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Whale shark
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name = Whale shark
| status = VU
| trend = down
| status_system = iucn2.3
| status_ref = Stories exist of vastly larger specimens — quoted lengths of 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 , and tells of reports of specimens surpassing .
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 long, and weighed approximately 37 tonnes (81,500 lb), which have been exaggerated to a more precise measurement of 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). 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 of those claims and they remain little more than "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 phytoplankton, macro-algae, plankton, krill 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 (anything above 2 to 3 mm in diameter is trapped). Any 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 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 between the full and quarter moons of May, June, and July.
The whale shark is an active feeder and targets concentrations of plankton or fish by olfactory cues. Rather than simply "vacuuming" constantly, it is able to pump water over its gills. The shark can circulate water at a rate up to 1.7 L/s (3.5 U.S. pint/s). The whale shark does not need to swim forward when feeding; it is often observed in a vertical position, "bobbing" up and down swallowing water and actively filtering it for food. This is in contrast to the basking shark, which is a passive feeder and does not pump water; it relies on its swimming to force water over its gills.
Behavior towards diversThis species, despite its enormous size, does not pose any significant danger to humans. It is a frequently cited example when educating the public about the popular misconceptions of all sharks as "man-eaters". They are actually quite gentle and can be playful with divers. There are unconfirmed reports of sharks lying still, upside down on the surface to allow divers to scrape parasites and other organisms from their bellies. Divers and snorkelers can swim with this giant fish without any risk apart from unintentionally being struck by the shark's large tail fin.
The shark is often seen by divers in The Bay Islands in Honduras, Thailand, the Philippines, the Maldives, the Red Sea, Western Australia, Gladden Spit Marine Reserve in Belize, Tofo Beach in Mozambique, Sodwana Bay in South Africa and at the Galapagos Islands.
The highest concentration of whale sharks to be found anywhere in the world is in the Philippines. From January to May, they congregate in the shallow coastal waters of Sorsogon province (at 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 Mexico's Baja California. Sometimes, they are accompanied by smaller fish, in particular, the remora. Recently, they have been seen in the vicinity of Tenggol Island, off the east coast of West Malaysia.They are also frequently spotted around other Coral Reefs along the West Malaysian coast including Kapas Island and Redang Island.
Recently 150 whale sharks have been tagged and identifed off the coast off Hol Box island, Mexico. The island is located north of Cancun in the gulf of Mexico. They visit the island from June through August and more have been identified every year. It's possible through authorised tour guides you can experience swimming with these enormous creatures.
ReproductionThe 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 female in July 1996 which was pregnant with 300 pups indicates that they are ovoviviparous. The eggs remain in the body and the females give birth to live young which are to long. It is believed that they reach sexual maturity at around 30 years and the life span has been estimated to be over 100 years.
Conservation statusThe 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. All fishing, selling, importing and exporting of whale sharks for commercial purposes has been banned in the Philippines since 1998, India in May 2001, followed by Taiwan in May 2007.
Whale sharks in captivityA 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, two males, Taroko, and Yushan, and two females, Alice and Trixie, are held in the Georgia Aquarium, in Atlanta. 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 males 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 Taiwan, where whale sharks are dubbed tofu sharks because of the taste and texture of the flesh.
See also
External links
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