Medium-sized butterfly ray with lozenge-shaped disc; disc wider than length; disc uniform brown to olive green with or without scattered pale/light-yellow spots; tail long and almost equal to disc length, with no dorsal and caudal fin; tail with 9-12 black and white bands alternating. Often confused with Gymnura japonica; Gymnura poecilura can be distinguished on the following characters: 9-12 bands on the tail, absence of the dorsal fin and spiracle tentacle, weakly developed dorsal/ventral dermal ridge-like structure present/absent on the tail. The total length of G. poecilura is much longer, 78.0–91.8 (%DW) as against 68.8–72.2 of G. japonica. G. poecilura is also characterised by smaller disc lengths and longer tails, 49.5–51.3 and 31.7–43.3 as against 50.0–54.0 and 20.3–21.8 (%DW). Black bands for G. poecilura range from 9 to 12 and for G. japonica from 6 to 8 (Jacobsen and Bennett 2009).

Biology

Length:  Males develop at around 35 cm DW, while females mature at about 41 cm DW, and they grow to a maximum size of at least 104 cm disc width (DW).

Gestation period: Unknown

Littter size: Size-at-birth is 22–26 cm DW, and reproduction is aplacental viviparous with litters of 1–7 pups. Upon capture, spontaneous abortion is common in this species, which may make it difficult to accurately estimate the size of the litter.

Life Expectancy: The Backwater Butterfly Ray (Gymnura natalensis) of South Africa, which develops at 6 years old and lives to a maximum age of 24, provides an estimate of generation length of 15 years.

Diet: Feeds mainly on fishes, occasionally, crustaceans and clams.

Habitat and Distribution

Habitat: The Longtail Butterfly Ray is demersal on inshore, sandy and muddy substrates.

Distribution: The Longtail butterfly ray can be found from the Red Sea and the Arabian/Persian Gulf in the Western Indian Ocean to the Philippines, and from Indonesia to southern Japan in the Northwest Pacific.

Depth: 0-75 m   

Commerical value

They are utilized in India. The meat is usually sold either fresh or dried for human consumption. In India, there is a specialized market selling only rays in Thalassery, north of Cochin.

Threats

Limited information currently available on the species from its distribution/exploitation range in the Indo-Pacific region makes it a threatened species; however, heavy bycatch mostly in trawl nets and the high fishing pressure makes it a highly vulnerable species.

References

• Muktha, M., Akhilesh, K.V., Sandhya, S. et al. Re-description of the longtail butterfly ray, Gymnura poecilura (Shaw, 1804) (Gymnuridae: Myliobatiformes) from Bay of Bengal with a neotype designation. Mar Biodiv 48, 1085–1096 (2018). https://doi.org/10.1007/s12526-016-0552-8