Study discovers sharks with positive buoyancy

Two deep-sea shark species swimming in the waters off the Hawaiian Islands are having a difficult time diving to deeper depths.

A joint study by the University of Hawaii at Manoa and the University of Tokyo has found that the sixgill and prickly sharks have positive buoyancy, making it more difficult for the two predators to swim downward.

Most sharks are negatively or neutrally buoyant and will sink if they stop swimming, making the discovery even more surprising for scientists.

“We didn’t expect to find evidence of positive buoyancy and ran two sets of experiments to confirm our initial observations of this phenomenon. This finding was a total surprise,” Carl Meyer, an assistant researcher at UHM’s Hawai’i Institute of Marine Biology (HIMB) and co-author of the study, said in a news release by the University.

Meyer and his team of researchers attached an accelerometer — like a flight data recorder — on the sharks’ fins, enabling them to collect data such as the animals’ swim speed, heading, tail beat frequency and body orientation. Using this data, they determined that the sixgill and prickly sharks had positive buoyancy.

UH Manoa said the researchers were using “the first ever shark-mounted camera on a deep-sea shark.”

While the sixgill and prickly sharks must work harder to swim deeper, scientists found the two species can swim uphill by gliding and without the use of their tails.

Scientists hope to build on this research by determining how this buoyancy affects the sharks’ daily tasks such as hunting and migrating.

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