A rare Sandtiger shark that may be a deep-water oceanic shark
The Bigeye Sandtiger (Odontaspis noronhai) is an extremely rare species of shark belonging to the family Odontaspididae, with a possible worldwide distribution. The Bigeye Sandtiger has only been spotted in a few locations, and is possibly a deep midwater oceanic shark, which its coloring supports. Research suggests that they may make diel vertical migrations. They are a large and bulky shark. There are a few characteristics that differentiate this shark from the other members of its family.
Family: Odontaspididae – Sandtiger sharks
Common Name– Mackerel Sharks
Common Name– Sandtiger Sharks
Status: IUCN Red List DATA DEFICIENT
Average Size and Length: Their length at birth is unknown. Mature males have been measured at greater than 220 cm/7.2 feet. Mature females have been measured at an average of 325 cm/10.7 feet. The maximum recorded length has been 360 cm/11.8 feet.
Current Rare Mythical Sightings: The first specimen was a female 5.6 feet long caught off Madeira in April 1941, on a longline set for Black Scabbardfish (Aphanopus carbo). The specimen was mounted and later formed the basis for a scientific description authored by German ichthyologist Günther Maul in a 1955 article for Notulae Naturae. He named the species noronhai in honor of Adolfo César de Noronha, the late Director of the Funchal Museum. Originally Maul assigned this new species to the genus Carcharias, which at the time was used for all members of the Sandtiger Sharks. When the Odontaspis came to be recognized as a valid genus separate from Carcharias, the Bigeye Sandtiger was reassigned as well given its resemblance to the Smalltooth Sandtiger (O. ferox). (Maul, G., 1955).
Teeth and Jaw: The mouth is large with the narrow teeth prominently exposed. It can be distinguished from the similar Smalltooth Sandtiger (O. ferox) by its teeth, which have only one lateral cusplet on each side. The corner of the mouth extends to behind the level of the eyes. There are several black patches inside the mouth, around the jaws, on the floor of the mouth.
There are 34–43 upper and 37–46 lower tooth rows; these include zero to two rows of small teeth at the upper symphysis (jaw midpoint) and two to four more rows at the lower symphysis. In each half of the upper jaw, the teeth in the first and second rows are large, those in the third and sometimes fourth rows are small, and those in the rows after are large again. Each tooth has a narrow, awl-like central cusp flanked by one smaller cusplet on each side; this contrasts with the Smalltooth Sandtiger, which has two or three lateral cusplets on each side.
Head: The Bigeye Sandtiger has very large eyes with an orangish hue, and green tinted pupils. They do not have nictitating membranes. The large eyes support the hypothesis that they are a mid to deep water oceanic shark. There are small spiracles just behind the eyes. The snout is large and bulbous.
Denticles: The skin is covered by overlapping dermal denticles, each with three horizontal ridges leading to marginal teeth.
Tail: The caudal peduncle has a crescent-shaped notch at the dorsal origin of the caudal fin. The lower lobe of the caudal fin is short but distinct, while the upper lobe is long and has a deep notch in the trailing margin near the tip.
Demographic, Distribution, Habitat, Environment and Range: The Bigeye Sandtiger is known from just a few confirmed records in the Atlantic and Central Pacific Oceans. Most known specimens have come from the Atlantic, where it has been found off Madeira, southern Brazil, Texas, eastern Florida, and the Mid-Atlantic Ridge. In the Pacific, they have been found from the Marshall Islands and Hawaii. The only evidence for its presence in the Indian Ocean is a set of jaws that may have originated from the Seychelles, though the South China Sea is another possibility. They may be worldwide in deep warm seas. They have been found in midwater in the open ocean near the bottom on the continental and island slopes in depths of 1,969-3,281 feet. It may spend most of its time in the mesopelagic zone. Research suggests that they may perform diel vertical migrations in the mid-ocean coming near the surface at night and staying in deep water by day. They may even participate in seasonal migration movements.
Diet: More than likely, it feeds on bony fishes and squid.
Aesthetic Identification: The Bigeye Sandtiger is a large and bulky shark. There are five pairs of gill slits, and there are black patches on the gill arches. The Bigeye Sandtiger differs from other Sandtiger sharks by being uniform unspotted dark reddish-brown to black color above and below. Their uniform coloring suggests that they are an oceanic midwater species. The first dorsal fin is larger than the second dorsal fin and anal fin. There is often a white blotch on the tip.
The pectoral fins are medium-sized and broad with rounded tips. The large first dorsal fin has a rounded apex and is positioned closer to the pectoral than the pelvic fins. The second dorsal fin is about half the size of the first and originates over the rear tips of the pelvic fins. The pelvic fins are almost as large as the first dorsal fin. The anal fin is smaller than the second dorsal fin and positioned behind it.
Biology and Reproduction: Their biology is unknown. Quite possibly they are ovoviviparous with oophagy like its other family members.
Males mature sexually at somewhere between 7.2 and 10.5 feet long, while females mature at around 10 feet long. No data is known on growth or aging.
A 2012 molecular phylogenetic analysis, based on mitochondrial DNA, supported a sister species relationship between O. noronhai and O. ferox but not a clade consisting of Odontaspis and Carcharias. Instead, Odontaspis was found to be closer to the Crocodile shark (Pseudocarcharias kamoharai), suggesting that it and Carcharias should be placed in separate families. (Naylor, G.J.; Caira, J.N.; Jensen, K.; Rosana, K.A.; Straube, N.; Lakner, C. (2012). “Elasmobranch phylogeny: A mitochondrial estimate based on 595 species“. In Carrier, J.C.; Musick, J.A.; Heithaus, M.R. (eds.). The Biology of Sharks and Their Relatives (second ed.). CRC Press. pp. 31–57.).
Behavioral Traits, Sensing and Intelligence: Their behavior is poorly known. They may perform diel vertical migrations.
One account of a Bigeye Sandtiger that had been caught alive noted that it behaved very aggressively, thrashing and snapping violently in and out of the water. (Humphreys R.L. Jr.; Moffitt, R.B.; 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.).
Bigeye Sandtiger Shark Future and Conservation: There is not enough data to evaluate. It has been caught incidentally by commercial fisheries on longlines and gillnets. Since 1997, the National Marine Fisheries Service (NMFS) has prohibited the taking of this species in United States waters.
Bigeye Sandtiger Shark Recorded Attacks on Humans: Not a threat to humans.