Scientists find deep-sea sharks with buoyancy

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COURTESY MARK ROYER / UNIVERSITY OF HAWAII
A sixgill shark equipped with an instrument package returns to deep water. In a study published recently, scientists from the University of Hawaii at Manoa and the University of Tokyo revealed that two species of deep-sea sharks — sixgill and prickly sharks — have positive buoyancy, meaning they have to work harder to swim downward than upward.

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COURTESY UH
Researchers find deep-sea species that have a tendency to drift toward the surface.

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COURTESY MARK ROYER / UNIVERSITY OF HAWAII
University of Hawaii researcher Carl Meyer attaches an accelerometer package to the pectoral fin of a large sixgill shark. A new study, co-written by Meyer, shows that some deep-sea sharks can glide uphill for minutes at a time without using their tails.

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New research on sharks that swim the water off Oahu indicates that not all of the deep-sea creatures are inclined to naturally sink — a surprising discovery that challenges much of the conventional wisdom among marine researchers.

The finding raises new questions about why some sharks would be inclined to rise to the surface, and what if any advantages it might give them in catching prey or conserving energy.

A recent study by scientists at the University of Hawaii at Manoa and the University of Tokyo indicates that at least two deep-sea shark species — sixgill and prickly sharks — are "positively buoyant," meaning the creatures are inclined to drift toward the surface instead of sink toward the ocean floor.

The study, co-written by UH assistant researcher Carl Meyer and published this month in the journal PLOS ONE, found that the sharks they studied had to work harder to swim downward than up. In some instances the sharks even "glided uphill," the study found.

Generally, it’s been widely accepted that sharks are either "negatively buoyant" — meaning they’re inclined to sink, or very close to having a neutral buoyancy where they neither sink nor rise, the study’s authors said.

"We didn’t expect to find evidence of positive buoyancy, and ran two sets of experiments to confirm our initial observations of this phenomenon," Meyer said in a statement. "This finding was a total surprise."

Meyer and his co-authors added that their findings are preliminary and will require further study to see just how widespread such positive buoyancy might be among other deep-sea sharks and organisms.

The 36 days worth of swimming data came from six shark test subjects — one prickly and five sixgill — that were monitored with special instruments after they had been captured off Kaneohe Bay, according to the report. The instruments monitored the subjects’ speed, heading and tail beat frequency, according to a UH release.

The study also included deploying the first-ever shark-mounted camera on a deep-sea shark, according to the release.