The whale shark (Rhincodon typus) is a large, distinctively marked member of the class Elasmobranchii. It is the largest shark and also the largest fish, the greatest size accurately recorded was 14 m long, but lengths up to 20 m have been reported. Not to be confused with the Basking shark (Cetorhinus maximus) the second largest fish.
The average whale shark is around 8 m long. A member of the order Orectolobiformes it is a filter feeder. The shark has a capacious mouth, up to 1.5 m wide and containing up to 300 rows of tiny teeth, as part of its feeding process it also has five large pairs of gill arches. The head is, naturally, wide and also flat with the small eyes towards the front of the snout. The body is mostly grey with a white belly, but three prominent ridges run along each side and the skin is marked with a 'checkerboard' of pale yellow spots and stripes. The shark has two pairs of dorsal fins and two of pectoral fins. The tail is large, with a much large top fin than lower in juveniles but semi-lunate in adults. The spiracles are just behind the shark's eyes. The whale shark is not an efficient swimmer - with the entire body in motion, unusual for sharks, a average speed of around 5 km/hr is achieved.
The shark feeds on phytoplankton, macroalgae, and planktonic (plankton, krill) or nektonic (small squid or vertebrates) life, the many rows of teeth playing no role in feeding. Water is actively drawn into the mouth and passes over gill rakers and then out through the gill arches. Any material caught in the rakers is swallowed. The shark can circulate up to 6000 l of water every hour but they are active feeders and target concentrations of plankton or fish by olfactory cues rather than 'vacuuming' constantly.
The whale shark is a tropical and warm water fish, operating near the surface (benthic) mostly in coastal waters throughout the world, except the Mediterranean. It ranges is restricted to about ±30 ° latitude. The shark is solitary and only rarely seen in groups. It is believed to be migratory but on what scale is uncertain, transoceanic has been suggested.
Like most sharks the reproductive habits of the whale shark are obscure. It was believed to by oviparous based on a single egg recovered off Mexico in 1956, but the capture of a pregnant female in 1995 containing 300 young indicates that they are viviparous with ovoviviparous development - the eggs remain in the body and the females give birth to live 40-60 cm young. It is believed that they reach sexual maturity at around 30 years and the life span has been variously estimated at 60 to 150 years.
The species was first identified in 1828 off the coast of South Africa. The family Rhincodontidae was not finalized until 1984.
The whale shark is fished for off Taiwan and in the Philippines. The population is unknown and the species is considered vulnerable by the IUCN.
In popular culture, this species is the leading example when it is explained that not all sharks are dangerous to humans. Nature documentaries will show footage of divers keeping pace with the giant fish and the shark pays them no mind.
