Radiocarbon dating of atomic bomb fallout found in sea turtle shells can be used to reliably estimate the ages, growth rates and reproductive maturity of sea turtle populations in the wild, a new study led by Duke University and NOAA researchers finds. The technique provides more accurate estimates than other methods scientists currently use and may help shed new light on factors influencing the decline and lack of recovery of some endangered sea turtles populations.

"The most basic questions of sea turtle life history are also the most elusive," said Kyle Van Houtan, fisheries research ecologist at NOAA's Pacific Islands Fisheries Science Center and adjunct associate professor at Duke's Nicholas School of the Environment. 

Van Houtan and his colleagues analyzed hard tissue from the shells of 36 deceased hawksbill sea turtles collected since the 1950s. The turtles either died naturally or were harvested for their decorative shells as part of the global tortoiseshell trade. The researchers worked with federal agencies, law enforcement and museum archives to obtain the specimens. 

The scientists were able to estimate each turtle's approximate age by comparing the bomb-testing radiocarbon accumulated in its shell to background rates of bomb-testing radiocarbon deposited in Hawaii's corals. Levels of carbon-14 increased rapidly in the biosphere from the mid-1950s to about 1970 as a result of Cold War-era nuclear tests but have dropped at predictable rates since then, allowing scientists to determine the age of an organism based on its carbon-14 content. 

Van Houtan and his team were able to estimate median growth rates and ages of sexual maturity in the collected specimens by comparing their radiocarbon measurements to those of other wild and captive hawksbill populations whose growth rates were known. 

This is the first time carbon-14 dating of shell tissue has been used to estimate age, growth and maturity in sea turtles. Previously, scientists employed other, less precise methods such as using turtle length as a proxy for age, or analyzing the incomplete growth layers in hollow bone tissue. 

The researchers published their peer-reviewed research Jan. 6, 2016, in the Proceedings of Royal Society B.