Scientists have made the surprising discovery that Greenland sharks can see, even though they live in deep, dark waters.
Greenland sharks live in the cold waters of the Arctic and North Atlantic, at depths of 200-1,000 meters (660-3,300 feet). They are the longest-living vertebrate known to science — some live for 400 years.
Scientists believed that Greenland sharks could barely see or were even blind because of their dark habitat and because many of the sharks have parasites in their eyes. Now, scientists have new evidence these sharks can actually see. And, they keep their vision for more than a 100 years.
Scientists at the University of Basel in Switzerland studied the shark’s DNA and eye tissue. They found that the sharks still had working genes for vision. Their eye tissue looked “beautifully intact,” said scientist Lily Fogg.
Because these sharks live in dark water, their eyes are different from human eyes. Humans have two kinds of photoreceptors: cones, for bright light, and rods, for low light. Greenland sharks only have rods, the scientists found. “They didn’t have any cones at all,” Fogg said.
So Greenland sharks can see, but they likely don’t see well, Fogg said. “It’s not really sharp … and that’s normal for species that live in dim habitats.” The sharks can detect some light and movement, which may help them find their prey.
The sharks in the study were all between 100 and 150 years old. Now, scientists want to study even older sharks to see if their vision lasts for centuries.
Greenland sharks appear to have a way to repair the DNA in their eyes. Understanding how the sharks preserve their vision could someday help humans protect our eyesight as we age.
This story is adapted from an article by Bobby Bascomb, published on Mongabay.
