Greenland sharks can live 400 years without losing their vision: Scientists once thought they were blind, now they know why

A shark that can live for centuries and holds surprising secrets to keeping eyes healthy for a lifetime is at the centre of an unusual dispute in Greenland. Earlier this year, The Avannaata municipality, of which Ilulissat is the administrative seat, approved a controversial plan to cull 1,000 sharks, offering 300 krone for every heart of a Greenland shark, according to a report in The Guardian. The plan was eventually dropped after Greenland’s government questioned whether it was legal, per The Guardian, but a future cull hasn’t been ruled out.

The proposal has brought attention to Greenland sharks, one of the least understood species on the planet. According to the Shark Trust, it is not only the world’s slowest shark, it is the second-largest carnivorous species, after the white shark. Greenland sharks reach about six to seven metres in length, they can live for more than 400 years. For a long time they were thought to be completely blind, although scientists have recently discovered this may not be true.

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According to Science Daily, researchers found healthy eye tissue and active proteins specially adapted for seeing blue light in the dim Arctic depths. DNA repair mechanisms may help keep their eyes functioning across centuries. The discovery could eventually offer new clues for protecting human vision as we age. "You see it move its eye," the University of California, Irvine associate professor of physiology and biophysics, pointing to the footage, said "The shark is tracking the light -- it's fascinating."

Why scientists thought Greenland sharks were blind

The Greenland shark lives in the dim depths of the ocean and is often infested with parasites that attach to its eyes. This is the main reason why scientists believed the large, long-lived species to be functionally blind. But UC Irvine researcher Dorota Skowronska-Krawczyk and colleagues have disproved this, challenging what is known about aging, vision, and longevity.

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Their cloudy-looking eyes can appear almost lifeless, and parasites are often found attached directly to the eyeballs. Because of those parasites and the extremely dark, murky environment in which the sharks live, scientists have long suspected that Greenland sharks may be functionally blind. However, a new research led by Skowronska-Krawczyk, however, suggests a very different picture.

What does the study on Greenland sharks show?

Published in Nature Communications, the findings suggest that a DNA repair mechanism may allow Greenland sharks to preserve their eyesight for centuries without showing signs of retinal degeneration. Their visual systems also appear specially adapted to the extremely low light levels of their Arctic habitat.

"One of my takeaway conclusions from the Science paper was that many Greenland sharks have parasites attached to their eyes -- which could impair their vision," she says. "Evolutionarily speaking, you don't keep the organ that you don't need. After watching many videos, I realized this animal is moving its eyeball toward the light, said Skowronska-Krawczyk.

The Greenland sharks examined in the study were caught between 2020 and 2024 with scientific long lines near the University of Copenhagen's Arctic Station on Disko Island, Greenland.

No signs of retinal cell death

Emily Tom, a UC Irvine Ph.D. student and physician-scientist in training in Skowronska-Krawczyk's laboratory, recalls the moment one of those preserved eyes arrived. "I opened the package, and there was a giant, 200-year-old eyeball sitting on dry ice just staring back at me," the 28-year-old says with a laugh. "We're used to working with mouse eyeballs, which are the size of a papaya seed, so we had to figure out how to scale up to a baseball-sized eyeball. Luckily, Dorota is very hands-on, both in her mentoring style and in the lab -- which you don't see a lot of with professors." "The lab smelled like a fish market," she says.

Tom performed histological and vision-specific analyses of the eye tissue. The researchers found no evidence of cell death in the retina. They also discovered that rhodopsin (a protein essential for vision in dim light) remained active in the shark retina. The protein was tuned to detect blue light, an adaptation that could help Greenland sharks see in the faint light available deep beneath Arctic waters.

The results suggest that the Greenland shark's remarkable lifespan does not necessarily come with the severe retinal deterioration that might be expected in such an old animal.

What Greenland sharks tell us about aging

For Skowronska-Krawczyk, the work raises the possibility that understanding how Greenland shark eyes remain healthy for centuries could eventually point researchers toward new strategies for preventing age-related vision loss.

The findings could also help guide research into eye diseases including macular degeneration and glaucoma. At the same time, they raise broader questions about how vision evolves, how tissues remain functional over extremely long periods and whether some of those protective mechanisms could ultimately be applied to humans.

Skowronska-Krawczyk says uncertainty surrounding federal research funding has created concerns about future support for this type of work, but she remains confident that "we will prevail."

"What I love about my work is that we are the first in the world to see results -- at the forefront, finding new mechanisms, rules and discoveries," Skowronska-Krawczyk says, looking over at the paused shark on the screen. "Then, being able to share this joy with students -- that's the best part of it."

Source: University of California - Irvine