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Blue whales react to human noises

Blue whales are less likely to emit calls when sonar sounds at certain frequencies are present, but more likely to emit calls when ships are nearby.

The loudest sound ever recorded from an animal was produced by a blue whale, according to scientists who study them. And no wonder, since blue whales are the largest animal ever known to have existed (official record length is 33.58 meters (110 feet, 2 inches). Yet the whales are sensitive to human noises also, according to a late February 2012 study from University of California San Diego.

Blue whale size in contrast to human size via Chris at Wikimedia Commons

Mariana Melcon and her colleagues found that blue whale vocal behavior is affected by man-made noise, even when that noise does not overlap the frequencies the whales use for communication. The researchers published this result February 29, 2012 in the open access journal PLoS ONE.

They said the whales were less likely to emit calls when mid-frequency sonar was present, but were more likely to do so when ship sounds were nearby, saying:

Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to stop calling at any time of day … Conversely, the likelihood of whales emitting calls increased when ship sounds were nearby. Whales did not show a differential response to ship noise as a function of the time of the day either.

Blue whale tail via Mike Baird on Flickr

The team studied blue whales in the Pacific Ocean off the coast of Southern California.

Blue whales emit their calls between 10 and 40 Hz. The human ear can typically perceive sounds down to 20 Hz. Blue whale calls last between 10 and 30 seconds. They’ve been known to call to each other over hundreds of miles, and the calls are thought to serve a purpose of connection across vast distances in the ocean. Blue whales are also thought to call to each other to recognize each other as species and individuals – and during feeding, alarm or courtship. Melcon and her colleagues wrote:

The long-term implications of disruption in call production to blue whale foraging and other behaviors are currently not well understood.

Bottom line: Mariana Melcon and her colleagues at University of California San Diego found that the vocal behavior of blue whales is affected by human noise, even when that noise does not overlap the frequencies the whales use for communication. The researchers published their study February 29, 2012 in the open access journal PLoS ONE.

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