Whale - biology.

Whale - biology. I INTRODUCTION Whale, large mammal that lives its entire life in the water. Whales have a fishlike body; however, their tail fins, called flukes, are horizontal rather than vertical, and they have paddlelike front limbs, called flippers. Their skin is smooth and glossy and, depending on the species, may be black, white, or a variety of colors and patterns. Beneath the skin is a thick layer of fat, called blubber, which provides insulation and serves as a source of stored energy. 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, which move their vertical tail fins from side to side when they swim, whales move their horizontal tail fins up and down to propel themselves through the water. Whales belong to the mammalian order Cetacea. Scientists classify whales into two groups. One group, known as the Odontoceti, or toothed whales, have jaws lined with pointed teeth that they use in hunting fish, squid, and other prey. Toothed whales also include dolphins and porpoises. The other whale group, called the Mysticeti, or baleen whales, lack teeth. These whales use giant, flexible combs of a material called baleen to filter small fish and tiny crustaceans from the water. 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 whales, including the blue, fin, humpback, and gray, undertake some of the longest migrations in the animal kingdom, traveling between the tropics in winter and subpolar waters in summer. Other whales do not migrate long distances or, like the killer whales, wander without specific migratory routes. II BODIES OF WHALES Whales are enormous in size compared to all other animals. The blue whale is one of the largest animals that has ever lived, reaching a length of over 24 m (80 ft) and a weight of 150 metric tons. Its heart is as big as a Volkswagen Beetle, and its body is almost as large and about as heavy as that of the largest known dinosaur. Whales have a streamlined, rounded body tapering in the rear to a pair of broad horizontal tail flukes that provide the main propulsive thrust for swimming. They have paddle-shaped flippers that help stabilize and steer the whale while swimming. The bones of the flippers resemble the jointed limbs and digits of land mammals. Many whales have a dorsal fin located at or behind the center of the back. A Skin A whale's skin feels much like smooth, wet rubber to the touch. The skin has no sweat glands or oil glands, and it is nearly devoid of hair. Beneath the skin is 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 nearfreezing waters. B Blowhole and Lungs Whales do not breathe through their mouths, but rather through a nostril, or blowhole, located on the top of the head. Toothed whales have only a single blowhole; baleen whales have two blowholes. The blowhole opens by a slight muscular contraction and closes automatically when the muscle relaxes. As a whale surfaces it exhales through the blowhole, creating a loud sound and characteristic cloud of mist known as the spout. The spout is caused by condensation from the exhaled warm, moist air, not from seawater trapped in the blowhole, as was once believed. Air taken in through the blowhole travels through the trachea (windpipe) to the lungs. Unlike for most land animals, the trachea does not connect to the throat. So when the whale opens its mouth underwater to feed, water does not rush into the lungs as it would in land animals. This structural arrangement enables the whale to breathe air and swallow food at the same time. The lungs transfer oxygen to the blood while removing the blood's carbon dioxide. Relative to body size, whale lungs are proportionally somewhat smaller than human lungs. But whale lungs are far more efficient: While human lungs exchange about 15 to 20 percent of their contents with each breath, whale lungs exchange about 90 percent with each breath. This means that whales can take up oxygen and dispose of carbon dioxide much faster than humans, enabling them to hold their breath underwater for long periods. C Digestive System When whales swallow food, it travels through the esophagus to a multichambered stomach that resembles the stomachs of ruminant hoofed animals such as cattle, sheep, and deer. In the first stomach chamber, a saclike extension of the esophagus, food is crushed. In the second chamber, digestive juices further break down food. Most cetaceans have a third stomach chamber, which regularly contracts to mash and thoroughly mix food with digestive juices. The stomach capacity of a large whale can reach 760 liters (200 gallons). From the stomach food moves through the intestine, where nutrients pass through the intestinal wall and are absorbed into the blood. Remaining waste materials are eliminated through the anus into the ocean. Cetaceans lack two internal organs found in most land mammals: the gallbladder