Bigeye sand tiger
Encyclopedia
The bigeye sand tiger 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).
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.
, 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 fin
s, 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 jaw
s 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.
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 otolith
s from unidentified bony fishes. Nothing is known of its reproduction, though it is presumed to be aplacental viviparous with oophagous
embryo
s 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.
on longlines, gillnet
s, 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.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of mackerel shark
Lamniformes
Lamniformes is an order of sharks commonly known as mackerel sharks . It includes some of the most familiar species of sharks, such as the great white shark, as well as more unusual representatives, such as the goblin shark and the megamouth shark.Members of the order are distinguished by...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
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
Smalltooth sand tiger
The smalltooth sand tiger or bumpytail ragged-tooth is a species of mackerel shark in the family Odontaspididae, with a patchy but worldwide distribution in tropical and warm temperate waters...
(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
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and is likely aplacental viviparous, as with the other mackerel sharks. The bigeye sand tiger is a bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
of deepwater fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
, but is so infrequently encountered that its population status cannot yet be determined by the International Union for Conservation of Nature (IUCN).
Taxonomy
The first bigeye sand tiger described by science was a 1.7 m (5.6 ft) female caught off MadeiraMadeira
Madeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
on a longline meant for the black scabbardfish
Black scabbardfish
The black scabbardfish, Aphanopus carbo, is a bathypelagic cutlassfish of the family Trichiuridae found in the Atlantic Ocean between latitudes 69° N and 27° N at depths of between 180 and 1,700 m...
(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 OceanAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, where it has been captured from off Madeira
Madeira
Madeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
, southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, and the Mid-Atlantic Ridge
Mid-Atlantic Ridge
The Mid-Atlantic Ridge is a mid-ocean ridge, a divergent tectonic plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. It separates the Eurasian Plate and North American Plate in the North Atlantic, and the African Plate from the South...
. This species may inhabit the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, based on a set of jaws that might have been collected in the Seychelles
Seychelles
Seychelles , officially the Republic of Seychelles , is an island country spanning an archipelago of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar....
. The presence of the bigeye sand tiger in the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
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
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
and Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
.
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
Spring (season)
Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...
, suggesting some type of migratory movement
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
.
Description
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the 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
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
and lacking a nictating membrane.
There are two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s, 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 jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
s and on the tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
. 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
Deep sea
The deep sea, or deep layer, is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms or more. Little or no light penetrates this part of the ocean and most of the organisms that live there rely for subsistence on falling organic matter...
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
Diel vertical migration
Diel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone...
into the epipelagic zone at night to feed. The stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
of a specimen from the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
contained squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
beaks and otolith
Otolith
An otolith, , also called statoconium or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. The saccule and utricle, in turn, together make the otolith organs. They are sensitive to gravity and linear acceleration...
s from unidentified bony fishes. Nothing is known of its reproduction, though it is presumed to be aplacental viviparous with oophagous
Oophagy
Oophagy , literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek ᾠόν and classical Greek φᾱγεῖν ....
embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s 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.
Human interactions
The bigeye sand tiger is caught as bycatchBycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
on longlines, gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
s, 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
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
. The National Marine Fisheries Service
National Marine Fisheries Service
The National Marine Fisheries Service is a United States federal agency. A division of the National Oceanic and Atmospheric Administration and the Department of Commerce, NMFS is responsible for the stewardship and management of the nation's living marine resources and their habitat within the...
(NMFS) prohibits the taking of this species in United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
waters.