The IUCN Red List of Threatened Species™
ISSN 2307-8235 (online)
IUCN 2008: T41656A45214163
Mustela itatsi, Japanese Weasel
Assessment by: Kaneko, Y., Masuda, R. & Abramov, A.V.
View on www.iucnredlist.org
Citation: Kaneko, Y., Masuda, R. & Abramov, A.V. 2016. Mustela itatsi. The IUCN Red List of
Threatened Species 2016: e.T41656A45214163. http://dx.doi.org/10.2305/IUCN.UK.20161.RLTS.T41656A45214163.en
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THE IUCN RED LIST OF THREATENED SPECIES™
Taxonomy
Kingdom
Phylum
Class
Order
Family
Animalia
Chordata
Mammalia
Carnivora
Mustelidae
Taxon Name: Mustela itatsi Temminck, 1844
Synonym(s):
• Mustela sibirica ssp. itatsi Temminck, 1844
Common Name(s):
• English:
Japanese Weasel
Taxonomic Notes:
Abramov (2000a, 2000b), based on morphotypic characteristics of the skull, body size, coloration and
baculum, positioned Japanese Weasel Mustela itatsi as a species distinct from Siberian Weasel M.
sibirica, of which it was formerly generally considered a subspecies (but see Graphodatsky et al. 1976).
Suzuki et al. (2011) documented interspecific and sexual differences in the skulls between M. itatsi and
M. sibirica, which together with trenchant genetic differences (Kurose et al. 2000, Masuda et al. 2012)
strongly support treatment as two species.
Assessment Information
Red List Category & Criteria:
Near Threatened ver 3.1
Year Published:
2016
Date Assessed:
March 3, 2015
Justification:
Although Japanese Weasel is widespread geographically in Japan, it is listed as Near Threatened because
it has recently retreated from much of western Japan: specifically, it has disappeared from much of the
lowlands, which are now occupied by the introduced Siberian Weasel Mustela sibirica. This latter has
already colonised 20 of 46 prefectures of three main islands, and although there the rate of population
decline has not been quantified, it is plausible that it warrants Near Threatened categorisation under
A2, A3 and A4 (a decline of about 25% over the last three generations, which is anticipated to continue
for the next three, with the continued range expansion of Siberian Weasel.
Previously Published Red List Assessments
2008 – Least Concern (LC) – http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T41656A10530315.en
2003 – Not Evaluated (NE)
Geographic Range
Range Description:
Japanese Weasel is endemic to Japan, occurring naturally on Honshu, Kyushu, Shikoku, Sado, the Oki
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
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Islands, Izu-Oshima, Awaji, Shoudo, Iki, the Goto Islands, Yaku and Tane. It was introduced to Hokkaido
in the 1880s (Inukai 1934) and, for the control of rats Rattus norvegicus and field mice Apodemus
speciosus, to about 50 small islands in Japan, including Rishiri, Rebun, the Izu Islands (Miyake, Hachijo,
Aogashima), Aoshima (Nagasaki Prefecture), Kuchino, Nakano, Suwanose, Hira, Akuseki, Kikai,
Okinoerabu, Yoron (Kagoshima Prefecture), Zamami, Aka, Minami-Daito, Kita-Daito, Irabu, Iriomote, and
Hateruma (Okinawa Prefecture) (Shiraishi 1982). It is disappearing from lowlands in the western part of
Japan (Sasaki et al. 2014). It was introduced to southern Sakhalin Island (Russia) in 1932, but there are
no reliable records from there since 1980 (Tumanov 2009) and it has probably now disappeared (A.V.
Abramov pers. comm. 2015). It has been found from sea-level to 336 m (Y. Kaneko pers. comm. 2014).
Country Occurrence:
Native: Japan
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
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Distribution Map
Mustela itatsi
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
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Population
The native global population of Japanese Weasel is in decline because it is disappearing from lowlands
in the western part of Japan (Sasaki et al. 2014).
Current Population Trend: Decreasing
Habitat and Ecology (see Appendix for additional information)
Japanese Weasel occurs in in most habitats across Japan, including grasslands, forests, villages, and
suburbs, but not, typically, in big cities (H. Sasaki pers. comm. 2006). Sometimes it lives near human
settlements and can attack chickens (A.V. Abramov pers. comm. 2014). Rodents, insects, amphibians and
reptiles make up the main part of its diet (H. Sasaki pers. comm. 2006). It shows the largest sexual size
dimorphism in the genus (females are only 68% the body length of males, and only 30% in body weight;
Masuda and Watanabe 2009). This causes sexual segregation in the choice of food items: males are
more specialists of mammals and crustaceans, whilst females are generalists consuming diverse food
such as insects, earthworms and fruits (Kaneko et al. 2013).
