Sonar ‘dinner bell’ attracts elephant seals deep in Pacific waters

Northern elephant seals can behave like Pavlov’s dog, responding to sonar deep in the Pacific Ocean to find fish to eat, according to the results of a study led by researchers at UVic.

The seals were captured on camera—surprisingly, and repeatedly—drawn by sonar to check out a 645-metre-deep research site at Barkley Canyon—just west of the Island—that was set up to study the effects of light and bait on fish.

“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,” said Héloïse Frouin-Mouy, lead author of the study published on Wednesday.

“The seals appeared to use this sound to locate an area with prey and may take advantage of fish disturbed by the camera lights, particularly targeting sablefish, their preferred meal as seen in the video footage,” she said.

Just as Ivan Pavlov’s 1890s experiments into the digestive response in dogs accidentally led to his psychological classical conditioning theory, these fish-foraging findings on the elusive seal also came by chance.

Researchers from UVic and Instituto de Ciencias del Mar (ICM-CSIC), a Barcelona-based research institute, set up a high-definition camera to study how fish react to an acoustic imaging sonar, LED lights, and an automatic bait release.

And look who came for dinner

To the researchers’ amazement, at least eight male elephant seals, ages four to seven, were observed on camera and detected by hydrophones on several visits to the Barkley Canyon, along Ocean Networks Canada’s (ONC) subsea cabled observatory NEPTUNE off the BC coastline between 2022 and 2023.

Published in the peer-reviewed PLOS ONE journal, the research is a first-ever peak into the inaccessible deep-sea behaviour of the large seals—named for their prominent proboscis, or tubular appendage used for sucking and feeding—who live primarily along the Mexican and Californian coastlines but who also have been spotted as far north as Race Rocks, and even Alaska.

Thanks to the surprise visits, marine biologists got a chance to study their sophisticated feeding strategies, prey preferences, and how they rested.

Clever and adaptable to find food

The repeated visits over 10 days by four seals allowed researchers to see signs the seals quickly learned to use the infrastructure around them to help find food.

“We became familiar with the mammals and ended up naming them in the paper after members of The Beach Boys to differentiate between the frequency of visits and observed habits,” said Frouin-Mouy, a visiting scientist to UVic’s biology department and assistant scientist at the University of Miami.

The seals mostly hunted for swimming sablefish, ignoring all kinds of stationary or drifting dinners in the form of prey options. Several seals were recorded by camera bobbing their heads and emitting low-frequency sounds while chasing their prey.

Time to take a break from all that swimming and eating

And when that was over, it was time to rest. Sonar video recorded seals taking power naps on the seafloor, something not previously seen from this species.

Researchers adapted the use of ONC’s subsea equipment for the fish study to observe the seals for almost one year. Results from the also completed fish acoustics experiment study are expected to be published soon.

Francis Juanes, a UVic biology professor and Liber Ero Chair for Fisheries Research, UVic adjunct professor Rodney Rountree, ICM-CSIC’s Jacopo Aguzzi, and ONC’s Fabio De Leo Cabrera also co-authored the paper.

‍ Fun Fact: ONC’s cabled observatories supply continuous power and internet connectivity to scientific instruments, cameras, and 12K+ ocean sensors. ONC, the federally funded UVic initiative, also operates coastal radar.