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 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 program Planet Earth filmed a whale shark feeding on a school of small fish.
The species was distinguished in April 1828 following the harpooning of a 4.6-metre (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. 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.
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".
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 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 near Inhambane 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.
Anatomy and appearance
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). 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. 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, 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.
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.
Behaviour 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, 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, the Seychelles, West Malaysia, Sri Lanka, and in Puerto Rico.
Whale sharks in captivity
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. One is on display in the Taiwan, Kenting National Museum of Biology and Aquarium. 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 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 Taiwan, 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 Hotel in Dubai. One Whale Shark lives in Dalian, China. As of October 2008, there is growing pressure to release the single whale shark in captivity in Dubai back to its natural environment.
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.
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 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.
- For a topical guide to this subject, see Outline of sharks.
- ^ a b Norman, Brad (2000). Rhincodon typus. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 11 May 2006. Database entry includes justification for why this species is vulnerable.
- ^ a b c d e f Ed. Ranier Froese and Daniel Pauly. "Rhincodon typus". FishBase. http://www.fishbase.org/Summary/SpeciesSummary.php?id=2081. Retrieved 17 September 2006.
- ^ Jurassic Shark (2000) documentary by Jacinth O'Donnell; broadcast on Discovery Channel, August 5, 2006
- ^ Martin, R. Aidan. "Rhincodon or Rhiniodon? A Whale Shark by any Other Name". ReefQuest Centre for Shark Research. http://elasmo-research.org/education/topics/ng_rhincodon_or_rhiniodon.htm. Retrieved 2009-09-12.
- ^ Compagno, L.J.V.. "Species Fact Sheet, Rhincodon typus". Food and Agriculture Organization of the United Nations. http://www.fao.org/fishery/species/2801/en. Retrieved 19 September 2006.
- ^ Gerald L. Wood, Animal Facts and Feats, 1990.
- ^ Summary of Large Whale Shark Rhincodon typus Smith, 1828)
- ^ Xavier Maniguet, Jaws of Death; 1991.
- ^ Rebecca Morelle.. "Shark-cam captures ocean motion". BBC News. http://news.bbc.co.uk/2/hi/science/nature/7727136.stm. Retrieved 30 July 2009.
- ^ a b Martin, R. Aidan.. "Elasmo Research". ReefQuest. http://www.elasmo-research.org/education/topics/d_filter_feeding.htm. Retrieved 17 September 2006.
- ^ "Whale shark". Icthyology at the Florida Museum of Natural History. http://www.flmnh.ufl.edu/fish/Gallery/Descript/Whaleshark/whaleshark.html. Retrieved 17 September 2006.
- ^ a b Compagno, Leonard J. V. (April 26, 2002). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date: Bullhead, Mackerel and Carpet Sharks. 2. Food & Agriculture Organization of the United Nations (FAO). ISBN 978-9251045435. http://books.google.com/books?id=cxxSN4YA2i8C&lpg=PA207&dq=%22whale%20shark%22%20diver%20gentle&pg=PA207#v=onepage&q=&f=false. Retrieved 2009-09-20.
- ^ Garrison, Tom. Essentials of Oceanography. Brooks Cole. pp. 312. ISBN 978-0495555315. http://books.google.com/books?id=srUHU4SrCT4C&lpg=PT340&dq=whale%20shark%20struck%20by%20tail&num=100&pg=PT340#v=onepage&q=whale%20shark%20struck%20by%20tail&f=false.
- ^ "Aquarium gains two new whale sharks". CNN.com. June 1 2007. http://www.cnn.com/2007/TECH/science/06/01/aquarium.whale.sharks.ap/index.html. Retrieved June 1, 2007.
- ^ "2nd whale shark dies at Ga. Aquarium". Yahoo.com. June 13 2007. http://news.yahoo.com/s/ap/20070613/ap_on_re_us/whale_shark_dies_1;_ylt=AnVHZffZC60_oQt3rO_bITUE1vAI. Retrieved June 13, 2007.
- ^ "Dubai hotel urged to free shark". bbc.co.uk. October 19 2008. http://news.bbc.co.uk/2/hi/science/nature/7678780.stm. Retrieved October 19, 2008.
- ^ Shoou-Jeng Joung1, Che-Tsung Chen, Eugenie Clark, Senzo Uchida and William Y. P. Huang. The whale shark, Rhincodon typus, is a livebearer: 300 embryos found in one ‘megamamma’ supreme. Environmental Biology of Fishes Volume 46, Number 3 / July, 1996
- ^ Dr. Eugenie Clark. "Frequently Asked Questions". http://www.sharklady.com/faq.html#A12. Retrieved 26 September 2006.
- ^ "Whale Shark (Rhincodon typus) Issues Paper", Biology of Whale Shark, Department of the Environment and Heritage (Australian Government), 2005, http://www.environment.gov.au/biodiversity/threatened/publications/recovery/r-typus-issues/biology.html
- ^ Whale Sharks Receive Protection in the Philippines
- ^ National Regulations on Whale Shark fishing
- ^ COA bans fishing for whale sharks
- 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
- Froese, Rainer, and Daniel Pauly, eds. (2004). "Rhincodon typus" in FishBase. November 2004 version.
- Rhincodon typus (TSN 159857). Integrated Taxonomic Information System. Retrieved on 16 November 2005.
- Whale shark (Rhincodon typus) at Wikimedia Commons
- Whale shark (Rhincodon typus) at Wikispecies
- Whale shark (Rhincodon typus) at Integrated Taxonomic Information System
- Whale shark (Rhincodon typus) at Animal Diversity Web
- Whale shark (Rhincodon typus) at IUCN Red List
- Whale shark (Rhincodon typus) at FishBase
- Whale shark (Rhincodon typus) at Ocean Biogeographic Information System