Round ribbontail ray

Appearance

The round ribbontail ray has a thick pectoral fin disc wider than it is long, with a smoothly rounded outer margin. The eyes are of medium size and are followed by larger spiracles. There is a short and broad curtain of skin between the oval nostrils, with a finely fringed trailing margin. The mouth is wide and curved, with faint furrows at the corners. There is a row of seven papillae on the floor, with the outermost pair smaller and set apart from the others. There are 37–46 tooth rows in the upper jaw and 39–45 tooth rows in the lower jaw. The teeth are small with a deep groove across the crown, and are arranged in a dense quincunx pattern into flattened surfaces.

The pelvic fins are small and narrow. The tail is relatively short, not exceeding the width of the disc, and bears one long, serrated stinging spine on the upper surface. The base of the tail is broad; past the spine the tail rapidly thins, and bears a deep ventral fin fold that runs to the tail tip. The upper surface of the disc and tail are roughened by a uniform covering of small, widely spaced granules. There is also a midline row of sharp tubercles on the back, with two shorter rows alongside. The first of these tubercles develop at a length of around 46 cm , over the "shoulders" and in the single midline row.

The dorsal coloration is light to dark gray, brown-gray, or purplish, becoming most intense towards the fin margins, with a highly variable pattern of irregular darker mottling and white speckles or streaks. The tail past the spine, including the fin fold, is uniformly black, while the underside is creamy white with darker fin margins and additional dots. Young rays are more plain in coloration than adults. One of the largest stingray species, the round ribbontail ray can grow to 1.8 m across, 3.3 m long, and 150 kg in weight.

Distribution

The round ribbontail ray has a wide distribution in the Indo-Pacific region: it is found from KwaZulu-Natal in South Africa northward along the East African coast to the Red Sea, including Madagascar and the Mascarenes; from there, its range extends eastward through the Indian subcontinent to Southeast Asia and Micronesia, occurring as far north as Korea and southern Japan, and as far south as Australia, where it is found from at least Ningaloo Reef off Western Australia to Stradbroke Island off Queensland, including Lord Howe Island. In the easternmost portion of its range, it has been reported from Cocos Island and the Galápagos Islands, with individuals possibly dispersing as far as Central America.

Bottom-dwelling in nature, the round ribbontail ray is typically found close to shore at a depth of 20–60 m , though it has been reported anywhere from the surf zone to a depth of 439 m . It favors sand or rubble bottoms in shallow lagoons or near coral and rocky reefs, and may also enter estuaries.

Behavior

The round ribbontail ray has nocturnal habits and rests motionless for much of the day, often near vertical structures, in caves, or under ledges. It may be solitary, or form small to large groups. This ray is frequently shadowed by one or more jacks or cobia ; these smaller fishes may feed on food stirred up by the ray's activities, or use the ray's body as cover for approaching their own prey. The round ribbontail ray hunts for bivalves, crabs, shrimps, and small bony fishes on the bottom. When feeding, it adopts a characteristic posture in which it presses the margin of its disc against the bottom and takes in water through its spiracles, which it blows through its mouth to uncover prey buried in the sediment. This species may fall prey to larger fishes such as sharks, and marine mammals. When threatened, it raises its tail over its back so that the spine faces forward, and waves it back and forth. Known parasites of this species include the monogenean ''Dasybatotrema spinosum'', ''Dendromonocotyle pipinna'', ''Neoentobdella garneri'' and ''N. taiwanensis'', and the nematode ''Echinocephalus overstreeti''.

Little information is available on the life history of the round ribbontail ray. Like other stingrays, it is aplacental viviparous: the unborn embryos are initially sustained by yolk, which is later supplemented by histotroph produced by the mother. Reproductive aggregations numbering in the hundreds have been observed at Cocos Island shortly after the onset of ''La Niña'', which brings cooler temperatures. During these periods a single female may be pursued by dozens of males. Females bear litters of up to seven pups, each measuring 33–35 cm across and 67 cm long. Off South Africa, birthing may take place in the summer. Males attain sexual maturity at a disc width of 1.0–1.1 m ; the maturation size of females is unknown.

Habitat

The round ribbontail ray has a wide distribution in the Indo-Pacific region: it is found from KwaZulu-Natal in South Africa northward along the East African coast to the Red Sea, including Madagascar and the Mascarenes; from there, its range extends eastward through the Indian subcontinent to Southeast Asia and Micronesia, occurring as far north as Korea and southern Japan, and as far south as Australia, where it is found from at least Ningaloo Reef off Western Australia to Stradbroke Island off Queensland, including Lord Howe Island. In the easternmost portion of its range, it has been reported from Cocos Island and the Galápagos Islands, with individuals possibly dispersing as far as Central America.

Bottom-dwelling in nature, the round ribbontail ray is typically found close to shore at a depth of 20–60 m , though it has been reported anywhere from the surf zone to a depth of 439 m . It favors sand or rubble bottoms in shallow lagoons or near coral and rocky reefs, and may also enter estuaries.The round ribbontail ray has nocturnal habits and rests motionless for much of the day, often near vertical structures, in caves, or under ledges. It may be solitary, or form small to large groups. This ray is frequently shadowed by one or more jacks or cobia ; these smaller fishes may feed on food stirred up by the ray's activities, or use the ray's body as cover for approaching their own prey. The round ribbontail ray hunts for bivalves, crabs, shrimps, and small bony fishes on the bottom. When feeding, it adopts a characteristic posture in which it presses the margin of its disc against the bottom and takes in water through its spiracles, which it blows through its mouth to uncover prey buried in the sediment. This species may fall prey to larger fishes such as sharks, and marine mammals. When threatened, it raises its tail over its back so that the spine faces forward, and waves it back and forth. Known parasites of this species include the monogenean ''Dasybatotrema spinosum'', ''Dendromonocotyle pipinna'', ''Neoentobdella garneri'' and ''N. taiwanensis'', and the nematode ''Echinocephalus overstreeti''.

Little information is available on the life history of the round ribbontail ray. Like other stingrays, it is aplacental viviparous: the unborn embryos are initially sustained by yolk, which is later supplemented by histotroph produced by the mother. Reproductive aggregations numbering in the hundreds have been observed at Cocos Island shortly after the onset of ''La Niña'', which brings cooler temperatures. During these periods a single female may be pursued by dozens of males. Females bear litters of up to seven pups, each measuring 33–35 cm across and 67 cm long. Off South Africa, birthing may take place in the summer. Males attain sexual maturity at a disc width of 1.0–1.1 m ; the maturation size of females is unknown.