When hunting for fish and squid, elephant seals use their whiskers to locate their prey in the deep sea, even in total darkness. Researchers report this in the specialist magazine “PNAS”. A field study has shown for the first time that seals can perceive the tiniest water movements of prey with their whiskers.

The deep sea is generally used to describe those areas of the sea that are not penetrated by sunlight and that are below a depth of at least 200 meters. For a long time it was unclear how seals hunt in this darkness: it was assumed that they were guided by the bioluminescence, i.e. the ability to generate light, which some of their prey have.

They found that at the beginning of their dives, the elephant seals kept their vibrissae tucked in until they reached the depth where their prey was. They then rhythmically moved the vibrissae back and forth during the hunt to look for hydrodynamic cues. In other words, they used their whiskers to sense the tiny water movements created by their swimming prey — similar to how land mammals explore their surroundings, the authors say. In fact, it is known from mice, for example, that they can sense the finest movements of air or water with their whiskers.

The bioluminescence of the prey, on the other hand, was only visible to the elephant seals in about 20 percent of the successful hunts. “Our results solve a decades-old mystery of how deep-diving seals locate their prey without the biosonar used by whales, and reveal another mammalian adaptation to total darkness,” said lead author Taiki Adachi of the University of California Santa Cruz in a statement together.

This investigation complements previous vibrissae studies conducted in captive mammals and advances the field of sensory ecology of foraging: “The next step is to conduct comparative field studies in other mammals to better understand how the vibrissae sense drives natural behavior of the individual mammalian species in different environments,” explains Adachi.