Mustela itatsi 

Scope: Global

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Carnivora Mustelidae

Scientific Name: Mustela itatsi
Species Authority: Temminck, 1844
Common Name(s):
English Japanese Weasel
Mustela sibirica ssp. itatsi Temminck, 1844
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 [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2016
Date Assessed: 2015-03-03
Assessor(s): Kaneko, Y., Masuda, R. & Abramov, A.V.
Reviewer(s): Duckworth, J.W. & Schipper, J.
Contributor(s): Wozencraft, C
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:

Geographic Range [top]

Range Description:Japanese Weasel is endemic to Japan, occurring naturally on Honshu, Kyushu, Shikoku, Sado, the Oki 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).
Countries occurrence:
Additional data:
Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:
Continuing decline in extent of occurrence (EOO):YesExtreme fluctuations in extent of occurrence (EOO):No
Continuing decline in number of locations:Yes
Extreme fluctuations in the number of locations:Unknown
Upper elevation limit (metres):336
Range Map:Click here to open the map viewer and explore range.

Population [top]

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
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology: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).
Generation Length (years):5.3
Movement patterns:Not a Migrant

Use and Trade [top]

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 [top]

Major Threat(s): 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 [top]

Conservation Actions: 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).

Citation: Kaneko, Y., Masuda, R. & Abramov, A.V. 2016. Mustela itatsi. The IUCN Red List of Threatened Species 2016: e.T41656A45214163. . Downloaded on 26 October 2016.
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