The scientific community has long held two key beliefs about the enigmatic Greenland shark – that they are the oldest living vertebrates and that they are functionally blind. However, recent groundbreaking research has challenged these long-held assumptions, exposing the profound mysteries surrounding this elusive species.
Described by one researcher as looking “already dead,” the Greenland shark is one of the least understood creatures on the planet. For decades, frustratingly little has been known about this mottled, baguette-shaped creature that can reach up to 20 feet in length. Their sedate pace is undercut by the remains of caribou, polar bear, moose, narwhal and beluga found in their stomachs, hinting at a more capable predator than previously thought.
But in a surprising discovery, researchers from five universities around the world found that the Greenland shark’s retinas are structurally pristine and capable of detecting light and contrast, debunking the belief that they are functionally blind. While most Greenland sharks’ eyes are cloudy and have parasitic copepods dangling from the cornea, extensive study on the structure, genetics and molecular function of their retinas showed they successfully withstood a sustained assault by parasites and the harsh Arctic conditions.
“Greenland sharks represent absolute mystery,” says Jena Edwards, a Canadian marine ecologist. “Even the things that we think we know, we’re still a little bit unsure about. Everything about them is a question mark.”
The new findings have also called into question another long-held belief – that Greenland sharks can live up to 500 years old. A widely cited 2016 study used carbon dating to estimate their longevity, suggesting some sharks could have overlapped with the lifetimes of historical figures like William Shakespeare and Galileo.
However, Nigel Hussey, one of the world’s leading Greenland shark experts, cautions that the carbon dating methodology “puts you in the ballpark” when looking at dates of tens of thousands of years, but has larger margins of error for shorter time frames. He believes the sharks may only live around 100 years, still an impressive lifespan.
“This type of dating method is challenging to use for ageing animals that are hundreds of years old,” Hussey explains. “In some ways, it was a surprise the paper was published in Science, one of the top tier ecology journals in the world. The technique requires further validation for use in this context.”
The profound unknowns surrounding the Greenland shark are amplified by the uncertainties of a rapidly changing Arctic. As the resource-rich region warms at a rate faster than anywhere else on Earth, scientists are racing to understand this generalist species that can adapt to a shifting ecosystem.
“They’re a generalist species that can eat anything. They’ll survive, even if the whole food web shifts and they have to feed on completely different things,” says Hussey. “But we still don’t know the basics, like where they reproduce or how many pups they have in a litter.”
The Greenland shark’s story serves as a cautionary tale against hubris and underscores the persistent knowledge gaps that remain, even for some of the planet’s most enigmatic creatures. As Hussey puts it, “We vastly underestimate” these “absolutely incredible animals” time and time again.
