Introduced Species Summary Project
Nutria (Myocastor
coypus)
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Common Name: Nutria (also: coypu, coypu rat, swamp beaver, nutria
rat)
Scientific
Name: Myocastor coypus (also: Myopatamus bonariensis)
Classification:
Phylum or Division: Chordata
Class: Mammalia or Sarcopterygii
Order: Rodentia
Family: Echimyidae or
Capromyidae (note: while the nutria exhibits traits of both these
families it is considered distinct enough to be placed in its own subfamily,
see below)
Subfamily: Myocastoridae
Identification: Often
mistaken for the larger beaver (Castor canadensis) or the smaller
muskrat (Odantara zibethicus), this semi-aquatic rodent has brown fur
with a white muzzle and chin. Its
large, orange incisors often emerge from beneath the lips. Unlike the flattened tail of the beaver
and muskrat, nutria have a long rounded tail, which is scaled with some
hair. Front feet are not webbed;
only the four of the five toes of the hind feet are webbed.
Original
Distribution: Native to coastal lakes and marshes of Argentina,
Bolivia, Brazil, Chile, Paraguay and Uruguay
Current Distribution: Coastal
areas in the five U.S. Gulf states, particularly Louisiana. Current population size is unknown but
at the height of the trapping industry, in the mid-1970s, an average of 1.5
million individuals was captured per year..
Site and
Date of Introduction: Nutria are generally thought to
have been first released into the marshes surrounding New Orleans in the 1930s
although the U.S. Geological Survey claims that an earlier population was
brought to California in 1899. Introduced into the U.S. as an
alternative to mink fur, trappers supposedly recaptured the initial Louisiana
population. Tabasco tycoon L.A.
McIlhenny kept a nutria ranch on Avery Island, LA where between 12 and 20
individuals escaped in 1938. 150
additional nutria escaped from this island during a hurricane in 1940.
In
addition to escapees from fur farms, populations have been introduced in the
Gulf states to control vegetation in lakes and ponds.
Mode(s) of Introduction: Imported
from South America for the fur industry.
Reason(s)
Why it has Become Established: Nutria are
very successful procreators.
Sexual maturity may be reached as early as four months of age with an
average age of maturity occurring at eight months. Mating season lasts all year. Females gestate for slightly more than four months and
anywhere between 1 and 11 pups may be born (with an average of 4-6). Females may enter estrous as soon as 24
hours after giving birth.
Nutria have also adapted well to
their new environment because they will eat almost any available terrestrial or
aquatic green plant. The marshes,
swamps and crop fields of their new habitat provide them with an abundant food
source. Described as “eating
machines”, newborn nutria begin feeding on plants within 24 hours of
birth.
Ecological
Role: In their native habitat of South American marshes and
coastal lakes, nutria are well adapted to regular periods of drought and
flood. Their ability to breed
quickly allows their populations to stabilize well after frequent crashes
caused by the drought-flood cycles.
However, without these regular cycles to regulate population size,
nutria numbers quickly grow out of control.
As mentioned above, nutria will
readily consume almost all available plant resources both wild and
cultivated. In marsh areas, they
compete with muskrat and waterfowl populations for food resources. They also have been reported on some of
Mississippi’s barrier islands where they feed on the roots of sea oats. (see Threats, below)
Crops preyed upon by nutria
include rice, sugar cane, and soybeans. Preferred wild species include: three-cornered grass,
cattail, bullwhip, alligator weed and duckweed. Alligators prey upon adult nutria; turtles, gar, snakes,
birds of prey and other swamp animals may eat juvenile nutria.
Benefit(s):
There are no direct benefits from the nutria population in its non-native
habitat. As mentioned above, some
nutria populations were established for the purpose of controlling invasive
aquatic plant populations in lakes in the Gulf region. However, their appetite for local plant
species made their presence more damaging than useful.
In South America, nutria fur is
used commercially. If the fur of
the nutria were to ever catch on in the United States, less mink would need to
be harvested.
Wetlands – The
voracious appetite of nutria for vegetation in wild areas has led to severely
damaged wetlands. By 1998
scientists had placed the total area of damaged wetlands in Louisiana alone at
over 100,000 acres. (Faibisch,
2001)
Barrier Islands - Where
Nutria feed on sea oats, sea dune stability may be threatened.
Wildlife – Recent
declines in muskrat populations have been attributed to competition with nutria
for food resources.
Crops –
Extensive damage has been reported in rice, soybean, and sugar fields both from
direct predation and from damage caused by nutria burrowing.
Parasites and diseases –
Louisiana nutria have been found to carry several diseases, viruses, and
parasites. Most notably, they
carry the nematode Strongyloides myopotami, which can cause a severe
itching rash in people handling nutria.
Control
Level Diagnosis: “Highest Priority”
- Sensitive wetland ecosystems around the Gulf of Mexico
require the highest level of protection.
Besides posing a threat to the numerous plant, animal and insect species
that populate wetlands, degradation of these fragile areas impacts the
surrounding Gulf of Mexico ecosystem.
For example, when nutria remove stabilizing grasses from marsh areas,
soil is washed into the Gulf by tides and by storms. This siltation of Gulf waters then threatens Gulf creatures
and habitats.
Damage to crops and the resulting
impact on the economy of the southeast also should be taken into consideration.
Control Method: Considerable
effort has been spent to encourage the trapping of nutria for fur and, more
recently, meat. While fur
harvesting was the original idea behind the importation of nutria, the demand
for fur is currently low. Fur
trapping peaked in the 1970s when prices were high and the pelts were sold
largely in Germany. During this
period, damage to wetlands and crops markedly decreased. Then in the early 1980s, the demand for
nutria fur plummeted. Prices fell
and trappers sought income elsewhere.
Since then the population has exploded. The Louisiana Department of Wildlife and Fisheries estimates
that one million nutria would need to be captured each year to mitigate the
damage they cause. In 1986, the Louisiana Fur and Alligator Advisory Council
was created in part to develop the market for nutria fur and meat. Current annual harvests average around
350,000, well short of required harvest levels.
To better control the destructive
nutria population, trapping for non-commercial purposes may need to be
considered. State or federal authorities should investigate the
possibility of capture and destruction of nutria individuals in a program
similar to the capture of feral pigs on the island of Hawai'i.
Author: Jessica L. Jenkins
Last Edited: 2/24/02
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Project Editor: James A. Danoff-Burg, Columbia University