Crocodile shark
Encyclopedia
The crocodile shark is a species 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...

 and the only member of the family Pseudocarchariidae. A specialized inhabitant of the mesopelagic zone, the crocodile shark can be found worldwide in tropical waters from the surface to a depth of 590 m (1,935.7 ft). It performs a diel vertical migration
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...

, staying below a depth of 200 m (656.2 ft) during the day and ascending into shallower water at night to feed. Typically measuring only 1 m (3.3 ft) in length, the crocodile shark is the smallest living 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...

. It can be distinguished by its elongated cigar-shaped body, extremely large eyes, and relatively small fins.

An active-swimming predator of pelagic bony fishes, 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 shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

, the crocodile shark has a sizable oily liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

 that allows it to maintain its position in the water column with minimal effort. The size and structure of its eyes suggests that it is adapted
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....

 for hunting at night. The crocodile shark is aplacental viviparous, with females typically giving birth to litters of four. The fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

es are 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 ....

, meaning that they feed on undeveloped eggs ovulated
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...

 for this purpose by their mother. Due to its small size, the crocodile shark poses little danger to humans and is of little commercial
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...

 importance. However, substantial numbers are caught as 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...

, leading it to be assessed as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...

 by the International Union for Conservation of Nature (IUCN). This species was responsible for damaging deep sea
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...

 fiberoptic cables
Optical fiber cable
An optical fiber cable is a cable containing one or more optical fibers. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed....

 when the technology was first deployed in 1985.

Taxonomy and phylogeny

The English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

 "crocodile shark" is derived from its Japanese
Japanese language
is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

 name mizuwani (水鰐, literally "water crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

"), which refers to its sharp teeth and habit of snapping vigorously when taken out of the water. Other common names for this species include Japanese ragged-tooth shark, Kamohara's sand-shark, and water crocodile. The crocodile shark was first described as Carcharias kamoharai in a 1936 issue of Zoological Magazine (Tokyo) by ichthyologist Kiyomatsu Matsubara, based on a 73.5 cm (28.9 in) long specimen found at the Koti Fish Market in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. The type specimen is a 1 m (3.3 ft) long adult male found at a fish market in Su-ao
Su-ao, Yilan
Su-ao , located in southern Yilan County, Taiwan, is an urban township that is famous for its seafood restaurants and cold springs. It is the destination of National Highway No. 5, Su-ao-Hualian Express Way, and North-Link Line of Taiwan Railway Administration...

, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

.

After being shuffled between the genera Carcharias
Carcharias
Sand sharks, or sand tigers, are lamniform sharks of the family Odontaspidae . They are found on both sides of the Atlantic coast, but most notably in the western Indian Ocean and in the Gulf of Maine...

and Odontaspis
Odontaspis
Odontaspis is one of two genera in the sand shark family, Odontaspididae. They are large-bodied sharks with long, conical snouts, broad-based dorsal and anal fins, and an asymmetrical caudal fin with a strong lower lobe. Their teeth are large, with prominent narrow cusps...

in the family Odontaspididae by various authors, in 1973 Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...

 resurrected Jean Cadenat's 1963 subgenus Pseudocarcharias from synonymy
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...

 for this species and placed it within its own family. The morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 of the crocodile shark suggests affinity with the megamouth shark
Megamouth shark
The megamouth shark, Megachasma pelagios, is an extremely rare species of deepwater shark. Since its discovery in 1976, only a few megamouth sharks have been seen, with 53 specimens known to have been caught or sighted as of 2011, including three recordings on film...

 (Megachasmidae), basking shark
Basking shark
The basking shark is the second largest living fish, after the whale shark. It is a cosmopolitan migratory species, found in all the world's temperate oceans. It is a slow moving and generally harmless filter feeder and has anatomical adaptations to filter feeding, such as a greatly enlarged...

 (Cetorhinidae), thresher shark
Thresher shark
Thresher sharks are large lamniform sharks of the family Alopiidae. Found in all temperate and tropical oceans of the world, the family contains three species all within the genus Alopias.-Taxonomy:...

s (Alopiidae), and mackerel sharks
Lamnidae
Lamnidae is a family of sharks, commonly known as mackerel sharks or white sharks. They are large, fast-swimming sharks, found in oceans worldwide....

