?The sharks, which live off the New South Wales and Queensland coasts, are thought to number few more than 400 individuals. Heavy sport-fishing in the 1960s and '70s reduced the population, but now scientists at Macquarie University in Sydney have found that the sharks are isolated from the west coast and South African populations, so chances of restocking from other sources is negligible.
Writing in the Royal Society journal Biology Letters, Dr Adam Gow used DNA testing to demonstrate that the eastern population of grey nurse sharks (also known as raggedtoothed sharks) is genetically different from other populations, and that there is little migration. The species, highly recognisable because individuals are popular exhibits in aquariums worldwide, is very vulnerable.
It also has a very slow reproductive rate - females generally give birth to few pups each year because of intrauterine cannibalism (the young eating each other in the womb) -so the population is slow to recover from any disaster, natural or human-induced.
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