How Whales Work

对我们来说,这些creatu的道路res from land to sea may seem like an odd turn of events. Why would a land mammal, specifically adapted for life on solid ground, evolve into a sea creature, spending much of its time away from air and sunlight? The best guess is that the whale's ancestors simply went where the food was. The ocean is filled with a wide variety of fish and crustaceans, while food along the coast can be scarce. Most likely, whale ancestors first ventured into the water to take advantage of this bounty.

To make this transition, whales had to overcome a number of obstacles. First of all, they had to contend with reduced access to breathable air. This led to a number of remarkable adaptations. The whale's "nose" moved from the face to the top of the head. Thisblowholemakes it easy for whales to breathe in air without fully surfacing. Instead, a whale swims near the surface, arches its body so its back briefly emerges and then flexes its tail, propelling it quickly to lower depths.

To breathe in air at the surface, a whale flexes amusclethat opens the blowhole and then inhales in the same way as any other mammal. When the whale relaxes the muscle, the blowhole closes, so it is safe to submerge again. Since they can only breathe at the surface, whales have had to developconscious breathing。They do not have the automatic breathing processes that we do. Contrary to popular belief, whales do not squirt seawater out of their blowholes. The spout people see is actually caused by exhaled air. Since the exhaled air is typically warmer than the surrounding air at the water's surface, it cools rapidly as it flows out. The water vapor in the air immediatelycondensesinto a liquid, giving the appearance of spraying water. Since each species of whale has a uniquely shaped blowhole (and many have two blowholes), they also have their own distinctive spout shape. Experienced whale-watchers can identify a particular species by its spout alone.

In the next section, we'll learn more about how whales breathe and find out how whalessleepand survive underwater.

In order to have much of a life in the ocean, whales had to be able to swim for long periods of time without coming up for air. To do this, they developed highly specialized respiratory systems. A whale'slungswork the same basic way ours do, but they make the most of each breath. In one breath, your body might absorb 15 percent of the oxygen you inhale. The whale, on the other hand, absorbs as much as 90 percent of the oxygen it breathes in. When you consider the immense size of a whale's lungs, that's a lot of oxygen per breath!. As in other mammals, whales store this excess of oxygen inmyoglobin, a specialized proteincellfound inmuscles。Whales have greater amounts of myoglobin than other animals, which allows them to store larger amounts of oxygen at a time.

Whales also make more efficient use of this oxygen. When they dive, theirheartbeats more slowly and select arteries are constricted. This slows the flow ofblood《没有减少某些器官血e. Essentially, a whale's specialized physiology gives it better "gas mileage" -- they make each breath last. Thesperm whale's respiratory system is among the most efficient in the world -- the huge animal can hold its breath for 80 to 90 minutes at a stretch. The beaked whale takes the prize, however. It can swim without a breath for as long as two hours.

Apart from the lack of breathable air, the most inhospitable element of the oceans is the extreme cold. Little sunlight penetrates the water's surface, and the temperature can drop below freezing even at relatively shallow depths. To deal with this biting cold, whales have developed a thick layer ofblubberall around their bodies.

Blubber, a layer of stored-upfatbeneath the skin and above the muscles, acts as a blanket to hold in the whale's body heat. In colder seasons, this insulating layer is the only thing keeping whales from freezing to death. Whales also use their blubber to store up energy for future use. Some species will feed heavily for half the year, when food is plentiful, and fast the rest of the year, living off their built-up blubber layer.

One of the less obvious difficulties of ocean life is getting a good night'ssleep。Since whales must make a conscious decision to breathe, it isn't feasible for them ever to be completely unconscious. They might not wake up in time to take a breath! Marine biologists have determined that whales get around this problem by letting only one-half of thebrainsleep at a time. In this way, the whale is never completely unconscious, but it still gets all the rest it needs.

We can't know for sure what this rest state feels like, but most likely, it is something like the semi-conscious state we experience as we begin to fall asleep. We're pretty close to unconsciousness, but have enough awareness of our surroundings to wake up completely if we need to. It's not uncommon to see a whalelogging、游泳慢慢沿着表面little movement. Presumably, whales behave this way when they are at rest.

Another problem with ocean life iswater pressure。Because of the pull ofgravity, water exerts greater pressure at lower depths than it does at higher depths; essentially, you feel the extreme weight of all the water above you. Humans and other land mammals can only swim down to a relatively shallow depth before the increased pressure crushes their bodies. This is because the air that mammals carry in their lungs exerts only a certain amount of outward pressure (pressure from the inside of your body). As the difference between the outward pressure in the lungs and the inward pressure of the water increases, there is a greater force pushing in on the sides of the body. At a certain point, this force exceeds the structural integrity of the rib cage, and the rib cage collapses. Obviously, this would kill a human being.

