New research in Hawaii waters is shedding light on the movements of one of the sea’s most mysterious and fearsome predators, the tiger shark.

In a pair of recent papers, marine scientists confirm that tiger sharks are profoundly accurate navigators but don’t spend much time at the surface — at least during the day.

Rather, the sharks engage in what scientists call "yo-yo diving," repeatedly swimming or gliding to depths below 300 feet, then back up again, most likely to pursue a variety of prey.

In October 2008, Carl G. Meyer of the University of Hawaii Institute of Marine Biology and colleagues caught four tiger sharks off Keahole Point on the Big Island and fitted them with devices that measure acceleration.

To two of the sharks, they also attached digital "lipstick cameras."

Together, the instruments represented "the most sophisticated tracking device ever deployed on a shark," Meyer said by e-mail. "The device is broadly analogous to the ‘black box’ found on aircraft, providing information on the shark’s exact orientation, speed and depth, as well as tail beat frequency. The camera provides a ‘shark’s-eye view’ of the environment as the shark swims."

They then tracked the four for about six hours by means of an acoustic pinger surgically implanted in each fish’s belly.

Three of the four sharks swam near the coastline, staying in water no deeper than about 1,600 feet.

The fourth headed for open ocean.

All four undertook "yo-yo diving," descending to an area where sea temperature drops rapidly and where many pelagic species like tuna like to hang out.

That area, called the thermocline, just above nutrient-rich cooler waters, was typically about 260 to 325 feet down.

An analysis of the sharks’ movements indicates that hunting is the impetus behind the yo-yo diving.

Other possible explanations — taking a restful glide, for instance — didn’t fit the data. The sharks rarely glided during descent.

The accelerometer occasionally showed "burst swimming," when the shark pours on the speed, apparently, the photos suggest, either to catch prey or to get away from pesky remoras or suckerfish.

"A combination of accelerometer and image data revealed burst swimming events and possible pursuit and capture of prey during vertical movements," Meyer and colleagues conclude in a paper published March 1 in the journal Marine Ecology Progress Series. "Collectively, these results suggest that yo-yo diving by tiger sharks might be an optimal search strategy enabling them to effectively comb large three-dimensional spaces for prey."

Meyer and co-author Yannis Papastamatiou, a marine biologist at the Florida Museum of Natural History in Gainesville, Fla., also collaborated on a second paper, published in the online edition of the Journal of Animal Ecology.

That study took a fresh look at the ability of tiger sharks and thresher sharks to swim long distances in straight lines, which the scientists call "directed walks," with few visual cues.

Using a math technique called fractal analysis, the researchers re-examined tracking data from acoustic transmitters on nine tiger sharks off the south shore of Oahu in 1999, nine blacktip reef sharks in the lagoons of Palmyra Atoll in 2009, and 15 thresher sharks off southern California in 2010. The statistical analysis determined whether the sharks were moving randomly or toward a known goal.

"At times, these tiger sharks were swimming across a deep channel, open ocean, often at night," Papastamatiou said. "So the question is, ‘What are they orienting to in such a seemingly featureless environment?’ It really just highlights how impressive their navigation can be."

The answer could be the shark’s sixth sense: magnetic reception.

"There is an increasing amount of evidence that lots of, if not all, animals can to a certain degree detect magnetic fields," Papastamatiou said. "That is something that could potentially be used over very large distances because there are gradients in the earth’s magnetic field and they could use those as landmarks. So, even swimming through open ocean, which seems featureless to us, may not be featureless to sharks if they could detect these magnetic fields."