Nutria 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 5 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.
Where are Nutria
Nutria inhabit fresh and brackish marshes, rivers, bayous, farm ponds, freshwater impoundments, drainage canals, swamps and various other types of wetlands. Although found in 16 U.S. states, nutria are native to South America. Their original range includes Argentina, Chile, Bolivia, Uruguay, Paraguay and southern Brazil. Due to 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 1940's because fur prices fell and nutria did not reproduce well in captivity. Many nutria were released into the wild.
Nutria have been 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.
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 48 hours after giving birth.
Litters average four to five young. However, nutria can have up to 13 young per litter and may have 3 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 8 weeks. Within 5 days of life, nutria can survive away from the mother.
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
Problems Caused by
As non-native species in Maryland, nutria have negative impacts on our marshes because:
1. They have high reproductive capacity.
2. They have no natural predators in Maryland.
3. They feed primarily on marsh plants, creating open water and removing habitat for native species, especially muskrat and waterfowl.
With no natural predators to help control population growth, nutria populations in Maryland have grown rapidly. Population estimates on 10,000 acres of Blackwater National Wildlife Refuge grew from about 250 animals in 1968 to an estimate of between 35,000 and 50,000 on 24,000 acres in 1998. 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 was unable to decrease the nutria over the past decade, because harvest rates remained between 5,000 to 10,000 nutria on each property every year.
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 7,000 acres of Olney three-square bulrush, a preferred food choice of nutria, since 1938; 53% of the remaining marsh was considered to be in unhealthy condition and likely to be lost in the future. Nutria were 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 became permanent, open water ponds.
A study, conducted in the early 1990's, demonstrated 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. After several growing seasons, the vegetation within the exclosures recovered, but vegetation in unfenced control plots continued to decline. This finding provided scientific evidence that nutria were directly instrumental in marsh loss in and around the Refuge, and it established that the marsh has some limited capability to recover in the absence of nutria.
Nutria 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. They also 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 salt water, 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 effected native muskrat populations. Where the larger, more aggressive nutria had become abundant, the muskrat 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.
In 1938, 20 individual nutria were introduced into Louisiana and within 20 years, the nutria population exceed 20 million animals. By 1962, the nutria had replaced the native muskrat as the leading furbearer in Louisiana.
What are We Going to Do?
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:
1. Research to determine population size, physiological status, and behavior
2. Restoration of wetlands
3. Public education and outreach
4. Testing of trapping strategies
In the second Phase 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. Progressive and systematic
trapping will be used to cover the entire area under study. This process will take two to five years.
Nutria Eradication or Control?
In the second phase 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 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.
During the second phase of the project, an initial test was 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. With the eradication of most of the nutria on Blackwater Refuge and continued efforts to monitor these areas, the new marsh restoration plantings have prospered.
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. This partnership and the nutria project serve as a model for similar projects in the 16 other states impacted by nutria.
For more information about nutria
U.S. Fish and Wildlife Service,
Mike Slattery (410) 573-4580
Glenn Carowan ( ) (410) 228-2692
MD Department of Natural Resources
Edith R. Thompson (410) 260-8555
Steve Kendrot (410-221-7857)