Some species of dolphins and whales adapted to the new environment by evolving echolocation, which allows them to "see" with their ears. How other marine mammals manage to hunt without echolocation has long been a mystery, though. A clue came from earlier studies by several researchers, which showed that seal whiskers are remarkably sensitive to even the slightest bending.

To test whether seal whiskers can detect the kinds of turbulence created by passing fish, Guido Dehnhardt of Ruhr University Bochum in Germany and his colleagues trained two harbor seals to chase a miniature, propeller-driven submarine. After the seals had learned the task, the team placed a mask over their eyes and headphones over their ears before launching the sub. After shutting off the sub's motor to eliminate acoustic clues, the researchers removed the headphones and allowed the blindfolded seals to begin their search. Even without the use of their eyes, the seals quickly began tracking the sub. Several lines of evidence suggest that the seals were relying solely on their whiskers. They closely followed the wake of a sub taking a curving path, even though sound waves and electrical fields would have guided them in a straight line instead. Moreover, once a seal found the sub's wake, it lost it in only 3% of the trials. When the researchers masked the seals' whiskers, they failed to find the sub, the researchers report in the 6 July issue of Science.

The work is "a huge step forward in pinniped foraging behavior and ecology," says Markus Horning of Texas A&M University in Galveston. It can explain some of the observations that Horning and his co-workers have made of Weddell seals hunting under the antarctic ice (Science, 12 February 1999, p. 993). Cameras placed on the back of the seals showed them swimming along curving paths just before catching fish. "The path that the seals take is what we'd expect if they were following a hydrodynamic trail," says Dehnhardt.

--CARL ZIMMER