Freshwater whipray

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Freshwater whipray
Himantura dalyensis csiro-nfc.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Superorder: Batoidea
Order: Myliobatiformes
Family: Dasyatidae
Genus: Urogymnus
Species:
U. dalyensis
Binomial name
Urogymnus dalyensis
Synonyms
  • Himantura dalyensisLast & Manjaji-Matsumoto, 2008

The freshwater whipray (Urogymnus dalyensis) is a little-known species of stingray in the family Dasyatidae, found in a number of large rivers and associated estuaries in northern Australia. Until recently, this species was regarded as a regional subpopulation of the similar-looking but much larger giant freshwater stingray (U. polylepsis) of Southeast Asia. Typically reaching 1 m (3.3 ft) across, the freshwater whipray has a distinctively shaped, rounded pectoral fin disc, a projecting snout, and a thin tail without fin folds. It is plain brown above and white below with dark marginal bands. It may occasionally travel onto land and can "breathe" out of water for up to 7 minutes. The freshwater whipray is an active hunter of small fishes and shrimps, and does not currently face substantial conservation threats.

Contents

Taxonomy

The first known specimen of the freshwater whipray was caught during a 1989 scientific expedition from the Daly River, after which it would eventually be named. Various authors have mistakenly referred to this ray as the estuary stingray (Hemitrygon fluviorium), or identified it with the similar U. polylepsis . Morphological and molecular phylogenetic studies have since found that this species is in fact distinct from U. polylepsis, and it was formally described by Peter Last and B. Mabel Manjaji-Matsumoto in a 2008 Commonwealth Scientific and Industrial Research Organisation (CSIRO) paper. The type specimen is a juvenile male 62 cm (24 in) across, collected from the Pentecost River. [2]

Distribution and habitat

The only Australian stingray confined to fresh and brackish waters, the freshwater whipray has been thus far been reported from the Daly, Fitzroy, Gilbert, Mitchell, Normanby, Ord, Pentecost, Roper, South Alligator, and Wenlock Rivers in northern Australia, and may well inhabit most large, tropical Australian rivers. [2] The stingrays in the Fly River, Papua New Guinea, may also belong to this species. [2] This bottom-dwelling species occurs at a depth of 1–4 m (3.3–13.1 ft). [3] Most individuals are found in water with a salinity of under 10 ppt, but some have been caught from water with a salinity of up to 30 ppt. [2]

Description

The freshwater stingray has an apple-shaped pectoral fin disc approximately as wide as long, with the leading margins almost straight and transverse. The moderately long, obtuse snout is flattened with a pointed tip that projects from the disc. The eyes are small and immediately followed by much larger spiracles. There is a broad, somewhat rectangular curtain of skin between the nares, with a subtly fringed posterior margin. The mouth is gently arched and contains a pair of large papillae near the center and 23 much smaller papillae near the corners. There are around 37 upper tooth rows and 45 lower tooth rows; the teeth are small, each with a horizontal ridge and groove, and arranged with a quincunx pattern. The pelvic fins are small, no more than a fifth as long as the disc width. The tail tapers from a narrow base to become thin and whip-like, and measures more or less twice the disc length. There is a single serrated stinging spine on top of the tail; the fin folds are absent. [2]

The entire upper surface of the disc is densely covered by small dermal denticles that are heart or oval-shaped around the "shoulders" and become tiny and granular towards the disc margins; there are also around 5 relatively large denticles at the center of the disc. The tail is roughened by denticles above and below, with the largest positioned in a midline row before the spine. The dorsal coloration is a uniform light brown to gray-brown, darkening to blackish past the tail spine. The underside of the disc and tail is white, with dark brown bands around the fin margins; the inner margin of the band is irregular, breaking up into small blotches that reach the belly. This species attains a disc width of 1.24 m (4.1 ft), but most do not exceed 1 m (3.3 ft) across. The freshwater whipray is close in appearance to the much larger giant freshwater stingray, but has a shorter, more obtuse snout and narrower dark ventral bands. The two species also differ in several morphometric and meristic characters. [2]

