The whale shark, Rhincodon typus, is a slow-moving filter feeding shark and the largest extant 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), and there are unconfirmed reports of considerably larger whale sharks. Claims of individuals over 14 metres (46 ft) long and weighing at least 30 tonnes (66,000 lb) are not uncommon. The whale shark is the sole member of the genus Rhincodon and the family, Rhincodontidae (called Rhiniodon and Rhinodontidae before 1984), which belongs to the subclass Elasmobranchii in the class Chondrichthyes. The species originated about 60 million years ago.

The whale shark is found in tropical and warm oceans and lives in the open sea with a lifespan of about 70 years.^[3] Although whale sharks have very large mouths, as filter feeders they feed mainly, though not exclusively, on plankton, which are microscopic plants and animals. However, the BBC program Planet Earth filmed a whale shark feeding on a school of small fish. The same documentary showed footage of a whale shark timing its arrival to coincide with the mass spawning of fish shoals and feeding on the resultant clouds of eggs and sperm.^[1]

The species was distinguished in April 1828 after the harpooning of a 4.6 metres (15.1 ft) specimen in Table Bay, South Africa. Andrew Smith, a military doctor associated with British troops stationed in Cape Town, described it the following year.^[4] The name "whale shark" comes from the fish's physiology, being as large as many whales^[5] and also a filter feeder like many whale species.

Distribution and habitat

The whale shark inhabits all tropical and warm-temperate seas. They are known to migrate every spring to the continental shelf of the central west coast of Australia. The coral spawning of the area's Ningaloo Reef provides the whale shark with an abundant supply of plankton. Primarily pelagic, seasonal feeding aggregations occur at several coastal sites such as the southern and eastern parts of South Africa; Gladden Spit in Belize; Ningaloo Reef in Western Australia; Great Rann of Kutch in India; 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 near Inhambane in Mozambique, and the Tanzanian islands of Mafia, Pemba, Zanzibar and, very rarely, Eilat, Israel. 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 at least 1,286 metres (4,219 ft),^{[citation needed]} and is migratory.^[3] On 7 February 2012, a large whale shark was found floating 150 kilometres (93 mi) off the coast of Karachi, Pakistan. The length of the specimen was said to be between 11 and 12 metres (36 and 39 ft), with a weight of around 7,000 kilograms (15,000 lb).^[6][7]

In 2011 the largest aggregation of whale sharks ever recorded was reported from the Yucatan coast of Mexico, in which more than 400 animals gathered in one place to feed on spawn from the little tunny, Euthynnus alletteratus.^[8]

Description

As a filter feeder it has a capacious mouth which can be up to 1.5 metres (4.9 ft) wide and contains 10 filter pads and between 300 and 350 rows of tiny teeth.^[9] 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.

Whale shark caught off Anping, Tainan County, Taiwan, on 30 March 1994. This specimen reportedly weighed 35.8 tonnes (79,000 lb) and is possibly the largest ever recorded.^[10]

Whale shark in main tank at Osaka Aquarium

The whale shark is the largest non-cetacean animal in the world. The average size of adult whale sharks is estimated at 9.7 metres (31.82 ft) and 9 tonnes (20,000 lb).^[11] The largest verified specimen was caught on 11 November 1947, near Baba Island, in 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).^[11] Stories exist of vastly larger specimens – quoted lengths of 18 metres (59 ft) and 45.5 tonnes (100,000 lb) 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). These measurements have been exaggerated to 43 tonnes (95,000 lb) and a more precise 17.98 metres (58.99 ft) in recent years. A shark caught in 1994 off Tainan County, southern Taiwan reportedly weighed 35.8 tonnes (79,000 lb).^[10] There have even been claims of whale sharks of up to 23 metres (75 ft) and 100 tonnes (220,000 lb). 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.^[12] 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,^[13] and small nektonic life such as small squid or vertebrates. It also feeds on small fish and the clouds of eggs and sperm during mass spawning of fish shoals.^[1] The many rows of vestigial teeth play no role in feeding. Feeding occurs either by ram filtration, in which the animal opens its mouth and swims forward, pushing water and food into the mouth, or by active suction feeding, in which the animal opens and closes its mouth, sucking in volumes of water that are then expelled through the gills. In both cases, the filter pads serve to separate food from water. These unique, black sieve-like structures are presumed to be modified gill rakers. Food separation in whale sharks is by cross-flow filtration, in which the water travels nearly parallel to the filter pad surface, not perpendicularly through it, before passing to the outside, while denser food particles continue to the back of the throat.^[14] This is an extremely efficient filtration method that minimises fouling of the filter pad surface. Whale sharks have been observed "coughing" and it is presumed that this is a method of clearing a build-up of particles from the filter pads. Whale sharks migrate to feed and possibly to breed.^[3][15][16]

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.^[3][15]

