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The tiger shark is a solitary, mostly nocturnal hunter. Its diet includes a wide variety of prey, ranging from [[crustacean]]s, [[fish]], [[Pinniped|seals]], [[bird]]s, [[squid]], [[turtle]]s, and [[sea snake]]s to [[dolphin]]s and even other smaller sharks. Due to its tendency to swallow virtually anything it encounters, including inedible manmade objects that linger in its stomach, the tiger shark has been nicknamed "the garbage can of the sea".<ref>{{cite web |url=http://finformation.blogspot.com/2011/05/items-found-in-stomach-of-tiger-sharks.html |title=Items Found in the Stomachs of Tiger Sharks |publisher=Finformation |accessdate=2013-08-29}}</ref> The tiger shark is considered a [[endangered species|near threatened species]] due to [[shark finning|finning]] and fishing by humans.<ref name="iucn"/>
The tiger shark is a solitary, mostly nocturnal hunter. Its diet includes a wide variety of prey, ranging from [[crustacean]]s, [[fish]], [[Pinniped|seals]], [[bird]]s, [[squid]], [[turtle]]s, and [[sea snake]]s to [[dolphin]]s and even other smaller sharks. Due to its tendency to swallow virtually anything it encounters, including inedible manmade objects that linger in its stomach, the tiger shark has been nicknamed "the garbage can of the sea".<ref>{{cite web |url=http://finformation.blogspot.com/2011/05/items-found-in-stomach-of-tiger-sharks.html |title=Items Found in the Stomachs of Tiger Sharks |publisher=Finformation |accessdate=2013-08-29}}</ref> The tiger shark is considered a [[endangered species|near threatened species]] due to [[shark finning|finning]] and fishing by humans.<ref name="iucn"/>

==Taxonomy==
The shark was first described by [[François Péron|Peron]] and [[Charles Alexandre Lesueur|Lessueur]] in 1822, and was given the name ''Squalus cuvier''.<ref name="FroesePauly"/> [[Johannes Peter Müller|Müller]] and [[Friedrich Gustav Jakob Henle|Henle]] in 1837 renamed it ''Galeocerdo tigrinus''.<ref name="flmnh"/> The genus, ''Galeocerdo'', is derived from the Greek ''galeos'', which means shark, and the Latin ''cerdus'', the word for the hard hairs of pigs.<ref name="flmnh"/> It is often colloquially called the man-eater shark.<ref name="flmnh"/>

The tiger shark is a member of the order [[Carcharhiniformes]], the most species-rich order of sharks, with more than 270 species also including the small [[catshark]]s and [[hammerhead shark]]s.<ref name="FroesePauly"/> Members of this order are characterized by the presence of a [[nictitating membrane]] over the eyes, two dorsal fins, an [[anal fin]], and five [[gill]] slits. It is the largest member of the Carcharhinidae [[Family (biology)|family]], commonly referred to as [[requiem shark]]s. This family consists of mostly slender but powerful mid- to large-sized sharks and includes some other well-known sharks, such as the [[blue shark]] (''Prionace glauca''), [[lemon shark]] (''Negaprion brevirostris''), and [[bull shark]] (''Carcharhinus leucas'').<ref name="SharkInfo"/>


==Anatomy and appearance==
==Anatomy and appearance==

Revision as of 13:43, 28 May 2014

For other uses, see Tiger shark (disambiguation).

Tiger Shark
Temporal range: 50–0 Ma[1] Early Eocene to Present
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Chondrichthyes
Subclass:
Elasmobranchii
Order:
Carcharhiniformes
Family:
Carcharhinidae
Genus:
Galeocerdo

Species:
G. cuvier
Binomial name
Galeocerdo cuvier
Péron & Lesueur, 1822
Tiger shark range
Synonyms

Squalus cuvier Peron and Lessueur, 1822
Galeocerdo tigrinus Müller and Henle, 1837

The tiger shark, Galeocerdo cuvier, is a species of requiem shark and the only member of the genus Galeocerdo. Commonly known as sea tiger, the tiger shark is a relatively large macropredator, capable of attaining a length of over 5 m (16 ft).[3] It is found in many tropical and temperate waters, and it is especially common around central Pacific islands. Its name derives from the dark stripes down its body which resemble a tiger's pattern, which fade as the shark matures.[4]

