The thought of hunting in complete darkness, hundreds of feet below the surface, with no light, no landmarks, and no real idea of where your next meal might be, is almost unsettling. Most animals don’t fare well in that situation. It’s just another Tuesday for the northern elephant seals off the coast of California.
In search of lantern fish and squid, these creatures frequently dive past the 1,000-foot mark, entering an area where sunlight just vanishes. For years, scientists were unsure of how they had discovered anything at all down there. It turns out that the solution was always right in front of them.
A decades-long puzzle may have been solved by a 2022 study that was published in the Proceedings of the National Academy of Sciences. Five free-ranging elephant seals in the vicinity of Año Nuevo State Park in California were fitted with tiny infrared video cameras by a team under the direction of Taiki Adachi, a marine ecologist at UC Santa Cruz. More than nine hours of deep-sea video were returned, and it provided an incredibly clear image of how these creatures actually hunt.
The video revealed something that scientists had only hypothesized about in captivity. The seals pushed their whiskers out in front of the muzzle and swept them rhythmically back and forth as they descended past the depth at which foraging starts, resembling hands reaching into the darkness. The whiskers retracted as they ascended again. The seals appear to know exactly what they’re doing and when, as evidenced by the behavior that flipped on and off like a mode change.
In terms of structure, seal whiskers differ from cat whiskers. The majority of mammals have round, smooth whiskers. The wavy, flowing ones of seals are important. The whisker’s uneven surface helps a swimming seal stay steady against the water’s resistance; movement alone does not cause it to vibrate. It only reacts to outside disruptions. A fish moving through the water creates a hydrodynamic wake, which is a trail of pressure variations and microcurrents that lasts for a few seconds. In a way, the seal’s whiskers are tuned to detect precisely that signal. In controlled environments, researchers have discovered that seals can follow the trail of an object that has already swum past and detect movement from a distance of more than 100 meters.
A seal by the name of Filou is mentioned in this context so frequently that it almost seems legendary. He lost the ability to track prey almost immediately after scientists fitted him with a nylon stocking over his whiskers to block sensory input. His ability returned as soon as the covering was removed. The demonstration was as clear-cut as science typically gets.
Although the Año Nuevo footage revealed that bioluminescence—the faint chemical light that some creatures emit—was present in only roughly one in five successful hunts, it does play a small part in deep-sea hunting. The seals were using only touch for the remaining 80%. Not audible. Not vision. In the dark and cold, touch at depth.
It’s worth taking a moment to consider that. It is truly hard to put into human terms what elephant seals are doing—reading the ghost of a fish’s movement through water, in the dark ocean, more than a kilometer below the surface. Feeling someone’s footsteps on a wooden floor after they’ve left the room might be the closest analogy.
Co-author Daniel Costa, a marine biologist at UC Santa Cruz, put it simply: “Their whiskers are almost like hands reaching out in front of them.” Adachi compared it to rodents, pointing out that rats use their whiskers to detect air movement in a similar basic manner. Seals, on the other hand, whisk much more slowly because water is denser.
The finer mechanics, such as how the brain precisely translates whisker vibration into a sense of location, direction, and prey size, are still being worked out by researchers. Additionally, there is conjecture—which has not yet been verified—that seals may be able to actively transmit and receive vibrations through their whiskers, which would be more akin to an active sensory system than a passive one. Ben Burville, an underwater cameraman at Newcastle University who has spent decades documenting seal behavior, has seen seals purposefully vibrate their whiskers and thinks there might be more going on than has been confirmed by researchers.
It is evident that these animals developed an amazing solution to a problem for which there is no obvious answer: how to locate food in an area where vision is impossible. And for longer than anyone was paying close enough attention to notice, they have been operating covertly just off the coast of California.