Whales can withstand this pressure because their bodies are more flexible. Their ribs are bound by loose, bendablecartilage, which allows the rib cage tocollapseto some degree under high pressure that would easily snap our bones. A whale's lungs can also collapse safely under pressure, which keeps them from rupturing. When the lungs collapse, the air inside them is compressed, maintaining a balance between inward and outward pressure. These adaptations are particularly important tosperm whales, which dive to depths of 7,000 feet (2,133.6 m) or more, hunting for the giant squid that live at these great depths.

In addition to adapting to the difficult conditions of ocean life, whales have also adapted to take full advantage of its rich resources. In the next sections, we'll look at some of the remarkable features that help whales catch their prey.

All 75 species of whale are carnivores, but their hunting methods vary considerably.Toothed whales, such as thesperm whaleand thekiller whale(ororca), hunt in the same basic way assharks。They have a row of strong teeth, and they tear into their prey or swallow it whole. Many toothed whales eat only small fish and other easy-to-catch prey. Orcas, on the other hand, may attack sea lions, seals and even other whales. Like wolves, polar bears and other land predators, they track and stalk their prey, picking out a weaker target (such as a babyhumpback whale). Orcas and other species usually hunt in packs, sometimes surrounding their prey. Despite these tendencies, orcas and most other toothed-whale species pose little threat to humans. In fact, many species seem to enjoy human company.

Some of these hunters have developedecholocationabilities to help them find their prey and locate any obstacles. Echolocation is a very simple concept: The whale emits a series of clicks (or other sounds) from its mouth or from organs in its head, and the sound waves travel out in the surrounding water. When the sound waves reach an obstacle or another animal, they bounce off of it and travel back to the whale. Water conducts sound very well, and whales have excellenthearing, so they may pick up even the faintest echoes from an object miles away.

In a volume of water with consistent pressure, sound will always travel at the same speed. By processing how long it takes the echo to return, the whale can calculate how far the sound wave traveled, and therefore determine how far away the object is. Like most animals, whales have two ears, one on each side of their head. This lets them determine the direction a sound is coming from. If the sound reaches the right ear first and is slightly louder in the right ear, the sound source is to the right; if it reaches the left ear first, it is to the left. In the dark world of the ocean, whales must sense their environment primarily through sound. In whales, a greater percentage of the brain is dedicated to processing aural information than to processing visual information. (In humans, the reverse is true.)

Echolocation is mainly found in toothed whales, such as dolphins and sperm whales, not their toothless cousins. Thetoothless-whale group-- which includes humpback whales, blue whales and many other species -- possess a unique feeding adaptation called a鲸须。The baleen is a wide plate in the whale's mouth, made up of hundreds of long, fringed blades, composed ofkeratin-- the same material in our fingernails. These blades form a sieve that the whale uses to filter small animals -- such as krill,plankton和小鱼——海水。因为这个unique attribute, toothless whales are usually referred to as鲸须whales。

There are two groups of baleen whales, distinguished by the way they use theses sieves.Skimmersopen their mouths and swim forward, catching fish, crustaceans and plankton as they go. After they've filtered a good bit of water, they knock any morsels loose and swallow them whole.Gulperstake in a mouthful of water and then push the tongue forward to force it all out through their baleen, catching any prey on the inside of the plate. Despite their large size, baleen whales typically have very small throats, measuring only a few inches across. This is all they need to devour the krill and other small creatures that make up their diet.

Since baleen whales filter water for theirfood, instead of ripping into their prey with sharp teeth, many people get the impression that they are passive hunters, simply cruising through the sea with their mouths open, snagging whatever happens to be in the way. But in fact, most baleen whales will seek out areas with high concentrations of food, and they may employ a number of tactics to catch their prey. Humpback whales, for example, trap fish with a sort ofbubble net。When it has located a school of fish near the ocean's surface, a humpback swims in a circle underneath them, releasing air out of its blowhole. This builds up columns of bubbles all around the school, so they are contained in one small area. Then the whale charges up from below, catching the fish in its baleen. Humpback whales may also emit a loud shriek as they approach the fish, apparently in an effort to disorient their prey.

Humpback whales and other whale species can produce a wide range of sounds, which they use to communicate with each other over long distances. In the next section, we'll explore the noises whales make and find out what this might say aboutwhale intelligence。

In the past hundred years, the world's attitude toward whales has changed drastically. The animals are no longer seen as fearsome creatures, as represented in "Moby Dick," and worldwide protection efforts have significantly reduced whale hunting. Through extensive observation, scientists have demonstrated that whales are generally peaceful, playful creatures, and that they posses a high level of intelligence. Today, whales seem pleasantly familiar to us, while in the past, they were monstrous strangers.

