Behavior

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The large eyes of crocodile sharks suggest that it is a visual hunter, specializing in bioluminescent and light-refracting prey (Martin 2003). Additionally, the crocodile shark is electroreceptive; it can sense changes in the surrounding electrical field (Martin 2003). Sharks, in general, also have a keen sense of chemical perception.

Communication Channels: visual ; electric

Other Communication Modes: photic/bioluminescent

Perception Channels: visual ; tactile ; chemical ; electric

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Conservation Status

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Due to small size and wide range in habitat, very little information has been accumulated on crocodile sharks. The current population size is unknown, however, crocodile sharks are vulnerable to catching by long-line fisheries (Martin 2003). There is no information to indicate trends in population size, but due to bycatch a population decline is probable (Compagno 2002). As a result, the IUCN Red List of Threatened Species has labeled crocodile sharks at low risk for extinction.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: near threatened

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Life Cycle

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At birth, crocodile sharks are 41 cm in length (Compagno 1984). Males mature at a length of about 74 to 100 cm and females mature at a length of about 89 to 102 cm (Martin 2003).

Development - Life Cycle: indeterminate growth

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Benefits

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Crocodile sharks have never been implicated in attacks on humans and are deemed harmless (Martin 2003). Thus, there are no known adverse effects of crocodile sharks on humans.

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Benefits

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Crocodile sharks do not provide many benefits to humans; their large, squalene-rich liver is a source of potential value (Martin 2003). However, crocodile sharks generally are discarded due to their small size and useless flesh (Compagno 1984).

Positive Impacts: body parts are source of valuable material

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Associations

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Very little is known about the role crocodile sharks play in the ecosystem to which they belong. However, sharks in general are usually important predators in aquatic ecosystems (Martin 2003).

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Trophic Strategy

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Crocodile sharks are carnivores; they eat small bony fish, squids, and shrimp (Compagno 1984). They have protrusible and muscular jaws that suggest they are capable of eating a wide variety of prey (Martin 2003). Beyond this, very little is known about the specific feeding habits of crocodile sharks.

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore , Molluscivore )

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Distribution

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Pseudocarcharias kamoharai (Crocodile sharks) can be found in nearly all subtropical and tropical oceans of the world (Compagno 1984).

Biogeographic Regions: palearctic (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); oceanic islands (Native ); indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Habitat

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Crocodile sharks are mostly pelagic; however, there have been some incidences where crocodile sharks have been found inshore (Compagno 1984). The known depth range of crocodile sharks from the water surface can reach 590 m (Martin 2003).

Range depth: 590 (high) m.

Habitat Regions: tropical ; saltwater or marine

Aquatic Biomes: pelagic

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Life Expectancy

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There are no data on the lifespan/longevity of crocodile sharks.

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Morphology

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Crocodile sharks are clearly distinguishable by huge eyes that lack nictitating eyelids and long gill slits that extend to the top of the head. Crocodile sharks have a slender, spindle-shaped body with two small, spineless dorsal fins. The second dorsal fin is less than half the size of the first dorsal fin. The pelvic fins are distinctly broad and round (Compagno 1984). Like all Lamniformes, crocodile sharks have 5 gill slits and a mouth that extends behind the eyes (Martin 2003). The size of adult crocodile sharks is on average 89 to 110 cm in length and between 4 to 6 kg in weight. The color of crocodile sharks can range from light to dark grey to dark brown. White or transluscent margins may also be found around the fins (Martin 2003). Some specimens have been found with whitish blotches on either side of the head between the corner of jaw and the first gill slit (Compagno 1984).

Range mass: 4 to 6 kg.

Range length: 89 to 110 cm.

Average length: 105 cm.

Other Physical Features: endothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Associations

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Very little is known about any anti-predator adaptations that the crocodile shark may exhibit. However, when removed from water, the crocodile shark snaps its powerful jaw vigorously, almost like a "crocodile." This may serve as a defense mechanism to fight off predators (Martin 2003). There are no known predators of crocodile sharks.

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Reproduction

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Crocodile sharks reproduce sexually through internal fertilization. There is little information on the mating systems of P. kamoharai.

