Click to enlarge. Credit: APPLIED PHYSICS LABORATORY, UNIV. WASHINGTON

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Quietly slipping to a depth of 1,000 metres, an undersea glider is recording whale song off the coast of Hawaii in unprecedented detail."

It is the first acoustic-equipped glider to be deployed to this depth in the ocean to target a specific marine mammal. Whales click or vocalize to communicate and to find food, and use echolocation to navigate, but surface acoustic devices typically can't record their sounds.

Since 27 October, the glider has made more than 60 dives, each lasting about 6 hours, and is due to be retrieved on 17 November. It will collect data on beaked whales, which seem particularly sensitive to man-made noise; several strandings of these whales have been associated with military sonar usage (see Nature 425, 575-576; 2003).

"We believe we have identified beaked whales," says Dave Mellinger of Oregon State University, Corvallis, part of the project team. "It was pretty exciting. You work a couple of years on a project, hope it will succeed, but you don't know until the equipment is wet."

The US Office of Naval Research is funding the $1.5-million project, which builds on more than a decade of using autonomous gliders to study ocean temperatures and currents. This glider is steered by an internal computer on a preprogrammed course, travelling at about 0.25 metres per second, and is expected to collect half a terabyte of data over the course of its cruise.

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