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The whale shark, Rhincodon typus, is a slow moving filter feeding shark, the largest living fish species. The largest confirmed individual had a length of and a weight of more than , but unconfirmed claims report considerably larger whale sharks. This distinctively-marked fish is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhinodontes before 1984), which belongs to the subclass Elasmobranchii in the class Chondrichthyes. The shark is found in tropical and warm oceans, lives in the open sea with a lifespan of about 70 years. The species 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, although the BBC programme Planet Earth filmed a whale shark feeding on a school of small fish.

Etymology

The species was distinguished in April 1828 following the harpooning of a specimen in Table Baymarker, South Africa. Andrew Smith, a military doctor associated with British troops stationed in Cape Townmarker described it the following year. He published a more detailed description in 1849. The name "whale shark" comes from the fish's physiology. As large as a whale, it too is a filter feeder.

Known as a deity in a Vietnamesemarker 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 distinctive patterns of spots. However, they go by "Sapodilla Tom" in Belize due to the regularity of sightings near the Sapodilla Cayes on the Belize Barrier Reefmarker.

In Africa, the names for the whale shark are very evocative: "papa shillingi" in Kenya came from the myth that God threw shillings upon the shark which are now its spots. In Madagascar the name is "marokintana" meaning "many stars".

Javanese also reference the stars by calling it "geger lintang," meaning "stars in the back". In the Philippines, it is called "butanding".

Distribution and habitat

The whale shark inhabits all tropic and warm-temperate seas. Primarily pelagic, seasonal feeding aggregations occur at several coastal sites such as Gladden Spit in Belizemarker; Ningaloo Reefmarker in Western Australiamarker; Útila in Hondurasmarker; Donsolmarker, Pasacaomarker and Batangasmarker in the Philippinesmarker; off Isla Mujeresmarker and Isla Holboxmarker in Yucatanmarker Mexicomarker; Ujung Kulon National Parkmarker in Indonesiamarker; Nosy Bemarker in Madagascarmarker Off Tofo Reef in Mozambiquemarker, and the Tanzanian islands of Mafiamarker, Pembamarker and Zanzibarmarker. Although typically seen offshore, it has been found closer to land, 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 , and is migratory.

Anatomy and appearance

As a filter feeder it has a capacious mouth which can be up to wide and can contain between 300 and 350 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 individual and are useful for counting populations. Its skin can be up to thick. The shark has a pair each of dorsal fins and pectoral fins. Juveniles' tails have a larger upper than lower fin while the adult tail becomes semi-lunate (crescent-shaped). Spiracles are just behind the eyes.

The whale shark is not an efficient swimmer since it uses its entire body, unusually for fish and contributes to an average speed of only around . The largest specimen was caught on November 11, 1947, near the island of Baba, not far from Karachimarker, Pakistanmarker. It was long, weighed more than , and had a girth of . Stories of vastly larger specimens—quoted lengths of are not uncommon in the popular shark literature—but no scientific records support their existence. In 1868 the Irish natural scientist Edward Perceval Wright obtained several small whale shark specimens in the Seychellesmarker, but claimed to have observed specimens in excess of , and tells of reports of specimens surpassing .

In a 1925 publication, Hugh M. Smith described a huge animal caught in a bamboo fish trap in Thailandmarker in 1919. The shark was too heavy to pull ashore, but Smith estimated that the shark was at least long, and weighed approximately , which have been exaggerated to a more precise measurement of and weight in recent years. A shark caught in 1994 near Tainan County in Southern Taiwanmarker reportedly weighed . There have even been claims of whale sharks of up to . 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 on one side and on the other. No reliable documentation exists for these claims and they remain "fish-stories".