The tiger shark is a solitary, mostly nocturnal hunter. Its diet includes a wide variety of prey, ranging from crustaceans, fish, seals, birds, squid, turtles, and sea snakes to dolphins and even other smaller sharks. Due to its tendency to swallow virtually anything it encounters, including inedible manmade objects that linger in its stomach, the tiger shark has been nicknamed "the garbage can of the sea".[5] The tiger shark is considered a near threatened species due to finning and fishing by humans.[2]

Anatomy and appearance

Profile photo of shark, accompanied by remora, swimming just above a sandy seafloor
Juvenile tiger shark in the Bahamas

Size

Among the largest extant sharks, the tiger shark ranks in size only behind the whale shark (Rhincodon typus), the basking shark (Cetorhinus maximus), the great white shark (Carcharodon carcharias), and the great hammerhead (Sphyrna mokarran). Very large specimens of some other species such as megamouth sharks (Megachasma pelagios), Pacific sleeper sharks (Somniosus pacificus), Greenland sharks (Somniosus microcephalus), and bluntnose sixgill sharks (Hexanchus griseus) can attain similar sizes as tiger sharks.[6][7] The tiger shark commonly attains a length of 3–4.2 m (9.8–13.8 ft) and weighs around 385–635 kg (849–1,400 lb).[6] Sometimes, an exceptionally large male tiger shark can grow up to 4.5 m (15 ft). Females are larger, and exceptionally big ones can reportedly measure over 5 m (16 ft). According to Guinness World Records, one female specimen caught off Australia reportedly measured 5.5 m (18 ft) long and weighed an exceptional 1,524 kg (3,360 lb), although her weight is thought to have been bolstered by her pregnant state at the time. Even larger specimens have been reported, but are unconfirmed.[7]

Biology

The skin of a tiger shark can typically range from blue to light green with a white or light-yellow underbelly. The advantage of this is that when it is hunting for its prey, when prey looks at the shark from above, the shark will be camouflaged since the water below is darker. And when prey is below the shark and looks up, of course because of the sun, it is lighter so that the light underbelly will also camouflage the shark. This is known as countershading. Dark spots and stripes are most visible in young sharks and fade as the shark matures. Its head is somewhat wedge-shaped, which makes it easy to turn quickly to one side.[4][8] They have small pits on the snout which hold electroreceptors called the ampullae of Lorenzini, which enable them to detect electric fields, including the weak electrical impulses generated by prey, which helps them to hunt.[9] Tiger sharks also have a sensory organ called a lateral line which extends on their flanks down most of the length of their sides. The primary role of this structure is to detect minute vibrations in the water. These adaptations allow the tiger shark to hunt in darkness and detect hidden prey.[10]

A reflective layer behind the tiger shark's retina, called the tapetum lucidum, allows light-sensing cells a second chance to capture photons of visible light, enhancing vision in low light conditions. A tiger shark generally has long fins to provide lift as the shark maneuvers through water, while the long upper tail provides bursts of speed. Tiger sharks normally swim using small body movements.[11] Its high back and dorsal fin act as a pivot, allowing it to spin quickly on its axis, though the shark's dorsal fins are distinctively close to its tail.[9]

Its teeth are specialized to slice through flesh, bone, and other tough substances such as turtle shells. Like most sharks, its teeth are continually replaced by rows of new teeth.[9]

Feeding

Tiger shark jaws

The tiger shark is an apex predator[12] and has a reputation for eating anything.[6] Young tiger sharks are found to prey largely on small fish, as well as various small jellyfish, cephalopods, and other mollusks. Around the time they attain 2.3 m (7.5 ft), or near sexual maturity, their prey selection expands considerably, and much larger animals become regular prey.[13] Numerous fish, crustaceans, sea birds, sea snakes,[14] marine mammals (e.g. bottlenose dolphins (Tursiops), common dolphins (Delphinus),[15] spotted dolphins (Stenella),[16] dugongs (Dugong dugon), seals and sea lions), and sea turtles (including the three largest species: the leatherback (Dermochelys coriacea),[17] the loggerhead (Caretta caretta)[18] and the green sea turtles (Chelonia mydas),[13]) are regularly eaten by adult tiger sharks. The tiger shark also eats other sharks (including adult sandbar sharks (Carcharhinus plumbeus)), as well as rays, and will sometimes even eat other tiger sharks.[4][13]

