Marine Biologists Ran Tests On Earth’s Biggest Fish – And Unlocked A Startling Radioactive Secret

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A team of researchers stands above the carcass of a whale shark, the largest of all of the ocean’s sharks. They and other experts have long struggled to understand one aspect of this species’ life – but soon, that will all change. In fact, they’ll soon unlock the long-standing mystery with the help of a radioactive secret passed over the decades.

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Although massive – it can grow to 60 feet in length – the whale shark has its subtleties. What irked scientists most over the years was that they couldn’t figure out the tropical sharks’ ages. But that annoyance gave researchers a reason to continue studying these docile creatures. How old were they – and how long would they stick around?

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In 2020 the researchers finally answered this question, thanks to the preserved remains of two whale sharks kept in Pakistan and Taiwan. And in adopting a new method for dating this incredible species, they discovered something else. That is, they saw a strange link between the creatures and a radioactive secret from decades past.

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Experts have spent over the years trying to figure out the lifespans of all different kinds of sharks. And they’ve actually uncovered some startling statistics. The Greenland shark, for example, can apparently live for almost three whole centuries. Meanwhile, great white sharks hang around the seas for approximately 100 years.

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However, calculating the same statistics for whale sharks hasn’t been as easy for scientists to confirm. For one thing, whale sharks tend to be a pretty elusive species to find and study. It’s particularly surprising that they’re so tough to track, considering they’re covered in spots and stripes and can measure in at 60 feet in length.

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When the whale shark became an endangered species in 2016, though, researchers came up with a new method for finding information about them. They drafted tourists to help them – all they had to do was report any whale shark sightings. Then, the pros cataloged all of the data to get an idea of how many of the extra-large fish were out there and where they tended to surface.

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The scientists published the results of their study in a 2017 volume of the journal BioScience. They recorded approximately 30,000 run-ins with whale sharks, which they attributed to about 6,000 individual fish. The sightings took place in 54 different countries, with the Maldives, Mozambique, Cancun in Mexico, Western Australia and the Philippines among their favorite hangouts.

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But the experts realized that their data hadn’t come from a very diverse group of whale sharks. Most of the creatures that they or the tourists had spotted were juvenile males that measured between 12 and 21 feet long. They couldn’t figure out where the adult whale sharks lived – or how old either age group was.

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Based on their findings, the scientists could see that the young males didn’t move around much – but that’s par for the course with whale sharks. In fact, the massive animals tend to move so slowly that many of them get hit by ships accidentally. Still, this lack of mobility didn’t make them any easier to research.

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Instead, at the end of that 2017 study, scientists still knew relatively little about the whale shark population. They didn’t know what the whale sharks did during the day, where they lived or how they mated. And they couldn’t definitively say how many of them existed – estimates ranged from 20,000 to 200,000.

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Of course, many other species make it easy for scientists to observe and understand them, and this is true in life and in death. But whale sharks don’t adhere to norms when they perish, either. When whales die, they float to the surface. But whale sharks, on the other hand, sink, leaving experts with little physical evidence to study.

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For many years, this left scientists with limited evidence to help them determine whale sharks’ ages. Experts had long relied on cutting into the animals’ vertebrae to find rings that could indicate age, similar to those in a tree trunk. They’d count these to figure out how old a particular whale shark was.

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However, scientists eventually had to stop using this method due to ongoing disputes about its accuracy. The problem was that they couldn’t calculate with certainty how much time each ring represented. With trees, each loop equals a year’s worth of growth, but the same couldn’t be said about the whale sharks’ markings.

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The method that would eventually help them to determine the age of whale sharks came from an unexpected source. In 2008 a trio of Danish scientists uncovered something that could be helpful in the field of forensics. Physicist Jan Heinemeier led a team who investigated a protein located in the eye of humans called lens crystallines.

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The nature of lens crystallines stays steady throughout a person’s life, in contrast to various other proteins in the human body. On top of that, they contain carbon and carbon-14, a radioactive isotope that experts can measure and use for dating. That’s because carbon-14 has always been on Earth at varying levels. Scientists, of course, have records of these fluctuations.

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When a lens crystalline forms, it comes with a so-called carbon-14 postmark, a level of the isotope that will remain preserved and reveal a person’s age. Heinemeier rightfully suggested this dating method would work well for forensics cases. In fact, just after the study was published, he received a request to crack a murder case in Germany with carbon-14 dating.

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A year later, Heinemeier fielded another appeal for help. This time, it came from marine biologist John Fleng Steffensen – an unlikely candidate for forensics help. But Steffensen had an idea, and he thought that Heinemeier could help him. He wanted to know if they could use the same dating method to calculate sharks’ ages.

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Steffensen’s focus was the Greenland shark, an 18-foot predator that inhabited the chilly waters around the country from which it got its name. The Greenland shark has something in common with the whale shark. That is, scientists have struggled to determine many of the details of their lifestyle, and they had no way to count the animals’ ages, either.

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But carbon-14 dating came to their rescue thanks to years’ worth of work from researchers. The group spent half a decade gathering Greenland shark eyeballs from fishermen who had inadvertently caught the predatory fish in their nets. With 28 pairs of shark eyes, they eventually had enough genetic information to complete their research.

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As previously mentioned, their findings revealed that Greenland sharks can live for hundreds of years. On top of that, their study opened the door for other shark-centric researchers to try the same or a similar method. And that’s exactly what the Australian Institute of Marine Science’s Mark Meekan decided to do.

