BBC:  Data from atomic bomb tests conducted during the Cold War have helped scientists accurately age the world’s biggest fish.
 Whale sharks are large, slow moving and docile creatures that mainly inhabit tropical waters.
 They are long-lived but scientists have struggled to work out the exact ages of these endangered creatures.  But using the world’s radioactive legacy they now have a workable method that can help the species survival.  Whale sharks are both the biggest fish and the biggest sharks in existence.  Growing up to 18m in length, and weighing on average of about 20 tonnes, their distinctive white spotted colouration makes them easily recognisable.  These filter feeders live on plankton and travel long distances to find food.  They are very popular with tourists in many locations, often allowing divers to swim alongside them.
 However, the species is now classified as endangered because of over-fishing in places like Thailand and the Philippines.
 Much about the species remains a mystery, especially how to age them correctly.
Researchers say this is fundamental to understanding their growth rates – information that’s considered crucial to saving the species in the long term.