Image: Courtsey of GUIDO DEHNHARDT, University of Bochum, Germany |
Marine mammals are often forced to find food in dark or turbid waters, where visibility is greatly reduced. Some creatures, such as dolphins, resort to echolocation. But others¿among them seals¿lack that ability. Now researchers at the University of Bonn and Ruhr-Universit¿t Bochum in Germany have discovered how seals locate prey when they can't see: they follow their whiskers.
In a study published in today's Science, Guido Dehnhardt and his colleagues used two trained male harbor seals¿named Henry (right) and Nick¿to show that a seal's whiskers are sensitive to the trails left behind swimming objects, such as fish, over long distances.
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The scientists first trained both seals to locate a small propeller-driven submarine. At the start of the experiment, they blindfolded the seals, covered their ears with earphones and held their heads above water as the submarine traveled underwater. When the submarine engine switched off, they removed only the seals' earphones, signaling to them to begin their search.
In a pool filled with naturally turbid seawater, Henry found and directly followed the submarine's trail almost 80 percent of the time. When his whiskers were covered with a stocking mask, though, he was unable to locate the submarine at all. Nick, who was in a freshwater pool, had a similar overall success rate and also failed to locate the submarine when his whiskers were covered. The results suggest that whiskers, and not visual or audible clues, lead seals to their prey.
The scientists propose that seals may be able to detect a swimming herring that is more than 335 feet away. "However, for a reliable estimate," they write, "we need to learn more about background noise in the wild as well as the aging of fish-generated trails under natural conditions."
