Japanese spurdog

Japanese spurdog
Conservation status
	; Endangered (IUCN 3.1)
Scientific 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]