Due to high risk of predatory attacks, dolphins often avoid regions inhabited by tiger sharks.[19] Tiger sharks may also attack injured or ailing whales and prey upon them. A group was documented attacking and killing an ailing humpback whale (Megaptera novaeangliae) in 2006 near Hawaii.[20] The tiger shark also scavenges on dead whales. In one such documented incident, they were observed scavenging on a whale carcass alongside great white sharks.[21]

Evidence of dugong predation was identified in one study that found dugong tissue in 15 of 85 tiger sharks caught off the Australian coast.[22] Additionally, examination of adult dugongs has shown scars from failed shark attacks.[23] Finally, dugong microhabitats shift similarly to those of known tiger shark prey when the sharks are abundant.[24]

The broad, heavily calcified jaws and nearly terminal mouth, combined with robust, serrated teeth, enable the tiger shark to take on these large prey.[19] In addition, excellent eyesight and acute sense of smell enable it to react to faint traces of blood and follow them to the source. The ability to pick up low-frequency pressure waves enables the shark to advance towards an animal with confidence, even in murky water.[11] The shark circles its prey and studies it by prodding it with its snout.[11] When attacking, the shark often eats its prey whole, although larger prey are often eaten in gradual large bites and finished over time.[11]

Notably, terrestrial mammals, including horses (Equus ferus caballus), goats (Capra aegagrus hircus), sheep (Ovis aries), dogs (Canis lupus familiaris), cats (Felis catus) and brown rats (Rattus norvegicus), are fairly common in the stomach contents of tiger sharks around the coasts of Hawaii.[13] Because of its aggressive and indiscriminate feeding style, it often mistakenly eats inedible objects, such as automobile license plates, oil cans, tires, and baseballs.[4]

Swimming efficiency and stealth

All tiger sharks generally swim slowly, which, combined with cryptic coloration, may make them difficult for prey to detect them in some habitats. They are especially well camouflaged against dark backgrounds.[19] Despite their sluggish appearance, tiger sharks are one of the strongest swimmers of the carcharhinid sharks. Once the shark has come close, a speed burst allows it to reach the intended prey before it can escape.[19]

Reproduction

Males reach sexual maturity at 2.3 to 2.9 m (7.5 to 9.5 ft) and females at 2.5 to 3.5 m (8.2 to 11.5 ft).[9] Females mate once every three years.[4] They breed by internal fertilization. The male inserts one of his claspers into the female's genital opening (cloaca), acting as a guide for the sperm. The male uses his teeth to hold the female still during the procedure, often causing the female considerable discomfort. Mating in the Northern Hemisphere generally takes place between March and May, with birth between April and June the following year. In the Southern Hemisphere, mating takes place in November, December, or early January. The tiger shark is the only species in its family that is ovoviviparous; its eggs hatch internally and the young are born live when fully developed.[6]

The young develop inside the mother's body for up to 16 months. Litters range from 10 to 80 pups.[6] A newborn is generally 51 to 76 cm (20 to 30 in) long.[6] This shark typically reaches maturity at lengths of 2 to 3 m (6.6 to 9.8 ft).[6][9] It is unknown how long tiger sharks live, but they can live longer than 12 years.[4]

Conservation

The tiger shark is captured and killed for its fins, flesh, and liver. It is caught regularly in target and nontarget fisheries. Several populations have declined where they have been heavily fished. Continued demand for fins may result in further declines in the future. Tiger sharks are considered a near threatened species due to excessive finning and fishing by humans according to International Union for Conservation of Nature.[2]

While shark fin has very few nutrients, shark liver has a high concentration of vitamin A which is used in the production of vitamin oils. In addition, the tiger shark is captured and killed for its distinct skin, as well as by big-game fishers.[6]

