The mysterious beaked whale is the target of a new undersea glider trying to track the deep-diving mammals by their high-frequency clicks and squeals.

A Seaglider unmanned underwater vehicle with an underwater microphone began patrolling the coast of Hawaii on October 27 and will finish up its initial mission on November 17. By then, it will have collected half a terabyte of data.

By applying software that automatically picks up beaked whale sounds from the rest of the sounds of the ocean, the researchers hope to gain a deeper understanding of how these rare whales live.

Whale Song Sound recording of orca whale squeals and clicks from a Seaglider test run in the Puget Sound. It’s been slowed down for human ears.

“They live far off shore, and they are not very obvious. When they surface, they are only up for a second or so and they are hard to see,” said Dave Mellinger, a marine scientist at Oregon State University who focuses on the automatic detection of whales from acoustic signals. “They are pretty cryptic. That makes them good acoustic candidates.”

The Seaglider is one of a host of new acoustic tracking tools that are helping scientists better understand the behavior of deep sea whales. Using autonomous underwater gliders, hydrophones, and sophisticated algorithms, they are a key tool in the race to map where whales live while whales are still living. For example, dedicated-listening buoys help protect right whales near Cape Cod while providing valuable scientific data.

The beaked whale appears to be particularly sensitive to the powerful sonar used by the world’s naval fleets. Over the past decade, dozens of these rare whales have died in a series of incidents that seem linked to naval exercises, even if it’s hard to prove the connection.

The carcasses that wash up on shore are consistent with the hypothesis that the whales respond to the sonar by surfacing too quickly, inducing the bends (.pdf). Nitrogen, and other gases that had been dissolved into the liquids inside their bodies by the high-pressure at depth, transform back into gas as the pressure is released. If they rise too fast, the amount of gas overwhelms the body’s natural systems for expelling it, causing bubbles to form in the bloodstream and tissues.

The only sure way to make sure that the whales aren’t injured by military sonar use is to ensure that there aren’t any whales in the area when the naval soundings occur. But that would require figuring out how to find and track the whales, which has proven difficult. It’s a big ocean and the high-frequency noises they make don’t carry in the water like the bass calls of a blue whale or humpback.

The U.S. Office of Naval Research, though, has been pouring money into learning more about the whales. Mellinger’s project received $1.5 million.

“We’ve been focusing on beaked whales because of the conservation implications of being able to find them,” Mellinger said.

A single glider can’t provide the breadth of monitoring they would need, but it’s possible fleets of gliders could.

The next step for Mellinger and his teammates could be to integrate and calibrate their data with information from U.S. Navy hydrophone arrays. Most of the Navy’s systems can’t record the high frequencies used by the beaked whales to locate their small squid prey, but some are sensitive enough to use.

“What we’d like to do is track a beaked whale using the Navy hydrophones and have a glider operating nearby,” he said. “We’re hoping to do that next year.”

via Rex Dalton/Nature

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