across a grid. Second sweeps will be made in randomly chosen trapped sites, and surveys will be conduced in these areas to listen for nutria calls and to find evidence of recent nutria activity. In this way, biologists hope to determine whether or not it is possible to eradicate nutria in this peninsula population. This process will take two to five years.

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What about wetlands restoration?

Also during Phase II of the project, an initial test is being run at the refuge on both the planting of Olney three-square bulrush and the spraying of sediment to raise the eroded planting surface in the marsh destroyed by nutria. This testing will help managers assess the feasibility and cost of restoring these marshes.

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How are we educating the public?

A variety of communication tools have been used to cultivate an understanding, nationally and locally, of the impact nutria are having on Maryland's marshes. The project has been covered by local and state news media many times over the past four years, as well as on the Discovery Channel, the National Geographic Channel, and CNN. Presentations on the project have been made by biologists before a wide variety of audience.

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What is the Partnership?

A critical element to the success of this project lies in the close partnership between several key government agencies: The U.S. Fish and Wildlife Service, the U.S. Department of Agriculture, the U.S. Geological Survey, the U.S. Army Corps of Engineers, the Maryland Department of Natural Resources, and the University of Maryland Eastern Shore. These agencies work on a "management team" to move the project forward and to keep a host of other partner organizations (26 in total) informed on its progress. This partnership works together to obtain necessary financial and other support for the project on a continuing basis. This partnership and the nutria project serve as a model for similar projects in the 15 other states impacted by nutria.

For more information about nutria contact:

U.S. Fish and Wildlife Service:
Mike Slattery (410) 573-4580

MD Department of Natural Resources:
Edith R. Thompson (410) 260-8555

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What's the latest news concerning the eradication/control efforts?

On Nov. 17, 2004, the Washington Post reported that the Blackwater Refuge staff and their partners had eradicated the destructive nutria from Blackwater Refuge. With continued vigilance, Maryland wildlife authorities should be able to keep nutria out of the Refuge and allow the marshes to recover. Read the Post article for more details: Blackwater Refuge Now Nutria-Free.

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Last updated: September 30, 2010