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Study: Camouflage bests super vision in the open ocean

"Hunting and avoiding being eaten in the open ocean is about seeing other animals before they see you," explained researcher Sonke Johnsen.

By
Brooks Hays
Silvery scales help fish reflect light and blend in to the open ocean. Photo by Justin Marshall/University of Queensland, Australia
Silvery scales help fish reflect light and blend in to the open ocean. Photo by Justin Marshall/University of Queensland, Australia

DURHAM, N.C., Aug. 22 (UPI) -- One wouldn't think camouflage would be a winning strategy in the open ocean, but for fish with shimmering silver scales like herring, sardines and mackerel, camouflage regularly beats super sight.

Unlike human eyes, the eyes of many marine species can process light polarization. Scientists long assumed this ability rendered the silvery disguise of tuna, amberjack, barracudas and others ineffective.

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Scientists at Duke University pitted polarized vision against shiny scales by photographing a variety of silver fish using a camera outfitted with a polarized lens filter. Researchers used a computer model to analyze the images and mimic the way marine species process polarized light.

The results showed polarized vision can pick out a reflection of polarized light -- bounced off the silver scales -- against the background of open ocean water. However, standard light cues like brightness work just as well from just as far away. In other words, polarized vision doesn't help marine creatures spot silvery scales from farther away. It offers no real advantage.

"Sighting distance is important, because hunting and avoiding being eaten in the open ocean is about seeing other animals before they see you," Sonke Johnsen, biology professor at Duke University, said in a news release. "Once you're seen, you're dead. It's over."

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The findings, detailed in the journal Current Biology, undermine the long-used explanation for why polarized vision is so popular among marine species.

"There's a lot polarized light underwater, and there are all these ocean animals that can see it, but we have no idea why," Johnsen concluded.

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