In 2010, Greenpeace International added the tiger shark to its seafood red list, which is a list of fish commonly sold around the world, and which have a very high risk of being sourced from unsustainable fisheries.[25]

Relationship with humans

Photo of shark hung by its tail on the shore
A large tiger shark caught in Kaneʻohe Bay, Oʻahu in 1966

Although shark attacks are a relatively rare phenomenon, the tiger shark is responsible for a large percentage of fatal attacks and is regarded as one of the most dangerous shark species.[26][27] They often visit shallow reefs, harbors, and canals, creating the potential for encounter with humans.[4] The tiger shark also dwells in river mouths and other runoff-rich water.[6][9] While the tiger shark is considered to be one of the sharks most dangerous to humans, its attack rate is low.[28] The tiger is second on the list of number of recorded attacks on humans, with the great white shark being first.[6][26] On average, three to four shark attacks occur per year in Hawaii, and most attacks are not fatal. This attack rate is surprisingly low considering thousands of people swim, surf, and dive in Hawaiian waters every day.[28] Attacks by tiger sharks in Hawaiian waters have been shown to increase between September and November, when tiger shark females are believed to migrate to the islands to give birth.[29]

Between 1959 and 1976, 4,668 tiger sharks were culled in an effort to protect the tourism industry. Despite these efforts, attacks did not decrease. It is illegal to feed sharks in Hawaii (except for traditional Hawaiian cultural or religious practices),[30][31] and interaction with them, such as cage diving, is discouraged. South African shark behavioralist and shark diver Mark Addison demonstrated divers could interact and dive with them outside of a shark cage in a 2007 Discovery Channel special.[32]

Mythology

The tiger shark is considered to be sacred na ʻaumakua (ancestor spirits) by some native Hawaiians who think their eyeballs have special powers of visual perception. This aligns with the general known facts about sharks and their highly developed senses.[28]

