Whale, large mammal that lives its entire life in the water. Like other mammals, whales have large, highly developed brains and nurse their young with milk. Among aquatic mammals, whales are the most completely adapted to life in the water. Whales resemble fish in many ways, but they are not fish. Fish are cold-blooded and breathe underwater using gills; whales, on the other hand, maintain a warm and constant body temperature of about 37°C (about 99°F) and breathe air with lungs. Unlike fish, whales move their tails up and down instead of side to side when they swim.
Whales are enormous in size compared to other mammals. Theblue whale is probably the largest animal that has ever lived, reaching a length of nearly 30 m (100 ft) and a weight of 180 metric tons. Its heart is as big as a Volkswagen Beetle and its body is larger and heavier than that estimated for any known dinosaur. The blue whale makes the loudest sound (over 150 decibels) of any animal, and can be heard over thousands of kilometers across entire oceans. Certain other whales, especially the dolphins, emit clicking sounds that bounce off objects. The returning echo is used as a sonar image of their underwater surroundings. They share this ability, called echolocation, with bats, shrews, and a few kinds of birds.
Whales are found in all the world's oceans and even in a few rivers. One species of dolphin, the pink river dolphin, lives only in the Amazon River and its larger tributaries. Some better-known whales, including the blue, finback,humpback, and gray whale, range widely and migrate between the tropics in winter and subpolar waters in summer. Humpbacks have separate populations in the Northern and Southern hemispheres and do not seem to cross the equator. Sperm whales and killer whales, or orcas, are wanderers without specific migratory routes. An individual sperm whale might, in its lifetime, swim around the world.
II. Types of Whales
There are at least 75 species of whale, each with its own unique characteristics. Whales range from black to white in color and from nearly 30 m (100 ft) to less than 2 m (7 ft) in size. They may live in salt water or fresh water, and can be found as far north as the Arctic Circle, and as far south as Antarctica. The most common way of classifying whales, however, is according to their feeding strategy. One group of whales has teeth, and the other does not.
A. Toothed Whales
The toothed whales have jaws lined with simple, pointed teeth. These whales actively hunt fish, squid, and other prey. Toothed whales vary in size from small harbor porpoises less than 2 m (6 ft) long to the great sperm whales, whose adults average 17 m (55 ft) long and weigh nearly 50 metric tons.
Among the more unusual toothed species are thenarwhal and the beluga, both inhabiting Arctic waters. The male narwhal possesses a single ivory tusk that grows almost 2.5 m (8 ft) long, straight forward from its head. Adult belugas are completely white and resemble large dolphins with rounded foreheads.
Most dolphins are 2 to 4 m (7 to 13 ft) long and possess an elongated beak, or rostrum. Killer whales are the largest of the dolphins, growing up to 8 m (25 ft) in length. Some dolphins, such as the Atlanticbottle-nosed dolphin, commonly live close to shore, while others, such as the Pacific spinner dolphin, live much of their lives far from land. There are several species of river dolphins inhabiting river systems in Asia and South America, including the Ganges, Yangtze, Amazon, and La Plata. They are nearly blind and find their way through murky waters using echolocation.
B. Baleen Whales
Instead of having teeth, the baleen whales have mouths lined with giant, flexible combs of a material calledbaleen, or whalebone, which is used to filter small fish and crustaceans from the water. There are three types of baleen whales: the rorquals, the gray whales, and the right whales. The rorquals have narrow, streamlined bodies and are the fastest swimming whales. The giant blue and fin whales are rorquals as are their smaller relatives, the minke and sei whales. The sei whale can swim at more than 35 km/h (22 mph) over short distances. Some rorquals make annual long-distance migrations of thousands of kilometers.
Gray whales live only in the North Pacific and measure up to 15 m (50 ft) in length. They are slow swimmers that stay near shallow waters where they can feed from the bottom.Right whales are thick-bodied, slow-swimming plankton feeders that reach 18 m (60 ft) in length. One right whale, the bowhead, lacks a dorsal fin, or back fin, enabling it to use its huge back to break through the thick Arctic ice for air. While not as fast as the rorquals, the gray and right whales are still capable of long-distance migrations.
