Whale shark: Difference between revisions
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==Naming== |
==Naming== |
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The species was first identified in April [[1828]] following the harpooning of a 4.6 meter (15 feet) specimen in [[Table Bay]], [[South Africa]]. It was described by Andrew Smith, a military doctor associated with British troops stationed in [[Cape Town]], the year following the capture. He proceeded to publish a more detailed description of the species in [[1849]]. The family ''Rhincodontidae'' was not finalized until [[1984]]. The name "whale shark" comes from the fish's large size; that is, a shark as large as a [[whale]]. |
The species was first identified in April [[1828]] following the harpooning of a 4.6 meter (15 feet) specimen in [[Table Bay]], [[South Africa]]. It was described by Andrew Smith, a military doctor associated with British troops stationed in [[Cape Town]], the year following the capture. He proceeded to publish a more detailed description of the species in [[1849]]. The family ''Rhincodontidae'' was not finalized until [[1984]]. The name "whale shark" comes from the fish's large size and eating habits; that is, a shark as large as a [[whale]] and shares a similar filter feeder eating mode. |
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==Distribution and habitat== |
==Distribution and habitat== |
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Revision as of 05:45, 18 September 2006
| Whale shark | |
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| Whale shark in Georgia aquarium | |
| Scientific classification | |
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| Family: | Rhincodontidae
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| Genus: | Rhincodon Smith, 1829
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| Species: | R. typus
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| Binomial name | |
| Rhincodon typus | |
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| Range of whale shark | |
Template:Sharksportal The whale shark, Rhincodon typus, is a gentle and slow filter feeding shark that is the largest living fish species. This distinctively-marked shark is the only member of its genus Rhincodon and is a member of the subclass Elasmobranchii of the class Chondrichthyes. The shark is found in tropical and warm oceans and lives in the open sea. The species is believed to have originated about 60 million years ago.[1]
Naming
The species was first identified in April 1828 following the harpooning of a 4.6 meter (15 feet) specimen in Table Bay, South Africa. It was described by Andrew Smith, a military doctor associated with British troops stationed in Cape Town, the year following the capture. He proceeded to publish a more detailed description of the species in 1849. The family Rhincodontidae was not finalized until 1984. The name "whale shark" comes from the fish's large size and eating habits; that is, a shark as large as a whale and shares a similar filter feeder eating mode.
Distribution and habitat
The whale shark inhabits the world's tropical and warm-temperate oceans. While thought to be primarily pelagic, seasonal feeding aggregations of the sharks occur at several coastal sites like Ningaloo Reef in Western Australia as well as Pemba, Útila, Honduras, Donsol, Philippines, and Zanzibar on the coast of East Africa. Its range is restricted to about ±30 ° latitude from these sites. It is found from the surface down to a depth of about 700 m.[2] The whale shark is solitary and rarely seen in groups unless feeding at locations with abundance of food like Ningaloo reef. Males range over longer distances than females, who seem to be attached to specific areas.
Anatomy and appearance
The whale shark is a filter feeder and as such the shark has a capacious mouth which can be up to 1.5 m (5 ft) wide and contain up to 300 rows of tiny teeth. It has five large pairs of gills. Two small eyes are located towards the front of the shark's wide, flat head. The body is mostly grey with a white belly; three prominent ridges run along each side of the animal and the skin is marked with a 'checkerboard' of pale yellow spots and stripes. These spots are unique to each whale shark. Because of the spots' uniqueness they can be used to identify each animal and make an accurate population count. But so far the whale sharks have not been fully and accurately counted. Its skin can be up to 10 cm (about 4 in.) thick. The shark has two pairs each of dorsal fins and pectoral fins. A juvenile whale shark's tail has a larger upper fin than lower fin while the adult tail becomes semi-lunate, or crescent-shaped. The shark's spiracles are just behind the eyes. The whale shark is not an efficient swimmer; the entire body is in motion while the animal swims. The result of this motion, one that is very unusual for sharks, is an average speed of around 5 km/h.
The largest specimen regarded as accurately recorded had a length of 12.65 meters (41.5 feet) and allegedly weighed more than 21.5 tons (47,300 lbs). It was caught on November 11, 1947, near the island of Baba, not far from Karachi, Pakistan. The girth of the specimen was 7 meters (23 feet).[3] Stories exist of specimens vastly larger, but few if any scientific records exist to support their existence. Quoted lengths of 18 meters (59 feet) are not uncommon in the popular shark literature. In 1868 the Irish natural scientist E. Perceval Wright spent time in the Seychelles, during which he managed to obtain several small whale shark specimens. He also claimed to have observed specimens in excess of 15 meters (49 feet), and tells of records regarding specimens surpassing 21 meters (69 feet).