and appendix. D Sense Organs The eyes of most whales are well adapted for life underwater. Strong muscles surrounding each eye change the shape of the eye's lens. This enables whales to focus their vision both underwater and above water. Whale eyes can withstand high pressure when the animal dives to great depths, and the tear ducts shed oily tears that enhance underwater vision and protect the eyes from the effects of salt water. The streamlined bodies of whales do not have the external ear structures called pinnae that land mammals use to gather airborne sound. But whales still have excellent hearing and can perceive a wide range of sounds, many of which are not audible to humans. For toothed whales that commonly hunt for food in the dark depths of the ocean, hearing is often enhanced by echolocation, in which the animals emit clicking sounds that bounce off objects. The returning echo is used as a sonar image of the underwater surroundings. Toothed whales share this ability with bats, shrews, and a few kinds of birds. Baleen whales have a poor sense of smell, and toothed whales lack smell entirely. Some whales, such as dolphins, can taste different chemicals in water to differentiate between sweet, sour, bitter, and salty, but in general the sense of taste in whales is limited. III BEHAVIOR OF WHALES Studies of whales in captivity have taught scientists much about the complex social behavior of whales. Since the late 1980s, advances in the use of satellite tracking systems have also broadened opportunities for scientists to observe how whales behave in the wild. A Swimming and Diving Whales swim by making powerful up-and-down movements of the tail flukes, which provide thrust. The power comes from body muscles that flex the lower spine up and down in a wavelike motion. The whale's flippers help the animal steer. In some species, such as humpbacks, the flippers are large and powerful and may be used for fighting among males or, more rarely, for warding off attacks by killer whales. Most whales remain near the surface of the ocean, but some dive to great depths and remain underwater for long periods ranging from 50 to 80 minutes. Whales possess interesting adaptations for diving, some of which are shared with other aquatic mammals such as seals. For example, whale lungs and adjoining air passages collapse under the pressure of a dive, forcing air into central parts of the lungs and thereby reducing the amount of nitrogen absorbed into the bloodstream. Too much nitrogen in the bloodstream can cause decompression sickness and a disorienting condition known as nitrogen narcosis. At the same time the whale's blood and muscles contain high concentrations of the oxygen-storing pigments hemoglobin and myoglobin. During prolonged dives these pigments supply 80 to 90 percent of the whale's oxygen. Also during a dive, the whale's heart rate slows to as low as three to five beats per minute. Arteries constrict, greatly reducing blood flow to many of the animal's organs. This conserves oxygen and maintains blood pressure in the life-supporting structures, such as the brain and heart. During a dive, the lack of oxygen in the whale's body triggers the buildup of lactic acid, a chemical produced when body tissues obtain energy by metabolizing sugar in the absence of oxygen. In most animals the buildup of lactic acid in muscle leads to fatigue and can cause cramps. For reasons not well understood, whales can tolerate the pain and fatigue caused by lactic acid accumulation in muscle tissue, enabling them to remain underwater for long periods. Baleen whales can hold their breath up to 50 minutes when diving, and of the toothed whales, sperm whales can hold their breath up to 80 minutes. Some whales, such as killer whales, regularly jump clear of the water and land on their back or side in a behavior known as breaching. Scientists are unsure why whales breach. Some theorize that this behavior may be a display of dominance used in courtship or may enable the whales to view their surrounding area. The loud sound that breaching makes as the whale lands in the water suggests to some scientists that it is used as a form of long-distance communication. B Migration Migration is a regular occurrence in many whale species. Most baleen whales migrate great distances to spend their summer months in the cooler waters of polar regions. There they feed on small shrimplike organisms called krill, as well as on other invertebrates and fish. During the fall these whales migrate to warmer waters to breed. Gray whales may travel up to 10,000 km (6,200 mi) from their feeding grounds off the coast of Alaska to their breeding grounds along Mexico's shores. Some humpback whales feed in the Southern Ocean around the Antarctic Peninsula and travel north of the equator to breed in the waters along Colombia. Toothed whales