Bluespotted ribbontail ray

Appearance

The pectoral fin disc of the bluespotted ribbontail ray is oval in shape, around four-fifths as wide as long, with a rounded to broadly angular snout. The large, protruding eyes are immediately followed by the broad spiracles. There is a narrow flap of skin between the nares with a fringed posterior margin, reaching past the mouth. The lower jaw dips at the middle and deep furrows are present at the mouth corners. There are 15–24 tooth rows in either jaw, arranged into pavement-like plates, and two large papillae on the floor of the mouth. The pelvic fins are narrow and angular. The thick, depressed tail measures about 1.5 times the disc length and bears one or two serrated spines well behind the tail base; there is a deep fin fold on the ventral surface, reaching the tip of the tail, and a low midline ridge on the upper surface.

The skin is generally smooth, save for perhaps a scattering of small thorns on the middle of the back. The dorsal coloration is striking, consisting of numerous circular, neon blue spots on a yellowish brown or green background; the spots vary in size, becoming smaller and denser towards the disc margin. The tail has two stripes of the same blue running along each side as far as the spines. The eyes are bright yellow and the belly is white. Individuals found off southern Africa may lack the blue tail stripes. The bluespotted ribbontail ray grows to 35 cm across, 80 cm long, and 5 kg .

Distribution

Widespread in the nearshore waters of the tropical Indo-Pacific region, the bluespotted ribbontail ray has a range that extends around the periphery of the Indian Ocean from South Africa to the Arabian Peninsula to Southeast Asia, including Madagascar, Mauritius, Zanzibar, the Seychelles, Sri Lanka, and the Maldives. It is rare in the Persian Gulf and Gulf of Oman. In the Pacific Ocean, this species is found from the Philippines to northern Australia, as well as around numerous Melanesian and Polynesian islands as far east as the Solomon Islands. Rarely found deeper than 30 m , the bluespotted ribbontail ray is a bottom-dwelling species that frequents coral reefs and adjacent sandy flats. It is also commonly encountered in the intertidal zone and tidal pools, and has been sighted near seagrass beds. Every summer, considerable numbers of bluespotted ribbontail rays arrive off South Africa.

Behavior

One of the most abundant stingrays inhabiting Indo-Pacific reefs, the bluespotted ribbontail ray generally spends the day hidden alone inside caves or under coral ledges or other debris , often with only its tail showing. At night, small groups assemble and swim onto shallow sandy flats with the rising tide to feed. Unlike many other stingrays, this species seldom buries itself in sand. The bluespotted ribbontail ray excavates sand pits in search of molluscs, polychaete worms, shrimps, crabs, and small benthic bony fishes; when prey is located, it is trapped by the body of the ray and maneuvered into the mouth with the disc. Other fishes, such as goatfish, frequently follow foraging rays, seeking food missed by the ray.

Breeding in the bluespotted ribbontail ray occurs from late spring to summer; the male follows the female and nips at her disc, eventually biting and holding onto her for copulation. There is also a documented instance of a male holding onto the disc of a smaller male bluespotted stingray , in a possible case of mistaken identity. Adult males have been observed gathering in shallow water, which may relate to reproduction. Like other stingrays, this species is aplacental viviparous: the embryos are initially sustained by yolk, which later in development is supplemented by histotroph produced by the mother. The gestation period is uncertain, but is thought to be between four to twelve months long. Females bear litters of up to seven young, each a miniature version of the adult measuring around 13–14 cm across. Males attain sexual maturity at a disc width of 20–21 cm ; the maturation size of females is unknown.

Known predators of the bluespotted ribbontail ray include hammerhead sharks and bottlenose dolphins ; it is also potentially preyed upon by other large fishes and marine mammals. When threatened, this ray tends to flee at high speed in a zigzag pattern, to throw off pursuers. Numerous parasites have been identified from this species: the tapeworms ''Aberrapex manjajiae'', ''Anthobothrium taeniuri'', ''Cephalobothrium taeniurai'', ''Echinobothrium elegans'' and ''E. helmymohamedi'', ''Kotorelliella jonesi'', ''Polypocephalus saoudi'', and ''Rhinebothrium ghardaguensis'' and ''R. taeniuri'', the monogeneans ''Decacotyle lymmae'', ''Empruthotrema quindecima'', ''Entobdella australis'', and ''Pseudohexabothrium taeniurae'', the flatworms ''Pedunculacetabulum ghardaguensis'' and ''Anaporrhutum albidum'', the nematode ''Mawsonascaris australis'', the copepod ''Sheina orri'', and the protozoan ''Trypanosoma taeniurae''. This ray has been observed soliciting cleanings from the bluestreak cleaner wrasse by raising the margins of its disc and pelvic fins.