The Seals Whiskers

More than just dashing good looks

Text and photos by Judy Ann Newton

Live interviews are always challenging for a writer, especially when the subject has been the focus of a major scientific experiment. You want to ask the right questions, not appear too stupid and photograph the subject’s best side.

I had 101 questions rattling through my mind as I swished through the first colours of Autumn on my drive to Cologne, Germany to interview Nick and Henry. Sometimes, if you don’t hit it off with your subject in the first few minutes of the interview, the whole effort is wasted. I had no idea how Nick and Henry would respond to me, but I was committed to the interview.

The moment I first saw them, I was in love. They were surrounded by about 50 other adoring fans and cameras were clicking like cicadas in the fields. I wedged my way to the front row, and tossed out a warm and friendly, ‘Hello, Henry’ as he passed by. Henry stopped, reversed his track and faced me. I spoke again, and I was rewarded with a big, sloppy wet splash of Henry’s front flippers. Nick was jealous of the attention and quickly appeared from an adjoining pool. He flopped over onto his back; performed some radical pirouettes underwater, and I knew that the interview was going to be great.

Nick and Henry had become the stars at the Cologne Zoo since they had become the subjects of an experiment called ‘HydrodynamicTrail-Following in Harbour Seals.’ A team of scientists, led by Dr Guido Dehnhardt of the Ruhr University Bochum, had discovered some startling facts about seal whiskers with the assistance of Nick and Henry.

The big eyes and drooping whiskers of a Harbour seals are hallmarks of their charm and character, but it was long suspected that there were more than good looks related to the whiskers. Each seal has about 80 hair follicles, between 1,000 and 1,600 nerve fibres per hair and approximately 25,000 individual receptors to detect vibrations in the water.

These whiskers are so highly refined that they can sense water movement measured in millionths of a metre. Since 1998, scientists had known that these whiskers were used for obstacle avoidance and ‘touch discrimination,’ but could these whiskers detect fish vibrations left by passing prey, and at what distances?

Nick and Henry had been trained in the zoo’s large outdoor pools to follow a custom-made propeller driven mini-submarine. The sub was designed to simulate the ‘hydrodynamic trail’- the vibration trail – a fish leaves in its wake. For the experiments, Henry was taken to a pool that reflected the murky conditions so common to harbour seals as they forage for food. He was fitted with headphones and a blindfold and his head was held out of the water while the mini-sub was sent on an erratic course through the pool and out of sight. The sub’s motor was turned off, the headphones were removed and Henry was on his own, deprived of the sense of sight, sound and smell. The test was performed hundreds of times and the results were videotaped and recorded.

Henry located the submarine 256 out of 326 times, but what was more startling was that in video recordings, 80% of the time Henry followed the same curved or erratic path as the submarine. The sub had a wake trail that lasted only 30 seconds, while a fish will leave a wake trail that lasts for three to five minutes, or approximately the amount of time it takes a goldfish to travel 164 feet/ 49 metres.

When Henry was not allowed to begin his search immediately after the submarine completed its course, he was still able to track the submarine 24 out of 30 times. In only three percent of the runs did Henry lose the submarine’s wake, but he was able to track it from a distance of 40 metres (131 ft). To verify the theory that the whiskers were the ‘guidance system’ for the seal, Henry was fitted with a ‘snout’ sock or stocking mask over his whiskers. Henry failed to find the submarine’s vibrations 30 out of 30 times.

Nick underwent the same experiments, but in clear water and had the same results. One more test offered the seals some acoustic assistance from the sub’s motor. In 37 out of 45 runs, or 82% of the time, the seals followed the submarine path precisely. When they were released before the submarine’s motor had been stopped, they located the submarine 10 out of 10 times.

The tests have resolved that the whiskers, or vibrissae, normally vibrate in a certain pattern and when a fish trail is encountered, the alteration in the vibration alerts the seal to the wake of the prey. The tests also concluded that the whiskers were equally attuned in clear or murky water conditions, even when the prey is as far as 49 metres (164 ft) away.

According to Dr Dehnhardt, ‘previously it was thought that hydrodynamic reception works only in the millimetre to centimetre range. For seals this would mean that they could have used the whiskers in a sit-and-wait strategy, not more. Now we have shown for the first time that hydrodynamic information can be used for a long-distance object location.’

So what is next for the sub-aquatic Super Star Duo? The tests will continue on their range of detection. Dr Dehnhardt says that the next phase of the research will involve training live fish to create a course in the pools for the seals to follow. He also wants to test his theories in the open wilds of the sea to determine the greatest distance at which a seal can detect a fish. Dr Dehnhardt does not discount the possibility that a more active fish, such as a herring, might be detected from a range of 180 metres (591 ft).

While research will eventually lead Nick and Henry for a ‘holiday at the seaside,’ they continue their daily regime of training, eating, sleeping and splashing journalists. And they seem more than contented.

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