Determining a shark’s age has long relied on killing the animal and counting the growth rings on its spine, a crude method and a rather abrupt ending to a life history that remains largely unknown by scientists. 

Now, however, researchers have found a way to read a shark’s age from its DNA alone.

Those researchers are from the University of Georgia and their study – now published in Molecular Ecology – applied what is known as epigenetic clocks, predictive models that measure chemical changes in an animal’s cells to estimate biological wear and tear. 

While the technique has already proven effective in dozens of other species, this is the first time epigenetic clocks have been used with sharks. 

Using samples from more than 50 zebra sharks held in aquariums across the southeastern United States, the team from the University of Georgia estimated each shark’s age to within two years of its true chronological age – the equivalent of mistaking a 27-year old for 26.

Unlike spine-ring counting, the method requires no harm to the animal. Instead, it offers a fast, noninvasive alternative that could transform how scientists track shark populations in the wild, where age has historically been near impossible to verify with precision.

And for conservation biologists, that precision matters. Understanding the age structure of a population – how many young, breeding-age and older individuals it contains – is fundamental to assessing its health and its capacity to recover from decline.

“Age structure is one of the most important things conservation biologists can measure,” said Benjamin Parrott, corresponding author of the study and an associate professor at UGA’s Savannah River Ecology Laboratory and Odum School of Ecology,

“If we could figure out how old wild sharks are, we could finally understand the age structure of their populations. That’s incredibly important for conservation or marine populations.”

The researchers believe the tool could extend beyond sharks, offering a new route into the biological aging of other marine species whose life cycles remain poorly understood.

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