A key part of wildlife conservation is a clear understanding of the age of animals and how long they can live. For biologists studying the world’s largest fish, this important information is not so easy to obtain. However, a new study suggests that Cold War-era atomic bomb tests could help fill some of the gaps, with scientists using nuclear isotopes for the first time to measure the age of whale sharks.
Carbon-14 is a radioactive element that is naturally present in the atmosphere and is absorbed by every organism on Earth. The atomic bomb testinthe 1950s and 1960s doubled the amount of carbon-14, increasing the concentration of carbon-14 in all organic matter since then. In this way, measuring the carbon-14 level in the tissue sample is a good reflection of the atmospheric level at a specific point in time. Moreover, since radioisotopes decay at regular, predictable rates, they are calibrated with other dating methods, such as the annual wheel, to show the rate at which an organic matter ages.
Whale shark vertebrae are characterized by the apparent growth rings on the bones of whale sharks as they age, and the number of these growth rings increases with age. There has been some speculation about the growth rate of these growth rings, with some studies suggesting that a new growth ring is formed every year, while others suggest that the growth ring is forming at a frequency of up to once every six months.
The researchers analyzed the growth rings of the carcasses of two whale sharks and assessed the carbon-14 levels throughout the whale shark. The different levels of radioisotopes in the growth ring then provide scientists with a clear picture of how often they form and infer the age of the animals.
Scientists say they have found that whale sharks have a growth ring deposit every year. Although some studies have shown that whale sharks can live up to 100 years, this approach allows the team to unambiguously verify the age of a whale shark, one of which is calculated as 50 years old. The study was published in the journal Frontiers in Marine Science.