Mystery of how seals use their whiskers finally solved by hidden cameras

The exact purpose and mode of function of the numerous thick whiskers which seals have on their faces has long fascinated marine biologists, but has ultimately remained a mystery – until now.

In the deep sea, no light penetrates to the depths which deep-diving seals hunt, yet despite the total blackout they are still able to easily locate their prey.

Among ocean-dwelling mammals, seals’ dependency on whiskers is unusual. Deep-diving whales and dolphins use active sonar to help them hunt, and while some creatures are bioluminescent, the light they give off carries very short distances.

The research team, which represents institutions including the University of Tokyo, the University of California, and the University of Exeter, among others, hypothesised that seals heavily relied upon their whiskers to help them find their prey in the dark.

To study the seals the research team placed small cameras on the side of the heads of female northern elephant seals, which allowed them to see how the animals’ whiskers moved while on the hunt.

These seals have the highest number of nerve fibres per whisker of any mammal.

Seals’ whiskers are similar to many other species of mammals’ whiskers, in that they are highly mobile, and can be controlled by the animal.

These kinds of whiskers are known as "vibrissae", which comes from the Latin word "vibrio" which means "to vibrate".

With the video cameras, the researchers observed the elephants seal foraging in the extreme environment of the deep, dark ocean.

The cameras were equipped with an LED red/infrared-light flash. This light was not visible to the seal, but it allowed the researchers to non-invasively observe how the seals use their whiskers as they approach their prey.

The cameras showed that the seals captured moving prey by sensing the water movement. With their whiskers extended forward ahead of their mouth, the seals performed rhythmic whisker movement – protracting and retracting their whiskers – to search for hydrodynamic cues, similar to the ways a terrestrial mammal explores its environment.

The research team said they took into consideration the possibility that light provided by the bioluminescence in some prey might help the seals in their hunt for food. But they said their findings reveal that while bioluminescence is important, the seals’ sensitive whiskers are the primary method they use to find their prey.

“Our findings solve a decades-long mystery about how deep-diving seals locate their prey without the biosonar used by whales, revealing another mammalian adaptation to complete darkness,” said Taiki Adachi, the project researcher at the National Institute of Polar Research and an Assistant Project Scientist of University of California Santa Cruz.

The team said their research in the field complements earlier whisker studies conducted on mammals in captive conditions.

“The next step is conducting comparative field studies on other mammals to better understand how whisker-sensing shapes natural behaviour in each mammalian species under different environments,” said Dr Adachi.

The research is published in the Proceedings of the National Academy of Sciences.