The whale shark (Rhincodon typus) is a slow-moving filter-feeding carpet shark and the largest known extant fish species. The largest confirmed individual had a length of 12.65Â m (41.5Â ft) and a weight of about 21.5Â t (47,000Â lb). Unconfirmed claims of considerably larger individuals, over 14Â m (46Â ft) long and weighing at least 30Â t (66,000Â lb), are not uncommon. The whale shark holds many records for sheer size in the animal kingdom, most notably being by far the largest living nonmammalian vertebrate. It is the sole member of the genus Rhincodon and the only extant member of 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 open waters of the tropical oceans and is rarely found in water below 22 °C (72 °F). Modeling suggests a lifespan of about 70 years, but measurements have proven difficult. Whale sharks have very large mouths and are filter feeders, which is a feeding mode that occurs in only two other sharks, the megamouth shark and the basking shark. They feed almost exclusively on plankton and are not known to pose a threat to humans.
The species was distinguished in April 1828 after the harpooning of a 4.6Â m (15Â 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. The name "whale shark" directly refers to the fish's size, being as large as some species of whales and also that it is a filter feeder like baleen whales.
Distribution and habitat
The whale shark inhabits all tropical and warm-temperate seas. The fish is primarily pelagic, living in the open sea but not in the greater depths of the ocean, although it is known to occasionally dive to depths of as much as 1,800 metres (5,900 ft). Seasonal feeding aggregations occur at several coastal sites such as the southern and eastern parts of South Africa; Saint Helena Island in the South Atlantic Ocean; Gulf of Tadjoura in Djibouti, Gladden Spit in Belize; Ningaloo Reef in Western Australia; Lakshadweep, Gulf of Kutch and Saurashtra coast of Gujarat in India; Útila in Honduras; Southern Leyte; Donsol, Pasacao and Batangas in the Philippines; off Isla Mujeres and Isla Holbox in Yucatan and BahÃa de los Ãngeles in Baja California, México; Maamigili island, Maldives; Ujung Kulon National Park in Indonesia; Cenderawasih Bay National Park in Nabire, Papua, Indonesia; Flores Island, Indonesia; Nosy Be in Madagascar Off Tofo Reef near Inhambane in Mozambique; the Tanzanian islands of Mafia, Pemba, Zanzibar; Gulf of Tadjoura in Djibouti, the Ad Dimaniyat Islands in the Gulf of Oman and Al Hallaniyat islands in the Arabian Sea; and, very rarely, Eilat, Israel and Aqaba, Jordan. 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 m (4,219 ft), and is migratory. 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 m (36 and 39 ft), with a weight of around 15,000 kg (33,000 lb).
In 2011, more than 400 whale sharks gathered off the Yucatan Coast. It was one of the largest gatherings of whale sharks recorded. Aggregations in that area are among the most reliable seasonal gatherings known for whale sharks, with large numbers occurring in most years between May and September. Associated ecotourism has grown rapidly to unsustainable levels.
Description
Whale sharks have a mouth that can be 1.5Â m (4.9Â ft) wide, containing 300 to 350 rows of tiny teeth and 10 filter pads which it uses to filter feed. Whale sharks have five large pairs of gills. The head is wide and flat with two small eyes at the front. Whale sharks are grey with a white belly. Their skin is marked with pale yellow spots and stripes which are unique to each individual. The whale shark has three prominent ridges along its sides. Its skin can be up to 10Â cm (3.9Â in) thick. The shark has a pair of dorsal fins and pectoral fins. Juveniles' tails have a larger upper fin than lower fin, while the adult tail becomes semilunate. The whale shark's spiracles are just behind its eyes.
The whale shark is the largest non-cetacean animal in the world. The average size of adult whale sharks is estimated at 9.7 m (31.82 ft) and 9 t (20,000 lb). Several specimens over 18 m (59.05 ft) in length have been reported The largest verified specimen was caught on 11 November 1947, near Baba Island, in Karachi, Pakistan. It was 12.65 m (41.50 ft) long, weighed about 21.5 t (47,000 lb), and had a girth of 7 m (23.0 ft). Stories exist of vastly larger specimens â€" quoted lengths of 18 m (59 ft) and 45.5 t (100,000 lb) are common in the popular 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 m (49.2 ft), and tells of shark specimens surpassing 21 m (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 the shark was at least 17Â m (56Â ft) long, and weighed around 37 t. These measurements have been exaggerated to 43Â t (95,000Â lb) and a more precise 17.98Â m (59.0Â ft) in recent years. A shark caught in 1994 off Tainan County, southern Taiwan, reportedly weighed 35.8Â t (79,000Â lb). There have even been unverified claims of whale sharks of up to 23 metres (75Â ft) and 100 tonnes (220,000Â lb). In 1934, a ship named the Maurguani came across a whale shark in the southern Pacific Ocean, rammed it, and the shark became stuck on the prow of the ship, supposedly with 4.6Â m (15Â ft) on one side and 12.2Â m (40Â ft) on the other. No reliable documentation exists for these claims and they remain "fish stories".