tend to travel in a nomadic fashion and do not exhibit regular long-distance migrations. One exception is the male sperm whale, which migrates long distances between mating and calving grounds near the equator and feeding areas in polar waters. Depending on the species, sex, age, and season, whales may travel alone, in pairs, or in small or large groups. A group of about 20 or fewer whales is called a pod; larger gatherings are called schools. Some groups consist only of males and some of both males and females. In some species, such as the pilot whale, the groups appear to have definite leaders. Killer whales live in family groups called matrilines. Each matriline is composed of an adult female and her offspring. Male parents of offspring do not live with the matrilineal group. Some male and female offspring stay with their matrilineal group for life, while other matrilineal groups are less stable, with members that come and go. Two or more matrilines may travel together in a pod. C Reproduction Most large species of whales migrate to the tropics to mate and give birth. 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. A newborn whale typically measures 30 percent or more of the mother's length and about 6 percent of her weight. A baby blue whale, for example, may be 7.6 m (25 ft) long and weigh 3 metric tons at birth. Mothers feed their newborns with milk, one of the primary reasons that scientists characterized whales as mammals. Newborn whales may nurse for up to a year before beginning to feed on their own. 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 a fat content of 3 to 5 percent in cow milk. Whales reach sexual maturity from 7 to 14 years of age, depending on the species. Whales may live from 20 to 60 years. Larger species live the longest. D Intelligence Scientists believe that whales are intelligent animals. An anatomical feature that scientists correlate with intelligence is the degree of folding of the upper surface of the whale's brain, the area known as the cerebral cortex. This folding increases the surface area of the brain and is found in other intelligent animals, such as elephants and dogs. 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 brain structure. Some whales in captivity exhibit extensive learning and problem-solving skills. Dolphin curiosity and their often-eager interactions with humans also suggest a high level of intelligence. Other research indicates that dolphins have a sense of self. Studies that presented individual dolphins with mirrors and video images found that the dolphins could recognize themselves and also distinguish themselves from other dolphins. Perhaps the most intriguing indication of whale intelligence came with the discovery in the 1970s of whale singing, most notably in humpbacks. 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. The Inuit people of Alaska have told researchers that they long observed that bowheads make sounds 'like a guitar playing inside the water.' Singing most commonly occurs in the winter mating grounds, suggesting that it may be part of a mating ritual. Scientists have been unable to prove that whale songs encode language in an intellectual sense. The whale songs may simply be longer versions of the mating songs also noted in birds and amphibians. Scientists have also observed killer whales teaching their young cultural practices. Certain killer whale pods have developed the habit of attacking sea lions on beaches. Scientists have observed adults in these pods teaching the young how to attack these sea lions. The adults make mock lunges toward the beach, then roll aside to permit the juvenile "trainees" to lunge toward the beach. All studies of whale intelligence are still preliminary, however. Scientists acknowledge that they are still far from accurately measuring, or even knowing how to measure, the intelligence of whales. IV TYPES OF WHALES There are more than 75 species of whale, each with its own unique characteristics. Whales range from black to white in color and from nearly 24 m (80 ft) to less than 1.2 m (4 ft) in length. 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. With such diversity, the most common way of classifying whales is according to how they feed. The Odontoceti, or toothed whales, use teeth, and the Mysticeti, or baleen whales, use horny, fringed plates called baleen. A Toothed Whales The toothed whales comprise sperm whales, beaked whales, narwhals, belugas, dolphins, and porpoises. Toothed whales commonly have teeth in the front of the lower jaw or in both jaws. Some toothed whales have teeth that are embedded in the jaw's gums. These teeth are not exposed and do not help the whale feed on prey. Toothed whales vary in size from small harbor porpoises less than 1.5 m (less than 5 ft) long to the great sperm whales, whose adults grow up to 18 m (59 