Researchers used an artificial fish in their experiment, to create a “trail” in the water that a seal could detect.
The described how a trained seal, named Henry, was able to indicate, with a twitch of its head, whether the fish moved to the right or to the left.
The team described the study in the Journal of Experimental Biology.
The study was led by Wolf Hanke of the Marine Science Centre at the University of Rostock, Germany. He explained how the seal wore a blindfold and headphones during the experiment to ensure that it could only pick up sensations from the water with its whiskers.
“The animals are actually enthusiastic to wear the mask because it means play time and [food rewards],” explained Dr Hanke.
He and his colleagues carried out the experiment in an open-air pool in a zoo in Cologne.
“We had a small box in the pool to achieve calm water conditions,” he explained. “The seal was trained to wait at a ball target and, when signalled, it entered the box.”
Inside the box, the scientists created a trail with their artificial fish, which was essentially a rubber fin on a stick that created a trail similar to the swimming motion of a real fish.
They operated the fin from outside the box, moving it from left to right or from right to left. The seal responded to the movement by turning its head in the direction that the fin had moved.
Hunting by whisker
The seal was able sense and indicate the direction in which the fin travelled up to 35 seconds after the movement had stopped.
“A fish can cover tens and hundreds of metres in that time, so whiskers compare well with the performance of whales and dolphins by echolocation,” Dr Hanke explained.
He believes that seals may also be able to “analyse” the structure of a trail to “work out” more about its source.
He and his colleagues have already embarked on experiments using different shapes of fin to create different water disturbances.
“They seem to be able to discriminiate between different shapes, which might even mean they discriminate between different species of fish,” he told BBC News.
“And we had a surprising result from an experiment with one seal following another,” he said.
“The trail left by the first seal was two metres wide, and the second, following seal was able to stay right in the middle of it, so it seems they can analyse the internal structure of a trail.”
The researchers are now embarking on experiments using live fish, to see how closely seals are able to follow their complex trajectory.