Crocodile sharks reproduce sexually through internal fertilization. Females are ovoviviparous; they retain the eggs of their offspring until they hatch (Martin 2003). Females exhibit aplacental viviparity; the developing embryos lack a connection to the mother and thus feed on the yolk sac and the other ova produced by the mother (oophagy)(Compagno 1984). The mother typically produces four pups per litter; the pups are miniature adults, capable of swimming and feeding (Martin 2003).

Range number of offspring: 2 to 4.

Average number of offspring: 4.

Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); ovoviviparous

Like all sharks, the crocodile shark provides no parental care after birth.

Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)

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Sharma, N. 2006. "Pseudocarcharias kamoharai" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pseudocarcharias_kamoharai.html
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Nitin Sharma, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Diagnostic Description

provided by FAO species catalogs
fieldmarks: A small, very distinctive oceanic shark, with huge eyes lacking nictitating eyelids, long gill slits, slender, spindle-shaped body, long-cusped prominent teeth in a long angular mouth with highly protrusable jaws, small pectoral fins, two small spineless dorsal fins and an anal fin, weak keels and precaudal pits on the caudal peduncle, an asymmetrical caudal fin with a long ventral lobe. Colour: grey or grey-brown dorsal surface, lighter ventral surface, and light-edged fins. Head much shorter than trunk. Snout moderately long, pointed and bulbously conical, not greatly elongated or flattened and blade-like. Eyes very large, length 3.6 to 4.9% of precaudal length.

Gill openings moderately long, length of first 5.4 to 8.2% of precaudal length, extending onto dorsal surface of head; all gill openings in front of pectoral-fin bases; no gill rakers on internal gill slits.

Mouth large, parabolic, ventral on head; jaws strongly protrusable to almost opposite snout tip but not greatly distensible laterally.

Teeth large, the anteriors narrow and awl-like, the laterals more compressed and blade-like, with 26 to 29/21 to 26 (45 to 52 total) rows; two rows of enlarged anterior teeth on each side of upper jaw, the uppers separated from the smaller upper lateral teeth by a row of small intermediate teeth; three rows of lower anteriors on each side, the first two rows enlarged but the third about as large as laterals; symphysials absent.

Trunk cylindrical and slender. Caudal peduncle slightly depressed and with low lateral keels and upper and lower crescentic precaudal pits present. Dermal denticles small and smooth, with flat crowns, small ridges and cusps, and with cusps directed posteriorly on lateral denticles.

Pectoral fins small, short and broad, much shorter than head in adults

; pectoral skeleton aplesodic with radials confined to fin bases.

Pelvic fins large, somewhat smaller than pectoral and first dorsal fins

; fin skeleton aplesodic.

First dorsal fin small, low, and angular

; fin skeleton aplesodic.

Second dorsal fin smaller than first but larger than anal fin; second dorsal fin with a broad nonpivoting base but anal fin pivotable. Caudal fin not lunate, dorsal lobe moderately long but less than half as long as rest of shark, ventral lobe short but strong.

Neurocranium moderately high, with a short to moderately elongated rostrum, depressed internasal septum and narrowly separated nasal capsules, large orbits with the supraorbital crests strong, small stapedial fenestrae, and with hyomandibular facets not extended outward. Vertebral centra strongly calcified, with well-developed double cones and radii but no annuli. Total vertebral count 146 to 158, precaudal count 80 to 88, diplospondylous caudal count 60 to 71.

Intestinal valve of ring type with 24 to 27 turns.

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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Distribution

provided by FAO species catalogs
Oceanic and circumtropical. Western Atlantic: Off Brazil. Eastern Atlantic: Southeast of Cape Verde Islands, between them and Guinea-Bissau, Guinea, Angola, and South Africa (Western Cape, vicinity of Cape Town and Cape Peninsula). Western Indian Ocean: Mozambique Channel between southern Madagascar, southern Mozambique and KwaZulu-Natal, South Africa, possibly south within Agulhas Current to off Eastern Cape. ? Eastern Indian Ocean: Bay of Bengal (possibly erroneous). Western North Pacific: Off Japan, Taiwan Island and Korean Peninsula; area between Marshall, Howland and Baker, Palmyra, Johnston and Hawaiian Islands. Western South Pacific: Australia (northeastern Queensland), west of New Zealand (North Island), Coral Sea, Indonesia (south of Sumatra near Sunda Straits and off Java). Central Pacific: Marquesas Islands, Hawaiian Islands, open ocean between Marquesas and Hawaiian Islands, open ocean between Hawaiian Islands and Baja California, around Line Islands, open water between Line Islands and southern Peru. Eastern Pacific: Mexico (off west coast of Baja California), Costa Rica, Panama and northern Peru.
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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Size

