Normally, when scientists determine the age of a fish, they use structures called otoliths with are also known as the 'ear bone'. However, when it comes to determining the age of whale sharks, this proves difficult due to the fact that, well... Whale sharks don't have otoliths.
Because whale sharks are missing this bone, it has been difficult for scientists to determine exactly how long a whale shark can live.
Alternatively, scientists know that the vertebrae of whale sharks develop bands, much like tree rings, but are unable to determine how long it takes a band to develop. So they still have a hard time using this method to determine a whale sharks age.
There have been some studies that show conflicting results with one stating that the rings in the vertebrae form over the span of one year and another stating it only takes 6 months. Because this method proves relatively unreliable scientists have turned to another form of data also found in the animal's vertebrae.
A naturally occurring isotope known as carbon-14 can be found stored in the vertebrae of these large creatures, and in the past has been used to date ancient fossils. It turns out that carbon-14 is also a byproduct of nuclear weapons.
During the Cold War, countries including China, the U.S., the Soviet Union, Great Britain and France launched nuclear weapon tests in the atmosphere and as a result, during that period, there was a massive spike of carbon-14. Now that spike can be measured decades later through the bones of fish.
Recently, they used this knowledge to determine the lifespan of whale sharks for the first time. Using the data from the stored carbon-14 levels, they were able to more accurately determine how long it takes for the rings in a whale shark's vertebrae to form. The new data, that was published in Frontiers in Marine Science confirmed that the rings form over one year.
With this new, more accurate data, researches were able to confidently sat that whale sharks can live upwards of 50 years. We bet the scientists developing nuclear weapons during the cold war never imagined the fallout from their work would be able to be used to further the scientific study of marine life.