Dasyatis fluviorum

Cladus: Eukaryota
Supergroup: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Classis: Chondrichthyes
Subclassis: Elasmobranchii
Superordo: Rajomorphii
Ordo: Rajiformes
Superfamilia: Dasyatoidea
Familia: Dasyatidae
Genus: Dasyatis
Species: Dasyatis fluviorum

Vernacular names
English: estuary stingray, estuary stingaree, brown stingray

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The estuary stingray, estuary stingaree, or brown stingray (Dasyatis fluviorum) is a species of stingray in the family Dasyatidae. It is found along the coasts of Queensland and New South Wales in Australia, and typically inhabits rivers and estuaries in mangroves. Growing to 93 cm (37 in) across, this yellow-brown to olive stingray has a rhomboid pectoral fin disc and a smooth, whip-like tail with both dorsal and ventral folds. Its long, narrow nostrils and row of thorns along the midline of the back are additional characteristic features.

Crustaceans and polychaete worms are the main food of the estuary stingray, though it has a perhaps undeserved reputation for consuming farmed shellfish such as oysters. This species has declined or disappeared in many parts of its historic range, likely from a combination of habitat destruction, commercial and recreational fishery activity, and persecution by shellfish farmers. As a result, the International Union for Conservation of Nature (IUCN) has assessed it as Vulnerable.
Taxonomy

The first reference to the estuary stingray in scientific literature was probably a record by 19th-century English naturalist William Saville-Kent of a "Trygon pastinaca" feeding on oysters in a Queensland estuary.[2] This species was formally described by Australian ichthyologist James Douglas Ogilby in a 1908 volume of Proceedings of the Royal Society of Queensland, based on a specimen collected from the Brisbane River. The specific epithet fluviorum means "of the rivers" in Latin.[3]

Distribution and habitat

Likely endemic to eastern Australia, the estuary stingray is found from Forster in New South Wales to Proserpine in Queensland.[1] Until the 1880s, it ranged as far south as Botany Bay, but was believed to have since disappeared from this area until it was rediscovered in 2010 in Wagonga Inlet near Narooma.[4] This species has also been reported from the Queensland peninsula of Cape York to Darwin in Northern Territory, as well as from New Guinea and the South China Sea; these additional records likely represent misidentifications.[1][5]

The estuary stingray is a marine and brackish water inhabitant typically found in shallow waters close to shore, though it has also been recorded to a depth of 28 m (92 ft) offshore. This bottom-dwelling species seems to have somewhat stringent habitat requirements, as it is only abundant in certain rivers and estuaries associated with mangroves. It has been known to swim inland beyond the limit of high tide.[1]

Description

The estuary stingray has a diamond-shaped pectoral fin disc with gently convex anterior margins and broadly rounded outer corners. The snout is wide and triangular, tapering to a point. The eyes are spaced well apart and are immediately followed by the spiracles. There is a short and broad flap of skin between the long and narrow nostrils, with a weakly fringed posterior margin. The small, bow-shaped mouth has deep furrows adjacent and contains a row of 5 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. The pelvic fins are relatively large.[5]

The tail measures twice as long as the disc, is broad and flattened at the base, and bears a serrated stinging spine on its upper surface. Past the spine the tail quickly tapers to become whip-like, and there is 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 to the base of the tail spine. This species is yellowish to greenish brown above, lightening towards the disc margins and darkening past the tail spine, and white below. It grows to at least 93 cm (37 in) across, and may reach a width of 1.2 m (3.9 ft).[5] The maximum recorded weight is 6.1 kg (13 lb).[6]

Biology and ecology

While the estuary stingray has gained infamy for being a voracious predator of oysters and other farmed shellfish, its diet consists mainly of crustaceans and polychaete worms.[1][5] In Moreton Bay, an important prey item is the soldier crab (Mictyris longicarpus). This species has been observed entering mudflats with the rising tide to forage for food.[1] Known parasites of the estuary include the tapeworms Heterocotyle chin and Shirleyrhynchus aetobatidis,[7][8] the nematode Echinocephalus overstreeti,[9] and the monogeneans Empruthotrema dasyatidis and Neoentobdella cribbi.[10][11] Like other stingrays, this species is aplacental viviparous. Newborns measure around 11 cm (4.3 in) across and 35 cm (14 in) long; males typically mature at 41 cm (16 in) across and females at 61 cm (24 in) across.[5]

