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Whale is the common name for marine mammals of the order Cetacea. The term whale is sometimes used to refer to all cetaceans, but in more common English usage it generally excludes the members of the Delphinoidea superfamily, such as dolphins and porpoises. These smaller species belong to the suborder Odontoceti (toothed whales), which also includes the sperm whale, killer whale, pilot whale, and beluga whale. The other suborder of cetaceans, Mysticeti (baleen whales), includes the blue whale, which is the largest animal known to have ever existed, the humpback whale, and many other animals that feed by straining seawater through long strips of baleen that they have in the place of teeth, and from which they get their name.

For centuries, whales have been hunted for meat and as a source of raw materials. By the middle of the 20th century, however, industrial whaling had left many species seriously endangered, and whaling was ended in all but a few countries. Several organizations have been founded to try to eliminate hunting of whales and other threats to whales' survival.

Origins and taxonomy



All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulate animals). Both cetaceans and artiodactyl are now classified under the super-order Cetartiodactyla which includes both whales and hippopotamuses. In fact, whales are the closest living relatives of hippos; they evolved from a common ancestor, the Indohyus, an approximately 48-million-year-old even-toed ungulate from the Kashmirmarker region of Indiamarker, around 54 million years ago. Whales entered the water roughly 50 million years ago.Cetaceans are divided into two suborders:
  • The baleen whales are characterized by baleen, a sieve-like structure in the upper jaw made of keratin, which they use to filter plankton from the water. They are the largest whale suborder.
  • The toothed whales use sharp teeth and prey on fish, squid, or both. An outstanding ability of this group is to sense their surrounding environment through echolocation.
A complete up-to-date taxonomical listing of all cetacean species, including all whales, is maintained at the Cetacea article.

Anatomy

Like all mammals, whales breathe air into lungs, are warm-blooded, feed their young milk from mammary glands, and have hair, although very little.

The whale body is fusiform. The forelimbs, also called flippers, are paddle-shaped. The end of the tail holds the fluke, or tail fins, which provide propulsion by vertical movement, unlike the horizontal movement of the tails of fish. Although whales generally do not possess hind limbs, some whales (such as sperm whales and baleen whales) have rudimentary hind limbs; even with feet and digits, hidden deep within their bodies. Most species of whale bear a fin on their backs known as a dorsal fin.

Beneath the skin lies a layer of fat called blubber. It serves as an energy reservoir and also as insulation. Whales have a four-chambered heart. Whales have spines, although the neck vertebrae are typically fused, which provides stability during swimming at the expense of flexibility. They have a vestigial pelvis bone.

Whales breathe through their blowholes, located on the top of the head so the animal can remain submerged while breathing. Baleen whales have two; toothed whales have one. Breathing involves expelling excess water from the blowhole, forming a vertical spout. Spout shapes differ between species and learning to recognize these shapes help people identify them.

The Blue Whale is the largest known mammal that has ever lived, and the largest living animal, at up to 35 m (105 ft) long and 150 tons.

Whales generally live for 40–90 years, depending on their species, and on rare occasions live over a century. Recently a fragment of a lance which had been used by commercial whalers in the 19th century was found in a bowhead whale off Alaska, showing the whale to be between 115 and 130 years old. Furthermore, a technique for dating age from aspartic acid racemization in the whale eye, combined with a harpoon fragment, indicated an age of 211 years for one male, making bowhead whales the longest lived extant mammal species.Whale flukes often can be used as identifying markings, as is the case for humpback whales. This is the method by which the famous Humphrey the whale was identified in three separate sightings.

Toothed whales such as the sperm whale, possess teeth with cementum cells overlying dentine cells. Unlike human teeth which are comprised mostly of enamel on the tooth portion outside of the gum, whale teeth have cementum outside the gum. Only in larger whales does enamel show where the cementum has been worn away on the tip of the tooth.

Anatomy of the ear

Whales' ears have specific adaptations to their underwater environment. In humans, the middle ear works as an impedance matcher between the outside air’s low impedance and the cochlear fluid’s high impedance. In aquatic mammals such as whales, however, there is no great difference between the outer and inner environments. Instead of sound passing through outer ear to middle ear, whales receive sound through their throat, from which it passes through a low-impedance, fat-filled cavity to the inner ear.

Behavior

Whales are widely classed as predators, but their food ranges from microscopic plankton to very large fish and, in the case of orcas, sometimes other sea mammals, even other whales. Whales such as humpbacks and blues eat only in arctic waters, eating mostly krill, which they swallow with enormous amounts of seawater, excreting the water through their baleen plates, while retaining the krill.

Whales do not drink seawater, instead indirectly extracting it from their food by metabolizing fat.

Males are called bulls; females, cows. The young are called calves.

Many whales also exhibit other surfacing behaviours such as breaching and tail slapping.

Because of their environment (and unlike many animals), whales are conscious breathers: they decide when to breathe. All mammals sleep, but whales cannot afford to become unconscious for too long because they might drown. It is thought that only one hemisphere of whale brains sleeps at a time, so that whales are never completely asleep, but still get necessary rest. Whales often sleep with only one eye closed.

