Seals use whiskers to track prey in the deep ocean, study shows

When in the deep, dark ocean, seals use their whiskers to track their prey, a study has confirmed after observing the marine mammals in their natural habitat.

It is difficult for light to penetrate the darkness of the ocean depths, and animals have devised a variety of adaptations to live and hunt there. Whales and dolphins, for example, use echolocation – the art of sending clicking sounds into the water and listening to their echo as they bounce off potential prey, in order to locate them. But deep-diving seals that don’t have the same acoustic projectors must have evolutionarily learned to deploy a different sensory technique.

Scientists have long assumed the secret weapons are their long, feline whiskers, who spent more than 20 years experimenting with artificial whiskers or blindfolded seals in a pool, given the difficulties of directly observing the hunters in the tenuous depths of the ocean.

Now a study may have confirmed the hypothesis, according to: Taiki Adachicassistant project scientist at the University of California, Santa Cruz, and one of the lead authors of the study published in Proceedings of the National Academy of Science Adachi and his team placed small video cameras with infrared night vision on the left cheek, lower jaw, back and head of five free-wheeling northern elephant sealsthe Mirounga angustirostris, at Año Nuevo State Park in California. They recorded a total of about nine and a half hours of deep-sea images during their seasonal migration.

Adachi and his team placed small video cameras with infrared night vision on the left cheek, lower jaw, back and head of 5 free-wheeling northern elephant sealsthe Mirounga angustirostris, at Año Nuevo State Park in California. They recorded a total of about nine and a half hours of deep-sea images during their seasonal migration.

Analyzing the videos, the scientists noticed that diving seals held back their whiskers during the early part of their dives and, once they reached a depth suitable for foraging, they rhythmically waved their whiskers back and forth, hoping feel some vibration caused by the slightest water movements of swimming prey. (Elephant seals like to eat squid and fish, and spend long periods of time at sea.) As they swim back to the surface, the whiskers curled back toward the face.

Less than a quarter of the time the seals were hunting, they were also able to see some bioluminescence — the light some creatures can emit deep underwater thanks to chemicals in their bodies — to track their meals with their sight. But for the remaining 80% of their hunt, they presumably only used their whiskers, according to Adachi. This technique is no different from rodents, Adachi notes. It’s just that since water is much denser than air, the beating rate is much slower in elephant seals.

“This makes sense,” said Sascha Kate Hooker, a pinniped researcher from the Sea Mammal Research Unit at the University of St Andrews, who was not involved in the study. “Of the deep-diving marine mammals, the elephant seal reaches the same depth as the sperm whale and the beaked whale, often more than a kilometer below the surface.”

Guido Dehnhardt, the director of the Marina Science Center at the University of Rostock, and a whisker research pioneer not involved in the study, welcomed the findings but was cautious about the amount of new information they represented. “My group had shown more than 20 years ago that the seal’s whiskers represent a hydrodynamic receptor system, and that the seals can use it, for example, to detect and track the hydrodynamic tracks of fish,” Dehnhardt said.

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The study is interesting technically, especially because the cameras used are so small, Dehnhardt said, but there’s still too much speculation. “It would be a great story if the seals carried a hydrodynamic measurement system in addition to a head-mounted camera [a machine that can measure the movement of fluids] so that whisker movements and hydrodynamic events can be related.”

In the future, Adachi plans to compare how other mammals use their whiskers to better understand how some animals’ superpowers shaped the foraging habits of the animal kingdom.

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