Taking the trend in selfies to new depths, video cameras mounted on the fins of reef sharks in Hawaii are giving scientists new insights into what the predators do all day.
One camera showed a sandbar shark starting its morning at about 300 feet (90.9 meters) below the surface, then swimming steadily upward as the day wore on, joining a mixed school of sandbar sharks, oceanic blacktips, and scalloped hammerheads.
The whole motley crew "spiraled up like a shark tornado," says Carl Meyer, who studies sharks at the University of Hawaii, in Kane'ohe on Oahu.
Another video captured a sandbar shark leisurely swimming along a reef, then suddenly darting away as it rushed to meet up with a female sandbar.
Tracking sharks is nothing new—researchers have been sticking satellite tags on these predators for years. But the data scientists got back was fairly coarse.
The new instrument packages that Meyer and Katsufumi Sato, of the University of Tokyo, attached to sharks off the coast of Hawaii are sensitive enough that the researchers can construct three-dimensional models of how these animals swim.
The technology will allow scientists to test long-held ideas about how sharks swim through the water and how much energy they expend while doing so.
"We're seeing behaviors that we simply couldn't see before," Meyer says. (Learn more about National Geographic's Crittercam project.)
Instruments called accelerometers and magnetometers record the fine details of a shark's position in the water, measuring the animal's acceleration and the magnetic field around it. Other instruments measure the depth and water temperature.
Meyer says these instruments are like having "a flight data recorder for sharks." And attaching video cameras to some of the sharks "helps us interpret what those data mean."
He thinks the schooling sharks were seeking protection from tiger sharks. Almost half of a tiger shark's diet in Hawaii consists of other sharks, he says.
And since tiger sharks are the largest commonly occurring coastal shark in the state—many reach 12 feet (3.6 meters) in length—smaller sharks like sandbars, oceanic blacktips, and hammerheads must work to stay off the menu.
Meyer and his colleagues are now retrieving their instrument packages from shallow-water sharks and analyzing the data. They've also started putting those instruments on deep-sea sharks like bluntnose sixgill sharks—which inhabit one of the least known environments on Earth.
"We've become very good in recent decades in figuring out where [sharks] go," Meyer says. "But now we need a better understanding of what they're doing in these ocean habitats."
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