ft) long and weigh nearly 55 metric tons. A1 Sperm Whales Sperm whales have a huge, barrel-shaped head with an extensive accumulation of fatty tissue, called the case, in the forehead region. Inside the case is a liquid wax called spermaceti, which was highly valued for making candles and other products during the 1800s. The sperm whale's S-shaped blowhole is near the tip of the snout instead of back on the head, as in other whales. When discharging air from the blowhole, sperm whales produce a characteristic short, wide spout of water that is directed forward and upward. The lower jaw is narrow and has from 16 to 30 teeth on each side. No exposed teeth are present in the upper jaw. Mature males may grow to about 18 m (about 59 ft) in length and weigh up to 55 metric tons, while females are smaller, growing to 12 m (39 ft). Feeding dives by sperm whales average about 45 minutes, although some whales have been observed to stay underwater for close to two hours. Sperm whales can dive to depths of 1,000 to 2,000 m (3,300 to 6,600 ft). Water at these depths is in complete darkness, and these whales probably locate their prey using echolocation. Sperm whales specialize in feeding on large deep-sea squid. Giant squid, measuring up to 18 m (60 ft) long including tentacles, sometimes fight back, leaving deep cuts and scratches on the sperm whale's body. A2 Beaked Whales Beaked whales are small to medium-sized whales with long, pointed snouts and, in males, two to four protruding teeth on the lower jaw. These whales have slight depressions in the body wall where flippers can be tucked, most likely to reduce drag while swimming. Beaked whales are deep divers and may remain below water for 30 minutes or longer. They have been sighted in polar, temperate, and tropical oceans. The migration pattern of beaked whales is not well understood, but most species seem to travel singly or in pairs and stay within a limited range. A3 Narwhals The narwhal is typically about 4.7 m (15 ft) long and weighs about 1 metric ton. Narwhals have only two teeth, both in the upper jaw. In females the teeth usually remain embedded in the gums. In males the right tooth remains embedded, but the left tooth commonly grows out into a spiraling ivory tusk that grows up to 3 m (10 ft) long, straight forward from its head. Scientists believe that males use this tusk in fights against rival males. Native to the cool waters of the Arctic and North Atlantic oceans where they live year-round, the narwhal is sometimes found in the company of belugas migrating with the seasonal movements of the Arctic ice. When narwhals surface after a dive, escaping air from the blowhole makes a shrill whistle. Females utter a low-pitched bellow to communicate with young. A4 Belugas Named for the Russian word byelukha, meaning "white," belugas are black or brown in color at birth, then lighten with age until about age five, when they become milky white. Belugas grow to a length of 7 m (23 ft) and weigh from 700 to 1,600 kg (1,500 to 3,500 lb). The upper jaw contains 20 teeth and the lower jaw contains 16 teeth. The beluga lives year-round in Arctic waters, traveling in groups ranging from five to ten individuals up to a thousand or more. They communicate with a series of whistles, squeaks, bell-like sounds, and clicking noises. A5 Dolphins Sleek and powerful swimmers found in all seas, dolphins have well-defined, beaklike snouts and, depending on the species, 2 to 250 conical teeth. There are 40 species of dolphins, and they range in size from the small tucuxi dolphin, which grows to about 1.2 m (4 ft) long and weighs about 50 kg (110 lb), to the killer whale, which can grow up to 9.8 m (32 ft) in length and weigh over 5,500 kg (12,100 lb). Killer whales are among the fastest toothed whales, achieving bursts of speed close to 50 km/h (30 mph). Some dolphins, such as the Atlantic bottlenose dolphin, commonly live close to shore, while others, such as the Pacific spinner dolphin, live much of their lives far from land. In Asia and South America, several species of river dolphins inhabit river systems such as the Ganges, Yangtze, Amazon, and La Plata. The Indian river dolphin is nearly blind and finds its way through murky waters using echolocation. A6 Porpoises Some people use the word porpoise to describe any small whale. But scientists typically apply the term to six species of whale. Compared to dolphins, porpoises are relatively small in size, averaging 1.5 m (5 ft) in length and 40 kg (88 lb) in weight. With some exceptions, porpoises have blunt, rather beaked snouts, and the upper and lower jaws each hold about 25 pairs of spoon-shaped teeth, which are expanded and flattened at the tips. Most porpoises have black or dark brownish-gray coloring on their backs and white or pale-gray coloring on their bellies. The common porpoise, also known as