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Whale Sharks, Belize
Whale Sharks, Belize

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 12.65 metres (41.50 ft) and a weight of more than 21.5 tonnes (47,000 lb), 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 6000 years ago. Although whale sharks have very large mouths, they feed mainly, though not exclusively, on plankton, microscopic plants and animals, although the BBC program Planet Earth filmed a whale shark feeding on a school of small fish.

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 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 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 700 metres (2,300 ft), and is migratory.

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. 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 10 centimetres (3.9 in) 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 5-kilometre-per-hour (3.1 mph). The largest specimen 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 (47,000 lb), and had a girth of 7 metres (23.0 ft). Stories of vastly larger specimens—quoted lengths of 18 metres (59 ft) 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 Seychelles, 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 described a huge animal 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 (82,000 lb), which have been exaggerated to a more precise measurement of 17.98 metres (58.99 ft) and weight 43 tonnes (95,000 lb) in recent years. A shark caught in 1994 near Tainan County in Southern Taiwan reportedly weighed 35.8 tonnes (79,000 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 for these claims and they remain 'fish-stories'.

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,[9] 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 2 to 3 millimetres (0.079 to 0.12 in) 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.

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, Thailand, the Philippines, the Maldives, the Red Sea, Western Australia (Ningaloo Reef, Christmas Island), Belize, Tofo Beach in Mozambique, Sodwana Bay (Greater St. Lucia Wetland Park) in South Africa, at the Galapagos Islands, off Isla Mujeres in Mexico, Seychelles, West Malaysia, Sri Lanka, and in Puerto Rico.

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 40 to 60 centimetres (16 to 24 in) 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 15 inches (380 mm) 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.

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