Biology and ecology

Little is known of the freshwater whipray's natural history. It feeds on small fishes and shrimps, and has been observed lunging up riverbanks and taking prey caught in its wash. [4] There is a male specimen on record that was adolescent at a disc width of 88 cm (35 in). [3]

Human interactions

The International Union for Conservation of Nature (IUCN) has noted that the prospects for freshwater whiprays in Australia are likely favorable. However, there is concern that the South Alligator River subpopulation in Kakadu National Park may be negatively affected by contaminants from exploratory uranium mines upstream. [1]

Related Research Articles

<span class="mw-page-title-main">Roughback whipray</span> Species of cartilaginous fish

The roughback whipray is a rare species of freshwater stingray in the family Dasyatidae, found over sandy bottoms in the Mae Klong and Chao Phraya Rivers of Thailand. Growing no more than 29 cm (11 in) across, this small ray has an oval pectoral fin disc and a whip-like tail without fin folds. It closely resembles the white-edge freshwater whipray in appearance, but can be distinguished by its coloration: light gray to dark orange-brown above and white below with a dark band along the lateral margins. Another identifying feature is a "pearl organ" at the center of the back, found in individuals of all ages. All of the original specimens of the roughback whipray were found with extensive wounds to the fins and tail. The International Union for Conservation of Nature (IUCN) has assessed this species as Endangered, citing the extensive habitat degradation and heavy fishing pressure within its limited range.

<span class="mw-page-title-main">Giant freshwater stingray</span> Species of cartilaginous fish

The giant freshwater stingray is a species of stingray in the family Dasyatidae. It is found in large rivers and estuaries in Southeast Asia and Borneo, though historically it may have been more widely distributed in South and Southeast Asia. The largest freshwater fish and the largest stingray in the world, this species grows up to 2.2 m (7.2 ft) across and can reach up to 300 kg (660 lb) in weight. It has a relatively thin, oval pectoral fin disc that is widest anteriorly, and a sharply pointed snout with a protruding tip. Its tail is thin and whip-like, and lacks fin folds. This species is uniformly grayish brown above and white below; the underside of the pectoral and pelvic fins bear distinctive wide, dark bands on their posterior margins.

<span class="mw-page-title-main">Mekong freshwater stingray</span> Species of cartilaginous fish

The Mekong freshwater stingray, Hemitrygon laosensis, is a species of stingray in the family Dasyatidae, restricted to the Mekong and Chao Phraya Rivers in Laos and Thailand; the occurrence in Chao Phraya is considered an introduction. Measuring up to 62 cm (24 in) across, this ray has an oval pectoral fin disc, a tail with both upper and lower fin folds, and a midline row of spine-like dermal denticles. A characteristic feature of this species is its bright orange underside. The Mekong freshwater stingray preys on invertebrates and is aplacental viviparous. It has been assessed as Endangered by the International Union for Conservation of Nature (IUCN), as it is threatened by overfishing and habitat degradation.

<i>Himantura fluviatilis</i> Species of cartilaginous fish

Himantura fluviatilis, the Ganges whip ray, is an obscure species of stingray in the family Dasyatidae, apparently endemic to the Ganges River system and adjacent marine waters. With an oval pectoral fin disc and long projecting snout, it closely resembles, and may be the same species as Himantura chaophraya. Growing to 1.4 m (4.6 ft) across, it is a plain dark colour above, and lighter below with wide dark bands on the lateral disc margins. The International Union for Conservation of Nature (IUCN) has listed this species as Endangered, as it faces overfishing and habitat degradation within its heavily populated range.

<span class="mw-page-title-main">Marbled whipray</span> Species of cartilaginous fish

The marbled whipray is a little-known species of stingray in the family Dasyatidae, native to several freshwater rivers in Southeast Asia. This species has an oval pectoral fin disc with an elongated, pointed snout and a very long, whip-like tail without fin folds. It is characterized by numerous heart-shaped dermal denticles and tubercles on its upper surface, as well as a reticulated pattern of brown blotches on a light background. The maximum recorded disc width is 36 cm (14 in). The marbled whipray has been assessed as Endangered by the International Union for Conservation of Nature (IUCN); it is heavily threatened by fishing and habitat loss, degradation, and fragmentation.

