Cowtail stingray

Appearance

The pectoral fin disk of the cowtail stingray is very thick, with almost straight anterior margins and rounded apices, and measuring 1.1-1.3 times as long as wide. The snout is broadly rounded and blunt. The eyes are very small and widely spaced. The mouth is narrow, with 20 rows of distinctive hexagonal, high-crowned teeth in each jaw and five papillae on the mouth floor. The tail is broad-based, with a filamentous tip and a single venomous spine located well backwards of the pelvic fins. There is no upper tail fold; the high ventral tail fold measures 2-3 times the height of the tail but does not reach the tip.

The disk surface is covered by a broad band of fine dermal denticles extending from near the tip of the snout to the upper surface of the tail, excluding the extreme margins of the disk. Newborns are entirely smooth but develop denticles quickly after birth. Juveniles have four circular tubercles at the center of the disk, which often become indistinct in adults. The coloration is a uniform grayish brown to black above and mostly white below. The tail fold and tip are black. This species may reach 3 meters long and 1.8 meters across, and 250 kg in weight.

Distribution

The cowtail stingray has a widespread distribution in the tropical waters of the Indo-Pacific, from South Africa and the Red Sea to Japan and Australia, including Melanesia and Micronesia. They are amphidromous and known to enter estuaries and rivers. This species is the most commonly reported stingray from fresh water in Southeast Asia, and there is a record from the Ganges River some 2,200 km from the sea. They are usually found on sandy bottoms in coastal waters and on coral reefs to a depth of 60 meters .

Behavior

Cowtail stingrays are solitary foragers that feed on bony fishes , crustaceans, polychaete worms, sipunculids, and molluscs. The cowtail stingray is in turn preyed upon by various species of hammerhead and requiem sharks, as well as by the bottlenose dolphin . When threatened, they consistently flee at a 45° angle away from the predator, a trajectory that allows them to maximize the distance covered while still keeping the predator within their field of vision.

Like other stingrays, reproduction in this species is ovoviviparous, with the embryos sustained in late development by histotroph delivered via specialized structures. The females giving birth to live young measuring 18 cm across or more. Single young individuals have been reported year-round in the Strait of Malacca; juveniles have more pointed snouts than adults. Adults are sometimes accompanied by remoras or trevallies. Known parasites of the cowtail stingray include ''Dendromonocotyle ardea'', ''Decacotyle tetrakordyle'', and ''Pterobdella amara''.

Observations of cowtail stingrays in Shark Bay, Australia, show that this species enters shallow, sandy flats during high tide to rest for a minimum of four hours. They often form small groups when resting, particularly when visibility is poor such as in turbid water or under low light conditions. The typical size of such groups is three individuals , arranged in a "rosette" formation with their tails pointing outward. This appears to be an anti-predator behavior, as the close circular arrangement of the rays allows them to see predators approaching from any direction. The rosette also orients their less critical tails, containing mechanoreceptors that comprise a secondary warning system, towards potential threats. The members of the group will flee in concert, reducing a predator's ability to target any one individual. Cowtail stingrays also preferentially form mixed-species groups with reticulate whiprays , likely because the whiprays are better able to detect predators due to their longer tails.

Habitat

The cowtail stingray has a widespread distribution in the tropical waters of the Indo-Pacific, from South Africa and the Red Sea to Japan and Australia, including Melanesia and Micronesia. They are amphidromous and known to enter estuaries and rivers. This species is the most commonly reported stingray from fresh water in Southeast Asia, and there is a record from the Ganges River some 2,200 km from the sea. They are usually found on sandy bottoms in coastal waters and on coral reefs to a depth of 60 meters .Cowtail stingrays are solitary foragers that feed on bony fishes , crustaceans, polychaete worms, sipunculids, and molluscs. The cowtail stingray is in turn preyed upon by various species of hammerhead and requiem sharks, as well as by the bottlenose dolphin . When threatened, they consistently flee at a 45° angle away from the predator, a trajectory that allows them to maximize the distance covered while still keeping the predator within their field of vision.

Like other stingrays, reproduction in this species is ovoviviparous, with the embryos sustained in late development by histotroph delivered via specialized structures. The females giving birth to live young measuring 18 cm across or more. Single young individuals have been reported year-round in the Strait of Malacca; juveniles have more pointed snouts than adults. Adults are sometimes accompanied by remoras or trevallies. Known parasites of the cowtail stingray include ''Dendromonocotyle ardea'', ''Decacotyle tetrakordyle'', and ''Pterobdella amara''.

Observations of cowtail stingrays in Shark Bay, Australia, show that this species enters shallow, sandy flats during high tide to rest for a minimum of four hours. They often form small groups when resting, particularly when visibility is poor such as in turbid water or under low light conditions. The typical size of such groups is three individuals , arranged in a "rosette" formation with their tails pointing outward. This appears to be an anti-predator behavior, as the close circular arrangement of the rays allows them to see predators approaching from any direction. The rosette also orients their less critical tails, containing mechanoreceptors that comprise a secondary warning system, towards potential threats. The members of the group will flee in concert, reducing a predator's ability to target any one individual. Cowtail stingrays also preferentially form mixed-species groups with reticulate whiprays , likely because the whiprays are better able to detect predators due to their longer tails.