Whale Shark (Rhincodon typus)
What does it look like?
The whale shark is the world’s biggest fish. It grows up to 12 m long! Its massive body, broad flattened head, rounded dorsal fin and crescent-shaped tail are decorated with a ‘checkerboard’ pattern of light spots and stripes on a darker background. These beautiful markings might serve as camouflage from predators in the dappled light of the ocean. They may also shield the fish from UV radiation. But since sharks have good eyesight, it’s also possible the markings are related to social activities such as mating displays. The markings don’t change as the fish grows older, and can be used to identify individual animals.
The whale shark has about 3,000 tiny teeth, but unlike its cousin the wobbegong (also found in Shark Bay) it does not hunt prey. Instead, it is a filter-feeder, sucking water into its mouth and sieving out tasty morsels such as krill, crab and coral larvae and small fish through mesh-like screens in its gills. It also hangs vertically with its mouth agape, letting food and water pour in. It can open its mouth more than 1 m wide, and capture food only 1 mm long! Only two other shark species, the megamouth shark and the basking shark, catch their food this way.
Where does it live?
The whale shark is found in warm seas about 30º north and south of the Equator. It inhabits deep water and shallow coastal seas as well as coral atolls and reefs. Although most often seen swimming close to the surface, it can dive to depths of about 700 m! It is thought to be highly migratory, travelling thousands of kilometres over several years. On the other hand, some individuals are known to return to the same place repeatedly within the space of a few weeks.
The whale shark’s movements are influenced by its diet. In Western Australia, sharks have been spotted between Kalbarri (on the mid-west coast) and Shark Bay in December and January. They have also been seen in South Passage
as late as April. A good place to see whale sharks is in Ningaloo Marine Park, north of Shark Bay. Usually loners, groups of whale sharks are drawn to Ningaloo by coral spawnings after the March and April full moons. The spawn lure masses of plankton and krill, which in turn lure schools of fish – and hungry whale sharks!
How does it breed?
Like all sharks, whale sharks fertilise their eggs inside their body. But the whale shark is unusual in that it is ovoviviparous (also called ‘aplacental viviparity’). This means the female gives birth to live young, called pups, which have developed from eggs hatched within her uterus. At birth a whale shark pup is about 55 cm long.
Any threats to its survival?
The whale shark is harmless to humans, but unfortunately the reverse is not true. Its large size, slow speed and habit of swimming at the surface make it easy to kill. As many as 1,000 whale sharks were slaughtered off India between 1999 and 2000. With whale shark products becoming increasingly popular in southeast Asian markets, it is feared this fishing is unsustainable. Although fully protected in Australian waters, this gentle giant is not protected in most of the 100 or more countries it is known to visit. Its numbers are decreasing, and it is now globally vulnerable to extinction.
For more information about Western Australian wildlife check out the WA Museum Fauna Base
to download a printable PDF of this fact sheet.