Seal Navigation: Right Under Their Noses

July 23, 2001

Animals that live in the water cannot depend on their eyes to find food and avoid objects. These animals need to use other sensory abilities because their environment is often dark and cloudy. Fish have a lateral line system to sense small changes in water pressure, and dolphins use echolocation to find their way. Sharks can detect small electrical signals in the water to find prey. New research provides clues to how seals navigate and find food: they use their whiskers!

When fish swim, they disturb the water and leave a wake behind. Scientists at the University of Bonn and Ruhr University Bochum in Germany wanted to know if harbor seals could detect this underwater wake. Instead of using fish, the scientists used a small submarine to create an underwater trail and trained two harbor seals to chase it. After the seals learned to find the sub, they were outfitted with headphones to eliminate sound and blindfolded to eliminate light. After the sub was launched, its motor was turned off and the seals' headphones were removed. The blindfolded seals then had to find the sub.

When a seal began its search, it extended its whiskers (called "vibrissae") to their most forward position. The seal also moved its head back and forth slightly. When the seal intersected the sub's water trail, it followed the sub. The seals found the sub in approximately 80% of the trials. When the seals failed to find the sub, it was most often because they never found the trail, not because they went off course. Furthermore, when the seals wore a stocking mask that covered their vibrissae, they were never able to locate the sub.

A final experiment investigated how the seals located the sub when it changed course. If the seals used sound to locate the sub, they should have taken short cuts to go directly to the sub after it made a course change (see figure on the left). However, the seals did not take any shortcuts. Rather, they followed the entire course of the sub and turned where the sub turned.

These experiments strongly suggest that the seals use their vibrissae to track moving underwater objects. Water currents set up by an object, such as a fish, move the seal's vibrissae. This movement causes activity in nerve fibers attached to the vibrissae. The neural activity is then sent to the seal's brain where it is analyzed. Finally, signals are sent from the seal's brain to control its movement and to help the seal find the object. This arrangement allows the seal to hunt successfully in dark, murky water.

This research gives you a good reason why you should never play "Marco Polo" with a will find you everytime!

Harbor Seal Brain
Image from the Mammalian Brain Collection


  • Dehnahardt, G., Mauch, B., Hanke, W. and Bleckman, H. Hydrodynamic trail-following in harbor seals (Phoca vitulina). Science, 293:102-104, 2001.

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