Whale sharks are the largest fish in the ocean—and one of the longest lived, a new study suggests. Sharks lack otoliths—bony structures in the skull that scientists use to estimate the age of most fish—which makes it tricky to estimate their age. So researchers measured the carbon-14 isotope in the cartilaginous vertebrae of two whale sharks and correlated it to the carbon-14 patterns created by Cold War–era bomb detonations, National Geographic reports. One of the whale sharks, a 10-meter-long female that was found stranded in Pakistan in 2012, was estimated to be 50 years old. Previous methods, such as estimating their age by comparing an individual’s length at different times using photographs, have estimated that whale sharks live up to 130 years, but bomb dating is the most accurate method yet, the researchers say. The results, published 6 April in Frontiers in Marine Science, are important to understand the growth rate and longevity of whale sharks, which is key to conservation and management efforts of this endangered species, the team says.