Behaviour toward divers

A whale shark at Ningaloo Reef

Despite its size, the whale shark does not pose significant danger to humans. Although massive, whale sharks are docile fish and sometimes allow swimmers to catch a ride,^[17] although this practice is discouraged by shark scientists and conservationists. Younger whale sharks are actually quite gentle and can play with divers. In July 2011, several sources reported, with photos, an incident of a diver who, allegedly, was nearly sucked into the mouth of a whale shark (but escaped unharmed) off the coast of Isla Mujeres, Mexico.^[18]

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), Taiwan, Panama (Coiba), Belize, Tofo Beach in Mozambique, Sodwana Bay (Greater St. Lucia Wetland Park) in South Africa, the Galapagos Islands, Isla Mujeres and Bahía de los Ángeles in Mexico, the Seychelles, West Malaysia, islands off eastern peninsular Malaysia, Sri Lanka, Oman, Fujairah, and Puerto Rico.^[17]

In captivity

A whale shark in the Georgia Aquarium

Two whale sharks are featured as the main attraction of Osaka Aquarium Kaiyukan and as of 2005, three whale sharks are in captivity at the Okinawa Churaumi Aquarium in Japan. The Ioworld Aquarium in Kagoshima, Japan, also features a single adult whale shark as a major attraction. One is also on display in the Taiwan, Kenting National Museum of Biology and Aquarium and 5 are on display at the Yantai Aquarium in China. Four whale sharks, two males, Taroko and Yushan,^[19] and two females, Alice and Trixie, live in the Georgia Aquarium, in Atlanta, USA. Two male whale sharks, Ralph and Norton, died in captivity at the Georgia Aquarium on 11 January 2007, and 13 June 2007, respectively. The two females were added on 3 June 2006 and two more males in 2007. All six whale sharks were imported from Taiwan, where whale sharks are dubbed tofu sharks because of the taste and texture of the flesh; the fishery from which they came has since closed. Two whale sharks live at Polar Ocean World in Qingdao, China. One whale shark was at the Atlantis Hotel in Dubai, but was released in March, 2010.^[20]

Reproduction

Neither mating nor pupping has been observed in whale sharks.

The capture of a female in July 1996 which was pregnant with 300 pups indicates that whale sharks are ovoviviparous.^[3][21][22] 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. There is evidence that the pups are not all born at once, but rather that the female retains sperm from one mating and produces a steady stream of pups over a prolonged period.^[23] It is believed that they reach sexual maturity at around 30 years and the life span is an estimated 70^[3] to 100 years.^[24]

On 7 March 2009, marine scientists in the Philippines discovered what is believed to be the smallest living specimen of the whale shark. The young shark, measuring only 38 centimetres (15 in), was found with its tail tied to a stake at a beach in Pilar, Philippines, and was released into the wild. Based on this discovery some scientists no longer believe that this area is just a feeding ground; it may also be that this site is a birthing ground as well.^[25]

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.^[2] It is listed, along with 6 other species of shark, under the CMS Memorandum of Understanding (MoU) on the Conservation of Migratory Sharks.^[26] In 1998, the Philippines banned all fishing, selling, importing and exporting of whale sharks for commercial purposes,^[27] followed by India in May 2001,^[28] and Taiwan in May 2007.^[29] They are currently listed as a vulnerable species; however, they continue to be hunted in parts of Asia, such as Taiwan and the Philippines.

In 2006, Resorts World Sentosa announced its plans to bring in whale sharks for their marine life park. This was met with opposition from seven notable conservation societies. In 2009, the plan was shelved in favour of a search for other alternatives.^[30][31]

In 2010, the Gulf of Mexico oil spill resulted in 4,900,000 barrels (780,000 m³) of oil flowing into an area south of the Mississippi River Delta, where one-third of all whale shark sightings in the northern part of the gulf have occurred in recent years. Sightings confirmed that the whale sharks were unable to avoid the oil slick which was situated on the surface of the sea where the whale sharks feed for several hours at a time. However, no dead whale sharks have been found.^[32]

In human culture

Snorkeling with whale shark near Isla Mujeres (Mexico) 30 August 2011

Snorkeling with whale shark.

Known as a deity in a Vietnamese culture, the whale shark is called "Ca Ong", which literally translates as "Sir Fish".^[33]

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 Reef.

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" and "balilan",^[34] while in Madurese, it is known as "kikaki".

The whale shark is featured on the reverse of the Philippine one hundred peso bill.

See also

For a topical guide to this subject, see Outline of sharks.

• List of sharks
• List of prehistoric cartilaginous fish

Sharks portal

References

General references

• "Whale Sharks, Whale Shark Pictures, Whale Shark Facts". Animals, Animal Pictures, Wild Animal Facts. National Geographic. http://animals.nationalgeographic.com/animals/fish/whale-shark/.