Japanese Butterfly Ray.
A large butterfly ray with a wide, vaguely kite-shaped disc. Disc width approximately 1.8-2.2 x length. Pectoral fin apices angular. Snout short.
Eyes very small. No tentacle present on posterior margins of spiracles. Spiracle has a concave inner margin. Mouth arched with a concave symphysis on lower jaw.
Skin completely smooth. Tail short. Dorsal fin absent. Caudal sting small but always present.
Dorsum brownish-grey, usually with a pattern of large, diffuse, dark spots or blotches centrally, and small dark spots around disc margin. White spot occasionally present posterior to one or both spiracles. Ventrum white or brownish. Tail with 5-9 black bands or completely black in some large specimens.
Maximum disc width 145cm. Disc width at birth 18cm.
Tropical to warm-temperate water. On sandy or muddy substrates, often in shallow bays. Max depth unknown.
Northwest Pacific Ocean. Japan, Korea, China, and Taiwan.
The Japanese butterfly ray is susceptible to a variety of gear types, including demersal trawl, gillnet, trammelnet and setnet fisheries throughout its range, and is known to be commercially fished off China. Population declines are reported to have occurred off Japan and China, but no information is currently available on the scale of these declines or the capture of this species in fisheries. Although the threat status of this species may be of significant concern, insufficient information is currently available on this species’ distribution, abundance and the extent of any declines to fully assess its status and therefore it is presently listed as Data Deficient. Further investigation is required into taxonomy and population trends in this species, to fully define its range and the extent of any decline and this assessment should be revisited once these issues are better resolved.
Ishihara, H., Wang, Y. & Jeong, C.H. 2009. Gymnura japonica. The IUCN Red List of Threatened Species 2009: e.T161630A5468369. https://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161630A5468369.en. Downloaded on 27 February 2021.
Aplacental yolk sac viviparous. Litter size 2-8. Gestation unknown.
Diet unrecorded but probably feeds mostly on small fishes like other butterfly rays.
Sedentary. Camouflages its body with sand by flapping its fins while resting on the bottom.
Reaction to divers
Fairly tolerant if not approached too closely. Will sometimes allow divers to slowly waft sand away from its disc but may bolt if it feels threatened.
Relatively common on dive sites on the south coast of Honshu Island including sites in Chiba, and the Izu Peninsula.