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The long lifespan of whale sharks is revealed by the remains of atomic bombs

Study author Mark Meekan swims with a whale shark.

Study author Mark Meekan swims with a whale shark.
photo:: Wayne Osborn

With the help of nuclear weapons tests from the 1950s and 60s, scientists determine the lifespan of the largest fish in the world.

While researchers have made great strides in understanding the behavior patterns of the endangered whale shark, there are some blatant holes when it comes to it basic details about this type, including how long individuals can life. T.Hey now got some help from a surprising Source: radioactive carbon, humans injected into the global carbon cycle during weapon tests that shows up in the whale shark vertebrae. The team used this “bomb radiocarbon” to age whale shark samples.

“The use of bomb radiocarbon assays as age validation for long-lived fish has been increasingly applied to both fish and sharks, and we have now applied this to whale shark vertebrae for the first time,” said Joyce Ong, the lead author’s study Rutgers University informed Gizmodo in an email.

The researchers acquired whale shark vertebrae samples that were used in a previous study. These samples were taken from a Taiwanese whale shark fishery before it closed in 2007 and a dead stranded whale shark in Pakistan. First, they photographed the vertebrae under a microscope and counted the number of ligaments in a cross-section of the bone, similar to counting tree rings. However, this method alone cannot calculate the age of the sharks because it is unclear how fast the rings grow.

This is where the radioactive bomb carbon comes into play. Countries, including the United States and the USSR, detonated atomic bombs in the atmosphere in the 1950s and 60s, leading to an increase in the radioactive carbon isotope carbon-14 in the global carbon cycle. This carbon is deposited in the food chain and can show up in animal tissues. Scientists can then use it as somehow Time stamp.

The researchers analyzed samples from two whale shark vertebrae using a technique called accelerator mass spectrometry (AMS) to calculate the frequency of the carbon-14 isotope. AMS essentially extracts parts of a sample and accelerates them in a particle accelerator to isolate and calculate their carbon-14 composition. They also have to compare it to the composition of something they knew the age of – they chose carbon-14 dissolved in seawater.

The analysis confirmed that one of the three innermost growth bands of the Taiwanese sharks formed in 1972. In the meantime, the gangs in the shark from Pakistan seemed to correspond to one-year steps in bomb carbon analysis, so the researchers could date the shark to 50 years old – the oldest whale shark ever. she published their results in the journal Frontiers in Marine Science.

Bomb carbon analyzes have already been used in Conservation, biology, and Forensic science. It is special important tool for learning Species of special interest such as whale sharks.

“If you know the age and size of a fish, You can calculate a growth rate. This is a critical parameter for management. because it tells you how resilient a crop is and how quickly it can recover when threats like overfishing reduce the size of the population, ”said Mark Meekan, study author and Research scientist in fish biology at the the Australian Institute of Marine Sciences, said Gizmodo in an email. “For whale sharks, it looks like they’re slowly growing to these big sizes. Sharks may not mature until around 30 years old. This means that whale shark populations are unlikely to spring back quickly if the number is reduced. “

Bomb carbon has its limits. IIt works best on long-lived species whose bodies can actually record the changing carbon 14 levels in the environment. In addition, mixing carbon-14 into deep water can make analysis difficult, Meekan said. Fortunately, whale sharks spend much of their time near the surface of the sea.

Gun testing was shameful and his legacy remains in the environment – but at least something good has come out of it.

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