Elephant seals use sonar signals to dine deep underwater

When we think of an elegant restaurant in a sophisticated setting, we probably think of expensive cities or secluded beach resorts. The depths of the Pacific Ocean don’t cross our mind. Yet, that is exactly where some northern elephant seals dine out, according to a new study led by University of Victoria researchers.

Observing the mysterious mammal

Published in PLOS ONE, this study provides a unique, unprecedented visual insight into the rarely observed behaviors of these elusive mammals in the deep sea.

The focus? Their advanced feeding techniques, prey choices, and even their rest habits.

At least eight male elephant seals, aged between 4 and 7, were observed using ONC’s observatory equipment during multiple visits to the research site situated 645 meters deep in Barkley Canyon. The observations were recorded between 2022 and 2023.

Surprise visitors

Researchers from the UVic, Instituto de Ciencias del Mar (ICM-CSIC), a Barcelona-based research institute, and ONC were initially studying the impact of light and bait on fish and invertebrate behavior. Little did they know, these clever seals had their eyes on the prize.

After reviewing camera footage, acoustic images, and sound data, the seals were discovered as unexpected visitors. The researchers surmised that the seals linked the sonar noise with potential prey, effectively considering it a “dinner bell.”

Hunting tactics of elephant seals

“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,” said Héloïse Frouin-Mouy, the lead author of the publication.

Héloïse Frouin-Mouy, a visiting scientist at UVic‘s biology department and assistant scientist at the University of Miami, conducted this research with her colleagues, including Francis Juanes, a UVic biology professor and Liber Ero Chair for Fisheries Research, and adjunct professor Rodney Rountree.

Other notable contributors were ICM-CSIC’s Jacopo Aguzzi and ONC’s Fabio De Leo Cabrera.

Unique observations of elephant seals

The findings suggest that the seals quickly adapted to use the infrastructure for more efficient foraging. In a span of 10 days, four seals were repeatedly seen visiting the research site.

“They returned often to feed more efficiently,” said Frouin-Mouy. “We became familiar with these seals, even distinguishing between their frequencies of visits and observed habits. We even ended up naming them after members of The Beach Boys.”

Remarkable discoveries

Their favorite dish? Actively swimming sablefish, ignoring all the other stationary or drifting prey options. The seals were even recorded on camera and hydrophone bobbing their heads and producing low-frequency sounds in pursuit of their prey.

In another fascinating revelation, these adolescent male northern elephant seals were found to be power napping on the ocean floor at Barkley Canyon – a sight never-before-seen.

The real-time monitoring capacity of NEPTUNE observatory played a crucial role in this discovery. It allowed the research team to adjust the use of ONC’s underwater instrument – initially deployed for the fish study – to detect the presence of seals and observe them for nearly a year.

Significance of elephant seal behavior

Understanding the foraging behaviour of northern elephant seals is not merely an academic exercise; it holds significant ecological implications.

As apex predators of the deep sea, these seals play a crucial role in maintaining the balance of marine ecosystems. Their prey choices, particularly for sablefish, can influence population dynamics within the ecosystem, thereby affecting the species that inhabit these underwater environments.

Moreover, insights gained from monitoring their behaviour provide invaluable data on how marine species may adapt to changes in their environment, which is increasingly under threat from climate change and human activity.

Future research directions

The revelations from this study pave the way for further exploration of the habits and habitats of marine mammals.

Future research could investigate not only the elephant seals but also the broader impacts of environmental changes on other deep-sea species.

By utilizing advanced technology similar to that employed in this study, researchers can delve deeper into marine behaviors and interactions, enriching our understanding of ocean dynamics.

This could ultimately inform conservation strategies aimed at protecting these delicate ecosystems, ensuring their sustainability for future generations.

Elephant seals beyond the ocean floor

Northern elephant seal colonies can be found from as far north as Alaska to as south as the Baja Peninsula. Typically, tracking of the seals’ movements is done using bio-tags, or primarily on land.

This research provides a rare look into their underwater behavior, unlocking a new perspective on these fascinating creatures that share our world.

“Understanding the underwater lives of marine mammals is still limited by our inability to fully study the animal’s behavior beneath the water, notably the tactics used by apex predators, such as pinnipeds, to capture their prey,” noted the researchers.

“Animal-borne tags have provided an opportunity to gain new insights into the diving and foraging behavior of pinnipeds.”

The study is published in the journal PLOS ONE.

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