Japanese Sleeper Ray.
A small sleeper ray with a teardrop-shaped body. Disc sub-circular. Snout short, tip weakly convex. Pectoral fin apices evenly rounded. Eyes partially encircled by much larger spiracles. Spiracles circular. Spiracular rim weakly raised, with no papillae. Nostrils with circular incurrent openings and narrow nasal flaps. Nasal curtain short, with deep central groove.
Pelvic fins broad. Tail broad based. Pronounced caudal keel. Single rounded dorsal fin, origin posterior to pelvic fin. Caudal fin much larger than dorsal fin. Upper caudal margin straight. Ventral and posterior caudal margin broadly convex.
Dorsum light brown to dark reddish brown, sometimes with dusky purple shadowing. Small dark blotched occasionally present. Ventrum white.
Maximum length 37cm. Size at birth 8cm.
Warm temperate to tropical seas. Benthic on soft bottoms and gravel at 12-140m.
Northwest Pacific. Found from Japan to China, including South Korea and Taiwan.
The Japanese Sleeper Ray (Narke japonica) is a bycatch in industrial and artisanal fisheries with multiple fishing gears including trawl, gillnet, and line, and is retained in Taiwan, and likely China, for fish meal. If discarded elsewhere, post-release survival is likely low. There are no species-specific population trends, although it is considered common in Taiwan where the observed landing rates have remained stable for the past 10–15 years (two to three generation lengths). Landings data of all skates combined from the Taiwan Exclusive Economic Zone (EEZ) and reconstructed catches of all sharks, skates and rays from the Japan, China, and South Korea EEZs indicate declines of 23–68% over the past three generation lengths (15 years). These levels of declines are not species-specific but are informative for understanding the broader levels of decline in batoids in the region. Significant habitat loss is also a threat to this species. Seasonal fishing bans and inshore trawl bans in China and Taiwan respectively, may provide the species some refuge from fishing pressure. It is inferred that the Japanese Sleeper Ray has undergone a population reduction of 30–49% over the past three generation lengths (15 years) due to levels of exploitation and a decline in quality of habitat, and it is assessed as Vulnerable A2cd.
Rigby, C.L., Chen, X., Ebert, D.A., Herman, K., Ho, H., Hsu, H. & Zhang, J. 2020. Narke japonica. The IUCN Red List of Threatened Species 2020: e.T161665A124524467. https://dx.doi.org/10.2305/IUCN.UK.2020-3.RLTS.T161665A124524467.en. Downloaded on 05 June 2021.
Aplacental viviparous. Litter size 1-9.
Poorly known. Capable of emitting mild electric shocks; probably to stun prey and as a defensive tactic.
Reaction to divers
Easy to approach. Generally remains motionless when approach.
The Japanese sleeper ray is rarely encountered by divers. It is most common at dive sites in the southern half of Japan (e.g. along the south coast of Honshu) and around Taiwan.
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Spot-tail Sleeper Ray Distinguishable by paired pale blotches on posterior disc, above pelvic fins, and at tail base.