NIAES APASD

Home What is APASD? How to use APASD? What's new? Copyright Link
Details of data
Country or region name   Japan
Organism group   mammal
Order name   Rodentia
Family name   Myocastoridae
Species name   Myocastor coypus
English common name   nutria
Substantially same species (synonym)  
Year of invasion or detection   1939
Native region   South America
Situation of establishment   Category 4: Settled after 1951, but not distributed all over the country
Taxonomic description
 
Expansion of distribution area
  The nutria was introduced in Okayama Prefecture during and after World War II to provide a source of fur. However, the nutria escaped into surrounding fields through broken fences or after the boom in rearing this species ended and the animals were abandoned. The escaped nutria became established around reclaimed land near Kojima Bay because the area provides very good conditions for this species: the habitat is warm, and there are many creeks with abundant aquatic plants.

The escaped nutria expanded their distribution around Okayama Prefecture during the 1970s (Miura, 1976). The escaped nutria have now expanded into the Okayama, Hyogo, Hiroshima, Gifu, Kyoto, Aichi, and Mie Prefectures. This expansion was estimated to represent secondary dispersal and increased the population that became established for the first time in the original habitat around the reclaimed land (Miura, 1994). It was reported that thus an original habitat existed in Gifu Prefecture too, which the expansion started (Okada et al., 1988).

Nutria suffer easily from frostbite, and amputation of the tip of the tail and of the legs is observed with high frequency at cold latitudes. As a result, they cannot inhabit regions where the water freezes.

Nutria live around slowly flowing rivers, in ponds, and in marshes, and seldom moves farther than 10 m from the water. They burrow their nests into the banks. They are usually nocturnal, and rest in their nests during the day. The burrows of nutria are complicated, with many branching tunnels, and sometimes reach lengths of more than 10 m. In winter, they construct floating nests on the water by gathering aquatic plants together; these structures are called "platforms", and the nutria often rest on them. The platforms typically range between 30 and 100 cm in diameter. The platform's surface is flattened, and often contains food residues and feces; the latter, which are sausage-shaped, are commonly observed on the platforms. The presence of platforms is a sure sign that an area is inhabited by nutria (Miura, 2002).

Environmental impact
  The impact of the nutria on riparian vegetation has been heavy because they eat the roots and rhizomes of these plants as part of their staple food. There have also been impacts on bivalve populations.

1) Simplification of the riparian flora

It is known that at least one aquatic plant, Trapa japonica, has been fed upon extensively by nutria and has vanished from certain areas. As a result, populations of residual plants that remain after browsing, such as the sweet flag (Acrus calamus), have increased as a result of increased room in which to grow. Such changes have simplified the riparian flora into less-diverse communities (Mori, 2003).

2) Predation on Anodonta woodiana (a bivalve)

It has been reported that nutria consume many Anodonta woodiana in agricultural reservoirs in Okayama Prefecture (Mori, 2002). Predation by nutria on freshwater bivalves has also been reported in England (Gosling, 1991). Because A. woodiana in ponds provides a bed for oviposition by freshwater fish and performs mass filtration of organic matter in the water, this predation may have grave consequences for the region's aquatic ecology.

Economic damage
  Nutria also cause damage by eating rice plants and vegetables grown around wetlands, and can cause safety problems around stream banks because of their habit of burrowing into these banks, leading to occasional collapses of stream banks.
Reproduction
  Reproduction is observed all year round. Nutria have no specific reproductive season; they are polyestrous and can potentially bear offspring two to three times in a year. Pregnant females of wild populations in Okayama Prefecture have been caught year-round. Nutria are mammals, with copulation-induced ovulation, and their pregnancy period is normally 127 to 132 days. The average number of babies per litter is about five. The number of fetuses averaged 5.87 in a wild population in Okayama Prefecture (Miura, 1994).
Growth
  Nutria are large aquatic rodents native to South America, and adults reach weights of more than 10 kg. They have forms adapted to an aquatic life, such as small, round ears, webbed hind legs, and female dugs arranged somewhat towards the back to help the babies suckle while in the water.

The birth weight of nutria is ca. 225 g, and the weight of the young increases by ca. 300 g each month, and can reach more than 5 kg after 20 months in captivity. The period until sexual maturity is estimated at 3 to 4 months for babies born in the summer, versus 6 to 7 months for babies born in the autumn (Miura, 1994). Nutria are sensitive to cold, and their mortality is highest in winter. The greatest longevity that has been observed in captivity is more than 10 years. If we accept the method for estimated ages based on the presence of cementum layers in the teeth, the greatest longevities in wild populations in Okayama Prefecture are 8 years for males and 11 years for females. Miura (1994) estimated that 60% of this wild population was younger than 1 year old.

Countermeasure
  Nutria can be efficiently prevented from invading agricultural and other areas by means of wire fences erected around rivers and ponds. However, this method is expensive and requires ongoing maintenance of the fences. A more effective approach may be to alter their habitat by removing important food species such as aquatic plants.

However, because nutria is an exotic species in Japan, it would be preferable to eradicate them. Nutria were designated as a species subject to hunting in 1963 in Japan, and their numbers have been controlled not only during an open season but also during a closed season based on Japanese laws on wildlife preservation and hunting. As nutria feed mostly at night, and hunting with guns is not permitted at night, the pressure exerted on populations of nutria by hunting is generally low.

