Mangrove Whipray: Urogymnus granulatus

Family: Dasyatidae

Common names

Mangrove Whipray.

Binomial

Urogymnus granulatus.

Synonyms

Dasyatis granulatus, Dasyatis ponapensis, Himantura granulata, Himantura ponapensis, Trygon granulata, Trygon ponapensis.

Identification

A large whipray with an oval disc that is notably longer than wide and very thick centrally. Snout short, and obtusely angular with a weakly protruding apical lobe. Anterior margins of disc straight or mildly concave. Pectoral fin apices broadly rounded. Pelvic fins very short.
Eyes small and protruding. Snout length approximately 1.5-2x combined eye and spiracle length. Mouth small with 2-7 oral papillae. Lower jaw somewhat arched. Labial furrows pronounced. Small, skirt-shaped nasal curtain with a fine fringe on the posterior margin.
Dorsum rough, but without enlarged thorns. Sparse denticles on mid-shoulders. Tail broad based then slender beyond sting; length 1.3-2.1 x disc width. Usually 1-2 caudal stings.

Colour

Dorsum brownish, yellowish, pinkish grey, or black with small scattered white flecks. Tail white beyond sting. Ventrum white in jveniles. Adults may have dark blotches on ventrum.

Size

Maximum disc width 141cm. Disc width at birth ~14cm.

Mangrove Whipray, Urogymnus granulatus. Foraging in a shallow creek on Magnetic Island, Queensland, Australia, Great Barrier Reef.

Conservation Status

ENDANGERED

The mangrove whipray is directly targeted and a retained bycatch across much of its range. It is captured in trawl, gill nets, hook and line, and longlines. Overfishing is high and increasing, except in Australia.
Large whiprays are slow to mature and have a low productivity, with a generation length of around 20 years. Consequently, it is suspected that the mangrove whipray has declined by 50–79% over the past three generation lengths.

Habitat

Tropical seas. The mangrove whipray occurs in a wide range of inshore habitats including mangroves, estuaries, sand flats, coral reefs, and rocky substrates, from the intertidal zone to 85m.

Distribution

Urogymnus granulatus has a widespread but patchy distribution throughout the Indo-West Pacific. It is found around Madagascar and the Seychelles, from Mozambique to Kenya, from the Red Sea to Sri Lanka, Bangladesh, in small pockets from the Andaman Islands through southeast Asia to Pulau, and south to Australia.

Reproduction

Matrotrophic viviparity. Litter size unknown.

Diet

The mangrove whipray feeds mostly on crustaceans; crabs and prawns.

Behavior

In Australian mangroves, this species moves into very shallow water with the rising tide to forage at the water’s edge.

Reaction to divers

Fairly difficult to approach. Will bolt if approached closely.

Diving logistics

Apparently quite easy to see on shallow reefs in the Red Sea and in the Maldives.

I photographed numerous small mangrove whiprays in a creek on the north side of Magnetic Island. They were impossible to approach on snorkel, but I was able to get close by patiently sitting in the mud at the water’s edge with my camera half submerged, waiting for them to swim by.