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Atomic Bombs and Whale Sharks: How to Calculate the Age of the Biggest Fish in the World?



WASHINGTON (Reuters) – Scientists have figured out how to calculate the age of whale sharks – the largest fish in the world – taking into account the radioactive effects of nuclear war tests during the Cold War.

FILE PHOTO: Visitors watch a whale shark in the Whale Shark Aquarium of the Chimelong Ocean Kingdom in Zhuhai, China, September 4, 2018. REUTERS / Bobby Yip

By measuring the level of carbon 14, a naturally occurring radioactive element that is also a by-product of nuclear explosions, the researchers found that different bands form in the shark cartilage vertebrae each year, like the growth rings of a tree.

It was already known that these gangs existed and increased in number when a shark aged. However, it was unclear whether new rings appeared annually or every six months.

The researchers compared the carbon 14 levels in the rings with data on fluctuations in their global presence during the busy years of atmospheric nuclear testing in the 1950s and 1960s.

“These elevated levels of carbon 14 first saturated the atmosphere, then the oceans, and migrated through animal nets to animals, creating increased levels in structures such as whale shark vertebrae,” said marine ecologist Joyce Ong of Rutgers University, New Jersey the study published this week in Frontiers in Marine Science.

Scientists can now calculate the age of a whale shark after its death – a ring corresponds to one year. However, it is equally important that the study found that these endangered sea giants have a very slow growth rate.

“Knowing the growth rate is critical to the management of marine species, as it determines the resilience of the population to threats such as fishing. Fast growing species have fast replacement rates and can withstand relatively high losses, while slow growing species have low replacement rates and are much less resilient, ”said marine biologist and co-author Mark Meekan of the Australian Institute of Marine Science in Perth.

Whale sharks are filter feeders that swim long distances through the world’s tropical oceans to find enough plankton to feed themselves. They have a brownish-gray color on the back and sides with white spots and a white underside.

The researchers tested the carbon 14 levels in long-dead whale sharks, the remains of which were stored in laboratories. The oldest tested, stored in Pakistan, had lived for 50 years.

“We thought it was possible for them to live up to 100 years old, but we weren’t sure because we didn’t have validated age data,” said Meekan. “We still can’t say for sure whether these sharks will be 100 years old, but it now seems much more likely that our largest shark was 50 years old and 10 meters long, and that’s well documented. These sharks can almost do become twice as big and be about 18 meters long. ”

Reporting by Will Dunham; Edited by Sandra Maler

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