Systems: Terrestrial
Use and Trade
The wide introduction of Japanese Weasel to parts of Japan to which it is not native, and to Sakhalin
(Russia) were driven by its perceived value as a predator of rodent pests. It was formerly bred in farms
(Masuda and Watanabe 2009). Males sometimes are hunted as a game animal (Masuda and Watanabe
2009).
Threats (see Appendix for additional information)
Japanese Weasel does not tolerate urbanisation and does not use artificial food (Kaneko et al. 2009,
Okawara et al. 2014). The small female Japanese Weasels might have difficulty breeding in lowland
western Japan, through competition with the introduced Siberian Weasel Mustela sibirica, and have
now retreated to hill areas in this part of Japan (Abe 2005, Sasaki et al. 2014). It is also possible that
even without the introduced potential competitor the species would have been insufficiently adaptable
to the wide variety of anthropogenic impacts in this part of Japan (A.V. Abramov pers. comm. 2014).
Japanese and Siberian Weasels are phylogenetically close, raising the possibility that they might
hybridise; however, Masuda et al. (2012 found no morphologically intermediate individuals among 15
Siberian Weasels from northern Kyushu, Shikoku and western Honshu, suggesting that hybridisation
might not be a threat.
Conservation Actions (see Appendix for additional information)
In Japan, female Japanese Weasels are protected from hunting by law (H. Sasaki pers. comm. 2006). The
species is ranked as 'near threatened' in the Red List of 10 prefectures in the western Japan (Sasaki et al.
2014).
Credits
Assessor(s):
Kaneko, Y., Masuda, R. & Abramov, A.V.
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
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Reviewer(s):
Duckworth, J.W. & Schipper, J.
Contributor(s):
Wozencraft, C
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
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Bibliography
Abe, H., Ishii, N., Ito, T., Kaneko, Y., Maeda, K., Miura, S. and Yoneda, M. 2005. A Guide to the Mammals
of Japan. Tokai University Press, Kanagawa, Japan.
Abramov, A.V. 2000a. The taxonomic status of the Japanese Weasel, Mustela itatsi (Carnivora,
Mustelidae). Zoologicheskii Zhurnal 79: 80–88. (in Russian with English abstract).
Abramov, A.V. 2000b. A taxonomic review of the genus Mustela (Mammalia, Carnivora). Zoosystematica
Rossica 8: 357–364.
Graphodatsky, A.S., Volobuev, V.T., Ternovsky, D.V. and Radjabli, S.I. 1976. G-banding of the
chromosomes in seven species of Mustelidae (Carnivora). Zoologicheskii Zhurnal 55: 1704–1709.
Inukai, T. 1934. The invasion and use of weasels in Hokkaido, Shokubutu oyobi Doubutu. 2(3): 13091317.
IUCN. 2016. The IUCN Red List of Threatened Species. Version 2016-1. Available at: www.iucnredlist.org.
(Accessed: 30 June 2016).
Kaneko, Y., Shibuya, M., Yamaguchi, N., Fujii, T., Okumura, T., Matsubayashi, K. and Hioki, Y. 2009. Diet of
Japanese Weasels (Mustela itatsi) in a suburban landscape: implications for year-round persistence of
local populations. Mammal Study 34: 97–106.
Kaneko, Y., Yamazaki, K., Watanabe, S., Kanesawa, A. and Sasaki, H. 2013. Notes on stomach contents of
Japanese Weasels (Mustela itatsi) in Ibaraki, Japan. Mammal Study 38: 281–285.
Kurose, N., Abramov, A.V. and Masuda, R. 2000. Intrageneric diversity of the cytochrome b gene and
phylogeny of Eurasian species of the genus Mustela (Mustelidae, Carnivora). Zoological Science 17:
673–679.
Masuda, R. and Watanabe, S. 2009. Mustela itatsi Temminck, 1844. In: S.D. Ohdachi, Y. Ishibashi, M.A.
Iwasa and T. Saitoh (eds), The wild mammals of Japan, pp. 240–241. Shoukadoh, Kyoto, Japan.
Masuda, R., Kurose, N., Watanabe, S., Abramov, A.V., Han, S.H., Lin, L.K. and Oshida, T. 2012. Molecular
phylogeography of the Japanese Weasel, Mustela itatsi (Carnivora: Mustelidae), endemic to the
Japanese islands, revealed by mitochondrial DNA analysis. Biological Journal of the Linnean Society 107:
307–321.
