#ThreatenedSpecies of the Week: Great White Shark (Carcharodon carcharias)

The Great White Shark (Carcharodon carcharias) is listed as Vulnerable under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), and under the WA Biodiversity Conservation Act 2016.

Photo credit: Michelle Yerman – Australian Museum.

The Great White Shark is a member of the Lamnidae family (mackerel sharks) and as such is a close relative of the Mako and Porbeagle sharks. It has a moderately stout, torpedo-shaped body, coloured blue-grey to grey-brown or bronze on the upper surface and white below. The snout is relatively short and bluntly conical, the teeth large, erect, triangular and serrated. The mouth extends beyond the eyes.

The Great White Shark is a large apex predator that grows to at least 6 metres in length and can weigh up to 3,000 kilograms. Great White Sharks are active, fast-swimming sharks that have counter current heat-exchangers in their circulatory system which allow them to maintain a body temperature up to 14 °C above that of the surrounding seawater. This enables individuals to tolerate a wide range of temperatures.

In Australia, ‘Great Whites’ have been recorded from central Queensland around the south coast to north-west Western Australia, but may occur further north on both coasts. Although capable of crossing ocean basins, the species is typically found from close inshore habitats (e.g., rocky reefs and shallow coastal bays) to the outer continental shelf and slope areas. Great Whites are often found in regions with high prey density, such as pinniped (seal) colonies. Within Australian waters, the majority of recorded Great White Shark movements occur between the coast and the 100 metre depth contour.

Study into Great White Shark populations is very difficult given the uncertainty about their movements, the uncertainty about rates of emigration and immigration from certain areas and the difficulty in estimating the rates of natural or fishing mortality. Accurate population assessments are not yet possible for any region. At the time of its nomination for listing as a protected species in 1996, it was proposed that the Australian population numbered less than 10,000 mature individuals.

The Great White Shark is however, uncommon compared to other sharks, and evidence (from game fishing, bycatch, and netting or from observational data) indicates a declining global population. Evidence also suggests that the population may have declined by at least 20 per cent over the last three generations and, in some areas, the species is considered to have declined even more substantially over the same period.

Great White Sharks eat a variety of prey including finfish, other sharks and rays, and marine mammals – such as seals, sea lions, dolphins and whales – as well as squid, crustaceans and seabirds. They are known to change their diet as they grow: juveniles less than 2.7 metres feed primarily on fish and other sharks and rays while larger sharks (3.4 metres and above) feed on marine mammals.

Great Whites, of about 3 metres in length and larger, frequently feed on Fur Seal (Arctocephalus pusillus doriferus and Arctocephalus forsteri) and Australian Sea Lion colonies in Australian waters. Pinnipeds (seals) have also been reported as the major prey item for large Great Whites off the western coast of North America.

Great White Sharks in Australia are threatened mainly by human activities, most likely related to commercial fishing – including capture as bycatch due to accidental entanglement in fishing gear. While targeted fishing by commercial or recreational fishers is no longer legal in Australia, accidental catch or bycatch, beach protection measures and illegal trade continue to cause injury and mortality to the species in Australia. There is also some concern over possible impacts of tourism-related activity, such as shark cage viewings.

Information Source: Government of Australia, Department of Environment and Energy and Department of Biodiversity, Conservation and Attractions.

Related Posts

Leave a reply