Japanese spurdog

Japanese spurdog
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: Squaliformes
Family: Squalidae
Genus: Squalus
Species:
S. japonicus
Binomial name
Squalus japonicus
Ishikawa, 1908
Range of the Japanese spurdog (in blue)

The Japanese spurdog (Squalus japonicus) is a dogfish, a member of the family Squalidae. It is found in the western Pacific Ocean – southeastern Japan and the East China Sea,[2] including the Republic of Korea, the Philippines, and the Arafura Sea.[3] It occurs in temperate and tropical waters along the continental shelf and slopes[4] and primarily feeds on teleost fish and squid.[2] It is caught as bycatch in commercial fishing, which has caused populations to decline.[5]

Description

Males measure 50 to 70 cm (19.7 to 27.6 in) long in adulthood, while females measure 56 to 80 cm (22 to 31.5 in) long.[5] Females are also higher in weight than males.[2] They have 25 to 27 teeth on their upper jaw and 20 to 24 teeth on their lower jaw.[4]

Distribution and habitat

The Japanese spurdog is found in the Pacific Ocean, in southeast Japan, China, North Korea, South Korea, and Taiwan.[5][4] Additionally, there is one record of S. japonicus being caught in a trawl net in the Arafura Sea, between Australia and Western New Guinea.[3] It is a demersal species, found on the continental shelf and upper slope[4] at depths of 52 to 400 m (170.6 to 1312 ft).[5]

Reproduction

They are viviparous, giving birth to between 2 and 8 pups each litter.[4] The pups are 19 to 30 cm (7.5 to 11.8 in) long at birth.[4] Gestation is 11 to 12 months[5] and they reproduce annually.[4] A study in the East China Sea found an equal sex ratio of both embryos and adults.[2]

Conservation

The Japanese spurdog is listed on the IUCN Red List as Endangered.[5] Populations in Japan have been stable since 1983, but shark abundance elsewhere in its range has been in decline since the middle of the twentieth century.[5] It is believed that S. japonicus abundance has declined in those areas as well.[5]

Its major threat is commercial fishing. Though not a commercial product itself, it is caught as bycatch in demersal fishing and used for meat or fish meal.[4]

References

  1. ^ Rigby, C.L.; Chen, X.; Ebert, D.A.; Herman, K.; Ho, H.; Hsu, H.; Zhang, J. (2020). "Squalus japonicus". IUCN Red List of Threatened Species. 2020: e.T161433A124484752. doi:10.2305/IUCN.UK.2020-3.RLTS.T161433A124484752.en. Retrieved 18 November 2021.
  2. ^ a b c d Yano, Toshikazu; Ohshimo, Seiji; Sakai, Takeshi; Yoda, Mari (2020). "Filling gaps in the biology and habitat use of two spurdog sharks (Squalus japonicus and Squalus brevirostris) in the East China Sea". Marine and Freshwater Research. 71 (12): 1719. doi:10.1071/MF19131. ISSN 1323-1650.
  3. ^ a b Russell, Barry C.; Houston, Wayne (1989). "Offshore fishes of the Arafura Sea". The Beagle, Records of the Northern Territory Museum of Arts and Sciences. 6 (1): 69–84.
  4. ^ a b c d e f g h Ebert, David A.; Fowler, Sarah; Dando, Marc (2021). Sharks of the world: a complete guide. Princeton: Princeton University Press. ISBN 978-0-691-20599-1.
  5. ^ a b c d e f g h IUCN (2019-08-30). Squalus japonicus: Rigby, C.L., Chen, X., Ebert, D.A., Herman, K., Ho, H., Hsu, H. & Zhang, J.: The IUCN Red List of Threatened Species 2020: e.T161433A124484752 (Report). International Union for Conservation of Nature. doi:10.2305/iucn.uk.2020-3.rlts.t161433a124484752.en.
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