Whales and Marine Mammals Impacted by Sonar Signals Far More Than We Realized

It turns out that noise pollution in the oceans may be more of an issue than we thought. Scientists have found that marine mammals likely hear sonar signals far more often, since commercially available sonar systems emit signals known to be within their hearing range.

Sonar is used by humans throughout the world's oceans. Since whales and other marine mammals rely heavily on their sense of hearing, these noises can disrupt their behaviors. That's why it's crucial to see exactly how much sonar might be impacting them.

The researchers evaluated the signals from three commercially available sonar systems designed to transmit signals at 200 kilohertz. While it's usually assumed that marine animals can't hear signals at 200 kilohertz, the scientists wanted to test that particular theory.

In the end, the researchers found that while most of the energy is transmitted near the intended frequency of 200 kilohertz, some of the sound leaks out to lower frequencies near the hearing range of killer whales and other marine mammals. In fact, the three sound systems produced signals as low as 90, 105 and 130 kilohertz.

"These signals are quiet, but they are audible to the animals, and they would be relatively novel since marine mammals don't encounter many sounds in this range," said Brandon Southall, one of the researchers, in a news release. "These sounds have the potential to affect animal behavior, even though the main frequency is above what they primarily hear. It may be that environmental assessments should include the effects of these systems. This may not be a major issue, but it deserves further exploration."

The findings reveal that even though these sonar signals aren't meant to be heard by marine mammals, they still are impacting these animals. Since high-frequency sonar pings several times per second, it's possible that it sounds like one, continuous, high-pitched hum or pint to the marine mammals.

"If you think of a keyboard on a piano, the ships would be hitting the low notes quite hard, the middle keys would be most of the sounds of the animals themselves, and the sonar systems we studied would be relatively quieter sounds in the top few octaves on the right of the keyboard," said Southall in a news release.

The findings are important for better understanding the impact of sonar. That said, future studies are needed to see how exactly these marine mammals might respond to this excess noise.

The findings are published in the journal PLOS One.