Some whales communicate with each other using lyrical sounds, called whale songs. These sounds can be extremely loud (depending on the species); sperm whales have only been heard making clicks, because toothed whales (Odontoceti) use echolocation and can be heard for many miles. They can generate about 20,000 acoustic watts of sound at 163 decibels.

Females give birth to a single calf. Nursing time is more than one year in many species, which is associated with a strong bond between mother and young. Reproductive maturity occurs typically at seven to ten years. This mode of reproduction spawns few offspring, but provides each with high survival probability.

The male genitals retract into body cavities during swimming, reducing drag and preventing injury. Most whales do not maintain fixed partnerships during mating; in many species the females have several mates each season. Newborns are delivered tail-first, minimizing the risk of drowning. Whale cows nurse by actively squirting milk so fatty that it has the consistency of toothpaste into the mouths of their young.

Whales are known to teach and learn, as well as cooperate, scheme, and even seem to grieve.

Human effects

Whaling

[[File:18th century arctic whaling.jpg|thumb |right |Eighteenth century engraving of Dutch whalers hunting Bowhead Whales inthe Arctic.]]

Some species of large whales are listed by various watchdog groups and governments as endangered due to reduced population resulting from commercial whaling. Large whales have been hunted commercially for whale oil, meat, baleen and ambergris (a perfume ingredient from the intestine of sperm whales) since the 1600s. More than 2 million whales were killed by the modern whaling industry in the early 20th century. By the middle of the 20th century, whaling left many populations severely depleted.

The International Whaling Commission introduced a six year moratorium on all commercial whaling in 1986, which extends to the present day. The moratorium is not absolute, however, and some whaling continues under the auspices of research or aboriginal rights; current whaling nations are Norwaymarker, Icelandmarker and Japanmarker and the aboriginal communities of Siberiamarker, Alaskamarker and northern Canadamarker.

Several species of small whales are caught as bycatch in fisheries for other species. In the Eastern Tropical Pacificmarker tuna fishery, thousands of dolphins drowned in purse-seine nets, until preventive measures were introduced. Gear and deployment modifications, and eco-labelling (dolphin-safe or dolphin-friendly brands of tuna), have contributed to a reduction in dolphin mortality by tuna vessels. In many countries, small whales are still hunted for food, oil, meat or bait.

Sonar interference

Environmentalists speculate that sonar used by advanced navies endangers some cetaceans, including whales. In 2003 British and Spanish scientists suggested in Nature that sonar is connected to whale beachings and to signs that the beached whales have experienced decompression sickness. Responses in Nature the following year discounted the explanation.

Mass whale beaching occur in many species, mostly beaked whales that use echolocation for deep diving. The frequency and size of beachings around the world, recorded over the last 1,000 years in religious tracts and more recently in scientific surveys, has been used to estimate the population of various whale species by assuming that the proportion of the total whale population beaching in any one year is constant. Beached whales can give other clues about population conditions, especially medical conditions. For example, bleeding around ears, internal lesions, and nitrogen bubbles in organ tissue suggest that whales are in fact not immune to the bends.

Following public concern, the U.S. Defense department was ordered by the 9th Circuit Court to strictly limit use of its Low Frequency Active Sonar during peacetime. Attempts by the UK-based Whale and Dolphin Conservation Society to obtain a public inquiry into the possible dangers of the Royal Navy's equivalent (the "2087" sonar launched in December 2004) have failed as of 2008. The European Parliamentmarker has requested that EU members refrain from using the powerful sonar system until an environmental impact study has been carried out.

Other environmental disturbances

Other human activities have been suggested by Marine Biologists to adversely impact whale populations, such as the unregulated use of fishing gear which catches anything that swims into it, collisions with ships and propellers, and waste contaminants.

Whales in culture

Whales are frequently portrayed in literature as violent creatures that attack shipping and kill or eat sailors, despite overwhelming evidence to the contrary, particularly in literature written prior to the modern scientific study of the creatures, or in period literature. A common whale-themed plot device concerns mariners who are swallowed whole by a whale, and find themselves trapped alive in the creature's belly. In some instances, the victims of these encounters escape, often by causing the whale sufficient gastronomic distress that it is forced to expel them; in cases, the victim is doomed.

In religion

Portrayals of whales or whaling in religion include:

  • The King James Version of the Bible mentions whales four times: "And God created great whales" (Genesis 1:21); "Am I a sea, or a whale, that thou settest a watch over me? (Job 7:12); "Thou art like a young lion of the nations, and thou art as a whale in the seas (Ezekiel 32:2); and "For as Jonas [sic] was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth" (Matthew 12:40).
  • Some cultures associate divinity with whales, such as among Ghanaiansmarker and Vietnamese, who occasionally hold funerals for beached whales, a throwback to Vietnam's ancient sea-based Austro-asiatic culture. The movie Whale Rider follows the trials of a girl named Paikia, who lives in such a culture, the Maouri of New Zealand.


See also



References

Further reading

  • Carwardine, M., Whales, Dolphins and Porpoises, Dorling Kindersley, 2000. ISBN 0-7513-2781-6
  • Williams, Heathcote, Whale Nation, New York, Harmony Books, 1988. ISBN 9780517569320


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