The whale shark, Rhincodon typus, is a slow moving filter feeding shark that is the largest living fish species. It can grow up to 60 ft in length and can weigh up to 13.6 tonnes (15 short tons). This distinctively-marked shark is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhinodontes before 1984), which is grouped into the subclass Elasmobranchii in the class Chondrichthyes. The shark is found in tropical and warm oceans and lives in the open sea and can live for about 70 years. The species is believed to have 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 (a whale shark was observed feeding on a school of small fish in the BBC program Planet Earth).
The species was identified in April 1828 following the harpooning of a 4.6-metre (15.1 ft) specimen in Table Bay, South Africa. It was described the following year by Andrew Smith, a military doctor associated with British troops stationed in Cape Town. He proceeded to publish a more detailed description of the species in 1849. The name "whale shark" comes from the fish's physiology; that is, a shark as large as a whale that shares a similar filter feeder eating mode. Known as a deity in a Vietnamese religion, the whale shark is called "Ca Ong", which literally translates as "Sir Fish". In Mexico, and throughout much of Latin America, the whale shark is known as "pez dama" or "domino" for its patterns of spots. Whale sharks go by the name of "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 about as it is believed that God threw shillings upon the shark which are now its spots, and in Madagascar whale sharks are known locally as "marokintana" which means "many stars". In Indonesia, the 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 the world's tropic and warm-temperate seas. While thought to be primarily pelagic, seasonal feeding aggregations of the sharks occur at several coastal cities 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 it is often seen offshore, it has also been found closer to shore, 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 whale shark and because of this they can be used to identify each animal and hence make an accurate population count. Its skin can be up to 10 centimetres (3.9 in) thick. The shark has a pair each of dorsal fins and pectoral fins. A juvenile whale shark's tail has a larger upper fin than lower fin while the adult tail becomes semi-lunate (or crescent-shaped). The whale shark's spiracles are just behind the eyes.
The whale shark is not an efficient swimmer since the entire body is used for swimming, which is unusual for fish and contributes to an average speed of only around 5-kilometre-per-hour (3.1 mph). The largest specimen regarded as accurately recorded 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 (47,300 lb), and had a girth of 7 metres (23.0 ft). Stories exist of vastly larger specimens—quoted lengths of 18 metres (59 ft) 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 15 metres (49.2 ft), and tells of reports of specimens surpassing 21 metres (68.9 ft).
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 17 metres (56 ft) long, and weighed approximately 37 tonnes (81,500 lb), which have been exaggerated to a more precise measurement of 17.98 metres (58.99 ft) 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 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 of those claims and they remain little more than "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 (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 move to different location during different seasons for feeding 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 basking shark, which is a passive feeder and does not pump water; it relies on its swimming to force water over its gills.
Behavior toward divers
This species, despite its 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. 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 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 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 40 centimetres (15.7 in) to 60 centimetres (23.6 in) long. It is believed that they reach sexual maturity at around 30 years and the life span has been estimated to be 70, possibly up 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 (38 centimeters) 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 thereafter freed and released into the wild. The incident also led the scientists to believe they may have pinpointed one of the possible birthing grounds of the whale shark.
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. 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 captivity
Two whale sharks are 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. One is kept and 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, 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 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 are held in captivity at Polar Ocean World in Qingdao, China. One whale shark is held in captivity in the Atlantis Hotel in Dubai. As of October 2008, there is growing pressure to release the animal back to its natural environment.
- For a topical guide to this subject, see Outline of sharks.
- ^ a b Jurassic Shark (2000) documentary by Jacinth O'Donnell; broadcast on Discovery Channel, August 5, 2006
- ^ 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.
- ^ 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.
- ^ 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
- ^ "Smallest Whale Shark Rescued in Sorsogon". http://www.wwf.org.ph/newsfacts.php?pg=det&id=144. Retrieved 11 March 2009.
- ^ Whale Sharks Receive Protection in the Philippines
- ^ National Regulations on Whale Shark fishing
- ^ COA bans fishing for whale sharks
- ^ "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.
- 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
- "Rhincodon typus". FishBase. Ed. Ranier Froese and Daniel Pauly. November 2004 version. N.p.: FishBase, 2004.
- 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