Blue Whales Impacted by Military Sonar Near California

Sound can travel for miles underwater, quickly moving across space as is affects marine species. Now, it turns out that military sonar in particular can impact ocean-dwelling animals. Scientists have discovered that loud noises cause blue whales off of the coast of California to change their behavior, which could affect their ability to survive.

Scientists have noted in the past that noise pollution affects whales. It's estimated that the northeastern Pacific is as much as 10-12 dB louder than it was in the 1960s, for example. Since sound travels much faster and farther in water than air, animals can also hear something occurring miles away. Researchers have previously found that loud noises, such as those caused during seismic-survey operations, can startle dolphins; they'll often dart to the surface, which can mean they develop "the bends," a potentially deadly illness.

In order to examine the impact on blue whales, the researchers tagged the mammals with non-invasive suction cups. These devices recorded acoustic data and high-resolution movements as the animals were exposed to controlled sounds. This allowed the researchers to receive a unique glimpse into their underwater behavior.

So what happened when the whales heard a sound? The scientists discovered that some of the whales engaged in deep feeding stopped eating and either sped up or moved away from the source of the noise. Yet not all whales responded to the noise--and not all in the same way.

"Blue whales are the largest animals that have ever lived," said John Calambokidis, one of the project's lead investigators, in a news release. "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."

Unfortunately, this region is also the site of military training and testing exercises that involve loud mid-frequency sonar signals. This means that the blue whales and their feeding patterns could be affected.

"These are the first direct measurements of individual responses for any baleen whale species to these kinds of mid-frequency sonar signals," said Brandon Southal, one of the researchers, in a news release. "These findigns help us understand risks to these animals from human sound and inform timely conversation and management decisions."

The findings are crucial for understanding how to limit the impacts of sound pollution on blue whales. Since the species is rare, it's important to keep disturbances to a minimum.

The findings are published in the journal Proceedings of the Royal Society B.