Okawara, Y., Sekiguchi, T., Ikeda, A., Miura, S., Sasaki, H., Fujii, T. and Kaneko, Y. 2014. Food habits of the
urban Japanese Weasels Mustela itatsi revealed by faecal DNA analysis. Mammal Study 39: 155–161.
Sasaki, H., Ohta, K., Aoi, T., Watanabe, S., Hosoda, T., Suzuki, H., Abe, M., Koyasu, K., Kobayashi, S., Oda,
S. 2014. Factors affecting the distribution of the Japanese Weasel Mustela itatsi and the Siberian Weasel
M. sibirica in Japan. Mammal Study 39: 133–139.
Shiraishi, S. 1982. Rat control by weasels. Saisyu to Shiiku 44(9): 414-419.
Suzuki, S., Abe, M. and Motokawa, M. 2011. Allometric comparison of skulls from two closely related
weasels, Mustela itatsi and M. sibirica. Zoological Science 28: 676–688.
Tumanov, I.L. 2009. Rare carnivorous mammals of Russia (small and middle-sized species). Branko, Saint
Petersburg, Russia.
Citation
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
6
Kaneko, Y., Masuda, R. & Abramov, A.V. 2016. Mustela itatsi. The IUCN Red List of Threatened Species
2016: e.T41656A45214163. http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
Disclaimer
To make use of this information, please check the Terms of Use.
External Resources
For Images and External Links to Additional Information, please see the Red List website.
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
7
Appendix
Habitats
(http://www.iucnredlist.org/technical-documents/classification-schemes)
Habitat
Season
Suitability
Major
Importance?
1. Forest -> 1.4. Forest - Temperate
-
Suitable
-
3. Shrubland -> 3.4. Shrubland - Temperate
-
Suitable
-
4. Grassland -> 4.4. Grassland - Temperate
-
Suitable
-
14. Artificial/Terrestrial -> 14.1. Artificial/Terrestrial - Arable Land
-
Marginal
-
14. Artificial/Terrestrial -> 14.2. Artificial/Terrestrial - Pastureland
-
Marginal
-
14. Artificial/Terrestrial -> 14.3. Artificial/Terrestrial - Plantations
-
Marginal
-
14. Artificial/Terrestrial -> 14.4. Artificial/Terrestrial - Rural Gardens
-
Suitable
-
Threats
(http://www.iucnredlist.org/technical-documents/classification-schemes)
Threat
Timing
Scope
Severity
Impact Score
1. Residential & commercial development -> 1.1.
Housing & urban areas
Ongoing
Minority (50%)
Negligible declines
Low impact: 4
Stresses:
1. Ecosystem stresses -> 1.1. Ecosystem conversion
1. Ecosystem stresses -> 1.2. Ecosystem degradation
Ongoing
Minority (50%)
Stresses:
2. Species Stresses -> 2.3. Indirect species effects ->
2.3.2. Competition
8. Invasive and other problematic species, genes &
diseases -> 8.1. Invasive non-native/alien
species/diseases -> 8.1.2. Named species (Mustela
sibirica)
Slow, significant
declines
Low impact: 5
Conservation Actions in Place
(http://www.iucnredlist.org/technical-documents/classification-schemes)
Conservation Actions in Place
In-Place Land/Water Protection and Management
Occur in at least one PA: Yes
Research Needed
(http://www.iucnredlist.org/technical-documents/classification-schemes)
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
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Research Needed
1. Research -> 1.2. Population size, distribution & trends
1. Research -> 1.3. Life history & ecology
3. Monitoring -> 3.1. Population trends
Additional Data Fields
Distribution
Continuing decline in area of occupancy (AOO): Yes
Extreme fluctuations in area of occupancy (AOO): No
Continuing decline in extent of occurrence (EOO): Yes
Extreme fluctuations in extent of occurrence (EOO): No
Continuing decline in number of locations: Yes
Extreme fluctuations in the number of locations: Unknown
Lower elevation limit (m): 0
Upper elevation limit (m): 336
Population
Population severely fragmented: No
Habitats and Ecology
Generation Length (years): 5.3
Movement patterns: Not a Migrant
© The IUCN Red List of Threatened Species: Mustela itatsi – published in 2016.
http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T41656A45214163.en
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The IUCN Red List Partnership
The IUCN Red List of Threatened Species™ is produced and managed by the IUCN Global Species
Programme, the IUCN Species Survival Commission (SSC) and The IUCN Red List Partnership.
The IUCN Red List Partners are: BirdLife International; Botanic Gardens Conservation International;
Conservation International; Microsoft; NatureServe; Royal Botanic Gardens, Kew; Sapienza University of
Rome; Texas A&M University; Wildscreen; and Zoological Society of London.
THE IUCN RED LIST OF THREATENED SPECIES™