Great White Shark
Great white sharks have been much in the news recently. Most significantly in relation to the Australian shark cull which is supposed to protect people from being attacked by the sharks on the beaches. More shocking still, though, is the realisation that shark nets are made not to be a barrier but a trap. They are designed to kill sharks longer than 2 metres. According to the Shark Angels group, in South Africa alone over 45000 sharks, turtles, dolphins and rays have been killed by nets and drumlines in the last 30 years.
Whilst (some) Australians are killing Great white sharks (Carcharodon carcharias), new research has found that they live 50 years longer than previously thought - to over 70 years of age!
Sharks are typically aged rather like counting tree rings, by counting growth band pairs deposited in their vertebrae. However, sharks grow more slowly as they get older and the band pairs become too thin to read. Using this method under-estimates the age of older sharks.
A new study used bomb radiocarbon dating on eight sharks caught between 1967 and 2010 in the Northwest Atlantic Ocean. This technique uses the discrete radiocarbon pulse in the environment caused by the detonation of nuclear bombs in the 1950s and 1960s as a “time stamp”. Radiocarbon levels incorporated into the band pairs are measured and related to a reference chronology to determine the absolute age of a fish.
White sharks are considered vulnerable under the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Although the Great White Shark is such a famous species of fish, very little is known about its biology. Its maximum size remains a matter of debate. Some estimate around 6 m and others 6.4 m or more. Lengths and ages at maturity for both sexes remain undetermined. A mature female of 500 cm was estimated to have reached around 14 to 16 years, but that was when the oldest individual reported was a female assumed to be not much more than 23. The real age at maturity may be much older.
White sharks travel thousands of miles across open oceans. There is a great site from Ocearch which lets you see the track individual sharks have taken. Go to http://www.ocearch.org/ and choose a great white shark to track.
Map of White Shark "Lydia's" path from the Bahamas, along
the east coast of America to Canada and the North Atlantic.
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Further Reading
Great White Sharks Live More than Seventy Years
Hamady LL, Natanson LJ, Skomal GB, Thorrold SR (2014) Vertebral Bomb Radiocarbon Suggests Extreme Longevity in White Sharks. PLoS ONE 9(1): e84006. doi:10.1371/journal.pone.0084006
Fergusson, I., Compagno, L.J.V. & Marks, M. 2009. Carcharodon carcharias. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. . Downloaded on 10 January 2014.
Great white sharks migrate thousands of miles across the sea, new study finds, Stanford Report
Shark Nets: A tangled web of destruction
Photo credit: Terry Goss, CC BY-SA 3.0
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