#ThreatenedSpecies of the Week: The Whale Shark

 

The Whale Shark is listed as Vulnerable and Migratory. Photo Credit: Ningaloo Coast and Coral Bay.
The Whale Shark is listed as Vulnerable and Migratory. Photo Credit: Ningaloo Coast and Coral Bay.

Rhincodon typus, more commonly known as The Whale Shark, is a stunning sea creature. Greyish in colour, bluish or brownish above, with a distinctive checkered pattern of creamy white spots between pale vertical and horizontal stripes are only part of what make them so special.

The Whale Shark is the world’s largest fish, with the largest accurately measured specimen being 12 m in length.

It has three prominent ridges along its flanks and a spiracle (small round hole) behind each eye.

This species has five large gill-slits, which are modified to function as filtering screens as well as to extract oxygen from the water.

Possible threats to the Whale Shark include: predation, habitat modification and degradation, shipping and boating, commercial fishing, illegal, unreported and unregulated fishing, disturbances of important habitat and tourism.

The Whale Shark is listed as ‘Vulnerable’ and ‘Migratory’ under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and as Specially Protected Fauna under the Wildlife Conservation Act 1950.

One of only three filter-feeding sharks (the other two being the basking and megamouth sharks), the whale shark feeds on minute organisms including krill, crab larvae, jellyfish etc.

Although they have approximately 3000 tiny teeth (each less than 6 millimetres in length), these teeth are not used while feeding.

Instead, the whale shark can sieve prey items as small as 1 millimetre through the fine mesh of the gill-rakers. They are able to open their mouth to a great width (greater than 1 metre) to optimise feeding.

This species is widely distributed in Australian waters. Although most common at Ningaloo Marine Park (and to a lesser extent at Christmas Island and in the Coral Sea), sightings have been confirmed further south than Kalbarri (on the mid-west coast of Western Australia) and Eden (on the New South Wales south coast). Whale sharks have also been recorded from Commonwealth waters between Australia and Indonesia.

The sharks (regularly) appear at locations where seasonal food ‘pulses’ are known to occur. The predictable annual whale shark aggregation at Ningaloo Marine Park is closely linked with an increase in productivity of the region. This is associated with a mass coral spawn which occurs around March/April each year.

Whale sharks have internal fertilisation and produce live young. Males can be distinguished by the presence of two claspers near the pelvic fin. These organs are absent in females.It is, at present, not known where whale sharks breed. Only one pregnant whale shark has ever been recorded. There have been very few juvenile whale sharks seen at any location throughout their range.

Whale sharks are regarded as highly migratory – although these ‘migration patterns’ are poorly understood. Additional information on the biology and ecology of whale sharks is needed to help with conservation and management.

Information Source: Government of Australia, Department of Environment and Department of Parks and Wildlife Western Australia.

 

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