provided by FAO species catalogs
This is the smallest living lamnoid, with maximum size at least 110 cm; size at birth about 41 cm; males adult at 74 to 110 cm; adolescent females examined 96 to 110 cm and adults recorded at 89 to 110 cm and presumably greater.
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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Brief Summary

provided by FAO species catalogs
A rare to locally abundant oceanic, epipelagic and possibly mesopelagic shark, usually found offshore and far from land but sometimes occurring inshore and near the bottom.Found at depths from the surface to at least 590 m. Its bicolorate, countershaded colour pattern, lack of an expanded iris and prominent green or yellow retinal reflection, and frequent occurrence in pelagic longline catches suggests that it primarily inhabits the epipelagic zone. There are several records of strandings in the Cape Town area, South Africa, possibly due to upwelling of cold water that may stun these sharks but in at least one instance as a discarded catch of an offshore longliner. The long body cavity, large liver, and small fins of this shark (microceanic habitus, Compagno, 1990a) give it a superficial resemblance to Isistius, Squaliolus, Euprotomicrus, Scymnodalatias, and other oceanic squaloids, as well as Odontaspis noronhai, and like these sharks its extremely large and oily liver is probably important in maintaining neutral buoyancy.Its habits are little known, but its firm body musculature, tough skin, small precaudal fins, and large caudal fin suggests that it is a relatively active species, which is also suggested by its behaviour when captured. Off Cape Point, South Africa, one jumped out of the water after a bait and was caught. It snaps strongly and vigorously when captured (S. Kato, pers. comm.) and can bite very hard. The large but nonreflective eyes of the crocodile shark suggest nocturnal activity in the epipelagic zone, and possibly a diel pattern of movement toward the surface at night and away from it in the day. The crocodile shark is ovoviviparous and a uterine cannibal, with the young having yolk sacs at 3 to 4 cm long but reabsorbing them and subsisting on eggs and possibly other young beyond this size. Number of young in a litter four, two per uterus; egg cases formed in the oviducts have 2 to 9 fertilized eggs, but apparently only two of these survive, possibly through elimination of extra rivals. An interesting question is why two young survive in each uterus in this shark and some other lamnoids, while in Carcharias taurus only one foetus per uterus is normally produced.

Feeding habits of this shark are sketchily known. Its long, flexed teeth, strong and long jaws, and its vigorous activity when captured adapt it to moderately large, active oceanic prey. Of seven specimens examined by the writer for stomach contents, the stomachs of four were empty and three others had a number of small bristlemouths (gonostomatids), possibly lanternfish (myctophids), unidentified fish scales, small shrimp, and squid beaks, including onychoteutids ( Moroteuthis robsoni), mastigoteuthids (Mastigoteuthis), pholidoteuthids (Pholidoteuthis ?boschmai), and cranchiids (Megalocranchia?) in their stomachs (M. Roeleveld and M. Lipinski, pers. comm., on identification of squid beaks). The jaws of the crocodile shark can be protruded for a considerable distance from its head.