Diet

The whale shark is a filter feeder—one of only three known filter feeding shark species (along with the basking shark and the megamouth shark). It feeds on macro-algae, plankton, krill, Christmas Island red crab larvae, and small nektonic life such as small squid or vertebrates. The many rows of teeth play no role in feeding; in fact, they are reduced in size in the whale shark. Instead, the shark sucks in a mouthful of water, closes its mouth and expels the water through its gills. During the slight delay between closing the mouth and opening the gill flaps, plankton is trapped against the dermal denticles which line its gill plates and pharynx. This fine sieve-like apparatus, which is a unique modification of the gill rakers, prevents the passage of anything but fluid out through the gills, trapping anything above in diameter. Material caught in the filter between the gill bars is swallowed. Whale sharks have been observed "coughing" and it is presumed that this is a method of clearing a build up of food particles in the gill rakers. Whale sharks migrate to feed and possibly to breed.

The whale shark is an active feeder, targeting concentrations of plankton or fish. It is able to ram filter feed or can gulp in a stationary position. This is in contrast to the passive feeding basking shark, which does not pump water. Instead, it swims to force water across its gills.

Behavior toward divers

This species, despite its size, does not pose significant danger to humans. Whale sharks serve as an example when educating the public about the popular misconceptions of sharks as "man-eaters". They are actually quite gentle and can play with divers. Divers and snorkelers can swim with this giant fish without risk apart from unintentional blows from the shark's large tail fin.

The shark is seen by divers in many places, including the Bay Islands in Honduras, Thailandmarker, the Philippinesmarker, the Maldivesmarker, the Red Seamarker, Western Australiamarker (Ningaloo Reefmarker, Christmas Islandmarker), Belizemarker, Tofo Beachmarker in Mozambiquemarker, Sodwana Bay (Greater St. Lucia Wetland Parkmarker) in South Africa, at the Galapagosmarker Islands, off Isla Mujeresmarker in Mexicomarker, Seychellesmarker, West Malaysia, Sri Lankamarker, and in Puerto Rico.

Whale sharks in captivity

Two whale sharks are featured as the main attraction of Osaka Aquarium Kaiyukanmarker and as of 2005, three whale sharks are in captivity at the Okinawa Churaumi Aquariummarker in Japanmarker. One is on display in the Taiwan, Kenting [[National Museum of Marine Biology and Aquarium|National Museum of Biologyand Aquarium]]. Four whale sharks, two males, Taroko, and Yushan, and two females, Alice and Trixie, live in the Georgia Aquariummarker, in Atlantamarker, USA. Two male whale sharks, Ralph and Norton, died in captivity at the Georgia Aquarium on January 11, 2007 and June 13, 2007 respectively. The two females were added on June 3, 2006 in hopes that reproduction in whale sharks could be studied in captivity. All six whale sharks were imported from Taiwanmarker, where whale sharks are dubbed tofu sharks because of the taste and texture of the flesh. Two whale sharks live at Polar Ocean World in Qingdao, China. One whale shark is at the Atlantis Hotelmarker in Dubai. As of October 2008, there is growing pressure to release these animals back to their natural environments.

Reproduction

The capture of a female in July 1996 which was pregnant with 300 pups indicates that whale sharks are ovoviviparous. The eggs remain in the body and the females give birth to live young which are long. It is believed that they reach sexual maturity at around 30 years and the life span is an estimated 70 to 100 years.

On March 7, 2009, marine scientists in the Philippines discovered what is believed to be the smallest living specimen of the whale shark. Measuring in length, about the length of a man's forearm, the young shark was found with its tail tied to a stake at a beach in Pilar, Philippines, and was released into the wild. Scientists believe that this site is a birthing ground.

Conservation status

The whale shark is targeted by commercial fisheries in several areas where they seasonally aggregate. The population is unknown and the species is considered vulnerable by the IUCN. In 1998, the Philippinesmarker banned all fishing, selling, importing and exporting of whale sharks for commercial purposes, followed by India in May 2001, and Taiwan in May 2007.

See also



References

General references


  • J. G. Colman (1997). A review of the biology and ecology of the whale shark. Journal of Fish Biology 51 (6), 1219–1234.
  • FAO web page on Whale shark


External links




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