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Whale

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Humpback whale [1]
Photo of Humpback whale with body (except for tail) belly-up in the air above the water.
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Subclass:
Eutheria
Order:
Cetacea

Whale (origin Old English hƿæl) is the common name for various marine mammals of the order Cetacea.[2] The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises[3], which belong to suborder Odontoceti (toothed whales). This suborder also includes the sperm whale, killer whale, pilot whale, and beluga whale. The other Cetacean suborder Mysticeti (baleen whales), are filter feeders that eat small organisms caught by straining seawater through a comblike structure found in the mouth called baleen. This suborder includes the blue whale, the humpback whale, the bowhead whale and the minke whale. All Cetacea have forelimbs modified as fins, a tail with horizontal flukes, and nasal openings (blowholes) on top of the head.

Whales range in size from the blue whale, the largest animal known to have ever existed[4] at Template:M to ft and 150 tonnes (150 long tons; 170 short tons), to various pygmy species, such as the pygmy sperm whale at Template:M to ft.

Whales collectively inhabit all the world's oceans and number in the millions, with annual population growth rate estimates for various species ranging from 3-13%.[5] 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, leading to the end of whaling in all but a few countries.

Taxonomy

Overhead photo of a long, thin, narrow-fluked whale with both pectoral fins extended
A Fin Whale
See also: List of whale species

Cetaceans are divided into two suborders:

  • The largest suborder, Mysticeti (baleen whales) are characterized by baleen, a sieve-like structure in the upper jaw made of keratin, which it uses to filter plankton from the water.
  • Odontoceti (toothed whales) bear sharp teeth for hunting. Odontoceti also include dolphins and porpoises.

Both cetaceans and artiodactyl are now classified under the super-order Cetartiodactyla which includes both whales and hippopotamuses. Whales are the hippopotamus's closest living relatives.[6]

Anatomy

Like all mammals, whales breathe air, are warm-blooded, nurse their young with milk from mammary glands, and have body hair.[citation needed]

Beneath the skin lies a layer of fat called blubber, which stores energy and insulates the body. Whales have a spinal column, a vestigial pelvic bone, and a four-chambered heart. The neck vertebrae are typically fused, trading flexibility for stability during swimming.[citation needed]hi

Blowhole(s)

Whales breathe via blowholes; baleen whales have two and toothed whales have one. These are located on the top of the head, allowing the animal to remain mostly submerged whilst breathing. Breathing involves expelling excess water from the blowhole, forming an upward spout, followed by inhaling air into the lungs. Spout shapes differ among species and can help with identification.

Appendages

The body shape is fusiform and the modified forelimbs, or fins, are paddle-shaped. The end of the tail is composed of two flukes, which propel the animal by vertical movement, as opposed to the horizontal movement of a fish tail. Although whales do not possess fully developed hind limbs, some (such as sperm whales and baleen whales) possess discrete rudimentary appendages, which may even have feet and digits. Most species have a dorsal fin.[citation needed]

Dentition

Toothed whales, such as the sperm whale, possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Only in larger whales, where the cementum has been worn away on the tip of the tooth, does enamel show.[7]

Instead of teeth, Baleen whales have a row of plates on the upper side of their jaws that resemble the "teeth" of a comb.

Ears

The whale ear has specific adaptations to the marine 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 the outer ear to the middle ear, whales receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear.[8]

Life history/behavior

See also: Cetacean intelligence

Vocalization

Spectrogram of Humpback Whale vocalizations. Detail is shown for the first 24 seconds of the 37 second recording Humpback Whale "Song". The ethereal whale "songs" and echolocation "clicks" are visible as horizontal striations and vertical sweeps respectively.
Humpback Whale "Song"
Recording of Humpback Whales singing and Clicking.
Problems playing this file? See media help.

Some species, such as the humpback whale, communicate using melodic sounds, known as whale song. These sounds can be extremely loud, depending on the species. Sperm whales have only been heard making clicks, while toothed whales (Odontoceti) use echolocation that can generate about 20,000 watts of sound at 163 decibels and be heard for many miles.[9] Whale vocalization is likely to serve many purposes, including echolocation, mating, and identification.