 (Lamnidae). More recent phylogenetic analyses, based on mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...

, have suggested that the crocodile shark is closely related to either the megamouth shark or the sand shark
Sand shark
Sand sharks, also known as sand tiger sharks or ragged tooth sharks, are lamniform sharks of the family Odontaspididae . They are found worldwide in temperate and tropical waters, including on both sides of the Atlantic coast, but most notably in the Western Indian Ocean and in the Gulf of Maine...

s (Odontaspididae). Alternately, analysis based on dentition
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...

 suggests that the closest relatives of the crocodile shark are the thresher sharks, followed by the mackerel sharks. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 Pseudocarcharias teeth dating to the Serravallian
Serravallian
The Serravallian is in the geologic timescale an age or a stage in the middle Miocene epoch/series, that spans the time between 13.65 ± 0.05 Ma and 11.608 ± 0.005 Ma...

 age (13.6–11.6 Ma) of the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...

 epoch have been found in Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, and are identical to those of the modern-day crocodile shark.

Distribution and habitat

The crocodile shark is almost circumtropical in distribution. In the Atlantic Ocean
Atlantic 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...

, it is known from off 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...

, Cape Verde
Cape Verde
The Republic of Cape Verde is an island country, spanning an archipelago of 10 islands located in the central Atlantic Ocean, 570 kilometres off the coast of Western Africa...

, Guinea-Bissau
Guinea-Bissau
The Republic of Guinea-Bissau is a country in West Africa. It is bordered by Senegal to the north, and Guinea to the south and east, with the Atlantic Ocean to its west....

, Guinea
Guinea
Guinea , officially the Republic of Guinea , is a country in West Africa. Formerly known as French Guinea , it is today sometimes called Guinea-Conakry to distinguish it from its neighbour Guinea-Bissau. Guinea is divided into eight administrative regions and subdivided into thirty-three prefectures...

, Angola
Angola
Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...

, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, and Saint Helena Island
Saint Helena
Saint Helena , named after St Helena of Constantinople, is an island of volcanic origin in the South Atlantic Ocean. It is part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha which also includes Ascension Island and the islands of Tristan da Cunha...

, though it has not yet been reported from the northwestern Atlantic. In 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...

, it occurs in the Mozambique Channel
Mozambique Channel
The Mozambique Channel is a portion of the Indian Ocean located between the island nation of Madagascar and southeast Africa, primarily the country of Mozambique. It was a World War II clashpoint during the Battle of Madagascar...

 and possibly the Agulhas Current
Agulhas Current
The Agulhas Current is the Western Boundary Current of the southwest Indian Ocean. It flows down the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong...

 and the Bay of Bengal
Bay of Bengal
The Bay of Bengal , the largest bay in the world, forms the northeastern part of the Indian Ocean. It resembles a triangle in shape, and is bordered mostly by the Eastern Coast of India, southern coast of Bangladesh and Sri Lanka to the west and Burma and the Andaman and Nicobar Islands to the...

. In the Pacific, it occurs from Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

, and the Korean Peninsula
Korean Peninsula
The Korean Peninsula is a peninsula in East Asia. It extends southwards for about 684 miles from continental Asia into the Pacific Ocean and is surrounded by the Sea of Japan to the south, and the Yellow Sea to the west, the Korea Strait connecting the first two bodies of water.Until the end of...

 in the northwest, southward to Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, and eastward to the western coast of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

 from Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...

 to Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

, including the Marshall
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...

, Phoenix
Phoenix Islands
The Phoenix Islands are a group of eight atolls and two submerged coral reefs, lying in the central Pacific Ocean east of the Gilbert Islands and west of the Line Islands. They are a part of the Republic of Kiribati. During the late 1930s they became the site of the last attempted colonial...

, Palmyra
Palmyra Atoll
Palmyra Atoll is an essentially unoccupied equatorial Northern Pacific atoll administered as an unorganized incorporated territory by the United States federal government...