III. Anatomy of Whales
The streamlined body of whales appears remarkably fishlike. The front limbs are modified as paddle-shaped flippers and the broad horizontal tail flukes provide the main propulsive thrust. The whale's skeleton closely resembles the skeletons of other mammals. For instance, the bones of the flippers resemble jointed limbs and digits and the neck has exactly seven vertebrae.
The whale's body is enveloped in a thick layer of fat called blubber that aids in buoyancy, serves as a source of stored energy, and helps preserve body heat. Blubber permits whales to stay warm even in near-freezing waters. In warmer waters they are able to release heat like a radiator by controlling blood flow to the skin. A whale's skin is free of sweat glands and oil glands, is nearly devoid of hair, and feels much like smooth, wet rubber to the touch.
Whales, like other mammals, have lungs. Whales do not breathe through their mouths, but rather through a nostril, or blowhole, located on the top of the head. The blowhole opens by a slight muscular contraction and closes automatically when the muscle relaxes. As a whale surfaces it exhales powerfully, creating a loud sound and a characteristic cloud of mist known as the spout. The spout is caused by condensation from the warm, moist air that is exhaled, not from seawater trapped in the blowhole, as was once believed.
Large tail flukes provide thrust for whales when they swim. The power comes from body muscles that flex the lower spine up and down in a wavelike motion. The forelimbs of whales are flippers used for steering as the animals swim. In some species, such as humpbacks, the flippers are large and powerful and may be used for fighting among males.
Whales are able to drink seawater and yet maintain the same low salt concentrations in their body fluids that other mammals do. For every liter of seawater a whale drinks, its highly efficient kidneys concentrate the salt into only two-thirds of a liter of urine for a gain of one-third liter of pure water. If a human were to drink a liter of seawater, it would require one and one-third liters of urine to remove the salt for a loss of one-third liter of water.
Whales possess interesting adaptations for diving, some of which are shared with other aquatic mammals such asseals. Whales can store very high oxygen concentrations in their blood and muscles. During a dive, the heart rate slows and arteries constrict to many of the animal's organs, greatly reducing blood flow into those areas. This conserves oxygen and maintains the blood pressure to vital systems, especially the brain, sense organs, and to the heart itself. During a dive, the lack of oxygen triggers the build up of carbon dioxide and lactic acid in the blood and muscles. Unlike most animals, whales are able to resist pain and fatigue caused by lactic acid accumulation in muscle tissue. Baleen whales can hold their breath up to 50 minutes when diving, and of the toothed whales, the sperm whales can hold their breath up to 80 minutes.
Whales have an excellent sense of hearing. They perceive sound that is waterborne and, as a result, they have been able to discard the external ear structures called pinnae that land mammals developed to gather airborne sounds. Whale external ears are reduced to small slits, but this does not hinder them from perceiving a wide range of sounds, many of which are not audible to humans.
IV. Feeding Habits
The feeding activities of whales are directly related to their mouth and jaw structure and whether they possess baleen or teeth. Baleen whales are filter feeders with expandable mouths and throats. Right whales have long, thin streamers of baleen for catching small prey. They swim slowly forward with open mouths continuously straining primarilykrill, but also copepods and other small organisms from the water.
Rorquals use a different style, called lunge feeding, to prey on krill and fish. These baleen whales move quickly into a dense school of prey and take a great gulp of up to 70 metric tons of water. With the mouth partly closed, the baleen curtains interlace from above and below, forming a filter at the front and sides of the mouth. The whale's throat muscles then contract, and water is forced out through the baleen as the food is trapped inside the mouth and then swallowed.
Groups of several humpback whales have been observed cooperating to trap schools of small fish. The humpbacks manage to corral fish inside a cylindrical column of bubbles released through the whales' blowholes. Each whale then takes its turn swimming inside the bubble curtain and rising to the surface with its mouth open, trapping many of the fish in its baleen net.