But even now, whales are still a mystery of sorts. A lot of information gathered by whale researchers has raised new puzzles about the animals.Whale communicationis particularly perplexing. Male humpbacks (also known asbulls), the most vocal whales, emit acomplex sequence of low moans, high squeals and clicking noises。These noises are sometimes combined insongsthat last as long as 30 minutes. The astounding thing about these songs is that whales will repeat them over and over again, verbatim. And in a particular region, every male will sing the same song, making small changes every once in a while so that it evolves into a completely different song over time.

This behavior seems to be related toreproduction。During mating season, a male humpback starts the long song sequence, cutting it short only to join a passing female whale (also known as acow), escorting her and her calf as they swim along. Eventually, the bull and cow may dive deep into the ocean, presumably to mate. It seems logical that the male's song is analogous to the bright plumage that birds display to attract a mate, except that the sound carries over many miles, attracting any other male humpbacks in the area. It's very odd that a male would call his own competition to him, unless he actually wanted to test his strength against others. Some whale researchers believe that the songs are actually acoustic contests of strength, similar to rams butting heads, or deer clashing their antlers.

Whales don't produce sounds the way we do. Our vocal-cord system wouldn't work too well underwater. Instead, whales produce sound bymoving inhaled air around the nasal cavity in front of their blowholes。In toothed whales, the sound-making system involves a complex arrangement of fatty tissues. In sperm whales and dolphins, these sound structures are so large that they form a pronouncedbulbous shape on the forehead。Scientists still don't understand exactly how whale sound production works, but they know it is unlike anything else we've encountered in the animal kingdom.

Humpback whales and most other species produce a wide range of sounds on a daily basis. In many species, whales seem to form close bonds with one another, and their calls may serve to let their companion whales know where they are and what they are doing. Water is an excellent fluid for conducting sound, and whale calls can be extremely loud, so they may communicate with one another over hundreds, perhaps thousands of miles. Whale experts are concerned that the noise pollution caused by boats,offshore drillingand other human activities in the ocean is drowning out these calls, shutting down the whale's long-distance communication system.

We still don't know what whales are actually saying to each other, but some researchers believe that whales possess sophisticated language capabilities. Whales have largebrains, with the complex folds biologists associate with higher intelligence, but the extent of their abilities is not clear. Many species do exhibit highly intelligent behavior, both in captivity and in the wild, learning complex tasks and demonstrating advanced problem-solving skills.

Whales also have excellent memories, as is evident in theirmigration patterns。As we'll see in the next section, individual whales seem to remember specific points along the coast and throughout the ocean, returning to the same choice feeding spots year after year.

One of the most intriguing aspects of whale behavior is the creatures'migration habits。Humpback whales in the Pacific Ocean will travel up and down the U.S. coast and out to Hawaii, returning to the samefood-rich areas year after year. They tend to migrate with the change of seasons, taking advantage of the warmer waters nearer the equator during the colder months and the overabundance of food in the Arctic during the warmer months. Most whale species do not migrate regularly across the equator, so there may be separate collections of each species in the Northern and Southern Hemispheres.

Scientists study whale migration in a number of ways. In many species, whales havedistinctive markings on their tails, which enable researchers to identify specific whales and track the sightings to get an idea of where and when the whale is traveling. Researchers also usesatellite tags, cigar-sizedradio transmittersthat communicate withsatellitesto track a whale's location. Researchers embed the barbed transmitters in a whales back using a basic crossbow. Since the blubber is thick and the barb is fairly small, the whales are not hurt by the shot.

Transmitters have shown that some whale species travel much greater distances than scientists previously estimated. Researchers have tracked humpback whales traveling thousands of miles in only a few weeks, swimming from high northern latitudes to equatorial latitudes and back again. Male sperm whales seem to be solitary wanderers, traveling from ocean to ocean with no particular pattern. A single sperm whale might easily swim around the entireEarthin its 70-year lifetime.

In most other whale species, migration is closely connected toreproduction。Generally, the female whales (cows) mate in the fall or winter, when they are in warmer waters, and give birth in the same region a year or so later. In the summer, between mating and birth, the cow will take advantage of the rich food resources of the colder northern waters. This builds up the energy the cow needs to suckle its calf.

Whale calves can swim as soon as they are born, and they rise to the surface to breathe soon after birth, but they need a lot of nurturing before they can venture out on their own. Depending on the species, whales may stick to their mother's side for a year or more before joining other young whales for extended play periods. For much of this time, the calf subsists only on its mother's milk. Cows have two teats, which are normally concealed inside slits behind the whale's abdomen, near the base of the tail. Whale milk is exceptionally rich, giving the calves the nutrients they need to grow to full size in a short period of time. A baby blue whale drinks 50 gallons (189 L) of milk every day and grows by as much as 10 pounds (4.54 kg) every hour. Of course, blue-whale calves are no shrimps to begin with. A newborn calf may measure 25 feet (7.62 m) from head to tail and typically weighs more than a full-grown African elephant.