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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Benefits

provided by FAO species catalogs
This shark is primarily caught as a discarded bycatch of pelagic longline fisheries for scombroids, but details are sketchy. Abe et al. (1969) noted that the species is often caught on tuna longlines, but discarded because of its small size and meat that is apparently unsuitable for the Japanese market. The liver of this species is very large and very high in squalene, and hence is of potential value. It also has been caught on squid jigs and occasionally washes up on beaches in the Cape Town area of South Africa. It may also be a discarded bycatch of pelagic squid fisheries as well as of pelagic net fisheries for scombroid fishes. Conservation Status : Conservation status is uncertain but of concern because of its epipelagic habitat and because it is an apparently widespread, discarded, and largely unrecorded bycatch of the burgeoning pelagic longline fisheries. It is too small to be of much value for fins, and is little-utilized for flesh, but has a large mouth and strong teeth and is readily caught on longline hooks fished near the surface. It does not appear to be abundant anywhere with the known exception of the Mozambique Channel in the western Indian Ocean during the 1960s, and catch records are very limited and largely confined to a small number of specimens (less than 50) deposited in museums. It was assessed as Limited Risk (Near Threatened) for the Red List of the IUCN Shark Specialist Group (L.J.V. Compagno and J.A. Musick, pers. comm.).
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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Diagnostic Description

provided by Fishbase
A medium-sized spindle-shaped shark with very large eyes lacking a nictitating membrane, long gill slits extending onto dorsal surface of head, lanceolate teeth, weak keel and precaudal pits on caudal peduncle (Ref. 6871, 43278). Small and low dorsal fins, with second dorsal fin less than half the size of the first but larger than the anal fin (Ref. 6871). Pectoral fin broad and rounded (Ref. 6871). Light or dark grey above, paler below, fins white-edged, sometimes with small white spots on body and a white blotch between mouth and gill slits (Ref. 13569).
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Recorder
Cristina V. Garilao
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Life Cycle

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Exhibit ovoviparity (aplacental viviparity), with embryos feeding on other ova produced by the mother (oophagy) after the yolk sac is absorbed (Ref. 50449). With 4 young in a litter, born at 40-43 cm (Ref. 11228).
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Recorder
Armi G. Torres
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Migration

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Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.
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Kent E. Carpenter
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Morphology

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Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0
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Cristina V. Garilao
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Trophic Strategy

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An oceanic species usually found offshore and far from land but sometimes occurring inshore. Feeds on small pelagic bony fishes, squids and shrimps.
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Recorder
Drina Sta. Iglesia
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Biology

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An oceanic species usually found offshore and far from land but sometimes occurring inshore (Ref. 9993, 43278, 58302). Epi- and mesopelagic, with occasional near-bottom occurrences (Ref. 43278, 58302). Although considered not dangerous to people, its powerful jaws, jaw muscles and teeth invite respect. Flesh not appreciated and therefore the catch is usually discarded (Ref. 247); utilized for its large, squalene-rich liver (Ref. 9993). Feeds on small pelagic bony fishes, squids and shrimps (Ref. 5578). Ovoviviparous, embryos feeding on yolk sac and other ova produced by the mother (Ref. 50449). With 4 young in a litter, born at 40 to 43 cm TL (Ref. 12288). Maximum length for female given in Romanove et.al 1994 (Ref. 44781). Common bycatch of tuna longline fisheries, and occasionally tuna gillnet fisheries (Ref.58048).
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Recorder
Kent E. Carpenter
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Importance

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fisheries: minor commercial; price category: unknown; price reliability:
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Kent E. Carpenter
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分布

provided by The Fish Database of Taiwan
廣泛分布於世界各熱帶及亞熱帶海域。臺灣東北部及東部海域有分布。
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臺灣魚類資料庫
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臺灣魚類資料庫

利用

provided by The Fish Database of Taiwan
主要以底拖網或深海延繩釣捕獲。肉質不佳,一般皆被漁民丟棄或以下雜魚處理;或有人利用其大且富含鯊烯(Squalene)的肝臟,加工成魚肝油,唯有報導食用大量鯊烯會引起中毒現毒。
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描述