Instead of feeding in open water, gray whales feed on the ocean bottom, primarily on amphipods, a type of small crustacean that lives in mud. Gray whales have the shortest, stiffest baleen fibers of all whales. They approach the ocean bottom sideways, sucking material containing food into the side of their mouth and forcing water and mud out through the coarse baleen on the other side.
Toothed whales catch larger prey than the baleen species. Using echolocation, they actively track and seize fish and squid. Perhaps the most formidable predator to appear on earth since Tyrannosaurus rex, the killer whale is the only whale to routinely pursue warm-blooded prey, chiefly seals and smaller dolphins, although they also eat fish. One classic study found parts of 13 dolphins and 14 seals in a dead killer whale's stomach. Occasionally, a group of killer whales will attack and kill a large whale such as a humpback.
Feeding dives by sperm whales last as long as 80 minutes and extend to depths of 2,000 m (6,500 ft). Water at these depths is in complete darkness and these whales find their prey by echolocation. Sperm whales specialize in feeding on large deep-sea squid. Giant squid, measuring up to 10 m (30 ft) long including tentacles, sometimes fight back, leaving deep cuts and scratches on the sperm whales.
Whales mate after extensive courtship rituals involving various sounds, postures, ritualized swimming, and touching and caressing. Gestation, the time between conception and birth, may range from about 10 months in river dolphins to about 16 months in sperm whales. Whales produce a single calf.
Most large species of whales migrate to the tropics to give birth and to mate. Humpbacks nurse the calf for several months before the young whale begins to feed on its own, although intermittent nursing may continue for a year or more. The largest whales can produce an estimated 600 liters (160 gallons) of milk per day. Whale milk contains 25 to 50 percent fat, compared to 3 to 5 percent in cow milk.
VI. Intelligence and Behavior
Studies of whales in captivity have taught us much about their physiology as well as their complex social behavior. Their learning and problem-solving skills, together with their curiosity and often eager interactions with humans, have led some scientists to believe that whales possess a high level of intelligence.
The large brains of whales also suggest a high intelligence. The sperm whale's brain is considerably larger than an elephant's brain and six times the size of a human brain. However, relative to the rest of the body, a sperm whale's brain is only about 0.02 percent of its body weight, while a human brain is about 2 percent. Reflecting their heightened sense of hearing, in those whales that rely on echolocation to perceive their surroundings, the areas of their brains that process sound information are far larger than the corresponding parts in humans. These animals tend to rely on hearing more than vision, which explains why the visual centers of their brains are smaller proportionally than those in humans. Another feature that scientists correlate with intelligence is the degree of folding of the upper surface of the brain, the area known as the cerebral cortex. This folding increases the surface area and has been observed in more intelligent animals. Whale brains generally show as much or more folding of the cerebral cortex as is seen in humans.
Complex behavior may reveal more about whale intelligence than sheer brain size. Perhaps the most intriguing indications of whale intelligence came with the discovery in the 1970s of whale singing, most notably in humpbacks. Singing is most common on the winter mating grounds, for example in the Caribbean and Hawaii. Singing humpbacks are males, more specifically, escort males that closely follow females and their year-old calves. These females are receptive to mating, and singing may be a mating ritual for humpbacks. There is no solid evidence that the songs encode language in an intellectual sense. The whale songs may be simply longer versions of the mating songs also noted in birds and amphibians.
Humpback songs, which may last more than 20 minutes, consist of a series of phrases or sequences. All of the singing whales of a particular migrating group sing very nearly the same song. The songs change progressively from year to year, resulting in entirely new songs after four or five years. Bowhead whales also sing and the Inuit people of Alaska have told researchers that they long observed that bowheads make sounds "like a guitar playing inside the water."
