University of Hawaii researchers are a step closer to understanding the biology and habits of elusive deep-sea sharks with new studies that have attached a camera to the sharks for the first time, and new data that reveals the animals are surprisingly buoyant.
UH Manoa scientists working in conjunction with the University of Tokyo analyzed swimming patterns on two species of the deep runners — sixgill and prickly sharks — founing the animals have to put greater effort into swimming downward than they do upward.
With most sharks sinking if they stop swimming, scientists have believed the sharks are either negatively or neutrally buoyant. The data on swimming performance of the deep-sea species, logged with a devise like a flight data recorder called an accelerometer, turned this wisdom on its head.
The device measured the shark’s speed, heading, orientation and tail movement, finding that the deep divers are able to glide upward for several minutes at a time without moving.
“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,” said Carl Meyer, assistant researcher at UH Manoa’s Hawaii Institute of Marine Biology.
Meyer thinks the positive buoyancy may give the hunters added stealth as they glide upward, motionless, to nab prey. Or it may help the sharks make their nightly migrations to shallower areas.
Meyer said that cameras will hopefully capture footage of the sharks feeding, and more research will hopefully shed light on many unanswered questions about the denizens of the deep.
“When I first downloaded the camera, I thought it had failed because all I saw were thousands of completely black frames,” said Meyer. “Suddenly a string of images appeared with a brightly-lit, alien-looking reef and strange deep-sea invertebrates. I was elated and realized that the black frames resulted from the shark swimming around too high in the water column for the camera strobe to illuminate the seabed.”
The animals typically range from 600 to 2,000 feet deep around Hawaii. Most of the deep-sea sharks here are smaller to medium sized species — gulpers, kitefins, black-bellied lantern sharks and false catsharks. The gigantic Pacific sleeper shark likely lives in Hawaii waters also.
“There is also a very good chance that other deep sea sharks exist around Hawaii, but we just haven’t discovered them yet,” Meyer said. “We would like to equip some of these other species with accelerometer devices to determine whether they also exhibit positive buoyancy.”
Researchers caught the sharks off Kaneohe, Oahu using baited hooks set 1,000 feet blow the surface. Hauled into bright, unfamiliar surface waters that are 20 to 40 degrees warmer than what the sharks are used to, the animals had to be quickly tagged and returned, Meyer said. The sharks resumed their natural behavior once they swam back to their deep sea habitat, he said.
