Somewhere on the seafloor of an oceanic canyon near Vancouver Island in 2022, scientists dropped a bundle of video and audio recording gear and a carousel loaded with 24 bottles. Each bottle contained a hefty sardine bathed in vegetable oil, and the carousel was programmed to release one sardine every two weeks to attract the deep-sea fish skulking in the area. The muddy bottom served as stomping grounds for sleek sablefish, noodly eelpouts and hagfish, and flabby snailfish, all of whom roam in nearly absolute darkness, aside from glimmers of bioluminescence.
At more than 2,000 feet deep, the observatory is one of many deep-sea observatories set up by Ocean Networks Canada, all capturing real-time data of creatures living in the area. The researchers wanted to learn if the fish in the canyon behaved differently around bait in the presence of artificial lights. "Some are attracted, and some avoid it," Héloïse Frouin-Mouy, a marine biologist and bio-acoustician specializing in marine mammals at the University of Miami, wrote in an email. The observatory had both video and acoustic cameras to monitor the behavior of fish with the lights on and off.
Rodney Rountree, a marine biologist specializing in ichthyology at the University of Victoria, was watching the footage when he noticed something strange—"a clawed 'hand' swooping down from the top of the screen," Rountree wrote in an email. "That's all I saw." To Rountree, the clawed hand looked just like the Creature from the 1954 film Creature From The Black Lagoon, a movie he watched as a kid. "However, after a few seconds I assumed it must have been a seal," he added.
As Rountree watched more of the videos, he saw several, increasingly unmistakable seals. Some stared directly into the camera as if they were showing off. The sight of an elephant seal at a deep-sea observatory seemed rare, and he reached out to Frouin-Mouy to see if she would write a short note on the observation. "Little did I know that the elephant seals would be so common at the site and that we would learn so much about their behavior," Rountree said. Their subsequent paper was recently published in PLOS One.
When Frouin-Mouy looked at the footage, she was thrilled. Northern elephant seals are absolute behemoths; males can grow longer than 13 feet and weigh nearly 4,400 pounds. When a male reaches puberty, he develops a floppy nose that he can inflate during mating displays. His neck thickens for protection during the many fights he will have with other male seals. But the males Frouin-Mouy saw onscreen had not yet grown into their noses. "The footage captured sub-adult male northern elephant seals, about which very little is currently known," she said.
Scientists actually know a great deal about elephant seals in general because the mammals are often scientists themselves, swimming around the ocean with a biologger or tracking device affixed to their heads. The seals migrate enormous distances twice each year, swimming from the beaches of California and Mexico, where they molt and breed, to their feeding grounds in the northern Pacific Ocean. And they dive as deep as 5,000 feet. But this research work is often given to female elephant seals, are they are easier to find and handle and more likely to survive. So no one knew much about where young male northern elephant seals hunted or what they ate.
Frouin-Mouy identified eight different boy seals from the footage, six of whom returned to the observatory multiple times. Each seal had distinct body marks and scars, as well as eyeliner-like markings that accumulate around their eyes while at sea. "In a playful nod to where these mammals are most often studied and observed onshore, I decided to name them after members of the Beach Boys," Frouin-Mouy said. So the roving seals became Brian, Dennis, Carl, Al, Mike, David, Blondie, and Bruce. (There was no ninth elephant seal to be named Ricky.)
The seals were not showing up at the observatory for a single sardine, however chunky, but rather the fishes that flocked to the contraption. "Sablefish and other fishes are strongly attracted to structure so even without bait, the observatories attract many fishes," Rountree said. And although some fishes fled when the LED lights of the observatory crackled to life, sablefish became even more attracted to the site. But the seals spent the most time around the observatory when the noise was emitted from the acoustic imaging sonar hydrophone, suggesting the seals had learned to associate the sonar noise with a banquet of fishes—like hearing a dinner bell and swimming over to feast.
Seals Al and David, both about six years old, only showed up once, with Al arriving on the scene in October and David popping up later in December. Mike, a seven-year-old seal, was the most loyal visitor to the site, returning nine times over the course of about a month. Many of the videos record the seals hunting sablefish, both successfully and unsuccessfully. One recording captured Dennis inspecting and then ignoring a snailfish, which is a very gelatinous fish. A later video recorded Dennis accidentally catching a snailfish instead of a sablefish and immediately spitting out the seemingly yucky morsel. "This is intriguing, considering these animals are known to sometimes consume hagfish despite their intense slime production," Frouin-Mouy said.
Before Dennis catches the snailfish, he can be seen bobbing his head. The observatory recorded low-frequency signals almost every single time the seals were seen head bobbing, and the researchers speculate the seals may be producing these sounds to startle their prey. Rountree was surprised that none of the sablefish made any noises upon being attacked, or even eaten. Researchers have recorded sablefish sounds in captivity, and some hypothesized the fish make such sounds in response to threats. "You don’t get more threatening than an elephant seal chasing you!" Rountree said. "Still no sounds."
Some seals hovered into view while taking a brief nap.
A recent paper in Science revealed the extreme sleep schedules of northern elephant seals, which fall into deep REM sleep while gradually plummeting into the deep. The seals sleep and sink for about 10 minutes, then swim back to the surface. It sounds frightening, but the deep sea is a much safer place for the seals, beyond the reach of surface-dwelling orcas and white sharks.
Still, the fact that so many seals were able to find and return to the observatory is somewhat of a navigational marvel. "We’re still puzzled by how these seals managed to locate such a small site in the vast open ocean, in complete darkness, and on multiple occasions," Frouin-Mouy said. The researchers suspect the seals rely on a combination of tools—listening for acoustic signals of the sonar signal, watching for visual cues of the LED, and sensing magnetic fields.
But the videos make it clear that, in the waters around the observatory, the eating was good. Sablefish, which can grow longer than three feet and live up to 90 years old, brim with omega-3 fatty acids. They are sumptuous food for both seals and people, many of whom also refer to the fish as black cod. Although we may dream of it, no human will ever know the taste of a sablefish as fresh as the ones gulped down by Brian, Dennis, Carl, Al, Mike, David, Blondie, and Bruce. But wouldn't it be nice!