Some studies have attempted to find intelligent meaning in the sounds of dolphins and to teach dolphins a symbolic language. These studies indicate that dolphins may be slightly superior to dogs in their abilities to communicate with humans. Research on communication among wild spinner dolphins in their own social world indicates that individuals behave abnormally when removed from a well-knit dolphin group. These studies also suggest that dolphins may convey information by elaborate postures and body language. These studies are preliminary, however, and scientists are still far from accurately measuring, or even knowing how to measure, the intelligence of whales.
Some whale species exist for the most part as solitary animals, whereas others live in family groups or in pods numbering hundreds of individuals. Observations of dolphins and other toothed whales have revealed a strong tendency toward cooperation, even among different species. In whales held in captivity, females of one species will assist a mother of another species as she gives birth, and will support the newborn calf, helping it to reach the surface to breathe. Aggressiveness is also observed in dolphins, chiefly in males that, in captivity at least, may attack the young of other species.
VII. The Origin of Whales
Whales most likely evolved from four-legged land animals that foraged for food or hunted for fish in swamps and along the ocean shore. Fossil evidence suggests that extinct carnivorous hoofed animals called mesonychids may be the closest relatives of these whale ancestors. However, recent studies comparing the genetic makeup of modern whales and hoofed animals have led some researchers to propose that whales are more closely related to the hippopotamus. The ancestors of whales gradually became more dependent on the ocean for food, passing through an amphibious stage like modern seals, before evolving into fully aquatic animals. Since the 1980s, exciting new discoveries of fossil whales have shed light on their evolution from the land to water. The fossil record of whales spans over 50 million years to ancestors such as Pakicetus that lived around the mouths of rivers in what is now Pakistan. Pakicetus was a four-legged, semiaquatic animal that measured about 2.5 m (about 8 ft) in length. It was clumsy on land, perhaps like modern sea lions, but its legs easily supported its weight. Pakicetus probably swam using an up and down flexing of the body to power its finlike feet in the manner ofotters. Unlike modern whales, it had nostrils instead of a blowhole and ears not designed to permit deep dives.
The whale fossil Rodhocetus was discovered in 1993. Dating from about 46.5 million years ago, this fossil came from fully marine sediments. Its legs were somewhat smaller than those of Pakicetus but it might have been able to waddle on land. Rodhocetus had a powerful tail, although it is not known whether this early whale had begun to evolve tail flukes.
A fossil whale from Egypt, Basilosaurus, dates from 42 million years ago and represents the stage of whale evolution in which the hind legs are very small but still visible. Adult Basilosaurus reached lengths of 15 m (50 ft), but its hind limbs grew to only 0.5 m (1.5 ft) long. Although all of the pelvic bones, leg bones, kneecaps, feet, and toe bones were present, these legs could not have been used to support such a large animal on land. Modern whales, which first appeared in the fossil record 5 million to 10 million years ago, have no visible hind limbs, although some species still have tiny pelvic and leg bones embedded in muscle near the spine.
Humans have hunted whales since prehistoric times (seeWhaling). Initially, they only killed and used whales that had become stranded on land, but eventually people began using hand-held harpoons and small boats to pursue whales at sea. Primitive subsistence whaling relied on coastal species such as the gray whale and the bowhead. Commercial whaling in the open sea developed into big business by the 1700s. The major whale product was the oil made from the blubber and used in oil lamps. Spermaceti, a thick liquid from the head of sperm whales, crystallizes into a soft wax when exposed to air and was used as an ointment and to make high-quality candles. It burned with an especially clear, smokeless flame and was the most valuable form of whale oil. Baleen was also in demand for several decades. Its resilient flexibility made it useful in a variety of products including umbrella spokes, horsewhips, and springy petticoats.
During the sailing ship era, when whales were caught by hand harpoon from oar-driven boats, the easiest whales to kill were the slower swimmers, such as grays, bowheads, humpbacks, sperm whales, and right whales. The giant rorquals were not hunted seriously because they were difficult to approach and usually much too fast for the whalers to catch. Heavy whaling pressure nearly decimated several species of whale during the 1800s. By 1850 the American whalers made up 80 percent of the world fleet and harvested over 10,000 whales per year. In 1849, however, a method was devised for distilling kerosene from petroleum. Just as many whales were nearing extinction, kerosene began to substitute for whale oil, and the whalers' markets gradually dried up for a brief time.
