Weddell seals chirp, whistle, and emit many different sounds under Antarctica’s ice at sound frequencies that humans cannot hear, according to a research team led by biologists from the University of Oregon.
During two years of recording at the underwater observatory in McMurdo Bay, nine types of tonal ultrasonic vocalizations of seals were recorded at a frequency of up to 50 kilohertz. Recall that people hear in the audio range from 20 to 20,000 hertz, or 20 kilohertz.
Weddell seals (Leptonychotes weddelii), the world’s southernmost mammals, inhabit Antarctica’s sea ice, using their large teeth to create air openings. They can dive to a depth of 600 meters, searching for prey, and remain underwater for 80 minutes. Researchers first identified 34 types of seal calls at sound frequencies in 1982, linking different sounds to different social interactions.
Study lead author Paul Chico, visiting professor at the UO Institute of Ecology and Evolution, began recording sound vocalizations of seals in 2017 after completing the McMurdo Oceanographic Observatory installation.
Over the next two years, the observatory’s broadband digital hydrophone – more sensitive than the equipment used in earlier recordings – picked up high-frequency vocalizations during passive monitoring of seals. Basically, the sounds of the seals were above 20 kHz. However, the overtones of some seal vocalizations exceeded 200 kHz.
What ultrasonic vocalizations mean in the Weddell seal repertoire is unknown. Seals belong to 33 species of swimming-legged mammals belonging to pinnipeds. It was believed that pinnipeds, including sea lions and walruses, only emit sound signals.
However, scientists speculate that ultrasonic vocalization could be used for echolocation, a biological sonar that dolphins, toothed whales, and bats use to navigate low-visibility conditions to avoid obstacles and find friends or prey.