Diet
The whale shark is a filter feeder â€" one of only three known filter-feeding shark species (along with the basking shark and the megamouth shark). It feeds on plankton including copepods, krill, fish eggs, Christmas Island red crab larvae and small nektonic life, such as small squid or fish. It also feeds on clouds of eggs during mass spawning of fish and corals. 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. This is an extremely efficient filtration method that minimizes fouling of the filter pad surface. Whale sharks have been observed "coughing", presumably to clear a build-up of particles from the filter pads. 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.
A juvenile whale shark is estimated to eat 21Â kg (46 pounds) of plankton per day.
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.
Whale sharks are known to prey on a range of planktonic and small nektonic organisms that are spatiotemporally patchy. These include krill, crab larvae, jellyfish, sardines, anchovies, mackerels, small tunas, and squid. In ram filter feeding, the fish swims forward at constant speed with its mouth fully open, straining prey particles from the water by forward propulsion. This is also called ‘passive feeding’, which usually occurs when prey is present at low density.
Behavior toward divers
Despite its size, the whale shark does not pose significant danger to humans. Whale sharks are docile fish and sometimes allow swimmers to catch a ride, although this practice is discouraged by shark scientists and conservationists because of the disturbance to the sharks. Younger whale sharks are gentle and can play with divers. Underwater photographers such as Fiona Ayerst have photographed them swimming close to humans without any danger.
The shark is seen by divers in many places, including the Bay Islands in Honduras, Thailand, the Philippines, the Maldives close to Maamigili (South Ari Atoll), the Red Sea, Western Australia (Ningaloo Reef, Christmas Island), Taiwan, Panama (Coiba Island), Belize, Tofo Beach in Mozambique, Sodwana Bay (Greater St. Lucia Wetland Park) in South Africa, the Galapagos Islands, Saint Helena, Isla Mujeres (Caribbean Sea), La Paz, Baja California Sur and BahÃa de los Ãngeles in Mexico, the Seychelles, West Malaysia, islands off eastern peninsular Malaysia, India, Sri Lanka, Oman, Fujairah, Puerto Rico, and other parts of the Caribbean. Juveniles can be found near the shore in the Gulf of Tadjoura, near Djibouti, in the Horn of Africa.
In captivity
Two whale sharks were featured as the main attraction of Osaka Aquarium Kaiyukan and as of 2005, three whale sharks were 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 was 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, 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 called 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.
Reproduction
Neither mating nor pupping of whale sharks has been observed.
The capture of a female in July 1996 that was pregnant with 300 pups indicated whale sharks are ovoviviparous. The eggs remain in the body and the females give birth to live young which are 40 to 60Â cm (16 to 24Â in) long. Evidence indicates the pups are not all born at once, but rather the female retains sperm from one mating and produces a steady stream of pups over a prolonged period. They reach sexual maturity at around 30 years and their lifespan is an estimated 70 to 100 years.
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 38Â cm (15Â in), was found with its tail tied to a stake at a beach in Pilar, Sorsogon, Philippines, and was released into the wild. Based on this discovery, some scientists no longer believe this area is just a feeding ground; this site may be a birthing ground, as well. Both young whale sharks and pregnant females have been seen in the waters of Saint Helena in the South Atlantic Ocean, where numerous whale sharks can be spotted during the summer.
Conservation status
There is currently no robust estimate of the global whale shark population. The species is considered endangered by the IUCN due to the impacts of fisheries, bycatch losses, and vessel strikes, combined with its long life span and late maturation. It is listed, along with six other species of sharks, under the CMS Memorandum of Understanding on the Conservation of Migratory Sharks. In 1998, the Philippines banned all fishing, selling, importing, and exporting of whale sharks for commercial purposes, followed by India in May 2001, and Taiwan in May 2007.
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.
In 2010, the Gulf of Mexico oil spill resulted in 4,900,000 barrels (780,000Â 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. No dead whale sharks were found.
This species was also added to Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in 2003 to regulate the international trade of live specimens and its parts.
Human culture
In Vietnamese culture, the whale shark is referred to as "sir fish".
In the Philippines, it is called butanding and balilan. The whale shark is featured on the reverse of the Philippine 100-peso bill. By law snorkelers must maintain a distance of four feet from the sharks and there is a fine and possible jail time for anyone who touches the animals.
See also
- List of sharks
- List of prehistoric cartilaginous fish
References
- Further reading
- "Whale Sharks, Whale Shark Pictures, Whale Shark Facts". Animals, Animal Pictures, Wild Animal Facts.Â
External links
- Whale Shark Photograph-identification Library
- Whale Shark And Oceanic Research Center
- Maldives Whale Shark Research Program
- Whale Sharks: Gentle Giants of the Seas
- Foundation for the Protection of Marine Megafauna
- Whale shark, Rhincodon typus at marinebio.org
- Whale Shark Fact Sheet, Fisheries Western Australia
- Albino whale shark photographed in Galapagos
- Photographs National Geographic
- A whale shark recorded defecating