The age of a shark can be estimated from the growth rings on its vertebrae, seen in this x-ray. Growth rings are laid down annually, but this may stop as the sharks get older. The rings can also be affected by local conditions such as food shortages, by the demands of reproduction, or by the shark’s health. The method is therefore not totally reliable. The age of other, bony fish, is calculated from rings on the otolith or earstone, which sharks do not have.
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