Little is known about the growth and age of elasmobranchs. Many of the conventional methods for aging animals, such as examining teeth, will not work with elasmobranchs.
Sharks grow slowly compared to bony fishes, possibly due to sharks' slow digestive time and feeding rates. There is considerable variation in age and growth rates between species and even between populations of the same species.
Growth rings are periodically deposited on the vertebrae of some sharks. Vertebrae can be stained and examined for these growth rings. Growth rings may stop developing in older sharks.
Examining the vertebrae of captive-born sharks after their death enables researchers to compare the number of growth rings with the shark's known age.
In some areas, tagged sharks are providing information about growth rates. Once a shark is caught, it is measured, tagged, and released. The shark is measured again when it is recaptured. Researchers correlate the measurements with the number of years since recapture and calculate a yearly growth rate.