the harbor porpoise, is widespread throughout the waters of the Northern Hemisphere. The spectacled porpoise lives in the deep fjords of Tierra del Fuego and in the waters surrounding the Falkland Islands. The Dall's porpoise is among the fastest swimmers of all cetaceans, reaching speeds up to 56 km/h (35 mph). B Baleen Whales Baleen whales are named for the long, horny plates of baleen, also known as whalebone, that are attached to the roof of the mouth. Each plate is a thin, triangular sheet with smooth sides made from a strong, elastic protein called keratin, the material that also makes up human hair and fingernails. The outer edge of the plate is straight, while the inner edge and tip are frayed into long, hairlike bristles that serve as a filter to trap minute marine life from seawater. Some baleen whales feed by skimming--that is, they swim through schools of fish or krill with their mouths open and lower jaw dropped clear of the baleen plates. Other species feed by gulping a single mouthful of food at a time. However they gather food, after sweeping up prey, baleen whales shut their mouths and force water out between the baleen plates. The baleen fringe prevents the small organisms from escaping. There are three types of baleen whales: rorquals, gray whales, and right whales. B1 Rorquals Rorquals comprise the blue, fin, humpback, Bryde's, sei, and minke whales. These whales are characterized by pleated throat grooves found on their undersides that extend from the throat to the flippers. While eating, these throat grooves expand, enabling the whale to swallow up to 70 metric tons of water. Rorquals typically have narrow, streamlined bodies and they are the fastest swimming baleen whales--the sei whale, for instance, can swim more than 40 km/h (25 mph) over short distances. The blue whale is the largest living animal on Earth, some reaching a length of more than 24 m (80 ft) and a weight of 150 metric tons. As its name suggests, the blue whale is blue-gray in color. The underside is lighter than the rest of the body and often has a yellowish tinge caused by a film of yellow algae that may grow on it. The blue whale makes the loudest sound of any animal--over 150 decibels. This sound, which is louder than the noise of a jet aircraft taking off, can travel over thousands of kilometers underwater. Blue whales have been protected from commercial hunting since 1966, but they remain rare. They are most commonly observed in the northeast Pacific and northwest Atlantic oceans. The fin whale is the second largest animal after the blue whale. It can grow to 24 m (78 ft) in length and weigh up to 70 metric tons. The fin whale has a gray back and white undersides; the white area extends up along the right side of the lower jaw but not the left. Fin whales are most common in the Southern Hemisphere, while smaller populations inhabit the North Atlantic and North Pacific. The humpback whale averages about 12 m (40 ft) in length and 30 metric tons in weight. It is black with varying amounts of white on the sides and belly. The humpback's long flippers may be one-third the length of its stocky body. Groups of several humpback whales have been observed cooperating to trap schools of small fish. The humpbacks 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. Bryde's (pronounced "broodahs") whale is named for a 19th-century Norwegian consul to South Africa named Johan Bryde who built the first whaling stations in South Africa. Bryde's whales are the only baleen whales that spend their entire lives in warm or tropical waters, preferably those with a temperature above 20°C (68°F). They can be found in both inshore and offshore waters of South Africa, Japan, Sri Lanka, Fiji, and western Australia. Bryde's whales have a pale gray, slender body that grows up to 14 m (46 ft) in length and weighs up to 24 metric tons. Whale watchers often look for three longitudinal ridges on top of the head to identify this species, which can often be mistaken for the sei whale. Sei (pronounced "say") whales are usually about 14 m (46 ft) long and weigh less than 20 metric tons. They are dark blue-gray or black with some white on the undersides. Sei whales are the only baleen whales that feed both by skimming and gulping. They live throughout oceans of the world and generally travel alone but sometimes gather in large loose schools. The minke whale is one of the smallest of the rorqual whales, growing up to 10 m (33 ft) in length and 10 metric tons in weight. Minke whales are gray-blue, with white bands across the flippers. They have a pointed head that appears V-shaped when viewed from above. Found in waters around the world, minke whales seem to prefer inshore waters. B2 Gray Whales Gray whales are slate-colored and measure up to 15 m (49 ft) in length. Unlike other whales that feed in open water, gray whales