A seal’s whiskers, scientifically known as vibrissae, are an active and sensitive sensory system. In the dark and murky underwater environments where seals hunt, these whiskers provide a sense of “touch” that extends far beyond the animal’s face. They allow seals to perceive their surroundings with great detail, functioning as a tool for locating food and understanding the underwater landscape when vision is limited. This sensory capability is fundamental to their success as marine predators.
The Unique Structure of Seal Whiskers
The effectiveness of a seal’s whiskers begins with their physical form. Unlike the smooth, tapered whiskers of many terrestrial mammals, those of a harbor seal have a wavy or beaded structure. This undulated shape is consistent along the length of the whisker. The cross-section of each whisker is oval rather than round, a design that contributes significantly to its function in water.
These whiskers are composed of keratin, but their complexity lies within the follicle at their base. Each whisker is embedded in a blood-filled tissue capsule, known as a blood sinus, surrounded by a dense network of nerve endings. A harbor seal’s whisker is connected to as many as 1,500 nerve cells, far exceeding the 200 nerve endings at the base of a cat’s whisker. This extensive innervation makes the whisker system highly sensitive.
The vibrissae are arranged in a precise grid-like pattern on the seal’s muzzle, allowing for comprehensive spatial awareness. This ordered arrangement ensures that the seal receives a detailed picture of the tactile stimuli in front of it. The combination of the beaded shape and the highly innervated follicle makes the whisker an exceptional sensory organ for its underwater tasks.
How Seals Hunt With Whiskers
When a fish swims, it leaves behind a disturbance in the water, a wake known as a hydrodynamic trail. Seals use their whiskers to detect these invisible trails, allowing them to hunt effectively in complete darkness. Studies have demonstrated that blindfolded seals can successfully follow the path of a fish or a miniature submarine by sensing the water movements left behind, sometimes seconds after the object has passed.
The undulated structure of the whiskers makes this feat possible. As a seal swims, its shaped whiskers cut through the water without significant vibration. This stability prevents the seal’s own movement from creating “noise” that would interfere with its ability to sense external disturbances. The wavy design neutralizes the swirling vortices that would form behind a smooth object, keeping the whisker still.
This system is so precise that a seal can determine not just the presence of a trail, but also glean information about the size and speed of the fish that made it. By analyzing the characteristics of the water disturbance, the seal can build a mental image of its prey’s recent movements. This allows it to follow and capture fish it cannot see.
The seal holds its whiskers in a forward, extended position to maximize this detection ability. Unlike rodents that actively sweep their whiskers back and forth, seals maintain a steady posture with their vibrissae while swimming. This stationary positioning enhances their sensitivity to the faint hydrodynamic signals that betray the location of a potential meal.
Exploring the Environment With Whiskers
Beyond tracking moving prey, seal whiskers serve as a tool for exploring the physical environment. Seals frequently engage in benthic foraging, searching for food on the seafloor. They use their whiskers for direct tactile exploration, pressing them against objects to determine their shape, size, and texture. This allows them to identify stationary food sources like shellfish and crustaceans.
This form of active touch provides information for navigating complex underwater terrain. By feeling the contours of rocks, crevices, and the composition of the seabed, a seal can create a detailed mental map of its surroundings. This is useful in dark or turbid waters. The whiskers function much like fingertips, helping the animal avoid obstacles and locate foraging spots.
The sensitivity of the whiskers allows for fine discrimination between different surfaces and objects. A seal can distinguish between a rock and a potential food item based on subtle textural differences. This tactile sense complements their other senses, giving them a more complete understanding of their world. Whether hunting or exploring, the whiskers are constantly gathering information.