Instead, nutria can be caught easily using box-type wire live-traps (30 x 40 x 75 cm) baited with carrots (Miura, 1992). As a result, such traps should be used whenever it is necessary to remove nutria in a hurry. Poisonous baits such as zinc phosphide are frequently used to control nutria in the West, where poisoned carrots are set on the floating platforms. For example, the eradication of nutria is conducted using this method in England (Miura, 2002).

Writer's name and affiliation
  ©Mori, I. Okayama Pref. Nature Conservation Center (Written in January 2005)

Similar species : 2
Organism group   mammal
Order name   Carnivora
Family name   Mustelidae
Species name   Lutra lutra
English common name   Eurasian otter
Substantially same species (synonym)  
Possibility of producing hybrids   No
Details  

Organism group   mammal
Order name   Carnivora
Family name   Mustelidae
Species name   Ondatra zibethicus
English common name   muskrat
Substantially same species (synonym)  
Possibility of producing hybrids   No
Details  

Host species : 1
Organism group   mammal
Order name   Carnivora
Family name   Mustelidae
Species name   Ondatra zibethicus
English common name   muskrat
Substantially same species (synonym)  

Photos of alien and similar species and damage : 12
No. Kind of Photo Photo Name of copyright holder and explanation of photo
1 Alien species mc1   © Okayama Pref. Nature Conservation Center. A nutria eating the bivalve, Anodonta wooiana..
2 Alien species mc2   © Okayama Pref. Nature Conservation Center. A swimming nutria.
3 Alien species mc3   © Okayama Pref. Nature Conservation Center. Waterside nests of nutria.
4 Alien species mc4   © Okayama Pref. Nature Conservation Center. Big and sharp incisors of nutria.
5 Alien species mc5   © Okayama Pref. Nature Conservation Center. Feces of nutria.
6 Alien species mc6   © Okayama Pref. Nature Conservation Center. Footprints of nutria.
7 Damage mc7   © Okayama Pref. Nature Conservation Center. Damages of rice plants by nutria.
8 Damage mc8   © Okayama Pref. Conservation Center. Zizania latifolia fallen down by nutria.
9 Damage mc9   © Okayama Pref. Nature Conservation Center. A lot of Zizania latifolia cut by nutria.
10 Damage mc10   © Okayama Pref. Nature Conservation Center. The kerf of Zizania latifolia caused by nutria.
11 Damage mc11   © Okayama Pref. Nature Conservation Center. Eaten and littered Sparganium crectum by nutria.
12 Damage mc12   © Okayama Pref. Nature Conservation Center. Leftover bivalves, Anodonta woodiana.

Reference : 8
1   Author   Gosling L.M. & Baker S.J.
Year   1991
Title   Coypu Myocastor coypus.
Magazine   The Handbook of British Mammmals (eds. G. B.Corbet and S. Harris).
Volume   Published for the mammal society by blackwell scientific publications.
Number  
Page   267-275
Summary  
Key Word   nutria, Myocastor coypus
PDF  

2   Author   Miura S.
Year   1976
Title   Dispersal of nutria in Okayama prefecture (In Japanese with English summary)
Magazine   J. Mamm. Soc. Japan
Volume   6
Number  
Page   231-237
Summary  
Key Word   nutria, dispersal, Okayama, establishment
PDF  

3   Author   Miura S.
Year   1992
Title   Trapping methods of nutria (In Japanese)
Magazine   Mammalian science
Volume   31
Number   2
Page   145-146
Summary  
Key Word   nutria, trapping method
PDF  

4   Author   Miura S.
Year   1994
Title   Nutria. (In Japanese)
Magazine   Data on Japanese rare wild species.
Volume   Ed. Suisantyou.
Number   Published by Nihon suisan shigen hogo kyoukai.
Page   539-546
Summary  
Key Word   nutria, rare species
PDF  

5   Author   Miura, S.
Year   2002
Title   Nutria. (In Japanese)
Magazine   Handbook of countermeasures for the damages caused by birds and animals.
Volume   Eds. Eguchi, Y., Miura, S. and Hujioka, M.
Number   Published by Japan Plant Protection Association.
Page   88-89
Summary  
Key Word   nutria, countermeasure, damage, animal, bird
PDF  

6   Author   Mori, I.
Year   2002
Title   A mass predation of unionid clams (Anodonta woodiana) by the feral nutria population.(In Japanese with English summary)
Magazine   Bull. of Okayama Pref. Nature Conservation Center
Volume   11
Number  
Page   49-58
Summary  
Key Word   nutria, predation, unionid clam, Anodonta woodiana
PDF  

7   Author   Mori, I.
Year   2003
Title   Feeding traces of coypu in the Okayama Prefectural Nature Conservation Center. (In Japanese with English summary)
Magazine   Bull. of Okayama Pref. Nature Conservation Center
Volume   11
Number  
Page   49-58
Summary  
Key Word   nutria, feeding
PDF  

8   Author   Okada, A., Tatsuzawa, S. and Murakami, O.
Year   1998
Title   Changes in distribution of nutria (Myocastor coypus) in Gifu prefecture. (In Japanese)
Magazine   Kansai shizen-hogo kikou kaihou
Volume   20
Number   2
Page   77-81
Summary  
Key Word   nutria, distribution, Gifu prefecture
PDF  

Habitat : 2
No. Habitat
1   pond/lake/river/riparian
2   riverside and swamp

back


Copyright (C) 2007 National Institute for Agro-Environmental Sciences. All rights reserved.