are slow swimmers that stay near shallow waters where they can feed from the ocean bottom. They feed 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, then forcing water and mud out through the coarse baleen on the other side. Gray whales live along the coast of North America from the Arctic Ocean to Baja California, Mexico. They migrate annually between summer feeding grounds in the Bering Sea and winter calving and breeding lagoons on the Pacific Coast of Baja, a round trip of some 19,000 km (12,000 mi). A second gray whale population once existed along the coasts of Korea and Japan but was virtually exterminated by commercial hunting early in the 20th century. A few individual gray whales still occasionally appear in these western Pacific waters. B3 Right Whales Scientists recognize three types of right whales: northern, southern, and bowhead, also known as the Greenland right whale. Right whales were so named by early whalers, who considered them the "right" whale to hunt because they swam slowly at 5 to 10 km/h (3 to 6 mph), floated in the water when dead, and were excellent sources of valuable oil and baleen. Right whales are thick-bodied and lack a dorsal fin. They may reach 18 m (59 ft) in length and weigh up to 70 metric tons. They have a callus-like, horny growth, called the bonnet, on top of the head. Right whales have long, thin streamers of baleen for catching small prey. They swim slowly forward with open mouths continuously straining primarily krill, but also copepods and other small organisms from the water. V ORIGIN OF WHALES Whales most likely evolved from four-legged land animals that foraged for food or hunted for fish along ocean shorelines. The ancestors of whales gradually became more dependent on the ocean for food, passing through an amphibian stage before evolving into fully aquatic animals. Recent work with whale fossils indicates that the anklebones of whale ancestors resembled those of artiodactyls, the group of even-toed hoofed mammals that includes pigs, deer, antelopes, and hippopotamuses. Molecular studies comparing the genetic makeup of modern whales to that of other animals indicates that the hippopotamus is the whale's closest genetic match. Based on these studies, scientists now generally agree that whales are most closely related to artiodactyls. 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, land animal that measured about 2.5 m (about 8 ft) in length. 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 smaller than those of Pakicetus and its hind feet were turned into webbed paddles. Rodhocetus was clumsy on land, perhaps like modern sea lions. It probably swam using an up-and-down flexing of the body to power its finlike feet in the manner of otters. Unlike modern whales, it had nostrils instead of a blowhole. Rodhocetus also had a powerful tail, although scientists do not know whether this early whale had begun to evolve tail flukes. A fossil whale known as 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. The adult Basilosaurus reached lengths of 15 m (50 ft), but its hind limbs resembled short sticks only 0.5 m (1.6 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 whale species still have tiny pelvic and leg bones embedded in muscle near the spine. VI WHALING Humans have hunted whales since prehistoric times (see Whaling). Initially, humans only killed whales that had become stranded on land, but eventually people began using handheld harpoons and small boats to pursue whales at sea. Primitive subsistence whaling relied on coastal species such as the gray whale and the bowhead. By the 1700s commercial whaling had developed into a major industry. The primary whale product was spermaceti, a thick liquid from the head of sperm whales. Spermaceti burns with a clear, smokeless flame and was highly valued for making candles. Baleen was also in demand for several decades for use in a variety of commercial products including umbrella spokes, bustles, bodices, collars, ruffs, and hoop skirts. Hunting for baleen whales was very profitable during the late 1800s, when baleen fetched as much as $7 per 0.45 kg (1 lb). One whale could provide as much as 1,360 kg (3,000 lb) of baleen. But once the manufacture of steel stays for corsets and other products came into fashion, the baleen industry declined. During the 1700s and 1800s, sailors captured whales by throwing hand harpoons from oar-driven boats. The easiest whales to kill with this method were the slower swimmers, such as grays, bowheads, humpbacks, sperm whales, and right whales. The giant rorquals were rarely hunted because they usually swam much too fast for the whalers to catch. By 1850 American whalers made up 80 percent of the world whaling fleet, and they harvested over 10,000 whales per year. This extensive whaling contributed to the near decimation of several species