atomic bomb radiation
January 8, 2016

Atomic bomb radiation in sea turtles’ shells helps scientists figure out their age

The atomic bomb may be mankind’s worst-ever invention, but the instrument of destruction does have a tiny consolation for biologists: The bomb’s radiation offers is a trustworthy way to approximate the age, rate of growth, and reproductive maturity of wild sea turtles, according to a new study.

Published in the journal Proceedings of Royal Society B, the study said dating via atomic bomb radiation is more accurate than conventional techniques and may offer new details declines and insufficient recoveries of some endangered sea turtles communities.

“The most basic questions of sea turtle life history are also the most elusive,” study author Kyle Van Houtan, a marine life at Duke University, said in a press release.

In the study, scientists reviewed hard tissue samples from the shells of 36 hawksbill sea turtles archived since the 1950s. The turtles either passed away naturally or were poached for their shells. The scientists worked with various agencies, law enforcement, and museum archives to get the specimens.

The researchers estimated each turtle’s age by comparing the bomb-testing radiocarbon accrued in its shell to background amounts of bomb-testing radiocarbon lodged in Hawaii’s corals. Amounts of carbon-14 greater rapidly in the biosphere from the mid-1950s to around 1970 due to Cold War-era nuclear tests, but have fallen at predictable rates since then, allowing researchers to ascertain the age of an organism by using its carbon-14 content.

The scientists could approximate median growth rates and ages of sexual maturity in their specimens by contrasting their radiocarbon measurements to those of other wild and captive hawksbill populations with known growth rates.

Process also reveals why populations aren't rebounding

In addition to giving researchers a more reliable tool for estimating turtle growth and maturity, the new process may reveal why some populations aren’t rebounding as rapidly as expected—despite years of serious conservation efforts.

“Our analysis finds that hawksbills in the Hawaii population deposit eight growth lines annually, which suggests that females begin breeding at 29 years—significantly later than any other hawksbill population in the world. This may explain why they haven’t yet rebounded,” Van Houtan said.

The study team’s method also revealed a warning sign for turtle populations.

“They appear to have been omnivores as recently as the 1980s,” Van Houtan said. “Now, they appear to be primarily herbivores. Such a dramatic decline in their food supply could delay growth and maturity, and may reflect ecosystem changes that are quite ominous in the long term for hawksbill populations in Hawaii.”

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