When in the deep, dark ocean, seals use their whiskers to stalk prey, a study has confirmed after observing the marine mammals in their natural habitat.
Light struggles to penetrate the darkness of the ocean depths, and animals have found a variety of adaptations to live and hunt there. Whales and dolphins, for example, use echolocation – the art of sending clicking noises through the water and listening to their echo as they bounce off possible prey, to locate them. But deep-diving seals that lack these same acoustic projectors must have learned through evolution to deploy another sensory technique.
Scientists have long speculated that the secret weapons were their long, cat-like whiskers, conducting more than 20 years of experiments with artificial whiskers or seals captive blindfolded in a swimming pool, given the difficulties of direct observation of hunters in the dark depths of the ocean.
Now a study may have confirmed the hypothesis, according to Taiki Adachi, assistant 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. Sciences..
Adachi and his team positioned small video cameras with infrared night vision on the left cheek, lower jaw, back and head of five free-ranging northern elephant seals, the Mirounga angustirostris, in Año Nuevo State Park in California. They recorded a total of about nine and a half hours of deep sea imagery during their seasonal migration.
Analyzing the videos, the scientists noted that the diving seals held their whiskers back during the first part of their dives, and once they reached a depth suitable for foraging, they rhythmically swept their whiskers back and forth. back, hoping to detect any vibration caused by the slightest water movements of swimming prey. (Elephant seals like to snack on squid and fish and spend a lot of time at sea.) Then, when they returned to the surface, the whiskers curled up again towards the face.
For less than a quarter of the time the seals hunted, they could also see bioluminescence – the light that some deep-sea creatures can emit thanks to chemicals in their bodies – to track their meals using view. But for the remaining 80% of their hunt, they probably only used their whiskers, according to Adachi. This technique is no different from rodents, Adachi noted. It’s just that because water is much denser than air, the whipping speed is much slower in elephant seals.
“It makes sense,” said Sascha Kate Hooker, a pinniped researcher at the University of St Andrews Marine Mammal Research Unit, who was not involved in the study. “Among deep-diving marine mammals, the elephant seal reaches the same depths as sperm whales and beaked whales, often well over a kilometer below the surface.”
Guido Dehnhardt, director of the Marina Science Center at the University of Rostock and a pioneer in mustache research who was not involved in the research, welcomed the results but was cautious about how much new information there is. they represented. “It was my group that showed more than 20 years ago that seal whiskers represent a hydrodynamic receptor system, and that seals can use it, for example, to detect and follow the hydrodynamic tracks of fish,” said Dehnhardt.
The study is particularly interesting from a technical point of view, especially with regard to the cameras used being so small, Dehnhardt said, but there is still too much speculation. “It would be a great story if the seals in addition to a front camera carried a hydrodynamic measurement system [a machine that can measure the movement of fluids] so that whisker movements and hydrodynamic events can be correlated.
In the future, Adachi would like to start comparing how other mammals use their whiskers, to better understand how the superpower of certain animals’ whiskers has shaped the foraging habits of the animal kingdom.