Dr Alastair Harry concludes in a newly published paper that counting growth rings on shark and ray vertebrae, the method commonly used to estimate age in elasmobranchs, can grossly underestimate their longevity.

Age was most often underestimated in larger and older sharks and rays, because the growth rings appeared to stop forming, or became unreliable indicators, beyond a certain age and size.

Age under-estimation averaged 18 years across all species, in some cases being out by as much as 34 years.

Grey nurse sharks (Carcharias taurus, also known as sand tiger sharks), for example, Dr Harry found could live for up to 40 years - twice as long as had been previously estimated.

The age of New Zealand porbeagle sharks had generally been underestimated by an average of 22 years.

Age was likely to have been underestimated in 30% of the 53 shark and ray populations covered in his study, and in half of all those validated using “bomb” carbon-dating, which measures carbon accumulated from nuclear-testing in the 1950s.

Such miscalculations could have serious effects on shark and ray conservation and management, he said.

The study is published in Fish & Fisheries here

*  Also on Divernet: 400-Year-Old Sharks 'Living Time Capsules'

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