It looks more like a worn sock than a fearsome predator. It moves slower than an escalator. By most accounts, it is a clumsy and near-sightless relic drifting in the twilight waters of the Arctic, lazily searching for food scraps.

But the Greenland shark, an animal one researcher (lovingly) said, “looks like it’s already dead”, is also one of the least understood, biologically enigmatic species on the planet.

But this month, scientists made a groundbreaking discovery: the sharks are not, in fact, blind. The newly published findings upend commonly held beliefs and expose the challenges of studying a shark that has long resisted the reaches of science. But the disruptive nature of the research also underscores the challenges scientists face in predicting how a rapidly changing climate might harm or help the elusive fish.

“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.”

Marine ecologist Jena Edwards on a fishing vessel used by the research team in Scott Inlet, Nunavut, northern Canada. Photograph: Eric Ste Marie

For decades, frustratingly little has been known about the shark, a mottled, baguette-shaped creature that reaches 20ft in length. Their sedate pace is undercut by the remains of caribou, polar bear, moose, narwhal and beluga found in their stomachs – and not all the prey is believed to be from scavenging.

“We’re taking blind shots in the dark. We have so little data that we make a hypothesis based on what we know, but need so much more research to fully understand what’s actually going on with these sharks,” she says.

Researchers have long held two key beliefs: they are the oldest living vertebrates and they are functionally blind. Both have long made sense, given that sharks are most commonly found in the cold Arctic waters, where light is minimal and where slow movements are often equated to a slower metabolism.

Greenland shark expert Nigel Hussey with a bio-logging sensor in Tremblay Sound, Nunavut. He says ‘we absolutely underestimate’ the species. Photograph: Eric Ste Marie

But in early January, researchers from five universities around the world found that the retinas appear structurally pristine and were capable of detecting light and contrast. While most Greenland sharks’ eyes are cloudy and have worm-like parasitic copepods dangling from the cornea, extensive study on the structure, genetic sequencing and molecular function of shark retinas showed they successfully withstood a sustained assault by parasites and harsh Arctic conditions.

For Nigel Hussey, one of the world’s leading Greenland shark experts, the results aligned with his own experiences on the ocean floor – and confirmed his belief they are “absolutely incredible animals” that, on nearly every occasion, “we vastly underestimate”.

Five years ago in a submersible off the coast of Svalbard, Norway, he observed Greenland sharks diving almost vertically between the surface and the sea floor, displaying a far greater range of movement than previously thought as they fine-tuned their knowledge of the location of hundreds of pounds of fish researchers had left at the bottom.

“Studying Greenland sharks is like finding a handful of puzzle pieces, but then realising it’s a thousand-piece puzzle,” says doctoral student Eric Ste Marie, who works with Hussey and was with him on that submersible trip. “We’re trying to kind of come to a complete picture of this animal, using only a small snapshot of their lives.”

A Greenland shark swims out of the darkness up to a post to which a meat or fish carcass is tied and begins to eatA baited remote underwater camera captures footage of a Greenland shark feeding in Tremblay Sound, Nunavut.

The trip, where the pair also observed that the sharks used their fins similarly to belugas for finely tuned movements, has caused Hussey to question many of the commonly held beliefs about the shark – including the idea they can live aslong as 500 years.

A widely cited study in 2016 used carbon dating to estimate the upper level of Greenland shark longevity. By the researchers’ estimates, some of the sharks in the ocean could have overlapped comfortably with Willam Shakespeare or Galileo. But Hussey says the specific carbon-dating methodology, commonly used to pinpoint where ancient artefacts fit within history, “puts you in the ballpark” when looking at dates of tens of thousands of years. But he cautions that the method has margins of error for shorter time frames.

“This type of dating method is challenging to use for ageing animals that are hundreds of years old. 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,” he says.

Eric Ste Marie studies a small Greenland shark in Scott Inlet, Nunavut. Photograph: Jena Edwards

Even the name Greenland shark serves as a misnomer. Despite the common belief that they exist only in the deep, the frigid temperatures of high northern latitudes means the creatures often appear in shallow water.

Headlines of the shark turning up in Caribbean waters doesn’t necessarily mean they are lost – but instead reflect the species are probably global circumnavigators, often existing at depths far below commercial fisheries.

“Even if they live only 100 years, how far can they travel in that time? How big does our scale of management need to be?” says Edwards. “Do we need to consider that one animal is likely moving across the whole of the Atlantic Ocean in its lifetime?”

The profound and disorienting unknowns surrounding the shark are amplified by the uncertainties of a changing Arctic. The resource-rich region, which has captured the interest of global superpowers, is warming at a rate faster than anywhere else on Earth.

“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. Warming Arctic temperatures will probably just push Greenland sharks to deeper, colder waters than southern latitudes.

Instead, Hussey is concerned about how little is known about Greenland shark reproduction. The last pregnant female was documented in 1950 and over 75 years later scientists still have no idea where the sharks reproduce, nor do they know how many pups are in a litter.

The research team’s field camp in Tremblay Sound, Nunavut. Photograph: Eric Ste Marie

The sharks also serve as a cautionary tale against hubris and underscore the knowledge gaps that persist.

“We get blinded by the stereotype. I think they’re tricky, I think they’re sharp and suspect they’re actually very capable predators,” says Hussey.

He and Ste Marie point to oral history of Inuit hunters that the sharks have been seen making predatory attacks in shallow waters. Hussey says there’s a chance they ambush mammals while they sleep or when they’ve found a breathing hole in the ice.

“If all they can do is scavenge, how the hell have they managed to live on this planet for so long? And I think it’s only a matter of time before we learn, once more, just how profoundly we’ve underestimated them.”