Cold War nuclear tests help determine age of world’s largest fish for the first time Radioactive elements from the tests allowed a whale shark to be carbon dated for the first time

The age of the world’s largest fish has been correctly determined for the first time with the help of atomic bomb tests conducted during the Cold War.

Nuclear weapons testing led to the radioactive element used in carbon dating saturating the oceans and moving through food chains to become present in every living thing on the planet, including whale sharks which usually grow to 10 metres.

This allowed scientists to work out that one whale shark they examined was 50 years old when it died, the first time such an age had been unambiguously verified.

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The discovery was published in the journal, Frontiers in Marine Science, and scientists who collaborated on the study said the finding will help ensure the survival of whale sharks, which are classified as endangered.

Cold War powers

Measuring the age of whale sharks is challenging because, like other sharks, they lack bony structures called otoliths which are used to assess the age of other fish.

Whale shark vertebrae feature distinct bands, similar to the rings of a tree trunk, and it was known that these increased in number as the animal grew older, however, scientists disagreed over the rate at which the bands formed.

During the 1950s and 1960s, Cold War nuclear powers conducted atomic bomb tests. A by-product of these tests was the temporary doubling in the atmosphere of a radioactive element called carbon-14.

Carbon-14 is used in ‘carbon dating’ to date ancient bones and artefacts because it has a constant rate of decay that is easily measured, making it ideal for providing age estimates for anything over 300 years old.

Carbon level tests

Scientists tested carbon-14 levels in the growth bands of two long-dead whale sharks stored in Pakistan and Taiwan.

“We found that one growth ring was definitely deposited every year,” said Dr Mark Meekan from the Australian Institute of Marine Science in Perth.

“This is very important, because if you over or under-estimate growth rates you will inevitably end up with a management strategy that doesn’t work, and you’ll see the population crash.”

“Our study shows that adult sharks can indeed attain great age and that long lifespans are probably a feature of the species. Now we have another piece of the jigsaw added,” concluded Dr Meekan.

Whale sharks are found in tropical oceans and feed almost exclusively on plankton and small fishes, posing no threat to humans.