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
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?
Credit: USFWS
Adult Nutria
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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.
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.
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.
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.
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.
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.
How have the nutria damaged the marsh?
Credit: USFWS
Nutria Destruction
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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.
What is the Nutria Exclosure Study?
Credit: USFWS
Nutria Exclosure
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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.
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.
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.
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.
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.
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.
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.
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
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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