A blue whale swims in the deep blue sea off the coast of Mirissa, in southern Sri Lanka, April 5, 2013. Sonar blips can mask whales’ vocalizations, deter them from their habitats and affect their hearing. (Joshua Barton/REUTERS)
Sonar noise may further threaten endangered whales, a study suggests

The oceans are increasingly cluttered with human-made noise, which can disturb even the largest animals on Earth, blue whales, new research shows.

Whales depend on vocalizations to communicate with other individuals in their species over long distances. But sonar blips that the U.S. military uses in underwater navigation, object-detection and communication are feared to mask whale calls, deter the marine mammals from their habitats and damage the animals’ hearing, researchers say.

Mid-frequency sonar signals (between 1 kHz and 10 kHz) have been blamed for mass strandings of deep-diving beaked whales. There are fewer cases of sonar-linked strandings of blue whales and other baleen whales.

To test how blue whales feeding off the coast of Southern California might be affected by mid-frequency sonar, a team of scientists exposed a group of the creatures to sonar sounds between 3.5 and 4 kHz that were not as loud as the kind the military uses. The whales were tagged with suction cups that recorded acoustic data and movements as the animals were exposed to the controlled sounds.

Although not all of the whales responded in the same way, some of the mammals avoided their feeding grounds and fled from the source of the noise, the researchers found.

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

There are only 5,000 to 12,000 blue whales remaining today, according to the National Oceanic and Atmospheric Administration. The new study suggests sonar may be a threat to the endangered species.

“Our results suggest that frequent exposures to mid-
frequency anthropogenic sounds may pose significant risks to the recovery rates of endangered blue whale populations, which unlike other baleen whale populations (i.e. humpback, grey and fin whales), have not shown signs of recovery off the western coast of North America in the last 20 years,” the researchers wrote.