It’s the rare mariner who has watched dolphins frolic in a bow wave and not come away from the experience with warm feelings toward these delightful creatures. And over the centuries, dolphins have been credited with various extraordinary heroics, including rescuing mariners from tragedy. Even though there is little scientific basis for these claims, they represent one of the most intriguing aspects of dolphin-human relations. These facts are enough to justify a look at the habits and habitat of dolphins.
In the fourth century B.C., the Greek philosopher Aristotle was conducting detailed scientific studies of dolphins. While many, perhaps most, of his observations were factually true (“the dolphin is directly viviparous”), other conclusions displayed a distinct lack of appropriate intellectual rigor (dolphins, he wrote, “can leap over the masts of large vessels”). Subsequently, a few decades after Christ, Pliny the Elder expanded upon Aristotle’s scientific understanding by contributing the fact that dolphins prefer to be called by the name Simon. He also related the story of a boy from the town of Iasus who intimately befriended a dolphin, which gave him rides to school each day.
In the Middle Ages, “knowledge” of dolphins continued to accrue: by then it was generally understood that dolphins could determine, based purely on the scent of a dead man’s floating cadaver, whether he had ever partaken of dolphin meat. If the man was judged “clean,” the dolphins would nudge his body to shore. Otherwise, they ripped into his flesh and fed upon his corpse.
As Europe recovered from the Middle Ages, some critical thinkers dismissed the hoopla surrounding dolphins. By 1802, one scientist cantankerously argued that “dolphins certainly exhibit no marks of particular attachment to mankind. If they attend on vessels navigating the ocean, it is in expectation of plunder, and not of rendering assistance in cases of distress.”
Herman Melville discussed the significance of dolphin sightings in Moby Dick in regard to atmospheric pressure gradients. Dolphins, he wrote, “invariably come from the breezy billows to windward. They are the lads that always live before the wind.” According to Melville, dolphins “are accounted a lucky omen,” and if as a sailor “you can withstand three cheers at beholding these vivacious fish, then heaven help ye.”However accurate Mel-ville may be regarding the advisability of greeting dolphins with a trio of huzzahs, his reference to them as “fish” is a misconception. Dolphins, like all whales, are mammals. They are warm-blooded, give birth to live young, and breathe airunlike fish. To add to the confusion, sailors in Melville’s Moby Dick, like many mariners, refer to all dolphins as porpoises, reserving the name “dolphin” for a fish also known as a mahi-mahi or dorado. This confusion can be cleared up with some definitions. First off, there are two major groups, or suborders, of whales living on earth today: the baleen whales and the toothed whales. The term “dolphin” refers to small whales, specifically small, toothed whales. Dolphins are contained in the family Delphinidae. The term “porpoise,” on the other hand, also refers to small, toothed whales. The distinction is sometimes fuzzy, but porpoises generally are smaller than dolphins (porpoises range from about four to 7.5 feet long, whereas dolphins are anywhere from 4.25 to 12.75 feet long), have lower dorsal fins (although some dolphins and porpoises actually have no dorsal fin at all), live in coastal waters, are more shy, and tend not to ride bow waves. Also, dolphin teeth are conical, whereas porpoise teeth are spade-shapedbut normally you could only check out this trait if you found a dead animal.
At one time or another, most bluewater sailors have been accompanied by dolphins riding bow waves. Naval researchers have demonstrated that dolphins conserve energy through this behavior. The scientists outfitted two bottlenose dolphins with heart rate monitors and trained them to travel beside a boat, outside of the bow wave and the wake. When the animals swam at a speed of 6.5 feet per second, their pulses pounded at a rate of 76 times per minute. When the researchers increased boat speed to 9.8 feet per second, they found that, not surprisingly, the dolphins expended more effort to keep up. But when boat speed was increased even further, to 13 feet per second, the dolphins refused to cooperate with the experiment any longer. Despite commands to remain beside the boat, the dolphins wisely chose instead to enter into the waves of the boat’s wake, where they could travel rapidly through the sea but exert almost no energy. And so it would appear likely that dolphins ride bow waves as freeloaders rather than as guides; this would account for the frequency of maritime accidents despite the worldwide presence of dolphins.
