Scientists have figured out that the world's biggest fish lives for a surprisingly long time, and the discovery comes courtesy of atomic bomb tests from decades ago. The fish is the enormous whale shark, and the study in Frontiers in Marine Science suggests they can live a century or more, reports the BBC. Researchers determined this in an unusual fashion: They measured the amount of carbon-14 in the skeletal remains of an adult female shark. As New Atlas explains, carbon-14 is a radioactive isotype, and all living creatures absorbed it during the Cold War testing of nuclear weapons. It's like a "chemical fingerprint," per Popular Mechanics. Scientists know the decay rate of the isotope, and by measuring it in tandem with growth rings on the whale shark's vertebrae, they were able to calculate the animal's age. (The rings alone are seen as unreliable.)
In this case, they concluded the shark was 50 years old. But it was a relatively small one—33 feet, far short of the 60-footers swimming in the ocean—meaning it still had years to grow. "The absolute longevity of these animals could be very, very old, possibly as much as 100-150 years old," study leader Mark Meekan of the Australian Institute of Marine Science tells the BBC. This isn't the first time carbon-14 dating has been used to calculate the age of sharks, but the application to whale sharks is seen as a big deal because the animals are endangered. Getting a better handle on longevity could lead to stronger protections. "This has huge implications for the species," says Meekan. "It suggests that these things are probably intensely vulnerable to overharvesting." (The gigantic creatures are notoriously difficult to study.)
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