Elephant seals use scientific sonar as a ‘lunch bell’

September 6 () –

Elephant seal specimens have been repeatedly filmed in the depths of the Pacific using scientific sonar as a ‘lunch bell’ for their fish feasts.

The study, published in PLOS ONE, provides a unique and first-time visual insight into the deep-sea behaviors of this elusive mammal, with a focus on its sophisticated feeding strategies, prey preferences and resting habits.

In total, At least eight male elephant seals, aged between 4 and 7 years, They were observed on camera and detected by hydrophones during multiple visits to the 645-meter-deep research site in Barkley Canyon along ONC’s (Ocean Networks Canada) NEPTUNE cabled underwater observatory off the west coast of British Columbia between 2022 and 2023.

The findings came almost by chance; Researchers from the University of Victoria (Canada), the Institute of Marine Sciences (ICM-CSIC) of Barcelona, ​​and the ONC were studying the effects of light and bait on the behavior of fish and invertebrates in Barkley Canyonusing a high-definition camera, acoustic imaging sonar, a hydrophone, a pair of LED lights and an automatic bait release system.

But a review of the camera, acoustic images and sound data revealed a surprise for visitors.

“We suspect that the seals They have learned to associate the sonar noise of the research instrument with the presence of food.a phenomenon known as the ‘lunch bell’ effect.

“Seals appear to use this sound to locate an area with prey and may take advantage of fish disturbed by the camera lights, especially blackfish, their preferred food, as seen in the video,” he says. in a statement Héloïse Frouin-Mouy, lead author of the publication.

In one case, repeated visits over 10 days by four of the identified seals to the research site also show that they quickly learned to use the infrastructure to forage “We became familiar with the mammals and We ended up naming them in the article as members of The Beach Boys to differentiate between the frequency of visits and the observed habits,” he says.

Adolescent males visiting the site predominantly targeted actively swimming sablefish, ignoring the more than a dozen other stationary or drifting prey options. Interestingly, Several individuals were recorded with a camera and a hydrophone moving their heads and producing sounds low frequency while chasing their prey.

Sonar videos also revealed seals napping on the seafloor in Barkley Canyon, another new and previously unseen behavior in adolescent male northern elephant seals.

NEPTUNE’s real-time monitoring capability allowed researchers to tailor the use of ONC’s underwater instruments deployed at the research site to study fish to detect the presence of seals and observe them for almost a year.

Although northern elephant seal colonies are found as far north as Alaska and as far south as the Baja California Peninsula, they are typically studied using biotags to track their movement, or are found primarily on land.

The results of the experimental study on fish acoustics, which has also been completed, will be published in the near future.