ITHACA, New York – During mating season, male bearded seals make loud calls to attract a mate. How loud? Well, even their “quiet” call can still be as loud as a saw.
These elaborate sounds are essential for the breeding of bearded seals, and they must be loud enough to be heard over their siblings’ loud tones.
But in the rapidly changing Arctic acoustic landscape, where noise from industrial activities is expected to increase dramatically in the next 15 years, bearded seals may need to modify contact behavior if they are to be heard above noise from ships and commercial activities.
However, bearded seals can only do so much. A study by the Center for Bioacoustics (CCB) of the Cornell Laboratory of Ornithology (CCB) found that when ambient underwater noise is very loud, bearded seals are no longer able to compensate until they are heard.
Study results, “Limited Acoustic Compensation for Loud Ambient Noise in Bearded Seals: Implications for Industrialization of the Arctic Ocean,” published February 24 in Proceedings of the Royal Society: Biological Sciences.
“We wanted to know if bearded seals would hear a louder sound when their habitat becomes noisy from natural sound sources,” said Michel Fournier, a postdoctoral researcher at CCB who led the study. “The goal was to determine if there was a ‘noise threshold’ beyond which the seals could not hear or not hear any louder. By identifying this naturally occurring threshold, we could make recommendations on keeping the sound too high for human activities.”
From spring through early summer, the habitat is submerged under the ice near Utqiagvik, Alaska, with the sounds of male bearded seals – a sound that can be described as “another world”.
Fournier and his colleagues heard thousands of bearded seal sounds recorded from the Arctic, Alaska, over a two-year period. Each call was carefully measured and compared to concurrent ambient noise conditions. They found that bearded seals hear louder because their underwater vocal habitat becomes more noisy, but there is an upper limit for this behavior. As expected, when the surrounding noise is very loud, the bearded seals are no longer able to compensate until they are heard.
As a result, with increasing ambient noise conditions, the distance from which individuals can be detected decreases.
“Given these are reproductive calls, it’s possible that seals are already calling the loudest possible sound – males desperately want females to hear them,” Fournier said. So it is not surprising that there is an upper limit. I am grateful that we were able to set this limit so that we can make responsible management options moving forward. ”
Bearded seals – or Ogruk in the Inupiaq language – are highly prized by the indigenous communities of Alaska in the high arctic. Since bearded seals are the center of subsistence and cultural activities in Inupiaq communities, threats to them threaten the communities that depend on them.
“This work would not have happened without the insight and guidance from Arctic communities,” Fournier said. “It was their energy that drove the Cornell plant to put water in the water. It is our duty to keep listening.”
The study was co-authored by Christopher Clark, CCB’s Chief Visiting Scientist; Holger Clinic, Director of the CCB and Assistant Professor in the Department of Fisheries and Wildlife, Oregon State University; Aaron Rice, lead ecologist at the China Construction Bank; And Margarita Silvestri from the Marine Environment Laboratory at the University of Sapienza in Rome.