<span class="mw-page-title-main">White-edge freshwater whipray</span> Species of cartilaginous fish

The white-edge freshwater whipray is an extremely rare species of stingray in the family Dasyatidae, native to four river systems in Southeast Asia. Measuring up to 60 cm (24 in) across, this ray has an oval pectoral fin disc and a very long, whip-like tail without fin folds. It can be identified by the presence of a sharply delineated white band running around the margin of its otherwise brown disc, as well as by its white tail and a band of dermal denticles along the middle of its back. This species feeds on benthic invertebrates and is aplacental viviparous. Its two long tail spines are potentially dangerous to humans. The International Union for Conservation of Nature (IUCN) has assessed the white-edge freshwater whipray as Endangered, as it is under heavy pressure from fishing and habitat loss, degradation, and fragmentation.

The pincushion ray or thorny freshwater stingray, is a little-known species of stingray in the family Dasyatidae, found in the rivers and lakes of West and Middle Africa. A heavy-bodied ray measuring up to 1.2 m (4 ft) across, this species can be distinguished by its rounded pectoral fin disk, reduced or absent stinging tail spine, and—in adults—numerous stout thorns covering its back and tail. In lieu of a long tail spine as in other stingrays, the pincushion ray employs these thorny denticles in defense. Seldom encountered since it was originally described, this species has been assessed as Critically Endangered by the International Union for Conservation of Nature (IUCN).

<span class="mw-page-title-main">Mangrove whipray</span> Species of cartilaginous fish

The mangrove whipray or whitetail stingray, is a species of stingray in the family Dasyatidae. It is widely distributed in the Indo-Pacific region from the Red Sea to northern Australia and Micronesia. A benthic inhabitant of shallow inshore waters, juvenile mangrove whiprays favor mangrove and estuarine habitats, while adults favor sandy to rocky areas in lagoons and coral reefs. This species can be identified by its thick, oval pectoral fin disc that is dark gray above with numerous white flecks, and by its relatively short, whip-like tail that is white past the stinging spine. It grows up to 1.4 m (4.6 ft) across.

<span class="mw-page-title-main">Reticulate whipray</span> Species of fish

The reticulate whipray or honeycomb stingray is a species of stingray in the family Dasyatidae. It inhabits coastal waters in the western Indian Ocean including the Red Sea, Natal and the Arabian Sea; also a Lessepsian transmigrant in the eastern Mediterranean. A large species reaching 2 m (6.6 ft) in width, the reticulate whipray has a diamond-shaped pectoral fin disc and an extremely long tail without fin folds. Both its common and scientific names refer to its ornate dorsal color pattern of many small, close-set dark spots or reticulations on a lighter background. However, the reticulate whipray is only one of several large spotted stingrays in the Indo-Pacific which, coupled with the variability of its coloration with age and locality, has resulted in a great deal of taxonomic confusion.

<span class="mw-page-title-main">Pink whipray</span> Species of stingray in the family Dasyatidae

The pink whipray is a species of stingray in the family Dasyatidae, with a wide but ill-defined distribution in the tropical Indo-Pacific from southern Africa to Polynesia. It is a bottom dweller that generally inhabits shallow water under 70 m (230 ft) deep, in sandy areas associated with coral reefs. Individuals exhibit a high degree of fidelity to particular locations. The pink whipray has a diamond-shaped pectoral fin disc wider than long, with a broad-angled snout and a very long, whip-like tail without fin folds. It has only a few small thorns on its back and is uniform brownish to grayish pink in color, becoming much darker past the tail sting. This large ray can reach 1.8 m (5.9 ft) across and over 5 m (16 ft) long.

