Ocean acoustics reveal dolphin diets

March 9th, 2009  |  by  |  Published in Multimedia, Research News

Kelly Benoit-Bird prepares to launch acoustical equipment

Kelly Benoit-Bird prepares to launch acoustical equipment

Keeping their ears to the ocean, a University of Hawaiʻi scientist and his former graduate student are using acoustics to discover new things about what and how dolphins eat at sea.

Using mechanically recreated killer whale pulses in Seattle waters, Hawaiʻi Institute of Marine Biology Researcher Whitlow Au learned that orca, as the dolphins are more accurately known, favor chinook salmon over coho or sockeye.

Chinook have the highest concentration of fats that orca seem to prefer, he reported to the Acoustical Society of America in November.

The gas in a salmon’s fish bladder creates a particularly effective reflector for acoustic energy underwater, and orca use echolocation to zero in on the distinctive signature of their favorite fish, Au found.

Working with Au, alumna Kelly Benoit-Bird, now an Oregon State University assistant professor, used underwater hydrophones to document the nighttime feeding dance of spinner dolphins off Oʻahu’s Leeward coast.

The dolphins form pairs, encircle a school of fish, then take turns feeding in pairs.

The rate of clicking sounds, commonly used for echolocation, peak just before feeding, possibly helping the dolphins coordinate their choreography, the scientists write in the January Journal of Acoustical Society of America.

Both scientists were honored in 2008; Au was voted president-elect of the Acoustical Society of America, and Benoit-Bird received the American Geophysical Union’s biennial Early Career Award for Ocean Sciences.

Up close with spinner dolphins

  • Listen to the clicking sounds used by spinner dolphins in echolocation, as captured on an underwater hydrophone.  
Spinner dolphins use echolocation to track, circle and feed on prey

Spinner dolphins use echolocation to track, circle and feed on prey

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