Traces left by nuclear-bomb testing in the 1950s and ‘60s can help researchers learn how old a whale shark is.
It’s been surprisingly hard to figure out how old a whale shark is. Now scientists have gleaned clues — ones written in the the sharks’ spines. The clues are visible thanks to the radioactive residues. They were left by nuclear-weapons tests during the Cold War.
As they grow, the vertebrae of whale sharks (Rhincodon typus) build up alternating stripes of opaque and see-through tissue. The process is similar to how tree trunks grow rings. Until now, scientists hadn’t known how fast those whale shark vertebrae gain a new growth band. Is it each year? Every six months? Not knowing that made it hard to gauge just how fast these sharks were growing or how long they lived.
Now researchers have measured levels of carbon-14 in the vertebrae of two whale sharks. That carbon is a radioactive isotope (energy-shedding form of the element). Both whales had lived during the 20th century. Soviet and American nuclear weapons tests in the 1950s and 1960s released that carbon-14 as fallout. Over time, it built up in Earth’s atmosphere and oceans — and in the bodies of animals that lived in the oceans. The researchers compared the amount of carbon-14 in the growth bands of whale shark vertebrae with the known carbon-14 levels in surface seawater in different years. That helped the researchers estimate when each band had formed.
The results showed that bands generally grew one year apart. Steven Campana and his team shared what they learned in the April 2020 Frontiers in Marine Science.