<span class="mw-page-title-main">Jenkins' whipray</span> Species of cartilaginous fish

The Jenkins' whipray is a species of stingray in the family Dasyatidae, with a wide distribution in the Indo-Pacific region from South Africa to the Malay Archipelago to northern Australia. This large species grows to 1.5 m (4.9 ft) across and has a broad, diamond-shaped pectoral fin disc and a whip-like tail without fin folds. It has a band of heart-shaped dermal denticles running from between the eyes to the tail on its upper surface, along with a characteristic row of large spear-like thorns along the midline. It is uniform yellowish brown above, becoming grayish on the tail past the stinging spine, and white below; there is apparently a spotted color variant that had previously been described as a different species, the dragon stingray.

<span class="mw-page-title-main">Pitted stingray</span> Species of cartilaginous fish

The pitted stingray is a species of stingray in the family Dasyatidae, endemic to the waters around Japan and the Sea of Japan. It typically found near the coast at depths of 40–60 m (130–200 ft), but may also venture into the open sea. Measuring up to 2 m (6.6 ft) across, the pitted stingray has a diamond-shaped pectoral fin disc with a characteristic "W"-shaped groove on the underside. The total length including the tail has a record of 2.8 m (9.2 ft). Other identifying characteristics of this species include its dark gray dorsal coloration with small white spots, and the presence of dorsal tubercles in adults. Pitted stingrays are caught as bycatch in coastal fisheries and brought to market. The International Union for Conservation of Nature (IUCN) does not yet have sufficient data to assess this species beyond Data Deficient. This species is now regarded as a population of the Short-tail stingray.

The roughnose stingray is a little-known species of stingray in the family Dasyatidae, generally found in shallow, estuarine waters associated with mangroves off Borneo, Sumatra, and possibly Java. Growing to 72 cm (28 in) across, this species has a rhomboid pectoral fin disc and a whip-like tail with a ventral fin fold. It is characterized by its pointed snout, which is covered by dermal denticles. Reproduction is aplacental viviparous, with females possibly bearing as few as one pup at a time. The International Union for Conservation of Nature (IUCN) has assessed the roughnose stingray as Endangered; it is threatened by overfishing and the destruction and degradation of its mangrove habitat.

The tubemouth whipray is a little-known species of stingray in the family Dasyatidae, named for its distinctive, highly protrusible jaws. It is found in shallow, brackish water near mangrove forests and large river mouths along the coasts of southwestern Borneo and southern Sumatra. Measuring up to 1 m (3.3 ft) across, this species has a diamond-shaped pectoral fin disc with an elongated, pointed snout and broadly rounded outer corners. The upper surface of the disc is a plain grayish or brownish in color, and covered by small, flattened dermal denticles. The tubemouth whipray is relatively common at present, but is heavily pressured by habitat degradation and coastal fisheries. The International Union for Conservation of Nature (IUCN) has listed it as Vulnerable.

The Hortle's whipray is a little-known species of stingray in the family Dasyatidae, occurring in shallow estuaries and mud flats off southern New Guinea. This species, growing to 71 cm (28 in) across, has a heart-shaped pectoral fin disc with a long, pointed snout and minute eyes. It has a wide dorsal band of dermal denticles extending from in front of the eyes to the tail, as well as scattered sharp denticles on the snout. The underside of the disc is a distinctive bright yellow in color, sometimes with darker markings around the nostrils, mouth, and gill slits. The Hortle's whipray is threatened by extensive seine fisheries and habitat degradation, leading the International Union for Conservation of Nature (IUCN) to assess it as Near Threatened.

<span class="mw-page-title-main">Black-spotted whipray</span> Species of stingray in the family Dasyatidae

The black-spotted whipray is a species of stingray in the family Dasyatidae, found in the coastal waters off southern New Guinea and northern Australia. Long thought to be a variant of the related brown whipray, this species has an angular, diamond-shaped pectoral fin disc and a whip-like tail without fin folds. It is characterized by its dorsal color pattern, which consists of a variably extensive covering of small, close-set dark, and sometimes also white spots, on a grayish-brown background. In addition, the tail has alternating light and dark saddles past the stinging spine. This species reaches a maximum recorded width of 80 cm (31 in).

