Scientists analyzed the radiocarbon from the vertebrae of four female and four male great white sharks that were captured in the Atlantic Ocean from 1967 to 2010.
The primary method of age estimation in fishes relies on counting growth increments in mineralized tissues, including otoliths, vertebrae, and fin rays.
Previously, researchers assumed that each stripe corresponded to annual growth, which isn't necessarily true throughout a shark's life. And because these bands can vary in width and coloration, it can be difficult to distinguish them.
The team analyzed the radiocarbon from the vertebrae of four female and four male great white sharks that were captured in the Atlantic Ocean from 1967 to 2010.
The approach takes advantage of the pulse of radiocarbon above natural levels that was produced as a result of atmospheric testing of thermonuclear devices during the 1950 s and ’60 s.
"The nuclear testing "provides a time stamp for us to determine when these tissue layers were deposited," study co-author Li Ling Hamady told LiveScience.
By counting the rings before and after that spike, the authors could deduce the age of the sharks. The team found the sharks' "tree ring" bands were laid down in annual stripes for small to medium-size sharks. After that, however, there was a change in how often these stripes appeared, and the bands became so thin that they were difficult to distinguish.