Researchers have noticed that blue whales exhibit strange behavior after exposure to military sonar.

The whales often change their diving behavior and avoid feeding areas after they hear the underwater sonar often used during military exercises, a Duke University press release stated.

"Whales clearly respond in some conditions by modifying diving behavior and temporarily avoiding areas where sounds were produced," lead author Jeremy Goldbogen of Cascadia Research said. "But overall the responses are complex and depend on a number of interacting factors."

Whether the whales responded to the sounds depended on if they were feeding, and if so how far below the surface they were.

The scientists used suction-cup tags which recorded acoustic stimuli and the whales movement as a response.

"The tag technology we use offers a unique glimpse into the underwater behavior of whales that otherwise would not be possible," Ari Friedlaender, a researcher at the Duke Marine Laboratory said.

The team found the whales responded to the sonar in different ways. Whales that were participating in "deep feeding" either sped up their activity or moved away from the sound.

"Blue whales are the largest animals that have ever lived. Populations globally remain at a fraction of their former numbers prior to whaling, and they appear regularly off the southern California coast, where they feed," John Calambokidis, a lead investigators of Cascadia Research said.

Southern California is host to a great deal of military testing sites that often use loud, mid-frequency sonar symbols. The exercises are believed to be responsible for other marine life getting stranded by shore.

"These are the first direct measurements of individual responses for any baleen whale species to these kinds of mid-frequency sonar signals," Brandon Southall, SOCAL-BRS chief scientist from SEA, Inc., and a researcher at Duke and the University of California Santa Cruz said. "These findings help us understand risks to these animals from human sound and inform timely conservation and management decisions."

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