Posted by: The ocean update | March 30, 2015

Porpoises, whales and dolphins use ‘sound searchlights’ (Denmark)


The researchers fitted porpoises with acoustic tags, recording and measuring sound as the animals approached targets

March 30th, 2015 (Victoria Gill). When porpoises hunt, they can widen or narrow the spread of the echolocation sound beams they emit, depending on where they are in the chase, BBC News reports.

In a study out of Denmark’s Aarhus University run by Danuta Wisniewska, harbor porpoises in a research enclosure (Ed Sibylline : fishes are able to come in, so they’re still hunting but it’s captivity !) off the Danish coast were outfitted with special tags that could detect sound.

Then researchers set up a series of microphones in the water. The tags on the porpoises and the microphones together helped the scientists map out the direction and breadth of the sounds the animals were emitting when tracking down fish.

Porpoises use echolocation to navigate and to track prey — sending out beams of sound and then using the return echo to locate things, such as a potential meal.

When hunting, the animals could widen the sound beam by about 50 percent when they were moving in for the kill. Wisniewska likened the approach to using a flashlight beam — it works best narrow for seeing things far away and wide for seeing up close. The closer in on the work you are doing, the wider the beam ought to be.

“This is similar to what we see in porpoises,” Wisniewska told BBC News. A structure in the animal’s forehead called the melon controls variation in the spread of the beam, the researchers said.

The scientists think the “flashlight” approach might also be used by other toothed whales and dolphins, according to BBC News. They hope sound might one day be used to warn the animals about nearby fishing nets into which they might swim while pursuing their prey.

Citation : Range-dependent flexibility in the acoustic field of view of echolocating porpoises (Phocœna phocœna). M. Wisniewska et al. March 20, 2015. eLife 2015;10.7554/eLife.05651.




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