Whale shark
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| Whale shark Fossil range: 60–0 Ma [1] | ||||||||||||||||
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 Whale shark from Taiwan in the Georgia Aquarium  Size comparison against an average human | ||||||||||||||||
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| Rhincodon typus (Smith, 1828) | ||||||||||||||||
 Range of whale shark |
The whale shark, Rhincodon typus, is a slow moving filter feeding shark that is the largest living fish species. It can grow up to 18 meters (60 ft) in length and can weigh up to 13.6 tonnes (15 short tons). This distinctively-marked shark is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhinodontes before 1984), which is grouped into the subclass Elasmobranchii in the class Chondrichthyes. The shark is found in tropical and warm oceans and lives in the open sea and can live for about 70 years.[3] The species is believed to have originated about 60 million years ago. Although whale sharks have very large mouths, they feed mainly, though not exclusively, on plankton, microscopic plants and animals (a whale shark was observed feeding on a school of small fish in the BBC program Planet Earth).[1]
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[edit] Naming
The species was identified in April 1828 following the harpooning of a 4.6-metre (15.1 ft) specimen in Table Bay, South Africa. It was described the following year by Andrew Smith, a military doctor associated with British troops stationed in Cape Town.[4] He proceeded to publish a more detailed description of the species in 1849. The name "whale shark" comes from the fish's physiology; that is, a shark as large as a whale that shares a similar filter feeder eating mode. Known as a deity in a Vietnamese religion, the whale shark is called "Ca Ong", which literally translates as "Sir Fish". In Mexico, and throughout much of Latin America, the whale shark is known as "pez dama" or "domino" for its patterns of spots. Whale sharks go by the name of "Sapodilla Tom" in Belize due to the regularity of sightings near the Sapodilla Cayes on the Belize Barrier Reef. In Africa, the names for the whale shark are very evocative: "papa shillingi" in Kenya came about as it is believed that God threw shillings upon the shark which are now its spots, and in Madagascar whale sharks are known locally as "marokintana" which means "many stars". In Indonesia, the Javanese also reference the stars by calling it "geger lintang," meaning, "stars in the back". In the Philippines, it is called "butanding".
[edit] Distribution and habitat
The whale shark inhabits the world's tropic and warm-temperate seas. While thought to be primarily pelagic, seasonal feeding aggregations of the sharks occur at several coastal cities such as Gladden Spit in Belize; Ningaloo Reef in Western Australia; Útila in Honduras; Donsol, Pasacao and Batangas in the Philippines; off Isla Mujeres and Isla Holbox in Yucatan Mexico; Ujung Kulon National Park in Indonesia; Nosy Be in Madagascar Off Tofo Reef in Mozambique, and the Tanzanian islands of Mafia, Pemba and Zanzibar. Although it is often seen offshore, it has also been found closer to shore, entering lagoons or coral atolls, and near the mouths of estuaries and rivers. Its range is generally restricted to about ±30 ° latitude. It is capable of diving to depths of 700 metres (2,300 ft), and is migratory.[3]
[edit] Anatomy and appearance
As a filter feeder it has a capacious mouth which can be up to 1.5 metres (4.9 ft) wide and can contain between 300 and 350 rows of tiny teeth.[5] 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 and because of this they can be used to identify each animal and hence make an accurate population count. Its skin can be up to 10 centimetres (3.9 in) thick. The shark has a pair 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 whale shark's spiracles are just behind the eyes.
The whale shark is not an efficient swimmer since the entire body is used for swimming, which is unusual for fish and contributes to an average speed of only around 5-kilometre-per-hour (3.1 mph). The largest specimen regarded as accurately recorded was caught on November 11, 1947, near the island of Baba, not far from Karachi, Pakistan. It was 12.65 metres (41.50 ft) long, weighed more than 21.5 tonnes (47,300 lb), and had a girth of 7 metres (23.0 ft).[6] Stories exist of vastly larger specimens—quoted lengths of 18 metres (59 ft) are not uncommon in the popular shark literature—but no scientific records exist to support their existence. In 1868 the Irish natural scientist Edward Perceval Wright spent time in the Seychelles, during which he managed to obtain several small whale shark specimens, but claimed to have observed specimens in excess of 15 metres (49.2 ft), and tells of reports of specimens surpassing 21 metres (68.9 ft).
In a 1925 publication, Hugh M. Smith describes a huge whale shark caught in a bamboo fish trap in Thailand in 1919. The shark was too heavy to pull ashore, but Smith estimated that the shark was at least 17 metres (56 ft) long, and weighed approximately 37 tonnes (81,500 lb), which have been exaggerated to a more precise measurement of 17.98 metres (58.99 ft) and weight 43 tonnes in recent years. A shark caught in 1994 near Tainan County in Southern Taiwan is reported to have weighed 35.8 tonnes (78,887 lb).[7] There have even been claims of whale sharks of up to 23 metres (75 ft). In 1934 a ship named the Maurguani came across a whale shark in the Southern Pacific Ocean, rammed it, and the shark consequently became stuck on the prow of the ship, supposedly with 4.6 metres (15.1 ft) on one side and 12.2 metres (40.0 ft) on the other.[8] No reliable documentation exists of those claims and they remain little more than "fish-stories".
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