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Whale

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Whales are the largest species of exclusively aquatic placental mammals, members of the order Cetacea, which also includes dolphins and porpoises. They are the largest mammals, the largest vertebrates, and the largest known animals in the world.

The term whale is ambiguous: it can refer to all cetaceans, to just the larger ones, or only to members of particular families within the order Cetacea. The latter definition is the one followed here. Whales are those cetaceans which are neither dolphins (i.e. members of the families Delphinidae or Platanistoidae), nor porpoises. This can lead to some confusion because Orcas ("Killer Whales") and Pilot Whales have "whale" in their name, but they are dolphins for the purpose of classification. Cetologists tend not to worry too much about such distinctions.

Size comparison between some well-known whales and other sea animals
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Size comparison between some well-known whales and other sea animals
Contents

Taxonomy

Cetaceans are divided into two suborders:

  • The baleen whales are characterized by the 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 whales.
  • The toothed whales have teeth and prey on fish and/or squid. 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 (i.e., endothermic), breast-feed their young, and have some (although very little) hair. The whales' ancestors lived on land, and their adaptions to a fully aquatic life are quite striking: The body is fusiform, resembling the streamlined form of a fish. 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. Although whales generally do not possess hind limbs, some whales (such as sperm whales, baleen whales, and humpback whales) have been seen having rudimentary hind limbs; some even with feet and digits. Most species of whale bear a fin on their backs. Beneath the skin lies a layer of fat, the blubber. It serves as an energy reservoir and also as insulation. Whales have a four-chambered heart. The neck vertebrae are fused in most whales, which provides stability during swimming at the expense of flexibility.

Whales breathe through blowholes, located on the top of the head so the animal can remain submerged. Baleen whales have two; toothed whales have one. When exhaling after a dive, a spout can be seen from the right perspective, the shape of which differs among the species. Whales have a unique respiratory system that lets them stay underwater for long periods of time without taking in any oxygen. Some whales, such as the Sperm Whale, can stay underwater for up to two hours holding a single breath.

Especially noteworthy is the Blue Whale, the largest known animal that has ever lived. It may be up to 30 meters long and weigh 180 tons.

Behavior

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Main article: Whale behaviour

Whales are broadly classed as predators, but their food ranges from microscopic plankton to very large fish. Males are called bulls; females, cows. The young are called calves.

Because of their environment (and unlike many animals), whales are conscious breathers: They have to decide when to breathe. So how do they sleep? All mammals sleep, and so do whales, but they cannot afford to fall unconscious state for too long, since they need to be conscious in order to breathe. The solution is that only one hemisphere of their brains sleeps at the time, so that whales are never completely asleep, but still get the rest they need. Whales "sleep" around 8 hours a day.

Reproduction

Whale females give birth to a single calf. Nursing time is long (more than one year in many species), which is associated with a strong bond between mother and young. In most whales reproductive maturity occurs late, typically at seven to ten years. This strategy of reproduction spawns few offspring, but provides each with a high rate of survival.

The genital organs are retracted into cavities of the body during swimming, so as to be streamlined and reduce drag. Most whales do not maintain fixed partnerships during mating; in many species the females have several mates each season. At birth the newborn is delivered tail-first, so the risk of drowning is minimized. Whale mothers nurse the young by actively squirting the fatty milk into their mouths.

Evolution of Whales

Whales, along with dolphins and porpoises, are descendants of land-living mammals, most likely of the Artiodactyl order. They entered the water roughly 50 million years ago. See evolution of cetaceans for the details [1] (http://news.bbc.co.uk/1/hi/sci/tech/1974869.stm).

Whales and Humans

Conservation

Most species of large whales are endangered as a result of whaling. However, river dolphins are the most at risk because of changes to the rivers they inhabit. The changes to rivers are mostly human-made i.e. the result of conventional economic development such as building large dams for purposes of irrigation or electricity. For example, the Three Gorges Dam on the Yangtze River in China is threatening the survival of the Yangtse Dolphin. Likewise, large dams being planned on the Irrawaddy River in Myanmar and the Mekong River along Thailand and Laos could lead to the extinction of the endangered Irrawaddy and Mekong Dolphins. Some of these dams like the Nam Theun 2 dam in Laos are also being supported by international nature conservation groups such as the World Conservation Union.

Whaling

Main article Whaling

For centuries large whales have been hunted for oil, meat, baleen and ambergris (a perfume ingredient from the intestine of sperm whales). Until the middle of the 20th century, whaling left many populations nearly or fully extinct. The International Whaling Commission introduced an open ended moratorium on all commercial whaling in 1986. For various reasons some exceptions to this moratorium exist; current whaling nations are Norway, Iceland and Japan and the aboriginal communities of Siberia, Alaska and northern Canada. For details, see whaling.

Bycatch

Several species of small whales are caught as bycatch in fisheries. Especially during the tuna fishery in the Pacific each year thousands of dolphins drown in the nets. In many countries, small whales are hunted for food, oil or bait meat.

Sonar and seismic testing

Environmentalists have long argued that some cetaceans including whales are endangered by sonar used by advanced navies.

In 2003 British and Spanish scientists have suggested in Nature that the sonar is connected to whale beachings and to signs that the beached whales have experienced decompression sickness (see a BBC report about the Nature article (http://news.bbc.co.uk/2/hi/science/nature/3173942.stm) or the Nature article itself (requires subscription) (http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v425/n6958/full/425575a_fs.html)). Mass whale beachings do occur amongst many species (most of them are beacked whales that make use of echolocation system for deep diving). The frequency and size of beachings around the world, recorded over the last 1000 years in religious tracts and more recently in scientific surveys, has been used to estimate the changing population size of various whale species by assuming that the proportion of the total whale population beaching in any one year is constant (reference?). Despite the concerns raised about sonar which may invalidate this assumption, this population estimate technique is still popular today.

Following public concern, the US Defense department has been ordered by a the US judiciary 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 so far failed. The European Parliament on the other hand has requested that EU members resist using the powerful sonar system until an environmental impact study has been carried out. [2] (http://home.businesswire.com/portal/site/google/index.jsp?ndmViewId=news_view&newsId=20041206005421&newsLang=en)

Conservationists are also concerned that seismic testing used for oil and gas exploration may also damage the hearing and echolocation capabilities of whales. They also suggest that disturbances in magnetic fields caused by the testing may also be responsible for beaching. See e.g. Seismic testing and the impacts of high intensity sound on whales, Lindy Weilgart, Department of Biology Dalhouise University (PDF format) (http://www.sustainability.ca/Docs/Impact%20of%20Seismic%20Surveys%20on%20Whales.pdf?CFID=9951883&CFTOKEN=72165442) or a typical press release from Greenpeace on the issue (http://whales.greenpeace.org/news/3aug2001.html)


Capture

A big attraction for ocean parks and zoos is keeping captured small whales, mostly dolphins. Because of their learning ability, they are also used by the military for marine warfare.

See also


Clipart and Animal Pictures

Further reading

  • Whales, Dolphins and Porpoises by Mark Carwardine, published by Dorling Kindersley, 2000. ISBN 0-7513-2781-6. Introductory guide to cetaceans.

External links

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