provided by The Fish Database of Taiwan
體呈紡錘型,細長。頭稍平扁。尾基上下方具一凹窪;尾柄具側突。吻中長而呈圓錐形。眼下,圓形,無瞬膜。前鼻瓣短而圓。口裂寬,深弧形,下頜較短,口閉時露齒;頜齒同型,錐狀,向內斜曲,齒根分叉,少數齒具小齒尖,大部分無。噴水孔小。背鰭2個,同型,第一背鰭稍大,起點於體中部,後緣斜直,上角鈍圓,下角微尖突;第二背鰭較小,起點與腹鰭後端相對,後緣斜直,上角鈍圓,下角微尖突;胸鰭寬小型,後緣微弧形,外角鈍圓,內角寬圓,鰭端伸達遠不及第一背鰭基底前部;尾鰭中長,尾椎軸稍上揚,上葉狹長,下葉前部顯著三角形突出,中部狹長,與後部間有一深缺刻,後部小三角形突出與上葉相連,尾端斜,後緣略凹入。體背側灰褐或暗褐色;腹側暗灰色。各鰭均呈暗褐色,後緣具狹白邊。
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棲地

provided by The Fish Database of Taiwan
大洋性近底棲中小型鯊魚,白天一般棲息於外海深達300公尺以下的水域,晚上會遷移至水上層覓食,有時會出現於近海淺水區。以小型硬骨魚、烏賊及蝦類為食。卵胎生,胎兒在子宮內有同種相殘習性,一胎可產下2-4尾幼鯊,剛產下之幼鯊體長可達40公分左右。不曾有報導其會攻擊人類,但強而有力的上下頜及利齒仍值得敬畏。
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Crocodile shark

provided by wikipedia EN

The crocodile shark (Pseudocarcharias kamoharai) is a species of mackerel shark and the only extant 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 (1,940 ft). It performs a diel vertical migration, staying below a depth of 200 m (660 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. 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 and shrimp, the crocodile shark has a sizable oily liver 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 for hunting at night. The crocodile shark is aplacental viviparous, with females typically giving birth to litters of four. The fetuses are oophagous, meaning that they feed on undeveloped eggs ovulated for this purpose by their mother. Due to its small size, the crocodile shark poses little danger to humans and is of little commercial importance. This species was responsible for damaging deep sea fiberoptic cables when the technology was first deployed in 1985.

Taxonomy and phylogeny

The English common name "crocodile shark" is derived from its Japanese name mizuwani (水鰐, literally "water crocodile"), which refers to its sharp teeth and habit of snapping vigorously when taken out of the water.[2] Other common names for this species include Japanese ragged-tooth shark, Kamohara's sand-shark, and water crocodile.[3] 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.[4] The type specimen is a 1 m (3.3 ft) long adult male found at a fish market in Su-ao, Taiwan.[5]

After being shuffled between the genera Carcharias and Odontaspis in the family Odontaspididae by various authors, in 1973 Leonard Compagno resurrected Jean Cadenat's 1963 subgenus Pseudocarcharias from synonymy for this species and placed it within its own family.[2][5] The morphology of the crocodile shark suggests affinity with the megamouth shark (Megachasmidae), basking shark (Cetorhinidae), thresher sharks (Alopiidae), and mackerel sharks (Lamnidae). More recent phylogenetic analyses, based on mitochondrial DNA, have suggested that the crocodile shark is closely related to either the megamouth shark or the sand sharks (Odontaspididae). Alternately, analysis based on dentition suggests that the closest relatives of the crocodile shark are the thresher sharks, followed by the mackerel sharks.[5] Fossil Pseudocarcharias teeth dating to the Serravallian age (13.6–11.6 Ma) of the Miocene epoch have been found in Italy, and are identical to those of the modern-day crocodile shark.[6]

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 slits are long, extending onto the dorsal 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.[5]

The pectoral fins are small, broad, and rounded. The pelvic fins are nearly as large as the pectorals. The first dorsal fin 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[5] 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.[7] 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).[7]

Distribution and habitat

The crocodile shark is almost circumtropical in distribution. In the Atlantic Ocean, it is known from off Brazil, Cape Verde, Guinea-Bissau, Guinea, Angola, South Africa, and Saint Helena Island, though it has not yet been reported from the northwestern Atlantic. In the Indian Ocean, it occurs in the Mozambique Channel and possibly the Agulhas Current and the Bay of Bengal. In the Pacific, it occurs from Japan, Taiwan, and the Korean Peninsula in the northwest, southward to Indonesia, Australia, and New Zealand, and eastward to the western coast of the Americas from Baja California to Chile, including the Marshall, Phoenix, Palmyra, Johnston, Marquesas, Line, and Hawaiian Islands in between.[5][8][9][10] In New Zealand this species has been recorded at the Three Kings Ridge, off the coast of Northland and on the northern Kermadec Ridge.[11]

