- Bigeye sand tiger
Bigeye sand tiger Conservation status Scientific classification Kingdom: Animalia Phylum: Chordata Class: Chondrichthyes Subclass: Elasmobranchii Order: Lamniformes Family: Odontaspididae Genus: Odontaspis Species: O. noronhai Binomial name Odontaspis noronhai
Range of the bigeye sand tiger Synonyms
Carcharias noronhai Maul, 1955
The bigeye sand tiger (Odontaspis noronhai) is a species of mackerel shark in the family Odontaspididae, possibly found worldwide at depths of 60–1,000 m (200–3,300 ft). It is extremely rare and poorly-known: despite intense fishing activity in many parts of its presumed range, only around 15 specimens have ever been captured. This species can be distinguished from the similar smalltooth sand tiger (O. ferox) by the shape of its teeth, which have only a single lateral cusp on each side, and by its uniform dark brown color. Little is known of its biology; it appears to feed on fish and squid and is likely aplacental viviparous, as with the other mackerel sharks. The bigeye sand tiger is a bycatch of deepwater fisheries, but is so infrequently encountered that its population status cannot yet be determined by the International Union for Conservation of Nature (IUCN).
The first bigeye sand tiger described by science was a 1.7 m (5.6 ft) female caught off Madeira on a longline meant for the black scabbardfish (Aphanopus carbo). The ichthyologist G. E. Maul named this species for Adolfo César de Noronha, late Director of the Funchal Museum. Until more specimens were examined and compared in the 1980s, some authors speculated that this species might represent a variant of the smalltooth sand tiger.
Distribution and habitat
The few known specimens of the bigeye sand tiger originated from locations scattered around the world. Most records are from the Atlantic Ocean, where it has been captured from off Madeira, southern Brazil, Texas, and the Mid-Atlantic Ridge. This species may inhabit the Indian Ocean, based on a set of jaws that might have been collected in the Seychelles. The presence of the bigeye sand tiger in the Pacific Ocean was at first suspected based on several teeth recovered from bottom sediments in the central North Pacific, more than a decade before definitive captures were made off the Marshall Islands and Hawaii.
The bigeye sand tiger is found over the continental slope from a depth of 100 m (330 ft) to over 1,000 m (3,300 ft) near the sea floor. It also occurs in the open ocean at a depth of 60–450 m (200–1,500 ft) in water 4.5–5.3 km (2.8–3.3 mi) deep. Off Brazil, bigeye sand tigers are only captured in a specific area in spring, suggesting some type of migratory movement.
The bigeye sand tiger is similar in appearance to the better-known sand tiger shark (Carcharias taurus), with a bulky body, bulbous pointed snout, and large mouth containing several rows of projecting teeth. Tooth shape is the most reliable way of distinguishing this species from Odontaspis ferox: in this species the teeth have a narrow central cusp with one small lateral cusp on each side, whereas in O. ferox there are two or three lateral cusps on each side. There are 34–43 tooth rows in the upper jaw and 37–46 rows in the lower; the large upper front teeth are separated from the lateral tooth rows by usually a single row of intermediate teeth. The eyes are relatively large and orange in color, with a greenish pupil and lacking a nictating membrane.
There are two dorsal fins, the first larger than the second and located closer to the pectoral fins than the pelvic fins. The first dorsal fin, pectoral fins, and anal fin have rounded tips. A pair of upper precaudal pits are present. The caudal fin is long and strongly asymmetrical, with an indistinct lower lobe. This species is dark chocolate brown to reddish brown in color. There are several black patches inside the mouth, such as around the jaws and on the tongue. The fins are black, sometimes with a white tip on the first dorsal fin or thin dark posterior margins. The maximum known length is 3.6 m (12 ft) for a male and 3.3 m (11 ft) for a female.
Biology and ecology
Accounts of bigeye sand tigers captured alive note extremely aggressive behavior, thrashing and snapping violently in and out of the water. Its large eyes suggest deepwater or nocturnal habits. The nighttime capture of bigeye sand tigers on pelagic longlines set at relatively shallow depths brings up the possibility that it migrates vertically into the epipelagic zone at night to feed. The stomach of a specimen from the Gulf of Mexico contained squid beaks and otoliths from unidentified bony fishes. Nothing is known of its reproduction, though it is presumed to be aplacental viviparous with oophagous embryos as with the other members of its family. Males and females are sexually immature at 2.2 m (7.2 ft) and 3.2 m (10.5 ft) respectively, indicating that maturation occurs at a larger size than in the sand tiger shark.
The bigeye sand tiger is caught as bycatch on longlines, gillnets, and purse seines, though aspects of its behavior may limit its susceptibility to such gear, hence the paucity of captures. This species is seldom utilized, and there is insufficient information for the International Union for Conservation of Nature (IUCN) to assess its conservation status beyond Data Deficient. The National Marine Fisheries Service (NMFS) prohibits the taking of this species in United States waters.
- ^ Amorim, A.F., Arfelli, C.A. and Fagundes, L. (2005). "Odontaspis noronhai". IUCN Red List of Threatened Species. Version 2010.1. International Union for Conservation of Nature. http://www.iucnredlist.org/apps/redlist/details/39336. Retrieved May 8, 2010.
- ^ a b c d e f Kerstetter, D.W. and Taylor, M.L. (2008). "Live release of a bigeye sand tiger Odontaspis noronhai (Elasmobranchii: Lamniformes) in the Western North Atlantic Ocean". Bulletin OF Marine Science 83 (3): 465–469.
- ^ Maul, G.E. (Jun. 30, 1955). "Five species of rare sharks new for Madeira including two new to science". Notulae Naturae of the Academy of Natural Sciences of Philadelphia 279: 1–14.
- ^ a b c d e Martin, R.A. Biology of the Bigeye Ragged-Tooth Shark (Odontaspis noronhai). ReefQuest Centre for Shark Research. Retrieved on April 18, 2009.
- ^ a b c d e f g Compagno, L.J.V. (2002). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date (Volume 2). Rome: Food and Agriculture Organization of the United Nations. ISBN 9251045437.
- ^ a b Humphreys (Jr), R.L., Moffitt, R.B. and Seki, M.P. (1989). "First record of the bigeye sand tiger shark Odontaspis noronhai from the Pacific Ocean". Japanese Journal of Ichthyology 36 (3): 357–362.
- ^ Froese, Rainer, and Daniel Pauly, eds. (2009). "Odontaspis noronhai" in FishBase. April 2009 version.
Extant mackerel shark species Kingdom Animalia · Phylum Chordata · Subphylum Vertebrata · Class Chondrichthyes · Subclass Elasmobranchii · Subdivision Selachii Alopiidae CetorhinidaeCetorhinus LamnidaeCarcharodon MegachasmidaeMegachasma MitsukurinidaeMitsukurina OdontaspididaeSmalltooth sand tiger (O. ferox) · Bigeye sand tiger (O. noronhai) PseudocarchariidaePseudocarcharias
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