See also

References

  1. ^ Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Chondrichthyes entry)". Bulletins of American Paleontology. 450: 560. ISBN 0877104506. Archived from the original on 2011-02-12. Retrieved July 2011. {{cite journal}}: Check date values in: |accessdate= (help)
  2. ^ a b c Template:IUCN
  3. ^ Froese, Rainer; Pauly, Daniel (eds.). "Galeocerdo cuvier". FishBase. July 2011 version.
  4. ^ a b c d e f g Ritter, Erich K. (15 December 1999). "Fact Sheet: Tiger Sharks". Shark Info. Retrieved July 2011. {{cite web}}: Check date values in: |accessdate= (help)
  5. ^ "Items Found in the Stomachs of Tiger Sharks". Finformation. Retrieved 2013-08-29.
  6. ^ a b c d e f g h i j Knickle, Craig. "Tiger Shark Biological Profile". Florida Museum of Natural History Icthyology Department. Retrieved July 2011. {{cite web}}: Check date values in: |accessdate= (help)
  7. ^ a b Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. ISBN 978-0-85112-235-9.
  8. ^ Canadian Shark Research Laboratory, Tiger Shark – Centre for Marine Biodiversity. Marine Biodiversity. Retrieved July 2011.
  9. ^ a b c d e f Tiger shark, Galeocerdo cuvier at marinebio.org Accessed July, 2011.
  10. ^ Tiger Shark – The Province of New Brunswick Canada. New Brunswick. Retrieved 2011-06-09.
  11. ^ a b c d "Tiger Shark". ladywildlife.com. Retrieved 2006-12-21.
  12. ^ Heithaus, Michael R. (2001). "The biology of tiger sharks, Galeocerdo cuvier, in Shark Bay, Western Australia: sex ratio, size distribution, diet, and seasonal changes in catch rates". Environmental Biology of Fishes. 61: 25–36. doi:10.1023/A:1011021210685.
  13. ^ a b c d Lowe, Christopher G.; Wetherbee, Bradley M.; Crow, Gerald L.; Tester, Albert L. (1996). "Ontogenetic dietary shifts and feeding behavior of the tiger shark, Galeocerdo cuvier, in Hawaiian waters" (PDF). Environmental Biology of Fishes. 47 (2): 203. doi:10.1007/BF00005044. Archived from the original (PDF) on 2009-01-07.
  14. ^ Heithaus, M. R. (2004). "Habitat use and foraging behavior of tiger sharks (Galeocerdo cuvier) in a seagrass ecosystem" (PDF). Marine Biology. 140 (2): 237–248. doi:10.1007/s00227-001-0711-7. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  15. ^ Heithaus, M. R.; Dill, L (2002). "Food availability and tiger shark predation risk influence bottlenose dolphin habitat use" (PDF). Ecology. 83 (2): 480–491. doi:10.1890/0012-9658(2002)083[0480:FAATSP]2.0.CO;2. Archived from the original (PDF) on 2009-03-06.
  16. ^ Maldini, Daniela (2003). "Evidence of predation by a tiger shark (Galeocerdo cuvier) on a spotted dolphin (Stenella attenuata) off Oahu, Hawaii" (PDF). Aquatic Mammals. 29 (1): 84–87. doi:10.1578/016754203101023915.
  17. ^ Tiger Sharks Killed for Eating Leatherback Turtles. Shark Defenders (2011-04-16). Retrieved on 2013-03-23.
  18. ^ Shark Bay Ecosystem Research Project. .fiu.edu. Retrieved on 2013-03-23.
  19. ^ a b c d Heithaus, Michael R. (2001). "Predator–prey and competitive interactions between sharks (order Selachii) and dolphins (suborder Odontoceti): a review". Journal of Zoology. 253: 53–68. doi:10.1017/S0952836901000061.
  20. ^ Office of National Marine Sanctuaries. "Humpback Whale Shark Attack: A Natural Phenomenon Caught on Camera". Retrieved July 2011. {{cite web}}: Check date values in: |accessdate= (help)
  21. ^ Dudley, Sheldon F. J. (2000). "Concurrent scavenging off a whale carcass by great white sharks, Carcharodon carcharias, and tiger sharks, Galeocerdo cuvier" (PDF). Fishery Bulletin. 98: 646–649. Retrieved 4 May 2010. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  22. ^ Simpfendorfer, Colin A. (1 January 2001). Environmental Biology of Fishes. 61 (1): 37–46. doi:10.1023/A:1011021710183. {{cite journal}}: Missing or empty |title= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  23. ^ Anderson, PK (1995). "Scarring and photoidentification of dugongs (Dugong dugon) in Shark Bay, Western Australia". Aq Mam. 21: 205.
  24. ^ WIRSING, A (1 July 2007). "Living on the edge: dugongs prefer to forage in microhabitats that allow escape from rather than avoidance of predators". Animal Behaviour. 74 (1): 93–101. doi:10.1016/j.anbehav.2006.11.016. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  25. ^ Greenpeace International Seafood Red list. greenpeace.org
  26. ^ a b "ISAF Statistics on Attacking Species of Shark". International Shark Attack File. Florida Museum of Natural History University of Florida. Retrieved 2008-05-04.
  27. ^ Ritter, Erich K. (15 February 1999). "Which shark species are really dangerous?". Shark Info. Retrieved July 2011. {{cite web}}: Check date values in: |accessdate= (help)
  28. ^ a b c "Tiger Shark Research Program". Shark & Reef Fish Research. Hawaii Institute of Marine Biology. Retrieved July 2011. {{cite web}}: Check date values in: |accessdate= (help)
  29. ^ Hawaii tiger shark migration in fall coincides with rise in bites
  30. ^ "Prohibition of Shark Feeding". Hawaii Department of Land and Natural Resources, Hawaii Department of Agriculture. Retrieved 2014-05-26.
  31. ^ "Federal Fishery Managers Vote To Prohibit Shark Feeding" (PDF). Western Pacific Regional Fishery Management Council. Retrieved 2014-05-26.
  32. ^ Donahue, Ann (30 July 2007). "Shark Week: 'Deadly Stripes: Tiger Sharks'". LA Times. Retrieved July 2011. {{cite web}}: Check date values in: |accessdate= (help)
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