I can “see” you with my whiskers
Hydrodynamic tracking in seals
Just imagine you are a seal under water - how does it look like? Do you see crystal clear, turquoise waters in your mind, with colourful tropical fish and sun beams breaking through the water surface? You should keep this in mind when planning your next holiday, but the reality often looks quite different: Seals often hunt for fish in dark, muddy waters with very low visibility and even though they have good eye sight, it doesn’t help them much when they are looking for prey. Many marine mammals overcome this problem by using sound and their hearing. Dolphins for example produce sounds (clicks) and listen to the reflection that is caused by objects and potential prey in their environment (echolocation). Seals don’t have this ability, though. So researchers were wondering for a very long time how seals are so successful at hunting their prey.
The results were stunning: Similar to fish, the submarine caused small movements in the water that functioned like a hydrodynamic trail. The seal used its whiskers (called vibrissae) to detect these water movements and to follow them exactly, as if on an invisible track. The vibrissae of harbour seals have a special surface structure (which looks wavy) to detect minimal changes in the water movement. Experiments with real fish have shown that a goldfish-sized prey can cause turbulences in the water that are detectable in the water column for a at least three minutes. So even in the murkiest of all waters, seals can detect their prey’s hydrodynamic movements with their vibrissae to catch their dinner.

Here is the video of the seal following the submarine’s hydrodynamic trail and the website of the Marine Science Center with more information about seal sensory systems.

Author: A. Loth
Illustrators: Dr. F. Hanke and A. Loth