Nonetheless, dolphins maintain a reputation for, upon occasion, saving people from drowning. If you should fall overboard, legend has it, or be plunged into the sea by a sinking ship, dolphins may swim to your aid and gently nudge you to the safety of shore. As best I can tell, there exists one recorded instance of this phenomenon actually occurring. In the middle of this century, a woman went swimming at a Florida beach. A strong undertow immediately began to suck her rapidly out to sea, despite her frantic efforts to stroke back to shore. She swallowed sea water and started to lose consciousness.
“With that,” she later wrote in a letter about the incident to Natural History magazine, “someone gave me a tremendous shove, and I landed on the beach, face down, too exhausted to turn over. I kept thinking that I must turn over and thank the person who helped me. It was several minutes before I could do so, and when I did, no one was near, but in the water about 18 feet out” a dolphin was leaping. Subsequently, a man ran down the beach and told the woman that he had seen the dolphin shove her limp body to shore. The editors of Natural History called it “the first personal account that has come to our attention of a [dolphin] behaving as legend has said it should.” But they also cautioned that “most students of animal behavior will probably explain the rescue as a result of the animal’s natural curiosity and playfulness.” Dolphins tend to approach any floating object inquisitively and nudge it with their beak or head. It was likely this normal, non-altruistic behavior that happened to save the woman, rather than a purposeful attempt by the dolphin to rescue her. To locate the woman’s body, this dolphin-savior may have used echolocation. Dolphins rely on this highly developed sensory adaptation for hunting. A swimming dolphin emits sounds, or clicks, some of which areaudible to thehuman ear as”creaking” sounds. By listening for echoes returning from objects blocking the path of the sound waves, in much the same way as a vessel’s depth sounder does, the animal can determine whether prey are in nearby waters, even when the prey are not visible. Once prey has beenlo-cated,thedolphincanusethe”melon” of its forehead to focus the sounds and obtain detailed information about the target. Dolphins have been trained to use their powers of echolocation to distinguish between different types of metals, so it is likely that they can distinguish between different types of fish based on acoustic information.
Dolphins feed on a wide range of fish: mullet, cod, hake, anchovies, herring, mackerel, haddock, and others. Rarely is a dolphin observed in the act of feeding, so it’s difficult to know their exact food preferences. Nonetheless, Risso’s dolphins are believed to rely heavily on squid as a food source; some other dolphins partake of squid as well. The boto, a freshwater dolphin found in the Amazon and Orinoco river systems, appears to specialize in eating “armored” bottomfish. The boto’s rear teeth are molar-shaped, helping them crush the armor of these fish. When feeding on fast-moving prey, dolphins benefit from their conical, pointed teeth; up to 130 of them line the jaw. Some dolphins occasionally supplement their fish-and-squid diet with mollusks and crustaceans, which they crush with their powerful jaws.
But sharp teeth and strong mandibles do not fully account for dolphins’ success in catching prey. They are capable of tremendous speeds and rapid acceleration. Pantropical spotted dolphins and northern right whale dolphins are among the fastest. The former can accelerate, in just two seconds, to a top speed of 36 miles per hour. Northern right whale dolphins can sustain speeds of 15 miles per hour for a 30-minute period with bursts up to 25 miles per hour. They leap repeatedly out of the water, skimming through the air for 20 or 25 feet per jump. This jumping behavior, known as “porpoising” even though dolphins are more likely than porpoises to engage in it, may enable the animal to swim faster. It makes breathing easier and may reduce drag on the body, as air induces less friction than water. High speed swimming is also facilitated by the dolphins’ muscular tail and their body form, which is superbly hydrodynamic. To swim most efficiently, dolphins would need laminar water flow, rather than turbulent flow, over their bodiessince turbulence works against efficient swimming. Some experts believe that certain dolphin species can achieve laminar flow by constantly monitoring and adjusting body shape, keeping it in the correct form for laminar flow.