of whale. Just as many whales were nearing extinction, in 1849 a new method became available for distilling kerosene from petroleum. When kerosene began to substitute for whale oil, the whalers' markets gradually dried up for a few decades. The whaling industry revived at the turn of the 20th century when the process of hydrogenation made it possible to process whale oil into soap and margarine. The invention of fast steam-powered ships and cannon-fired harpoons with exploding heads made it easier to capture even the fast-swimming rorquals. Captured whales were ground up on factory ships to make lubricants, soaps, cosmetic products, and animal feeds. In the first half of the 20th century Japan and Norway were the primary whaling nations. More than 2 million whales were killed by mechanized whaling techniques in the early 20th century. In 1910, for example, 176 blue whales were killed; by 1931 the harvest had exploded to 30,000. Blue whales became ever scarcer over the years until 1966, when hunting for blue whales in the Southern Hemisphere was banned by international agreement. Other species that had been considerably depleted in the Northern Hemisphere a century earlier, such as the humpback, were driven toward extinction. Today many species remain highly vulnerable to extinction, particularly right, bowhead, gray, and blue whales. To prevent whale extinction and to help whale populations recover, several countries and conservation organizations around the world have rallied to protect whales. In 1946 the International Convention for the Regulation of Whaling, signed by 14 whaling nations, agreed to regulate the conduct of whaling worldwide. The convention established the International Whaling Commission (IWC) in 1948. The purpose of the IWC was to set limits on the numbers and size of whales that could be hunted, to designate open and closed seasons and areas for whaling, and to compile catch reports and other statistical and biological records related to whaling. However, since 1982 the IWC has called for a halt, or moratorium, on the commercial hunting of all whales, including dolphins and porpoises. Whale-hunting abuses by a few nations continue, however. VII THREATS TO WHALES In addition to whaling, whales are endangered by increasing ocean pollution. This is particularly true of dolphins and other species that live in coastal waters. These animals eat contaminated fish and other food, and their body tissues build up large concentrations of toxic chemicals such as lead, mercury, and pesticides. Underwater noise pollution from ship motors, oil drilling and production, and the operation of undersea machinery may also threaten whales. This noise pollution is increasing, as is the use of loud sounds to develop sonar images. Geologists use sonar to study the structure of ocean water masses, the seafloor, and underlying rock. Fishermen and scientists use sonar to survey fish populations. Navy ships use sonar to probe for submarines and in warfare activities. Scientists believe that the intensity of noise levels in some ocean areas may interfere with the transmission of whale calls or the whales' ability to locate food. In particularly noisy areas, noise pollution may severely disorient whales, causing them to strand themselves on shore in a behavior known as beaching. Recent evidence suggests that some sonar is loud enough to cause physical injury to whales. Interactions of whales in the wild with humans have also negatively affected whale populations. Whale-watching expeditions are a popular boating activity. Occasionally boaters cruise too close to whales, preventing the animals from hunting for food or inadvertently separating mothers from their calves. Whales may move quickly to evade a boat or may exhibit aggressive defensive behaviors. These actions sometimes cause boats to accidentally collide with the animals and injure them. Scientific classification: Whales belong to the order Cetacea. There are two suborders: Odontoceti (toothed whales) and Mysticeti (baleen whales). The toothed whale suborder includes sperm whales, classified as Physeter catodon; beaked whales in the family Ziphiidae; narwhals, classified as Monodon monoceros; and belugas, Delphinapterus leucas. Toothed whales also include members of the dolphin family, Delphinidae, and the porpoise family, Phocoenidae. The baleen whale suborder includes members of the rorqual family, Balaenopteridae. Important rorquals include the blue whale, which is classified as Balaenoptera musculus, the fin whale, which is classified as Balaenoptera physalus, and the humpback whale, which is classified as Megaptera novaeangliae. The gray whale is a member of the family Eschrichtiidae and is classified as Eschrichtius robustus. The right whale belongs to the Balaenidae family. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.