Human interactions

Historical records and anecdotal observations strongly indicate that the once-abundant estuary stingray has experienced a significant range contraction and population decline off New South Wales and southern Queensland, though it remains common in Hervey Bay and parts of Moreton Bay.[1] The reclamation of muddy bays and mangroves for development has likely played a major role in this decline, as well as bycatch mortality from inshore commercial fisheries using bottom trawls and line gear, which is exacerbated by the practice of "spiking", or piercing the ray's cranium with a metal bar or sharpened stick to move it. This species is also readily captured and often killed by recreational anglers. Finally, its reputation for damaging shellfish has led to persecution by commercial shellfish farmers.[1] Because of these factors, the International Union for Conservation of Nature (IUCN) has assessed the estuary stingray as Vulnerable. This species is likely found in several Marine Protected Areas (MPAs), but at present these zones provide inadequate protection against fishing.[1] The Queensland government has listed this species on the "Back on Track species prioritisation framework".[12]

References

1. ^ a b c d e f g h i Kyne, P.M., D.A. Pollard and M.B. Bennett (2003). Dasyatis fluviorum. In: IUCN 2003. IUCN Red List of Threatened Species. Downloaded on January 8, 2010.
2. ^ Last, P.R. (2002). "Freshwater and Estuarine Elasmobranchs of Australia". in Fowler, S.L., T.M. Reed and F.A. Dipper. Elasmobranch Biodiversity, Conservation and Management. IUCN. pp. 185–193. ISBN 2831706505.
3. ^ Ogilby, J.D. (August 25, 1908). "On new genera and species of fishes". Proceedings of the Royal Society of Queensland 21: 1–26.
4. ^ "Rare stingray discovered in Wagonga inlet" (January 20, 2010). Narooma News. Retrieved on January 23, 2009.
5. ^ a b c d e Last, P.R. and J.D. Stevens (2009). Sharks and Rays of Australia (second ed.). Harvard University Press. pp. 435–436. ISBN 0674034112.
6. ^ Froese, Rainer, and Daniel Pauly, eds. (2010). "Dasyatis fluviorum" in FishBase. January 2010 version.
7. ^ Chisholm, L.A. and I.D. Whittington (November 1996). "A revision of Heterocotyle (Monogenea: Monocotylidae) with a description of Heterocotyle capricornensis n. sp. from Himantura fai (Dasyatididae) from Heron Island, Great Barrier Reef, Australia". International Journal for Parasitology 26 (11): 1169–1190. doi:10.1016/S0020-7519(96)00113-0.
8. ^ Beveridge, I. and R.A. Campbell (January 1998). "Reexamination of the trypanorhynch cestode collections of A.E. Shipley, J. Hornell and T. Southwell, with the erection of a new genus, Trygonicola, and redescriptions of seven species". Systematic Parasitology 39 (1): 1–34. doi:10.1023/A:1005852507995.
9. ^ Moravec, F. and J.L. Justine (2006). "Three nematode species from elasmobranchs off New Caledonia". Systematic Parasitology 64 (2): 131–145. doi:10.1007/s11230-006-9034-x. PMID 16773474.
10. ^ Whittington, I.D. and G.C. Kearn (July 1992). "Empruthotrema dasyatidis n. sp. (Monogenea: Monocotylidae) from the olfactory sacs of Dasyatis fluviorum (Rajiformes: Dasyatidae) from Moreton Bay, Queensland". Systematic Parasitology 22 (3): 159–165. doi:10.1007/BF00009663.
11. ^ Whittington, I.D. and G.C. Kearn (2009). "Two new species of Neoentobdella (Monogenea: Capsalidae: Entobdellinae) from the skin of Australian stingrays (Dasyatidae)". Folia Parasitologica 56 (1): 29–35.
12. ^ Estuary stingray (August 31, 2007). Queensland Department of Environment and Resource Management. Retrieved on January 23, 2009.