By the turn of the 20th century, the process of hydrogenation made it possible to process whale oil into soap and margarine. Whale meat was still desired for human and animal food. Finally, the invention of fast steam-powered ships and cannon-fired harpoons with exploding heads ushered in a new era of whaling. With these new technologies, even the big rorquals were caught easily, and the whale slaughter began again. Japan, Norway, and Russia were the primary whaling nations.
In 1910 only 176 blue whales were killed; by 1931 the harvest exploded to 30,000. Blue whales became ever scarcer over the years until 1966, when only 70 blue whales were caught worldwide. That year the International Whaling Commission (IWC) banned hunting for blue whales in the Southern Hemisphere. Other species such as the humpback, however, which had been considerably depleted in the Northern Hemisphere a century earlier, were now driven toward extinction. These magnificent animals were ground up on factory ships to make lubricants, soaps, cosmetic products, and animal feeds.
IX. Whale Conservation
Most large whales are now very scarce. Their reproductive rates are so low that even if completely protected from whaling, some species will take many decades, perhaps a century or more, to rebuild their populations to healthy numbers. Several countries and conservation organizations around the world are seeking to protect whales. In 1946 whaling nations established the International Whaling Commission (IWC). Unfortunately, member countries cannot always agree on the type of protection needed for the scarcer species and on quotas for hunted species, and the IWC has no power to enforce its agreements. Whale-hunting abuses by a few nations continue to be uncovered. Humpbacks, which are supposedly protected in all oceans, are still hunted today.
The decimation of huge numbers of rorquals and other large whales over the years has caused krill and other whale prey species populations to increase, especially in the Antarctic. Some marine ecologists think that this ecosystem change is responsible for recent increases in the numbers of penguins and crabeater seals, which also feed on krill.
In addition to whaling, whales are endangered by increasing pollution in the oceans. This is particularly true of dolphins and other species that live in coastal waters. These animals build up large concentrations of toxic chemicals such as lead, mercury, and pesticides in their bodies from eating contaminated fish and other food. More and more whales are becoming stranded on beaches and dying; it appears that some of these animals have had their sense of echolocation damaged by infectious disease or parasites.
Even healthy whales may now be unable to hear well in the sea. Underwater noise pollution is steadily increasing and may be drowning out the tremendous calls of the blue and fin whales. Whales could once heard across thousands of kilometers of ocean, but some researchers believe noise pollution is now interfering with this form of long-distance communication between animals. As we learn more about whales and the ecology of the ocean, we have new chances, and new motivations, to protect these magnificent animals.
Scientific classification: Whales belong to the order Cetacea. There are two suborders: Mysticeti (baleen whales) and Odontoceti (toothed whales). The baleen whale suborder includes members of the rorqual family, Balaenopteridae. Important rorquals include the blue whale, which is classified as Balaenoptera musculus, and the fin whale, which is classified as Balaenoptera physalus. Other baleen whales include the humpback whale, which is a member of the family Balaenopteridae and is classified as Megaptera novaeangliae, and the gray whale, which is a member of the family Eschrichtiidae and is classified as Eschrichtius robustus.
The toothed whale suborder includes members of the dolphin family, Delphinidae. The bottle-nosed dolphin is classified as Tursiops truncatus, the pink river dolphin is classified as Inia geoffrensis, and the orca is classified as Orcinus orca. Other toothed whales include the sperm whale, which is a member of the family Physeteridae and is classified as Physeter catodon, and the beluga whale, which is a member of the family Monodontidae and is classified as Delphinapterus leucas.
John L. Culliney, B.A., Ph.D.
Professor of Biology, Hawaii Pacific University. Author of Islands in a Far Sea: Nature and Man in Hawaii and other books.
HOW TO CITE THIS ARTICLE
"Whale," Microsoft® Encarta® Online Encyclopedia 2000
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