Since the gestation and rearing periods are so long in most whale species, and the suckling so draining, cows only give birth every two to four years. This slow reproductive rate means that any substantial whale hunting may have a detrimental effect on whale populations.

In the next section, we'll take a look at a fascinating acrobatic feat performed by whales -- breaching.

One of the most spectacular behaviors in the animal kingdom is whalebreaching。In this jaw-dropping acrobatic feat, whales weighing many tons build up enough velocity underwater to launch themselves above the ocean's surface, twist in the air and fall back, producing a tremendous splash.

Whale researchers still aren't sure why whales do this, but they have a number of guesses. It may be that the huge splashing sound is used tocommunicatewith other whales, especially when there is a lot of other noise underwater. Another idea is that the whales are trying toknock off crustaceans and other parasites attached to their body。Some researchers think breaching may be ademonstration of prowess, and that it could play some role incourting rituals。最流行的一种观点是,鲸鱼的信徒ach simplyfor the fun of it。Most likely, breaching serves many different purposes that vary depending on the species and situation.

In the next section, we'll discuss the differences between whales and dolphins. Think of it as explaining the difference between two cousins in the same family.

In some cases, scientists use the termwhaleto describe all animals in the orderCetacea.This includes large species such as humpback and blue whales, as well as smaller species, such as the bottle-nosed dolphin. Most of the time, people use the term "whale" only to describe the larger whale species, and refer to smaller cetaceans as dolphins or porpoises.

Dolphins, which make up the familyDelphinidae, are toothed whales characterized by their relatively small size, bulbous head and beaked snout. Orcas and pilot whales are also included in this family, though they are much larger and their beak is less pronounced. Porpoises, members of the familyPhocaenidae, are small toothed whales that have a rounded head rather than a beaked snout.

In the next section, we'll explore the history of whale hunting and conservation to see how the relationship between whales and people has evolved over the years.

In the past, the main contact that humans had with whales was in hunting them. In some cultures, whale meat was a majorfoodsource dating back to prehistoric times. Whales were highly prized game because, like the woolly mammoth or bison, a single kill yielded an incredible amount of meat. But by the 1700s, when worldwide whaling really took off, the focus had shifted from the meat to a rich oil derived from whale blubber. Since it was the primary lamp fuel in many parts of the world, whale oil was big business throughout the 1700s and into the 1800s.

In this era, whale鲸须was also highly prized. The keratin material, commonly referred to aswhalebone, combines great strength and flexibility. These qualities made it an ideal choice for a variety of products, including ladies' corsets, riding crops and umbrellas. Whale teeth, engraved with inscriptions and decorations, were also very popular, particularly among the upper class.

The surge of whaling in this time had a profound impact on many whale species. Since whales only reproduce once every year, or, in many species, once every few years, they are devastated by excessive hunting. A female whale might live 50 years or more, giving birth to dozens of calves in that time, so the loss of even one female whale has a far-reaching effect on the entire population. Additionally, reduced whale numbers upset the sea's ecological balance, leading to an overabundance of krill in many areas, which can lead to population booms in other species that feed on the creatures.

With the invention of the harpoon gun and the increased speed and mobility of steam-powered boats, whalers could take aim at crafty species that had eluded them before. This, along with the rising popularity of whale-oil cosmetics, led to an unprecedented period of whaling in the late 1800s and early 1900s. By the 1940s, it was clear that some whale species were nearing extinction. To secure the future of the industry, the major whaling nations bound together in 1946 and signed theInternational Whaling Convention。As part of this agreement, the nations established theInternational Whaling Commission, an independent organization charged with researching whale populations and regulating whaling practice.

Over the years, the commission instituted even stricter regulations on whaling practice, in light of new evidence that whale populations were still dwindling. In 1986, the commission instituted a worldwide moratorium on whaling, as it had become clear that any widespread hunting could lead to species extinction. Today, the commission only allows for small-scale hunting by certain aboriginal cultures and hunting for scientific purposes. Some nations, most notably Japan and Norway, continue to allow commercial whaling, claiming that they are only controlling regional whale populations.

Under these regulations, many whale species have bounced back from the brink of extinction, but others, such as theright whale, are still in serious danger. According to whale-conservation organizations, the survival of these species depends on even stricter whaling regulations and more vigilant campaigns against illegal whaling operations. If these conservation efforts succeed, endangered whale species have a good shot at replenishing their numbers and continuing their mastery of the oceans for another 50 million years.