Many open ocean fishes and sharks swim in a yo-yo pattern, repeatedly climbing and diving, but until recently, scientists weren’t sure why.
Researchers at the University of Hawaiʻi at Mānoa’s Hawaiʻi Institute of Marine Biology, Japanese National Institute of Polar Research and the University of Florida outfitted tiger sharks with digital still cameras and accelerometers, which recorded swimming speed, depth, temperature and acceleration as the sharks swam off the west coast of Hawaiʻi Island.
The sharks beat their tails almost continually as ascended and descended and rarely glided downwards, which ruled out a theory that they use yo-yo diving to conserve energy. However, bursts of speed during vertical movement were linked to camera images showing encounters with prey fish, leading the scientists to conclude that yo-yo diving is an effective strategy in the search for food across the sharks’ large three-dimensional home ranges.
“These findings are exciting because they have given us unprecedented new insights into the behavior of these huge and difficult to study marine predators,” explains HIMB Associate Researcher Carl Meyer, the lead U.S. scientist of the project. “We have only recently developed tools allowing us to directly measure the behavior in sufficient detail to understand what these animals are actually doing.”