Friday, December 16, 2011

Singing Whales Steal Spotlight From Earthquakes by Helen Shen

Underwater earthquake recordings could help track the endangered and poorly understood fin whale, according to research presented here last week at the annual meeting of the American Geophysical Union. Most quake researchers cull the whale's booming calls from their seafloor recordings. But one group of seismologists has flipped things around to harvest an extensive repertoire of fin whale songs.

The second-largest among whales, fin whales (Balaenoptera physalus) live in many of the world's oceans. Yet, relatively little is known about their social habits, breeding grounds, and seasonal migration paths. The animals stick mostly to deep waters far offshore, so following them by visual surveys and radio tagging can be difficult and costly.

Seismologist William Wilcock of the University of Washington, Seattle, wondered if there was a better way. From 2003 to 2006, his group had measured undersea earthquakes that occur as new sea floor forms. Implanted in the ocean floor, their seismic detectors also picked up fin whale calls, which—at 17 to 35 hertz—overlap in frequency with Earth's rumblings. To extract earthquake information efficiently, the group developed computer programs to detect and filter out whale songs.

Using a similar strategy to weed out seismic vibrations brought the singing whales to center stage. "We just turned the code around," says Dax Soule, a graduate student in Wilcock's lab. In 3 years, the researchers recorded about 300,000 fin whale calls near the Endeavour hydrothermal vents on the Juan de Fuca Ridge, near Vancouver Island in Canada.

Whale songs pulsed against each of eight sea floor sensors at slightly different times and strengths. The scientists traced the likely origin of each vocalization by the pattern of ringing that spread across the detectors, locating whales with a precision of about 500 meters. Soule also inferred that regularly spaced calls at 25- to 30-second intervals probably came from single animals, while shorter intervals of about 13 seconds hinted at two animals conversing. Clusters of more tightly spaced calls suggested whales traveling in larger groups.

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