Estuary Stingray

The estuary stingray has a diamond-shaped pectoral fin disc about as wide as long, with gently convex anterior margins and broadly rounded outer corners. The snout is wide and triangular, and tapers to a point. The small, widely spaced eyes are immediately followed by the spiracles. Between the long and narrow nostrils, there is a short and broad "skirt" of skin with a weakly fringed posterior margin. The small, bow-shaped mouth is surrounded by deep furrows and contains a row of five papillae across the floor, with the outermost pair tiny and set apart from the others. The teeth are small and arranged into pavement-like surfaces. There are five pairs of gill slits beneath the disc. The pelvic fins are relatively large. The tail measures twice as long as the disc, and is broad and flattened at the base. On its upper surface is at least one, often two serrated stinging spines. Past the spines, the tail quickly tapers to become whip-like and bears a well-developed keel above and a long, low fin fold beneath. There are wide patches of small dermal denticles with flattened crowns between the eyes and over the middle of the back, along with a midline row of enlarged thorns that become progressively longer until they reach the base of the sting. Aside from the thorns at the base, the tail is smooth. …

The range of the estuary stingray spans approximately 1,700 km (1,100 mi) along Australia's eastern coast, from Repulse Bay in Queensland to the Hacking River in New South Wales. It is most common in southern Queensland, including in Hervey Bay and Moreton Bay. This species was formerly suspected to have disappeared from Botany Bay and Port Jackson in the 1880s, but recent observations have shown this is not the case. Additional species records from the Cape York Peninsula, Northern Territory, New Guinea, and the South China Sea probably represent misidentifications of other stingrays, primarily the freshwater whipray (Himantura dalyensis) and the Merauke stingray (D. longicauda). The habitat requirements of the estuary stingray appear to be rather stringent, as significant numbers are only found at particular locations. It prefers tidal rivers and the intertidal flats of estuaries and bays, which are lined with mangroves and have sandy to muddy bottoms. This species is rarely found outside these sheltered areas, though it has been recorded to a depth of 28 m (92 ft) in offshore waters. It inhabits marine and brackish waters, and may be able to tolerate fresh water as well as it has been known to swim upriver beyond the limit of high tide. Surface water temperatures within its range vary from 24–29 °C (75–84 °F) in the north to 17–23 °C (63–73 °F) in the south. …

Despite its reputation for preying voraciously on oysters and other farmed shellfish, the estuary stingray's diet in fact consists mainly of crustaceans and polychaete worms. In Moreton Bay, an important prey species is the soldier crab (Mictyris longicarpus). This ray has been observed entering mudflats with the rising tide to forage for food. Known parasites of the estuary stingray include the tapeworm Shirleyrhynchus aetobatidis, the nematode Echinocephalus overstreeti and the monogeneans Heterocotyle chin, Empruthotrema dasyatidis and Neoentobdella cribbi. Like other stingrays, the estuary stingray exhibits aplacental viviparity, with the developing embryos sustained initially by yolk and later by histotroph ("uterine milk") produced by the mother. Females probably produce offspring every year. Courtship, in which the male follows the female and bites her disc, has been observed at night in water approximately 80 cm (31 in) deep in Hays Inlet from July to October. The newborns measure around 11 cm (4.3 in) across and 35 cm (14 in) long. Young rays have been caught in the Nerang and Macleay Rivers and in Hays Inlet; such fresh or brackish environments may serve as nurseries. Males mature at around 41 cm (16 in) across and seven years of age, and females mature at around 63 cm (25 in) across and 13 years of age. …