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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. The term
whale is ambiguous: it can refer to all cetaceans, just the largest ones, or only to members of particular families within the order Cetacea. This latter definition is the one
followed within Wikipedia. Whales are those cetaceans which are neither dolphins (i.e. members of the families Delphinidae or Platanistoidae) or porpoises. This can lead to some confusion
as Orca (Killer Whales) and Pilot Whales have "whale" in their name, but are dolphins from the perspective of
classification. Cetologists tend not to worry too much about making a distinction.
Taxonomy
Cetaceans are divided into two suborders:
- The baleen whales are characterized by the baleen, sieve-like structures in the upper jaw made from keratin,
which they use to filter plankton from the water. They comprise the largest living animal species.
- The toothed whales possess teeth and prey on fish or squid. An
outstanding ability of this group is to perceive their environment by echolocation.
A complete up-to-date taxonomical listing of all cetacean species, including all whales is maintained at the Cetacea article.
Evolution
Like all members of the order, whales evolved from land mammals which returned to the sea undergoing aquatic adaptation, probably in the Eocene, between 55 and 34 million years ago. The precise ancestry of whales is still obscure, as there is no
commonly agreed succession, but they are thought to have evolved from a group of carnivorous artiodactyla (even-toed hoofed animals). In 2001, two important
47-million-year-old partial fossils, named Rodhocetus balochistanensis and Artiocetus clavis, were discovered in Balochistan, Pakistan. These fossils represent intermediate forms between land-living ungulates and whales and are evidence that the whales' closest relatives on land might be
hippos, which had been previously suggested by DNA studies. The first fully marine cetaceans, like Basilosaurus, appeared 40 million years ago.
Anatomy
Like all mammals, whales breathe air into lungs, are warm-blooded (i.e., endothermic), breast-feed their young, and have some (very little) hair. The whales' adaptions to a fully
aquatic life are quite conspicuous: The body is fusiform, resembling that of a fish. The forelimbs, also called flippers, are
paddle-shaped. The end of the tail holds the fluke, which provides propulsion by vertical movements. Whales do not possess hind
limbs, small bones inside the body are the only remains of the pelvis. Most species of whales 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, whhich 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 one blowhole. When breathing out 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 any oxygen. Some whales, such as the Sperm Whale, can stay
underwater for up to two hours in a single breath.
Especially noteworthy is the Blue Whale, the largest animal that has ever
lived. It may be up to 30 meters long and weigh 180 tons.
Behaviour
Main article: Whale behaviour
Whales are broadly classed as predators, but their food ranges from microscopic plankton to very large fish. The male is called a bull; the female, a cow; and the young, a calf.
Because of their environment, whales are conscious breathers: They have to decide when to breath. So how do they sleep? All
mammals sleep, and so do whales, but they cannot afford to fall in unsconscious state of sleep for too long periods of time,
since they need to be conscious in order to breath. The solution is that only one hemisphere of the brains of the whale sleeps at
the time, so 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, provided 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 minimizied. Whale mothers nurse the young by actively squirting the
fatty milk into their mouth.
Whales and Humans
Conservation
Most species of large whales are endangered as a result of whaling. However, most affected are the river dolphins by changes to the rivers they inhabitate.
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
Environmentalists have long argued that some cetaceans including whales are endangered by sonar and especially by the very powerful sonar used by the US defense department. British scientists have recently
suggested (in the journal 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 or the Nature article itself
(requires subscription) ).
Mass whale beachings do occur naturally amongst many species and in fact 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, under that assumption that the proportion of the total whale population
beaching in any one year is constant. Despite the concerns raised about sonar as mentioned above which may invalidate this
assumption, this population estimate technique is still popular today [1].
Whales in culture
Whales in the Bible
The Bible mentions whales four times: Genesis 1:21 "And God created great whales"; "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). (All quotations from
King James version).
Famously, the Book of Jonah (in the King James and some other
translations) does not use the word "whale" at all, referring throughout to a "fish" or a "great fish": "Now the LORD
had prepared a great fish to swallow up Jonah. And Jonah was in the belly of the fish three days and three nights." (Jonah 1:17).
This detail was used to dramatic effect in Clarence Darrow's
cross-examination of fundamentalist William Jennings
Bryan in the 1925 Scopes Trial,
as depicted in the drama "Inherit the Wind" by Jerome Lawrence and Robert E. Lee.
Herman Melville and Bharat
The hunting of whales is the subject of one of the classics of the English language literary canon, Herman Melville's Moby Dick. Melville classed
whales as "a spouting fish with a horizontal tail", despite science suggesting otherwise the previous century. In fact Melville
said "the grounds upon which Linnaeus would fain have banished the whales from the
waters" but says that when he presented them to "my friends Simeon Macey and Charley Coffin, of Nantucket ... they united in the opinion that the reasons set forth were altogether insufficient. Charley
profanely hinted they were humbug."
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
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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