The deep ocean is a dark region, but deep-diving seals can easily identify their prey in it. Using field study, a multinational research team has gained a deeper understanding of how seals employ their whiskers to locate prey.

The findings of the team were reported in the Proceedings of the National Academy of Science.

Bioluminescence, the light that some organisms carry in their bodies, provides light in deep ocean regions where no sunlight reaches. However, the amount of light produced by bioluminescence is quite limited. Toothed whales may hunt in these dark waters by employing active biosonar, often known as echolocation, to locate their prey. Deep-diving seals also hunt in these waters. However, they lack the active sonar that whales use to aid in hunting.

The researchers theorized that the seals use their well-developed whiskers to find prey.

Most mammals, unlike humans, have vibrissae, or moving facial whiskers. Vibrissae is derived from the Latin word “vibrio,” which meaning “to vibrate.” It emphasizes the reception of vibration information and is used to characterize the seals’ whiskers. Due to the difficulties in studying whisker movement in a mammal’s natural surroundings, researchers have been unable to fully comprehend the natural movement and function of their face whiskers until now.

Previous research had used single whiskers, artificial models, or captive animals in experimental settings. The group wanted to find out how seals use their whiskers in the deep ocean, where they live. The researchers fitted small video loggers to free-ranging female northern elephant seals, selecting elephant seals for their very sensitive whiskers. The quantity of nerve fibers per whisker in these seals is the highest of any mammal. The video recorders were installed on each seal’s cheek to examine how it moved and used its whiskers in front of its mouth.

The researchers used video loggers to observe the elephant seals hunting in the harsh habitat of the deep, dark ocean. An LED red/infrared-light flash was included with the video logger. This light was invisible to the seals, but it let the researchers to monitor how they use their whisker as they approach their prey in a non-invasive way. The cameras revealed that the seals were able to capture their moving prey by detecting the movement of the water. The seals used rhythmic whisker movement—protracting and retracting their whiskers—to hunt for hydrodynamic cues with their whiskers stretched forward front of their mouth, similar to how a terrestrial mammal investigates its environment.

The researchers took into possibility that the light produced by bioluminescence in some animals could aid seals in their hunt for food. But their research shows that even though bioluminescence is important, seals mostly use their sensitive whiskers to find their food.

Seals use their whiskers to hunt for, pursue, and catch 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,” added Taiki Adachi, Project Researcher at the National Institute of Polar Research / Assistant Project Scientist at the University of California Santa Cruz.

This research complements previous captivity-based studies on mammalian whiskers and advances the subject of the sensory ecology of foraging.

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

Image Credit: Getty

You were reading: New Research Solves A Decades-long Mystery About Deep-diving Seals