<span class="mw-page-title-main">Brown whipray</span> Species of cartilaginous fish

The brown whipray is a species of stingray in the family Dasyatidae, common in inshore, muddy habitats along the northern coast of Australia. It has often been confused in literature for the honeycomb stingray and the black-spotted whipray, which until recently was thought to be the same species. This species has an angular, diamond-shaped pectoral fin disc and a long, very thin tail without fin folds. It is plain brown above, sometimes with white dots or flecks near the edge of the disc, and white below; the tail is dark all over, with alternating dark and light bands near the tip. The maximum recorded disc width is 74 cm (29 in).

<span class="mw-page-title-main">Blackedge whipray</span> Species of cartilaginous fish

The blackedge whipray is a little-known species of stingray in the family Dasyatidae, found in the coastal waters of the Bay of Bengal and the Gulf of Mannar. Attaining a disc width of 1.8 m (5.9 ft), this species has a diamond-shaped disc with two small concavities on either side of the snout tip, and a long, whip-like tail without tail folds. It is characterized by large thorns with star-shaped bases scattered over the disc, and by the wide, black marginal bands on the underside of the disc. The International Union for Conservation of Nature (IUCN) currently lacks sufficient data to assess the blackedge whipray beyond Data Deficient.

<span class="mw-page-title-main">Leopard whipray</span> Species of cartilaginous fish

The leopard whipray is a little-known species of stingray in the family Dasyatidae, found in the Indian and Pacific Oceans from the Andaman Sea to the Coral Triangle. It is found close to shore at depths shallower than 70 m (230 ft), over soft substrates. Attaining a width of 1.8 m (5.9 ft), this species has a diamond-shaped pectoral fin disc with a pointed snout and an extremely long, whip-like tail without fin folds. Adult rays have a leopard-like dorsal pattern of dark brown rings on a yellowish brown background, as well as a row of enlarged, heart-shaped dermal denticles along the midline of the disc. Newborns and small juveniles have large, solid dark spots and few denticles. The leopard whipray is caught by fisheries in many parts of its range, primarily for meat.

<span class="mw-page-title-main">Honeycomb whipray</span> Species of cartilaginous fish

The honeycomb whipray is a species of stingray in the family Dasyatidae, found widely in the shallow coastal waters of the Indo-Pacific from India to the Malay Archipelago. This large species grows to 1.3 m (4.3 ft) across and has a diamond-shaped disc with rounded corners and a projecting, pointed snout. Its tail is long and whip-like, without fin folds. Adults have a striking dorsal color pattern consisting of large, dark brown rings and reticulations delineated by thin yellow lines, while juveniles have a pattern of large dark spots. This ray can also be distinguished from its similar relatives by an enlarged, pearl-like dermal denticle at the center of the back, which is followed by a few thorns. The International Union for Conservation of Nature (IUCN) has assessed the honeycomb whipray as endangered, as it faces heavy fishing pressure and habitat degradation across much of its range.

References

  1. 1 2 Kyne, P.M. (2016). "Urogymnus dalyensis". IUCN Red List of Threatened Species . 2016: e.T195319A104250402. doi: 10.2305/IUCN.UK.2016-3.RLTS.T195319A104250402.en . Retrieved 26 July 2023.
  2. 1 2 3 4 5 6 Last, P.R.; Manjaji-Matsumoto, B.M. (2008). "Himantura dalyensis sp. nov., a new estuarine whipray (Myliobatoidei: Dasyatidae) from northern Australia". In Last, P.R.; W.T. White; J.J. Pogonoski (eds.). Descriptions of new Australian Chondrichthyans. CSIRO Marine and Atmospheric Research. pp. 283–291. ISBN   978-0-1921424-1-2. (corrected) ISBN   1-921424-18-2 (invalid, listed in publication).
  3. 1 2 Froese, Rainer; Pauly, Daniel (eds.) (2018). "Urogymnus dalyensis" in FishBase . October 2018 version.
  4. Last, P.R.; J.D. Stevens (2009). Sharks and Rays of Australia (second ed.). Harvard University Press. p. 442443. ISBN   978-0-674-03411-2.