From distribution records, the crocodile shark's range seems to be bound by the latitudes 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.[12] The crocodile shark is usually found in the pelagic zone 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, possibly after being stunned by upwellings of cold water.[5] In March 2017, one crocodile shark washed ashore dead off the coast of Devon, England in Hope Cove, the first ever seen off the coasts of the United Kingdom. Thus far, it remains unknown as to why this particular shark was present so far north of its normal range.[13][14]

Biology and ecology

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Deepwater fishes such as bristlemouths are preyed upon by the crocodile shark.

With a long body, small fins, and large liver rich in squalene and other low-density lipids, the crocodile shark is convergently similar to mesopelagic dogfish sharks such as the cookiecutter shark (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 in the water column with little effort.[5][7] Like many other inhabitants of the mesopelagic zone, the crocodile shark apparently migrates 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.[12]

The large eyes of the crocodile shark, equipped with a reflective green or yellow retina and lacking an expanded iris, suggest that it is a nocturnal hunter that relies on sight to pick out the silhouettes or bioluminescence of its prey.[7] 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, South Africa, jumped out of the water in pursuit of bait. Its diet consists of small to medium-sized bony fishes (including bristlemouths and lanternfishes), squid (including onychoteuthids, mastigoteuthids, pholidoteuthids, and cranchiids) and shrimp.[5] Crocodile sharks are not known to be preyed upon by any other species.[12]

The crocodile shark is aplacental viviparous and typically gives birth to litters of four, two pups to each uterus. The gestation period is unknown but believed to be long. The embryos have yolk sacs at 3–4 cm (1.2–1.6 in) long; once the yolk sac is fully absorbed they become oophagous: the mother produces large numbers of thin-walled egg capsules that contain 2–9 eggs 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.[15] It is unclear how two crocodile shark fetuses 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).[7] There is no defined reproductive season.[12]

Human interactions

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Significant numbers of crocodile sharks are caught accidentally by fisheries.

With its small size, non-cutting teeth, and oceanic habitat, the crocodile shark is not considered dangerous to humans. However, it has a powerful bite that invites caution.[7] This species is a common bycatch of various pelagic longline fisheries meant for tuna and swordfish. The largest numbers are caught by the Japanese yellowfin tuna fishery and the Australian swordfish fishery, both operating in the Indian Ocean.[12] This species is also sometimes caught on squid jigs and in tuna gillnets.[3][5] It is usually discarded due to its small size and low-quality meat. However, its oily liver is potentially valuable.[7] 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.[1] In June 2018 the New Zealand Department of Conservation classified the crocodile shark as "Data Deficient" with the qualifier "Secure Overseas" under the New Zealand Threat Classification System.[16]

After AT&T installed the first deep sea fiberoptic cable between Gran Canaria and Tenerife in the Canary Islands 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 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 tape beneath a dense polyethylene coating.[7]

