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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 in current taxonomy, but in more common English usage it generally excludes the members of the Delphinoidea superfamily, such as dolphins and porpoises.[1] 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. Whales are among the most charismatic animals, and are often passionately loved and defended by fans worldwide.


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 around 54 million years ago.[2][3] Whales entered the water roughly 50 million years ago.[4] 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 (105ft) long and 150 tons.

Whales generally live for 40–90 years,[citation needed] 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.[5] 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.[6][7] 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.[8]

Anatomy of the ear
See also: Evolution of cetaceans

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 lower jaw, where it passes through a low-impedance, fat-filled cavity.[9][10]

Behavior
A Humpback Whale breaching.

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.

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.[citation needed]

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.[12]

Whales are known to teach and learn, as well as cooperate, scheme, and even seem to grieve.[13]

Human effects

Whaling
Main article: Whaling
A fossil whale bone found at a California Beach.
World map of International Whaling Commission (IWC) members/non-members(member countries in blue).
World population graph of Blue Whales (Balaenoptera musculus).
Eighteenth century engraving of Dutch whalers hunting Bowhead Whales in the 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.[14] 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 Norway, Iceland and Japan and the aboriginal communities of Siberia, Alaska and northern Canada.

Several species of small whales are caught as bycatch in fisheries for other species. In the Eastern Tropical Pacific 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.

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.[15] Responses in Nature the following year discounted the explanation.[16]

Mass whale beachings 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.[13]

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 Parliament has requested that EU members refrain from using the powerful sonar system until an environmental impact study has been carried out.

Whales in culture
Whale weather-vane atop the Nantucket Historical Association Whaling Museum displaying a Sperm Whale.