Whale sharks ( Rhincodon typus) are the world’s largest fish. These magnificent animals are generally between 4 and 12 metres long although a fully grown whale shark may reach up to 18 metres in length... A 12-metre whale shark may weigh as much as 11 tonnes and have a mouth over a metre wide.

In addition to their enormous size, whale sharks can be identified by three prominent ridges along each side of their body and a distinct pattern of white spots and stripes. Despite their huge size these gentle giants are actually filter feeders and cruise the worlds oceans looking for plankton.

Whale sharks have thousands of tiny teeth arranged in more than 300 rows, but they neither bite nor chew their food. They filter great quantities of sea water either by actively sucking water into their mouths or by cruising along near the surface of the water with their large mouths agape. Planktonic organisms, including small crustaceans like krill and copepods, are strained from the water through the whale sharks gills by a fine mesh of gill rakers. They are also thought to supplement their diet periodically with squid and small fish such as anchovies and sardines.

Little is known about the whale shark's life cycle or exactly how long they live. It is speculated however, that whale sharks may have a life span of over 100 years, reaching maturity at around 30 years of age. Evidence suggests that sexual maturity in both sexes may not occur until sharks are over nine metres in length. It has been confirmed that they are ovoviviparous (egg cases hatching in utero, with the female giving birth to live young), although the period of gestation is unknown and the number of live born also remains unclear.

As so little is known about this amazing creature the whale shark is now protected in Australian waters under both State (Wildlife Conservation Act 1950 and the Conservation and Land Management Act 1984) and Federal (Environment Protection and Biodiversity Conservation Act 1999) legislation. This means that it is an offence to either disturb, harm or fish for whale shark in any way. However, the unique opportunity of swimming with these gentle giants has resulted in the development of an increasingly popular, seasonal ecotourism industry in Western Australia.

Distribution of whale sharks

Occurrences of whale sharks have been reported in all tropical and warm temperate seas apart from the Mediterranean. They are found in a band around the equator between about 30° north and 35° south in water temperatures of 18°C to 30°C in both coastal and oceanic waters. The sharks occur throughout the Indian Ocean and have also been reported near the Maldives, Seychelles and Comores Islands and along the coastlines of Madagascar, South Africa, Mozambique, Kenya, Pakistan, India, Sri Lanka, Thailand, Malaysia and Indonesia. In Australia, the best scuba diving locations to see whale sharks occur mainly off northern Western Australia, the Northern Territory and Queensland, with isolated reports from New South Wales and Victoria.

Occurrences of the whale shark are patchy and unpredictable. However, research has shown that the sharks appear to prefer areas with surface water temperatures between 21°C and 25°C, where cool nutrient-rich upwellings mingle with warm plankton-laden waters. The sharks are thought to be highly migratory but there is currently limited evidence to support this, although it is clear that different locations appear to be preferred at different times of the year. The animals are generally encountered singly but aggregations of over a hundred animals have been seen, which suggests that schooling does occur.

Ningaloo Reef in Western Australia is one of only a few places in the world where they appear regularly in any numbers, in near-shore waters where they are easily accessible to observers... the online travel agency of Holidays Allover can organise exclusive scuba diving trips to coincide with the arrival of the whale sharks. The mass spawning of over 200 species of coral in March and April each year is part of a chain of biological events that heralds the arrival of the whale shark to Ningaloo Reef, a popular area for shark diving in Australia. The whale sharks swim and feed in the waters around the Ningaloo Marine Park for a further four months before disappearing from the area for another year around June and July.