Hunting in groups
However, dolphins often use an entirely different strategy for hunting: they work in groups. Along the South African coast, bottlenose dolphins sometimes seem to show a division of labor while hunting. While some individuals round up the fish school toward shore, other dolphins linger in deeper waters, possibly patrolling to ensure that the fish school could not escape. A similar strategy is employed offshore, where there is no land to act as a barrier. Instead, the dolphins split into two groups. One group chases the fish toward the other group, which is positioned as a barrier. In other instances, dolphins take advantage of a peculiar characteristic of fish schools: the tendency for the school to compact itself into a tight clump, or ball. This fish behavior likely evolved as a defense against predators who get confused and are unable to attack effectively when confronted by a shimmering school of rapidly swimming prey. Dolphins, for some reason, do not get confused and instead work this situation to their advantage. A group of dolphins will surround a school of fish and spur them to begin swimming in a circle, like a carousel. The dolphins constrict the size of the carousel by swimming tightly around the trapped fish. Depending on how many fish are in the school, the carousel may be fairly large, up to 450 feet across. The panicked fish may even try to escape by leaping up and out of the water. Eventually, the dolphins all take prey from the carousel.
The dolphin family of whales includes approximately 26 species of what normally are thought of as “dolphins,” plus about six species of somewhat larger toothed whales, such as the orca, which are not considered dolphins in common parlance. Dolphins inhabit virtually all the oceanic waters of the globe, as well as many coastal seas and some freshwater ecosystems. However, many species have quite restricted ranges. The Atlantic hump-backed dolphin, for example, is normally encountered only along the West African coast from Mauritania to Cameroon, and Peale’s dolphin lives only near the southern tip of South America. Other dolphins, such as the Indo-Pacific hump-backed dolphin, are fairly widely distributed but generally do not ride bow waves or otherwise interact with mariners; some species actually actively avoid boats, especially in areas where tuna fishing is common. In the Atlantic Ocean, dolphins that are both widely distributed and most likely to approach vessels include the common dolphin, striped dolphin, short-snouted spinner dolphin, long-snouted spinner dolphin, pantropical spotted dolphin, Atlantic spotted dolphin, bottlenose dolphin, and Risso’s dolphin. In the Pacific Ocean, species most likely to be encountered by mariners include the common dolphin, long-snouted spinner dolphin, pantropical spotted dolphin, bottlenose dolphin, Risso’s dolphin, and Pacific white-sided dolphin.
Of the species with large geographical ranges, the common dolphin is among the most readily identified at sea. It is distinguished by the yellowish or tan band that stretches along the side of its body from the eye to below the dorsal fin. No other species displays this trait. The common dolphin, the familiar bottlenose dolphin, and the striped dolphin all share a similar geographical range. They are found in tropical to temperate waters around the globe. In the Atlantic, all three species range from Newfoundland and the United Kingdom to southern Africa and South America. In the Pacific, they are distributed from central California and Japan to South America and Australia. However, within this worldwide range, common and striped dolphins occur mainly offshore, whereas the bottlenose tends to affiliate more often with land. Risso’s dolphins also share this global distribution, plus they may live as far north in the Pacific as the latitude of Alaska.
Long-snouted spinner dolphins and pantropical spotted dolphins share more or less the same geographical range, one which encircles the globe like the range of the common dolphin. These two species occur primarily in tropical waters, but occasionally they range into warm temperate seas. In the Atlantic Ocean, these species live from New England and Northern Africa south to Brazil and southern Africa. In the Pacific Ocean, they range from Mexico and Chile across to Japan and Australia.
Although it may be unwise to ditch your EPIRB and rely instead on rescue by dolphins, certainly there is no substitute for the company of dolphins during a long voyage. When a pod of dolphins approaches in a flurry of spray to join your vessel for a jaunt, an instant bond always seems to developat least from the human perspective. At those times, the belief of many ancient cultures that dolphins are simply people who were transformed into creatures of the sea may not seem so far fetched.
Formerly a marine biologist, Peter Taylor is now an editor at Islands magazine in Santa Barbara, Calif.