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.
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.
A complete up-to-date taxonomical listing of all cetacean species, including all whales is maintained at the Cetacea article.
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, 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 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.
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.
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
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.
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.
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.
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.
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.
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. Melville acknowledged "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." Melville's book is an extraordinary work, part adventure story, part metaphysical allegory, and part natural history; it is essentially a complete summary of nineteenth-century knowledge about the biology, ecology and cultural significance of whales.
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.