References

  1. ^ a b Kyne, P.M., Romanov, E., Barreto, R., Carlson, J., Fernando, D., Fordham, S., Francis, M.P., Jabado, R.W., Liu, K.M., Marshall, A., Pacoureau, N. & Sherley, R.B. 2019. Pseudocarcharias kamoharai. The IUCN Red List of Threatened Species 2019: e.T39337A2900108. https://doi.org/10.2305/IUCN.UK.2019-1.RLTS.T39337A2900108.en. Downloaded on 26 July 2019.
  2. ^ a b Martin, R.A. Pseudocarchariidae. ReefQuest Centre for Shark Research. Retrieved on December 24, 2008.
  3. ^ a b Froese, Rainer and Pauly, Daniel, eds. (2008). "Pseudocarcharias kamoharai" in FishBase. December 2008 version.
  4. ^ Matsubara K. (1936). "A new carcharoid shark found in Japan". Zoological Magazine (Tokyo) (in Japanese). 48 (7): 380–382.
  5. ^ a b c d e f g h i j 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. pp. 71–74. ISBN 92-5-104543-7.
  6. ^ Cigala-Fulgosi, F. (1992). "Additions to the fish fauna of the Italian Miocene. The occurrence of Pseudocarcharias (Chondrichthys, Pseudocarchariidae) in the lower Serravallian of Parma Province, Northern Apenniens". Tertiary Research. 14 (2): 51–60.
  7. ^ a b c d e f g h Martin, R.A. Biology of the Crocodile Shark (Pseudocarcharias kamoharai). ReefQuest Centre for Shark Research. Retrieved on December 24, 2008.
  8. ^ Edwards, A.J. (1993). "New records of fishes from the Bonaparte Seamount and Saint Helena Island, South Atlantic". Journal of Natural History. 27 (2): 493–503. doi:10.1080/00222939300770241.
  9. ^ Long, D.J.; Seigel, J.A. (1997). "A crocodile shark Pseudocarcharias kamoharai (Selachii: Lamnidae) from pelagic waters off Baja California, Mexico". Oceanides. 12 (1): 61–63.
  10. ^ Melendez, R.; Lopez, S.; Yanez, E. (2006). "New data of Pseudocarcharias kamoharai (Matsubara, 1936) (Chondrichthyes: Lamniformes: Pseudocarchariidae), off northern Chile". Investigaciones Marinas Universidad Catolica de Valparaiso (in Spanish). 34 (2): 223–26.
  11. ^ Roberts, Clive; Stewart, A. L.; Struthers, Carl D.; Barker, Jeremy; Kortet, Salme; Freeborn, Michelle (2015). The fishes of New Zealand. 2. Wellington, New Zealand: Te Papa Press. p. 63. ISBN 9780994104168. OCLC 908128805.
  12. ^ a b c d e Romanov, E.V., Ward, P., Levesque, J.C. and Lawrence, E. (2008). "Preliminary analysis of crocodile shark (Pseudocarcharias kamoharai) distribution and abundance trends in pelagic longline fisheries". IOTC Working Party on Environment and Bycatch (WPEB) Bangkok, Thailand.
  13. ^ "Archived copy". Archived from the original on 2017-03-02. Retrieved 2017-03-02.CS1 maint: archived copy as title (link)
  14. ^ https://www.independent.co.uk/environment/crocodile-shark-discovered-uk-first-time-tropical-hope-cove-plymouth-a7607586.html
  15. ^ Fujita, K. (May 1981). "Oviphagous embryos of the pseudocarchariid shark, Pseudocarcharias kamoharai, from the central Pacific". Japanese Journal of Ichthyology. 28 (1): 37–44.
  16. ^ Duffy, Clinton A. J.; Francis, Malcolm; Dunn, M. R.; Finucci, Brit; Ford, Richard; Hitchmough, Rod; Rolfe, Jeremy (2018). Conservation status of New Zealand chondrichthyans (chimaeras, sharks and rays), 2016 (PDF). Wellington, New Zealand: Department of Conservation. p. 11. ISBN 9781988514628. OCLC 1042901090.

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Crocodile shark: Brief Summary

provided by wikipedia EN

The crocodile shark (Pseudocarcharias kamoharai) is a species of mackerel shark and the only extant 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 (1,940 ft). It performs a diel vertical migration, staying below a depth of 200 m (660 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. 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 and shrimp, the crocodile shark has a sizable oily liver 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 for hunting at night. The crocodile shark is aplacental viviparous, with females typically giving birth to litters of four. The fetuses are oophagous, meaning that they feed on undeveloped eggs ovulated for this purpose by their mother. Due to its small size, the crocodile shark poses little danger to humans and is of little commercial importance. This species was responsible for damaging deep sea fiberoptic cables when the technology was first deployed in 1985.

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Description

provided by World Register of Marine Species
Found offshore but sometimes occurring inshore and near the bottom. Its long, flexed teeth suggests small to moderately large active oceanic prey. Ovoviviparous, with 4 young in a litter. Nocturnal and possibly make a diel pattern of movement toward the surface at night and away from it in the day. Jaws can be protruded a considerable distance from its head. Liver is very large and very high in squalene.
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bibliographic citation
Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (02/2021). Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (02/2021).
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