“His delights were dolphin-like; They showed his back above The element they lived in.”
Shakespeare in “Antony and Cleopatra“
This is how the Egyptian queen indicates her appreciation of Antony, to describe the manner in which the latter could enjoy the pleasures of life, as if to the manner born.
Throughout America, there are huge aquariums in which trained dolphins perform various tricks like walking on top of their flukes( tail) on the surface of the water, leaping, diving and playing with balls. The tricks are learned by repeatedly being rewarded for success.
However the dolphin’s friendly and playful behaviour is in sharp contrast to its diabolical behaviour in the seas.
Everyday somewhere in Neptune’s empire, in the wine-dark seas near New Zealand, or in the warm waters off the coast of Southern California, a dolphin moves like a torpedo in the inky depths below, in hot pursuit of a shoal of fish, its favourite food. But slowly and surprisingly, the fleeing fish suddenly break formation and begin to swim about in a chaotic and disorganised fashion. Taking advantage of this confusion, the dolphin moves in at an accelerated pace and swallows as many fish as possible. It then rises to the surface for a breath of fresh air and dives back into the deep for more food.
Scientists have long wondered how the dolphin is able to locate the food in the darkness under the oceans surface and why, after a hot pursuit, the fish suddenly give up their protective formation and give themselves up to the dolphin. After years of research, they found that a dolphin locates fish by emitting ‘sonar’ signals that bounce off the fish and are picked up by its supersensitive hearing organs.
Dolphins do of course also use their eyesight for’ hunting. In fact, they can jump 20 feet into the air to grab a fish. Deep inside the sea where light does not penetrate dolphins can locate their victims with the help of echoes just as bats do. A blindfolded dolphin can ‘echo locate’ a small coin tossed into the water 40 feet away and catch it in its mouth even before the coin reaches the bottom. Human beings would naturally be tempted to think of such feats as mere animal tricks, but one must learn to appreciate that dolphins have developed this amazing capacity to hear out of a sheer necessity for survival. The water in which they live does not permit great use or exploitation of the visual mechanism except at short distances. Hence, dolphins have to depend to a large extent on ‘hearing’. A dolphin that cannot locate its prey in the dark would end up starving. According to one theory, some dolphins may hunt only at night when vision is practically inoperative.
Scientists have only recently been able to understand the manner in which dolphins can echo locate objects. Marine biologist Kenneth Norris observed as early as four decades ago that a blindfolded dolphin was able to swim through a maze of threads by detecting and avoiding threads as small as 2 mm in diameter. Dolphins give out a steady clicking sound while swimming. A dolphin uses frequencies of about 2,00,000 vibrations per second, comparable to those used by a bat. The frequency of the clicks picks up as the animal approaches an object. When the clicks bounce back, they indicate the direction of the object and the time they take to come back gives the dolphin an idea of the object’s distance. It can also estimate the rate of approach or retreat and the approximate size of the object as well as the nature of the object.
Dolphins emit and also hear sounds on a much higher frequency range than humans can. High-frequency sounds are more easily discernible under the noisy sea than low-frequency sounds. As many of the dolphins’ sounds are beyond the human hearing range, scientists are only now in a position to listen in on a sound world never heard before with the help of special equipment. It is known that apart from the ultrasound, dolphins make different kinds of noises.Twenty different sounds that they make have been identified so far. These include sounds that serve to keep a group together while travelling, call signs that facilitate recognition of individual animals and also warning cries. But no one has yet shown that dolphins like chimpanzees put sounds together to form the equivalent of the two word sentences that can be regarded as the beginning of language. Scientists speculate that the dolphin produces the ultrasound with the larynx and the ‘melon’, i.e. the large cushion of fatty tissue on the dolphin’s forehead.
The second phenomenon that has long baffled scientists is the virtual surrender and total disorientation of the fish while pursued by a dolphin. Some scientists had been inclined to believe that after a long chase the fish become too exhausted for further swimming. A new hypothesis may, however, solve the mystery. The origin of this hypothesis can be traced back to a paper on whales published several years ago by two Russian cetologists (experts on whales, dolphins and porpoises). They suggested that the sperm whale might be able to use its great nose to somehow project sounds loud enough to stun its prey.
Another Russian scientist suggested subsequently that when squid and fish are located, the sperm whale’s ultrasonic beam narrows and focuses on them. Then its frequency sharply increases and the prey is stunned. The sperm whale has to hold its breath for about half an hour to operate at great depths in sea. Sperm whales pick up speed and then plough along the ocean bottom, picking up stones and other objects as well as small sea creatures—a food gathering method which does not exactly appear productive!
But if one realises that the whale generates high intensity sonic impulses, it becomes possible to postulate that these impulses have a stunning and disorienting effect. This could mean that the animal ploughs its way along the sea as it expects to find lying on the floor, and waiting to be harvested, the fish that it has earlier stunned or killed.
Two scientists in the United States who happened to read the paper of the Russian scientists on whales began to entertain the possibility that the sonic pulse theory might equally apply to dolphins, which can be regarded as small frisky whales. One of them once noticed that a group of fish being hody chased by dolphins did indeed gradually lose escape reactions. The wandering fish were easily scooped up with a net. Later, experiments involving the use of artificial sound also indicated that sonic frequencies can, in fact, have a disorienting effect on fish. Some divers near Argentina have noticed anchovies being pursued by dolphins but paying no attention to them and appearing totally disoriented, indicating that they may well have been affected by high frequency sounds emitted by dolphins which, however, could not be heard by the divers.
There is some evidence to show that though the high frequency sounds emitted by dolphins cannot be heard by human beings they can be ‘felt’, at least under some circumstances. Some divers have experienced feather-like touches on the back of their necks while swimming underwater among dolphins. They are of the opinion that the touches are actually the feeling of the dolphins’ sonar or sound signals being bounced off their necks.
It is universally accepted that dolphins are friendly and intelligent creatures.The sight of a dolphin jumping through hoops and giving aquarium employees rides on their backs is familiar to people. But several mysteries regarding dolphins are yet to be explained. For example: (i) Why do dolphins race alongside boats or and swim inshore and allow bathers to embrace and stroke them? (New Zealand’s famous dolphin named Pelors Jack used to come out to great steamships as they passed through Cook Strait between North and South Islands.This dolphin, which became a tourist attraction, would actually dance about in front of the steamer appearing to guide it through the channel like a pilot boat.) (ii) Do dolphins seek out ships because they like the throb of the engines? (iii) Do dolphins view visitors to beaches as a potential source of food handouts? (iv) Why do some dolphins leap into the air and spin on their longitudinal axes about four times before they plunge back into the water? (v) What did dolphins look like when they were land animals before a change in the environment forced them back into the sea?
The coming decades will lead to more discoveries about the dolphins which will probably solve many such mysteries. One cannot but conclude that dolphins are truly marvels of nature’ s engineering. A proper understanding of their communication techniques, particularly their ability to call each other by specific names as indicated by their whisdes, a recently discovered phenomenon and navigational skills can be of immense practical use. For instance, the echo location principle has been adopted in designing the SONAR (sound navigation and range) apparatus for locating the position and assessing the depth of submerged objects in the seas and oceans.