In a 1925 publication Hugh M. Smith describes a huge whale shark which was caught in 1919 in a bamboo fish trap in todays Thailand. The shark was too heavy to pull ashore, but Smith estimates that the shark was at least 17 meters (55.7 feet) and weighed approximately 37 tonnes (81,500 lbs). Recent records says this shark was actually accurately measured at 17.98 meters and weighing 43 tonnes. Unverified claims of almost absurd lengths, such as 23 meters (75 feet) have been occasionally referred to. In 1934 a ship named the "Maurguani" came across a whale shark in the Southern Pacific ocean; the ship rammed the huge shark viciously, and it consequently got stuck on the prow of the ship: 4.6 meters (15 feet) on one side and 12.2 meters (40 feet) on the other.[4] Of course, no reliable documentation exists of those claims, they are and remain little more than "fish-stories".
Diet
The whale shark feeds on phytoplankton, macro-algae, plankton, krill or nektonic life (small squid or vertebrates). The many rows of teeth play no role in feeding, instead, water is actively drawn into the mouth and is passed over gill and then out through the gill arches. Any material caught in the filter between the gill bars is swallowed.[5][2] The shark can circulate water at a rate up to 1.7 L/s (3.5 US pint/s). The sharks, however, are active feeders and target concentrations of plankton or fish by olfactory cues rather than simply 'vacuuming' constantly. According to sailors, whale sharks congregate at reefs off the Belizean Caribbean coast, supplementing their ordinary diet by feeding on the roe of giant cubera snappers, which spawn in these waters in May, June and July, and between the full and quarter moons of these months. Whale sharks are also regularly sighted off the Honduran Bay Islands, particularly Utilla.
The whale shark does not need to swim forward when feeding, it have been observed in a vertical position, 'bobbing' up and down swallowing water and activly filtering it out while feeding.[5][2]
Behaviour towards divers
When it is explained that most sharks are not dangerous to humans, this species is used as the leading example. Divers and snorkelers can swim around the giant fish without any problems apart from the risk of being hit by the shark's large and muscular tail fin.
The shark is often seen in Thailand, the Maldives, the Red Sea, Western Australia (Ningaloo Reef), Gladden Spit Marine Reserve in Belize, and at the Galapagos islands. They are regularly seen from December to May in the Philippines (Donsol). Lucky divers have also come across whale sharks in the Seychelles and in Puerto Rico. Between December and September, they are well known to swim along the bay of La Paz in the Mexican Baja California. Sometimes, they are accompanied by smaller fish.
Reproduction
Like most sharks, the reproductive habits of the whale shark are obscure. Based on the study of a single egg recovered off the coast of Mexico in 1956, it was believed to be oviparous, but the capture of a pregnant female in July 1996 containing 300 young whale sharks[1] indicates that they are viviparous with ovoviviparous development.[2] The eggs remain in the body and the females give birth to live 40 to 60 cm young. It is believed that they reach sexual maturity at around 30 years and the life span has been estimated to be between 60 and 150 years.
Conservation status
The whale shark is targeted by artisanal and commercial fisheries in several areas where they seasonally aggregate. The population is unknown and the species is considered vulnerable by the IUCN. Whale sharks are known to frequent the waters off Donsol in the Sorsogon province of the Philippines.
Whale sharks in aquariums
A whale shark is featured as the main attraction of Osaka Aquarium Kaiyukan and as of 2005, three whale sharks are being studied in captivity at the Okinawa Churaumi Aquarium in Japan. Four whale sharks, including two males, Ralph and Norton, and two females, Alice and Trixie, are held in the Georgia Aquarium, which opened in 2005, in Atlanta. The two females were added on June 3, 2006 in hopes that their reproduction could be studied in captivity. All four whale sharks were imported from Taiwan.
See also
References
- Template:IUCN2006 Database entry includes justification for why this species is vulnerable
- FAO web page on Whale shark
- Froese, Rainer; Pauly, Daniel (eds.). "Rhincodon typus". FishBase. November 2004 version.
- "Rhincodon typus". Integrated Taxonomic Information System. 16 November.
{{cite web}}: Check date values in:|date=and|year=/|date=mismatch (help)
- ^ Jurassic Shark (2000) documentary by Jacinth O'Donnell; broadcast on Discovery Channel, August 5, 2006
- ^ a b c d Ed. Ranier Froese and Daniel Pauly. "Rhincodon typus". FishBase. Retrieved 17 September.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help) - ^ Gerald L. Wood, "Animal Facts and Feats", 1990.
- ^ Xavier Maniguet, "Jaws of Death"; 1991.
- ^ a b Martin, R. Aidan. "Elasmo Research". ReefQuest. Retrieved 17 September.
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External links
- Whale shark, Rhincodon typus at marinebio.org
- Whale Shark Pictures - Whale shark pictures from Shark-Pictures.com
- ECOCEAN Whale Shark Photo-identification Library
- Whale Shark Project
- Whale shark facts & pictures
- Whale sharks
- TimeAsia.com: Best of Asia, Best Animal Encounter
- Follow the paths of migrating Whale Sharks
- Whales Sharks off the coast of Utila, The Bay Islands, Honduras
- Whale Shark profile and whale sharks in Belize from The Nature Conservancy
- Ningaloo Reef Teach
- Whale Shark Video
- Whale shark research in Mozambique