Japanese Spurdog

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Common Names: Japanese spurdog, Japanese dogfish, spiny dogfish.

Binomial Name: Squalus japonicus

Family: Squalidae

Identification: A relatively slender bodied dogfish with a long, pointed snout. Small medial barbells on anterior nasal flaps. Body uniformly reddish grey above with no spots. Dorsal fins may be dusky towards apices. First dorsal high with dusky margin. First dorsal fin spine about .5 x length of anterior fin margin. Second dorsal fin smaller with a distinct notch on trailing edge. Second dorsal fin spine about .75 x length of anterior fin margin. Anal fin absent. Caudal fin and pectoral fins have white trailing margins. Caudal may appear dusky in juveniles. Caudal fins of neonates have a dark or black caudal notch. Belly white.

Size: Maximum length 95cm. Length at birth 19-30cm. Length at maturity - males 50-70cm, females 56-80cm.

Habitat: Continental shelf from 52-400m.

Distribution: The Japanese spurdog has a very limited range in the Northwest Pacific Ocean. It is restricted to Japan, Korea and Taiwan. A long-snouted form present in the Philippines has recently been described as a separate species; the Western longnosed spurdog Squalus nasutus.

Behavior: Unknown. 

Reproduction: Ovoviviparous. Litter size from 2-8.

Conservation Status: Listed by the IUCN as 'Data Deficient' but Japanese spurdogs are taken in fisheries off Japan, Taiwan (Province of China) and probably elsewhere throughout their range.There are no species-specific catch data available and the species may be confused with other Squalus species. Squalus japonica may have limiting life history characteristics, similar to other deepwater dogfish, thus will not be sufficiently fecund to withstand high levels of exploitation and there is concern, given that it is apparently fished over large areas of its range. A lack of information on the species’ population size, or any indicator of population trend precludes an assessment beyond Data Deficient at this time. Research is required to ascertain the importance of this species to fisheries and bycatch levels.

Images: Tateyama, Honshu, Japan.

Similar species: The Japanese spurdog shares its range with a number of other dogfish.

1. The shortspine spurdog S.mitsukurii has a proportionately shorter nose, a shorter first dorsal spine, more defined dark/dusky apices on each dorsal, a less defined notch in the trailing edge of the second dorsal fin and a dusky patch around the caudal notch.

2. The Japanese shortnose spurdog S.brevirostris is a more robust species with a much shorter snout.

3. The recently described Taiwan spurdog S.formosus has a shorter snout and a higher, more upright first dorsal fin.

4. The North Pacific spiny dogfish S.suckleyi has a shorter snout, an overall larger size and (usually) small white spots on its back.

5. Blainville's dogfish S.blainville

Reaction to divers: Rarely if ever encountered by divers. Likely, this species would flee if approached by divers unless bait is used.

Diving logistics: The Japanese spurdog lives beyond recreational limits. The shallowest records of this species are from Suruga Bay on the south side of Honshu Island, Japan. Appropriately trained technical divers may be able to bait this species in at 50m+. There are a number of dive shops on the Izu Peninsula that run trips to dive sites in Suruga Bay.

References and citations: 

Tanaka, S. & McCormack, C. 2009. Squalus japonicus. The IUCN Red List of Threatened Species 2009: e.T161433A5422974. http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161433A5422974.en