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It was decidedly more difficult for Meekan to find genetic samples for his study, even though he was using skeletons and not eyes. Luckily, he and his team found a pair of whale shark skeletons in two different countries – Pakistan and Taiwan. The former had perished in 2012 and had 15 more growth rings in its vertebrae than the Taiwanese whale, which fishermen had caught in 2005.

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The rings came in handy this time around, too. Meekan and his colleagues used carbon-14 dating to determine once and for all that each ring represented a year of the whale shark’s life. He told National Geographic in 2020, “Basically what we showed is we have a timestamp within the vertebrae. We count the bands from there, and they appear to be annual.”

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Meekan added that the ring-counting method confirmed some theories that the experts had held for a long time, too. He told Reuters, “We thought that it was possible that they could reach ages of as much as 100 years. But we weren’t really sure, as we had no validated data on age.”

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The scientists’ two samples seemed to confirm this long-standing theory, thanks to the whale shark skeleton from Pakistan. It measured in at about 33 feet in length, and they determined the creature to have been 50 years old. Considering it was only half the size of full-grown whale sharks at a half-century in age, Meekan said they could deduce that the creatures likely lived to be around 100.

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The researchers pulled carbon-14 from the vertebrae samples, then compared it to carbon samples that had already been dated. That’s how they knew the whales were 50 and 35 years old – just as the rings showed. So, Carbon-14 dating helped to clarify the ring theory, but it also uncovered a radioactive secret of the seas, as well.

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Specifically, from the end of the 1940s onward, several countries around the world tested atomic bombs in the lead up to the Cold War. These practice runs were conducted by the United States, the Soviet Union, France, China and the United Kingdom. In doing so, they released massive amounts of carbon-14 into the atmosphere.

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Ultimately, these atomic bomb tests doubly increased the levels of atmospheric carbon-14. The radioactive material didn’t just float into the air, though. It also soaked into the ocean and got into the food chain. This meant that it ended up inside of animals’ bodies – and in the vertebrae of whale sharks.

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Every living creature has carbon-14 in its system, regardless of whether or not it was around at the time of the Cold War. But those that lived during these tests have “incorporated that spike in Carbon-14 into their hard parts,” Meekan told CNN. He continued, “That means we’ve got a time marker within the vertebrae that means we can work out the periodicity at which those isotopes decay.”

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So, scientists could determine the whale sharks’ ages all thanks to the world’s history in radioactive weapon-making. And knowing how old these creatures live has presented experts with a slew of new considerations regarding their chances of survival in the future. This is important, of course, especially after their classification as endangered in 2016.

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Taylor Chapple is a shark-centric researcher at Oregon State University. Speaking to National Geographic, he elaborated on the importance of carbon-14 dating in his line of work. He said, “This study is really important because it gets rid of some of those questions about the age and growth patterns of whale sharks.”

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Experts need to know how fast that whale sharks grow – and what their lifespan is – to understand how likely they are to fall victim to extinction. In general, species that reproduce hastily will stick around for longer. Meanwhile, the slow-to-grow whale shark has seen its population continue to dwindle over a 75-year span.

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Chapple also highlighted the importance of having “real data from real animals.” Meekan’s findings, the Oregon State University researcher said, “[add] a really critical piece of information to how we globally manage whale sharks.” For instance, the data could push experts to devise ways for fishermen to avoid tangling the massive fish in their nets.

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This conservational step would be a particularly important one. Even fishermen who aren’t looking to capture whale sharks in their nets sometimes do so anyway. And such a mistake could be hugely damaging to the species’ population, which would take too long to recover from so many quick, unnecessary deaths.

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Meekan summed it all up when he spoke to the BBC after the study’s publication. He said, “The absolute longevity of these animals could be very, very old, possibly as much as 100 to 150 years old. This has huge implications for the species. It suggests that these things are probably intensely vulnerable to over-harvesting.”

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On top of that, Meekan said that the study had inadvertently explained why whale sharks had disappeared from their usual haunts, such as Taiwan and Thailand. The slow-growing creatures couldn’t rebound from the fishing taking place in those countries. He said, “They are just not built for humans to exploit.”

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That statement sounds particularly poignant next to another conservational worry. That is, the rise of whale shark tourism. In some places, including Oslob, Philippines, shark-watching has raised eyebrows for all the wrong reasons. That’s because participants get too close to the massive fish – or even feed them.

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But experts want to find a middle ground. Ideally, one that supports both the undersea species and those who depend on them for an income. Meekan explained to National Geographic, “Ecotourism keeps a lot of people out of poverty in many developing countries around the world, in particular in Southeast Asia.”

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Meekan continued, “We have a responsibility not just to the sharks, but also to those communities to make sure they’ve got a future.” On that note, whale sharks were the perfect creature to help. The fish biologist told the BBC, “Whale sharks are a fantastic ambassador for marine life and one that has lifted so many people out of poverty.”

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And while the study’s findings seem to point to a bleak future for the whale shark, Meekan saw it differently. He hearkened back to the carbon-14 findings – and the world’s atomic-testing past – in the conclusion of his interview with the BBC. He said, “This is a good news story – and it shows there is a silver lining to the mushroom cloud after all.”

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Of course, whale shark-related research only continued after Meekan’s team concluded their study. In May 2020 researchers revealed that they had tracked a female for 10 months, and that she’d journeyed nearly 10,000 miles in just under two years. Her astonishing trek was longer than any other whale shark they had followed in the past.