Northern elephant seals use deep-sea research sonar as dinner bell
A new study by researchers from the University of Victoria found that northern elephant seals were often spotted on camera in the deep Pacific Ocean. They used sonar from an Ocean Networks Canada (ONC) observatory, which acted like a dinner bell, to help them find their next meal of fish.
The research published in PLOS ONE gives us a rare look at how this hard-to-find mammal acts in the deep sea. It highlights their clever ways of finding food, what they like to eat, and how they rest.
In total, researchers spotted at least eight male elephant seals, aged between 4 and 7 years, using cameras and hydrophones during several trips to the 645-meter-deep research area at Barkley Canyon. This location is part of ONC’s underwater cabled observatory, NEPTUNE, situated off the west coast of British Columbia, between 2022 and 2023.
The discoveries were made unexpectedly when researchers from UVic, the Instituto de Ciencias del Mar (ICM-CSIC) in Barcelona, and ONC were looking into how light and bait influence the behavior of fish and invertebrates at Barkley Canyon. They used a high-definition camera, acoustic imaging sonar, a hydrophone, a set of LED lights, and an automatic bait release system for their study.
But a review of the camera, acoustic images and sound data revealed the surprise visitors.
“We suspect the seals have learned to associate sonar noise from the research instrument with the presence of food—a phenomenon known as the ‘dinner bell’ effect.
Héloïse Frouin-Mouy, the main author of the study, explains that the seals seem to use this sound to find places where they can catch food. They might also go after fish that get startled by the camera lights, especially sablefish, which is their favorite food, as shown in the video.
Frouin-Mouy, who is a visiting scientist at UVic in the biology department and also works as an assistant scientist at the University of Miami, teamed up with Francis Juanes, a biology professor at UVic and the Liber Ero Chair for Fisheries Research. They also worked with adjunct professor Rodney Rountree. The paper was co-authored by Jacopo Aguzzi from ICM-CSIC and Fabio De Leo Cabrera from ONC.
One example is that four of the seals visited the research site multiple times over 10 days. This shows that they quickly figured out how to use the setup to find food more effectively, according to Frouin-Mouy.
She explains that they got to know the mammals really well and decided to name them in their paper after The Beach Boys members to help tell apart how often they visited and what they did.
The teenage boys who came to the site mainly focused on catching sablefish that were swimming around, completely overlooking the more than twelve other types of fish that were either still or drifting nearby. Some of them were even caught on camera and a hydrophone, moving their heads up and down and making low sounds while they were trying to catch their food.
Sonar videos showed that seals were taking naps on the ocean floor at Barkley Canyon, which is a brand new behavior for the young male northern elephant seal that we’ve never seen before.
NEPTUNE’s ability to monitor things in real-time helped the researchers change how they used ONC’s underwater tools at the study site. This way, they could detect the seals and watch them for almost a whole year.
Northern elephant seals can be spotted in places as far north as Alaska and as far south as the Baja Peninsula. Scientists usually study them by using biotags to follow their movements, but they are mostly seen on land.
Results from the also-completed fish acoustics experiment study will be published in the near future.
Credit – University of Victoria
