What Happens When Bearded Seals Aren’t Loud Enough?

When it’s time to find a mate, male bearded seals make a ruckus. These marine mammals are incredibly loud and can be heard from as far away as 12 miles. Their elaborate calls can last as long as three minutes.

But as their underwater habitat grows noisier, bearded seals struggle to be heard, a new study finds.

The largest species of Arctic seal, bearded seals are mostly solitary animals. But during mating season in spring through early summer, they compete with the ever-increasing underwater sounds to be heard by potential mates.

Researchers at the Cornell Lab of Ornithology's Center for Conservation Bioacoustics (CCB) wanted to know how resilient seals would keep getting louder as the din around them grew.

“Male bearded seal calls are a long loud downsweeping trill that sounds similar to cartoon sound effects associated with UFOs. It's beautiful and eerie at the same time,” Michelle Fournet, the postdoctoral research associate who led the study, tells Treehugger. (You can listen to their call in the video below.)

“Males use these sounds to attract mates and deter competitors, the louder their calls the more mates will hear them, and the more acoustic space they take up. Altogether, this means their likelihood of breeding is higher if they are louder.”

Fournet and her team were inspired to research the changing noise threshold and its impact as a threat of climate change.

“As Arctic sea ice declines more vessels are expected to sail through these waters, and vessels are very loud. If seals can't hear each other, they are less likely to successfully mate,” she says.

For the study, researchers listened to thousands of recorded bearded seal vocalizations from Arctic Alaska covering a two-year period. They measured each call and compared it to the ambient noise conditions.

“We found that seals called louder when their environment got noisier, but there is an upper limit to how much they compensate,” Fournet says. “When their habitat gets noisy enough, they can't or won't continue to call louder. This is probably because they are calling as loud as possible already, and they've reached their limits.”

As ambient noise gets louder, the seals’ calls are able to be detected over shorter distances.

The results of the research were published in the Proceedings of the Royal Society B: Biological Sciences.

When Industrialization Increases

The study only looked at how seals would respond to the impact of natural underwater noise pollution. But the researchers point out that the Arctic soundscape is rapidly changing with industrial activities expected to dramatically increase over the next 15 years. So seals may need to change their calling behavior in order to be heard above the sounds of ships and commercial activities.

“In this study, we didn't look at noise from human sources — we looked at natural sounds,” Fournet says. “By seeing how seals respond under natural conditions (i.e. in an undisturbed state, how loud is too loud), we can inform managers about upper level noise limits that need to be avoided when industrialization increases.”

She points out that seals are not alone in turning up the volume when the world around them gets turbulent. Many vertebrates (including humans) get louder when their environment gets noisy. It’s an involuntary reflex called the Lombard effect to change vocal production in noisy situations.

“What was surprising is that we were able to identify this threshold when the ocean wasn't yet that noisy,” Fournet says. “If seals are reaching their upper calling limit in the absence of anthropogenic noise, which this study found they are, then once we add in anthropogenic noise we may have a larger problem.”

Researchers say that conservation scientists can use the findings as they discuss vessel regulations and marine mammal management in the high Arctic.

Bearded seals are important to some communities in the Arctic which rely on them as a resource.

“We want to understand what the noise limit for bearded seals was in advance of this region getting too noisy,” Fournet says. “The hope is that this work will inform management to keep the Arctic quiet for the seals, and the communities that rely on them.”