The Washington Post

Deepwater shark species have evolved visual abilities to maneuver in low light

Several deepwater sharks have evolved specialized visual abilities that allow them to detect both predators and prey in areas of low visibility to a greater degree than previously known, according to an Australian researcher who shared her findings last week at a conference in Aberdeen, Scotland.

Amy Newman, a graduate student at the University of Western Australia, studies the eye and visual center of the brain of several shark species. By examining sharks caught accidentally off the northwestern cost of New Zealand at depths of 2,460 to 3,609 feet, she determined that they had photoreceptors in their retinas that would allow them to spot specific threats.

The beige catshark and McMillan’s catshark — both rare species — had an unusually high density of light-detecting cells in a small part of the retina, which would allow them to detect animals approaching them from behind. That’s a major advantage in avoiding predators to species as small as these; a McMillan’s catshark reaches an average 1.6 feet in length as an adult.

“The environmental conditions an animal is exposed to are reflected in the animal itself, so by investigating eye structure we can find out more about how deep-sea animals use the available light for survival and to predate,” said Newman, who presented her findings at the World Conference on Marine Biodiversity.

In addition to those two species, Newman also found specialized patterns in the retina of the New Zealand lanternshark, the rough longnose dogfish, the prickly dogfish and the flatnose catshark.

Newman noted that most species she examined had an increased cell density “in the temporal region of the retina,” which allows them to sample more of the visual field in front of them.

“This most likely aids in the detection of bioluminescent prey as the shark swims along in the water,” she said in a statement.

Juliet Eilperin

Juliet Eilperin is The Washington Post's White House bureau chief, covering domestic and foreign policy as well as the culture of 1600 Pennsylvania Avenue. She is the author of two books—one on sharks, and another on Congress, not to be confused with each other—and has worked for the Post since 1998.

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