More to a Dolphin Than Meets the Eye

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It was dark and stormy when the ship Brindle approached the French Pass off the coast of New Zealand. The ship was bound for Sydney, Australia. The ship’s captain had decided to take a shortcut. He would steer his ship through, rather than around, the D’Urville Island. The sailors knew that this route was a risky one, filled with dangerous currents and hidden rocks. But they had been willing to take the risk to save time. No one had counted on a storm at sea to double the danger.

Suddenly a dolphin was seen leaping out of the water. Some of the sailors wanted to kill it, but luckily, they were stopped. The dolphin seemed to be showing a safe route through the channel. With little besides luck to guide his ship safely to its destination, the captain decided to follow the dolphin. Days later, the Brindle arrived in Sydney, thanks to a willing captain and a lone dolphin.

This true story illustrates one of the dolphin’s most amazing abilities – echolocation. As the word itself suggests, echolocation is a way of locating objects by listening for the echo of sound signals.

Here is how echolocation works. First, the dolphin sends out a series of sound waves ahead of it. If the sound waves hit an object such as a rock or a fish, they bounce back to the dolphin. Otherwise, the sound waves keep moving through the water. When the sound waves bounce back, the dolphin hears them and knows that something is ahead. If they don’t bounce back, the dolphin knows that its path is clear.

Arthur McBride was the first to recognize that dolphins use echolocation. He made his discovery in 1947 with the help of some fishing nets. McBride had been trying to capture dolphins off the coast of Florida. As a curator of the nearby Marine Center, now called Marineland, he wanted to exhibit them to the public.

McBride had already spent several days trying to lure the dolphins into his fine mesh nets. He worked during the day. He worked at night. He even worked in dark waters where the dolphin couldn’t possibly see his nets. No matter where or when he worked and no matter how he arranged his nets, McBride couldn’t catch a single dolphin. Finally, he switched to nets that had wider mesh. Only then did he succeed.

Later, he asked himself why one kind of net worked well, while another kind didn’t work at all. Then the answer came to him. The dolphins weren’t relying on their sight to avoid his nets.

They were relying on echolocation. McBride reasoned that most sound waves would bounce back from the fine-meshed nets. These echoes would then warn the dolphins away. But the wide-meshed nets would have just the opposite effect. Most sound waves would pass through the large holes in these nets. Thus the dolphins would hear few, if any, echoes, and they would not be warned away.

Since 1947, scientists have learned more about dolphins. It seems that these sea mammals are always making sounds. Their sounds may be low. Or they may be so high that people cannot hear them.

Dolphins have a larynx, or voice box, just like other mammals. But their voice box does not contain vocal cords. Instead, it has pockets of air in it. Dolphins probably make sounds by manipulating or vibrating these air pockets.

These sounds are controlled by an organ on the dolphin’s forehead. This organ is called a melon. It works with sound in much the same way as the lens in a camera works with light. The melon focuses the sound into beams or waves. It then sends these waves out into the water in front of the animal. When the dolphin moves its head right and left or up and down, the sound waves also move. By changing position in this way a dolphin can figure out the exact size of an object - even if the object is almost a kilometer away.

Dolphins seem to enjoy performing for the public. And they and other sea mammals do so at marine shows each year. People are continually amazed to see a dolphin recover a tiny stone from the bottom of a huge pool. Some dolphins have even been known to rescue lost divers. A super sonar system helps them accomplish all these feats.

Dolphins are also patient animals. This makes it easy for scientists to study them. Knowledge gained from these studies is being used in many ways. For one thing, sonar devices for blind people are now being used. These devices are based on echolocation. If dolphins can navigate by using sound instead of sight, researchers ask, why can’t people? Instruments that give off sound waves can warn users of objects in their path.

As their research continues, the scientists who study dolphins and other sea mammals are likely to uncover more interesting facts. Perhaps some of the findings will prove helpful to people. Whatever is found, it’s already clear that there is a lot more to a dolphin than meets the eye or the ear.