Scientists discovered that whenever northern elephant seals hear sounds emitted from sonar equipment, they dive to a depth of 645 m to forage.
The study was conducted by scientists from the University of Miami and the University of Victoria and published in the journal Plos One. Accordingly, when studying how deep-sea fish and invertebrates respond to different stimuli in the waters of Barkley Canyon, south of Vancouver Island, the team discovered that every time the device emitted a sona pulse – sound waves that propagate underwater, northern elephant seals dived to feed, like a meal bell.
They found that eight northern elephant seals regularly visited their device, located at a depth of 645 m, whenever it emitted a sonar sound.
“We suspect that the seals have learned to associate the sonar sounds from the research device with the presence of food—a phenomenon known as the ‘meal bell’ effect,” Héloïse Frouin-Mouy, lead author of the study, said in a statement. “The seals appear to use these sounds to locate prey areas and may have taken advantage of fish caught in the camera light, specifically targeting sablefish, their favorite food, as seen in the video.”
The eight seals, named after members of The Beach Boys: Brian, Dennis, Carl, Mike, Al, David, Blondie, and Bruce, appear to have perfected their hunting skills by sensing the “good vibes” from the sonar equipment. “We were familiar with these mammals and ended up naming them to differentiate between frequency of visits and observational habits,” Frouin-Mouy explained.
Along with documenting the “meal bell” effect, the researchers also discovered a previously unseen resting behavior in juvenile elephant seals. The team’s footage showed several “Beach Boys” taking regular “naps” on the seafloor in Barkley Canyon, lying still for several minutes. The longest nap lasted 8 minutes and 40 seconds, after which the individual had to return to the surface to breathe.
Barkley Canyon is a stretch of seafloor with geologic features that seep thermogenic gases, attracting a wide variety of creatures. In a previous experiment at the site, scientists placed humpback whale bones 890 meters (2,700 feet) deep in the underwater canyon. Using a specialized camera system, the team observed that the submerged feast attracted a wide variety of scavengers, from tiny crustaceans to king crabs.