, Johnston
Johnston Atoll
Johnston Atoll is a atoll in the North Pacific Ocean about west of Hawaii. There are four islands located on the coral reef platform, two natural islands, Johnston Island and Sand Island, which have been expanded by coral dredging, as well as North Island and East Island , an additional two...

, Marquesas
Marquesas Islands
The Marquesas Islands enana and Te Fenua `Enata , both meaning "The Land of Men") are a group of volcanic islands in French Polynesia, an overseas collectivity of France in the southern Pacific Ocean. The Marquesas are located at 9° 00S, 139° 30W...

, Line
Line Islands
The Line Islands, Teraina Islands or Equatorial Islands, is a chain of eleven atolls and low coral islands in the central Pacific Ocean, south of the Hawaiian Islands, that stretches for 2,350 km in a northwest-southeast direction, making it one of the longest islands chains of the world...

, and Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...

 in between.

From distribution records, the crocodile shark's range seems to be bound by the latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s 37°N and 44°S, where the average sea surface temperature is 20°C (68°F). This species is not evenly distributed but is rather locally abundant in certain areas, suggesting that it is not strongly migratory
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...

. The crocodile shark is usually found in the pelagic zone
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...

 from the surface to a depth of 590 m (1,940 ft). It is occasionally encountered inshore near the bottom and has been known to strand on the beaches of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, possibly after being stunned by upwellings of cold water.

Description

The crocodile shark has a spindle-shaped body with a short head and a bulbous, pointed snout. The eyes are very large and lack nictating membranes (protective third eyelids). The five pairs of gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...

s are long, extending onto the dorsal
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...

 surface. The sizable, arched jaws can be protruded almost to the tip of the snout and contain large teeth, shaped like spikes in the front and knives on the sides. There are fewer than 30 tooth rows in either jaw; in the upper jaw, the first two large teeth are separated from the lateral teeth by a row of small intermediate teeth.

The pectoral fins are small, broad, and rounded. The pelvic fins are nearly as large as the pectorals. The first 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...

 is small, low and angular; the second dorsal fin is smaller than the first but larger than the anal fin. The caudal fin is asymmetrical with a moderately long upper lobe. The caudal peduncle is slightly compressed with weak lateral keels. The dermal denticles are small, with a flattened crown bearing small ridges and backward-pointing cusps It is dark brown above and paler below, sometimes with a few dark blotches on the sides and belly and/or a white blotch between the corner of the mouth and the first gill slit. The fins have thin translucent to white margins. The crocodile shark grows to a maximum length of 1.1 m (3.6 ft). Most individuals are 1 m (3 ft) long and weigh 4–6 kg (9–13 lbs).

Biology and ecology

With a long body, small fins, and large liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

 rich in squalene
Squalene
Squalene is a natural organic compound originally obtained for commercial purposes primarily from shark liver oil, though plant sources are used as well, including amaranth seed, rice bran, wheat germ, and olives. All plants and animals produce squalene, including humans...

 and other low-density lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

s, the crocodile shark is convergently similar
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 to mesopelagic
Mesopelagic
The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all...

 dogfish sharks
Squaliformes
Squaliformes is an order of sharks that includes about 97 species in seven families.Members of the order have two dorsal fins, which usually possess spines, no anal fin or nictitating membrane, and five gill slits. In most other respects, however, they are quite variable in form and size...

 such as the cookiecutter shark
Cookiecutter shark
The cookiecutter shark , also called the cigar shark, is a species of small dogfish shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from as deep as . It migrates vertically up to every day, approaching the...

 (Isistius brasiliensis). The liver may comprise a fifth of the shark's weight, and acts as an incompressible float that allows it to maintain neutral buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

 in the water column with little effort. Like many other inhabitants of the mesopelagic zone, the crocodile shark apparently migrates
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...

 closer to the surface at night to feed and descends into deeper water during the day, being rarely found above a depth of 200 m (660 ft) during daytime.

