Thorntail stingray

Appearance

One of the largest members of its family, the thorntail stingray reaches at least 4 m long, 1.8 m across, and 214 kg in weight. This species has a diamond-shaped pectoral fin disc about one-fourth wider than long, with sinuous leading margins converging to a slightly protruding snout tip and rounded outer and trailing margins. The mouth is slightly arched; there are five papillae across the floor with the outermost pair smaller and set apart from the others. The tooth rows number 25–43 in the upper jaw and 29–48 in the lower jaw, and are arranged with a quincunx pattern into pavement-like surfaces.

The pelvic fins have rounded tips and gently curved trailing margins. The whip-like tail measures about twice the length of the disc and bears one or two long stinging spines with up to 88 serrations. A narrow fin fold runs beneath the tail and ends well before the tail tip. Large juveniles and adults have a row of large, sharp thorns running along the midline of the back from behind the eyes to the tail spine, and thorns of various sizes are also scattered about the dorsal surface of the disc. The tail behind the spine is densely covered by stout thorns. This species is a uniform dark brown or gray to black above and whitish below. The longer tail, presence of thorns, and absence of white dots atop the disc differentiate this species from the short-tail stingray , another giant stingray that shares its range.

Distribution

The thorntail stingray is found off southern Africa from Algoa Bay, South Africa to Barra da Falsa, Mozambique and Réunion, as well as off Australia from Shark Bay to northern New South Wales, Lord Howe Island, Norfolk Island, and New Zealand. It is fairly common off Australia and New Zealand and less so elsewhere. Favoring inshore habitats with soft bottoms, this benthic species is commonly encountered in estuaries and lagoons, around rocky and coral reefs, and over reef flats. In Australia, it has been known to swim up rivers. Off New Zealand, large groups of thorntail stingrays have been seen inside caves and beneath rocky arches. This species is known to occur as deep as 440 m .

Behavior

During the day, thorntail stingrays are often seen resting on patches of sand. This species preys mainly upon crabs, mantis shrimp, bivalves, polychaete worms, and conger eels. Off New Zealand, both it and the short-tail stingray regularly fall prey to local killer whales . A known parasite of this species is the nematode ''Echinocephalus overstreeti''. Thorntail stingrays have been reported to congregate in warm, shallow waters during the summer, possibly for reproductive purposes. This species is aplacental viviparous like other stingrays.

Habitat

The thorntail stingray is found off southern Africa from Algoa Bay, South Africa to Barra da Falsa, Mozambique and Réunion, as well as off Australia from Shark Bay to northern New South Wales, Lord Howe Island, Norfolk Island, and New Zealand. It is fairly common off Australia and New Zealand and less so elsewhere. Favoring inshore habitats with soft bottoms, this benthic species is commonly encountered in estuaries and lagoons, around rocky and coral reefs, and over reef flats. In Australia, it has been known to swim up rivers. Off New Zealand, large groups of thorntail stingrays have been seen inside caves and beneath rocky arches. This species is known to occur as deep as 440 m .During the day, thorntail stingrays are often seen resting on patches of sand. This species preys mainly upon crabs, mantis shrimp, bivalves, polychaete worms, and conger eels. Off New Zealand, both it and the short-tail stingray regularly fall prey to local killer whales . A known parasite of this species is the nematode ''Echinocephalus overstreeti''. Thorntail stingrays have been reported to congregate in warm, shallow waters during the summer, possibly for reproductive purposes. This species is aplacental viviparous like other stingrays.