The Greenland shark's visual system reveals functional adaptation despite ocular parasitism.

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For decades, the Greenland shark was known as a nearly blind animal, living slowly in the icy waters of the Arctic and North Atlantic. However, a new scientific study has revealed something surprising: despite its appearance and extreme age—it can live for over 400 years—this species can see better than scientists imagined.

The study shows that, even with its eyes frequently covered by parasites, the Greenland shark can still perceive contrasts and movements in its environment. This is essential for its survival in deep, dark waters, where light is scarce and every visual stimulus counts.

Researchers discovered that the animal's vision does not depend on fine details, but on a high sensitivity to light, allowing it to identify shadows and silhouettes. In practice, this means that it doesn't need to "see well" like a human to locate prey or orient itself in the ocean.

This discovery changes the way we see—literally—one of the longest-living vertebrates on the planet. Far from being a blind giant adrift, the Greenland shark turns out to be an extreme example of adaptation to the deep, icy environment in which it has lived for centuries.

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A study published in Nature Communications analyzed the visual function of the Greenland shark (Somniosus microcephalus), a species known for its extreme longevity, estimated at up to 400 years. Although individuals frequently present parasites attached to the cornea, the results indicate that vision remains functional.

The research demonstrated that the shark's retina is adapted to low-light environments, exhibiting high sensitivity to light at the expense of visual acuity. This pattern suggests a visual system specialized in detecting contrasts and movements, rather than fine spatial details.

According to the authors, even with the partial obstruction caused by the parasites, light transmission is still sufficient to allow for ecologically relevant visual responses. This challenges the idea that ocular infestation would render the animal functionally blind.

The findings reinforce the understanding that the Greenland shark's sensory system evolved to maximize efficiency in deep, cold, and dark environments, demonstrating a physiological adaptation consistent with its extreme longevity and ecological niche.

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Sources:  The visual system of the longest-living vertebrate, the Greenland shark | Nature Communications Tubarões da Groenlândia vivem 400 anos e enxergam bem; estudo descobre como | CNN Brasil

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