Greenland sharks could be the world's longest-living vertebrates
The Greenland shark, a massive creature that thrives in sub-Arctic waters, may be the oldest animal in the world, a new study finds.
Researchers estimated that the sharks have an average lifespan of at least 272 years. That’s roughly six decades older than the previous contender for longest-living vertebrate: the bowhead whale.
The study, published Thursday in the journal Science, sheds new light on the little-known Greenland shark (Somniosus microcephalus), which is rarely observed in its natural environment.
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The sharks prefer chilly waters, between 30 to 50 degrees Fahrenheit, and can swim down to 7,200 feet below the surface. They also clock in at around 2,220 pounds.
“It’s remained a mystery for a long time how old these sharks could get,” Julius Nielsen, the study’s lead author and a doctoral fellow in marine biology at the University of Copenhagen in Denmark, told Mashable.
“I consider that we have found the oldest animal in the world,” he said, adding that the exact lifespan of Greenland sharks remains uncertain.
Nielsen and researchers from Denmark, Norway, Greenland, the U.K. and U.S. studied 28 female Greenland sharks that were accidentally caught as by-catch in commercial fishing operations.
The team determined that the biggest shark — stretching over 16-feet-long — was likely between 272-years-old and 512-years-old, with a 95 percent probability for that age range. Within that range, the most probable age was nearly 400-years-old.
Image: Julius Nielsen
The oldest known bowhead whale, by comparison, was 211-years-old.
“If you only focus on the shark’s single-year age, it’s not a certain result,” Nielsen said. “But we are quite confident that the age range for the largest shark is a good estimate.”
The marine biologist explained that conventional methods for determining the ages of fish don’t apply to Greenland sharks, which makes it harder to know with certainty just how old these creatures are.
In many fish, body tissue calcifies and shows growth layers — like rings on a tree trunk — that scientists can count. But Greenland sharks don’t have hard calcified tissue or show growth layers in their eyelids.
Image: Julius nielsen
So Nielsen’s research team studied the sharks’ eye lenses using carbon dating techniques. Based on their assumptions about how carbon behaved in the atmosphere during the last 500 years, they arrived at their estimated age range.
“This is the best estimate that can be produced at the moment,” Nielsen said. “I hope these age ranges can be improved and narrowed down.”
But Simon Thorrold, a biologist who was not involved in the Science study, argued that carbon dating alone could not effectively determine the Greenland shark’s approximate age range.
“They need to make a few assumptions about the biology of the Greenland shark that we don’t actually know,” Thorrold, who directs the Woods Hole Oceanographic Institution’s Ocean Life Institute in Massachusetts, told Mashable.
“I do not have much confidence in the data or their conclusions,” he added.
Still, Thorrold didn’t dispute that Greenland sharks are extremely old animals. And he said their long lifespans — regardless of the exact age — make it all the more crucial to protect them from commercial fishing operations and other human-related pressures on their habitats.
Female Greenland sharks likely give birth every couple of years to only a handful of pups, much like whales.
A fish like cod, by contrast, reproduces much more frequently and in higher numbers.
That means cod populations can, at least theoretically, recover more quickly from threats like fishing or pollution, but Greenland sharks are much slower to bounce back, raising the risk that they could one day vanish from the ocean, Thorrold said.
Even cod populations in some areas, like the waters off New England, have failed to rebound despite fishing restrictions. This may not bode well for the Greenland shark.
“It doesn’t matter whether they get to 100 or 400-years-old, the point is the same,” he said. “We have to be careful and think about managing or conserving this species in the way we do whales.”
