Whale
From Wikipedia, the free encyclopedia.
Whales comprise about eighty species of large, 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 which leads to difficulties, as the Killer Whale and the Pilot Whale are members of the family Delphinidae and technically dolphins. The cetaceans are divided into two suborders: Mysticeti - the baleen whales - and Odontoceti - the toothed whales.
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2 Evolution 3 Anatomy 4 Behaviour 5 Whales and Humans 6 See also 7 References and external links |
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.
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. 40 mln years ago appeared the first fully marine cetaceans, like Basilosaurus.
Anatomy
Like all mammals, whales breathe air into lungs, are warm-blooded (to be precise, endothermic), breast-feed their young, and have some (very little) hair. The whales' adaptions to a fully aquatic life are quite conspiciuous: 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.
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
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 can't 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 the other 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.
Whales and Humans
Conservation
Most species of large whales are endangered.
Whaling
Main article Whaling For centuries they have been hunted for oil, meat, baleen and ambergris (a perfume ingredient from the intestine of sperm whales). Until the middle of the 20. century, whaling nearly extincted many populations. The International Whaling Commission introduced an open ended moratorium on all commercial whaling in 1986. Norway lodged a protest to the zero catch limits in 1992 and is not bound by them. Special permits to allow whale killing for scientific purposes is also granted. Many anti-whaling campaigners dispute how much scientific value this research has, claiming it to be a mere cover for a commercial catch.
Quotas regulate traditional whaling for aboriginal ethnic groups, e.g. in the United States, Siberia and Pacific island nations and commercial catch of Minke Whale in Norway. Whaling is also kept up in Japan, Iceland and Canada.
Several small whales is each year caught as bycatch in other 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 to gain food, oil or bait meat. However, most endangered are the river dolphins by changes to the rivers they inhabitate.
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 the 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
References and external links
- Private communication between Asbjorn Bjorgvinsson, curator of the Husavik Whale Centre and .
- Cetacea site
- Greenpeace (anti-whaling) site
- High North Alliance (pro-whaling) site
- Kate Wong: "The Mammals that Conquered the Seas", Scientific American, Vol 286, No 5, May 2002
- Whales, Dolphins and Porpoises by Mark Carwardine, published by Dorling Kindersley, 2000. ISBN 0-7513-2781-6. A very good introductory guide to cetaceans. It is inexpensive yet comprehensive.