The large eyes of the crocodile shark, equipped with a reflective green or yellow retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

 and lacking an expanded iris, suggest that it is a nocturnal hunter that relies on sight to pick out the silhouettes or bioluminescence
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...

 of its prey. Little is known of the crocodile shark's feeding habits; it is thought to be an active, fast-swimming predator based on its strong musculature, large tail, and behavior when captured. On one occasion, a crocodile shark off Cape Point
Cape Point
Cape Point is a promontory at the southeast corner of the Cape Peninsula, which is a mountainous and scenic landform that runs north-south for about thirty kilometres at the extreme southwestern tip of the African continent in the Republic of South Africa. Table Mountain and the city of Cape Town...

, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, jumped out of the water in pursuit of bait. Its diet
Diet (nutrition)
In nutrition, diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. With the word diet, it is often implied the use of specific intake of nutrition for health or weight-management...

 consists of small to medium-sized bony fishes (including bristlemouths and lanternfish
Lanternfish
Cooper Lanternfishes are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. They are aptly named after their conspicuous use of bioluminescence...

es), 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...

 (including onychoteuthids, mastigoteuthids, pholidoteuthids, and cranchiids) and shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

. Crocodile sharks are not known to be preyed upon by any other species.

The crocodile shark is aplacental viviparous and typically gives birth to litters of four, two pups to each uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...

. The gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...

 is unknown but believed to be long. The 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 have yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...

s at 3–4 cm (1.2–1.6 in) long; once the yolk sac is fully absorbed they become 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 ....

: the mother produces large numbers of thin-walled egg capsules that contain 2–9 eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 each, which are then consumed by the unborn embryos. The abdomens of the embryos become characteristically distended with ingested yolk material, which can make up a quarter of the embryo's total weight. It is unclear how two crocodile shark fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

es manage to share a single uterus, when in some other oophagous mackerel sharks such as the sand tiger shark (Carcharias taurus), only one fetus survives in each uterus. The pups are born at approximately 40 cm (16 in) long; males attain maturity at 74–110 cm (29–43 in) and females at 89–102 cm (35–40 in). There is no defined reproductive season.

Human interactions

With its small size, non-cutting teeth, and oceanic habitat, the crocodile shark is not considered dangerous to human
Human
Humans are the only living species in the Homo genus...

s. However, it has a powerful bite that invites caution. This species is a common 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 various pelagic longline fisheries meant for tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...

 and swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...

. The largest numbers are caught by the Japanese yellowfin tuna
Yellowfin tuna
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...

 fishery and the Australian swordfish fishery, both operating in the Indian Ocean. This species is also sometimes caught on squid jig
Jig (fishing)
Jigging is the practice of fishing with a jig, a type of fishing lure. A jig consists of a lead sinker with a hook molded into it and usually covered by a soft body to attract fish. Jigs are intended to create a jerky, vertical motion, as opposed to spinnerbaits which move through the water...

s and in tuna 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. It is usually discarded due to its small size and low-quality meat
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...

. However, its oily
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...

 liver is potentially valuable. No data is available on the population status of the crocodile shark, though it is probably declining from bycatch mortality. Coupled with its low reproductive rate, this has led the International Union for Conservation of Nature (IUCN) to assessed it as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...

.

After AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...

 installed the first deep sea fiberoptic cable
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

 between Gran Canaria
Gran Canaria
Gran Canaria is the second most populous island of the Canary Islands, with a population of 838,397 which constitutes approximately 40% of the population of the archipelago...

 and Tenerife
Tenerife
Tenerife is the largest and most populous island of the seven Canary Islands, it is also the most populated island of Spain, with a land area of 2,034.38 km² and 906,854 inhabitants, 43% of the total population of the Canary Islands. About five million tourists visit Tenerife each year, the...

 in the Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...

 in September 1985, the system suffered a series of shorts that necessitated costly repairs. It was discovered that attacks from the crocodile shark were responsible for most of the failures, possibly because they were attracted to the electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...

 around the cables. Since crocodile sharks are not benthic in nature, they were presumably biting the cables as they were being deployed. The problem was solved by protecting the cables with a layer of steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 tape beneath a dense polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

coating.

External links

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