Reproduction

Males are called 'bulls', females, 'cows' and newborns, 'calves'. Most species do not maintain fixed partnerships and females have several mates each season.[10] [11]

The female delivers usually a single calf tail-first to minimize 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] Nursing continues for more than a year in many species, and is associated with a strong bond between mother and calf. Reproductive maturity occurs typically at seven to ten years. This mode of reproduction produces few offspring, but increases survival probability.

Male genitals retract into body during swimming, reducing drag and preventing injury.[citation needed]

Socialization

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

Sleep

Unlike most animals, whales are conscious breathers. All mammals sleep, but whales cannot afford to become unconscious for long because they may drown. It is thought that only one hemisphere of the whale's brain sleeps at a time, so they rest but are never completely asleep.[14]

Surfacing behavior

Photo of humpback whale with most of its body out of the water and its pectoral fins extended
A Humpback Whale breaching.
Main article: Whale surfacing behavior

Many whales exhibit behaviors such as breaching and tail slapping that expose large parts of their bodies to the air.

Lifespan

Whale lifespans vary among species and are not well characterized. Whaling left few older individuals to observe directly. R.M. Nowak of Johns Hopkins University estimated that humpback whales may live as long as 77 years.[15] In 2007, a 19th century lance fragment was found in a bowhead whale off Alaska, suggesting the individual could be between 115 and 130 years old.[16] Aspartic acid racemization in the whale eye, combined with a harpoon fragment, indicated an age of 211 years for another male, which, if true would make bowheads the longest-lived extant mammal species.[17][18] The accuracy of this technique has been questioned because racemization did not correlate well with other dating methods.[19]

Ecology

Feeding

Whales are generally classed as predators, but their food ranges from microscopic plankton to very large animals.

Toothed whales eat fish and squid which they hunt by use of echolocation. Orcas sometimes eat other marine mammals, including whales.

Baleen whales such as humpbacks and blues feed only in arctic waters, eating mostly krill. They imbibe enormous amounts of seawater which they expel through their baleen plates. The water is then expelled and the krill is retained on the plates and then swallowed.[12] Whales do not drink seawater but indirectly extract water from their food by metabolizing fat.[12]

Relation to humans

Whaling

Main article: Whaling
Photo of a solid brown object with white spots and a hole in the center
A fossil whale bone found at a California Beach
Map showing IWC non-members such as Canada and most Middle Eastern and African countries in white
World map of International Whaling Commission (IWC) members/non-members(member countries in blue)
Diagram showing the pre-whaling of 275,000, 1930's population of 30-40,000, mid-60's population of 650-2,000 and 1994 population of less than 5,000
World population graph of Blue Whales (Balaenoptera musculus)
Engraving showing manned rowboats and sailboats in the foreground and a steep-sided mountain in the background. Each boat is pointing at a whale. The lead man in each boat is pointing a rod with a large arrowhead on the end at a whale. Two three-masted large ships are in the center of the engraving.
Eighteenth century engraving of Dutch whalers hunting Bowhead Whales in the Arctic

Some species of large whales are listed as endangered by multinational organizations such as CITES along with governments and advocacy groups primarily due to whaling's impacts. They have been hunted commercially for whale oil, meat, baleen and ambergris (a perfume ingredient from the intestine of sperm whales) since the 1600s.[20] More than 2 million were taken in the early 20th century,[21] and by the middle of the century, many populations were severely depleted.

The International Whaling Commission banned commercial whaling in 1986.[22] The ban is not absolute, however, and some whaling continues under the auspices of scientific research[22] or aboriginal rights; current whaling nations are Norway, Iceland and Japan and the aboriginal communities of Siberia, Alaska and northern Canada.

Bycatch

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.[citation needed] In many countries, small whales are still hunted for food, oil, meat or bait.[citation needed]

See also: Marine Mammals and Sonar

Environmentalists speculate that advanced naval sonar endangers some cetaceans, including whales. In 2003 British and Spanish scientists suggested in Nature that the effects of sonar trigger whale beachings and to signs that such whales have experienced decompression sickness.[23] Responses in Nature the following year discounted the explanation.[24]

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, have 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 health problems. For example, bleeding around ears, internal lesions, and nitrogen bubbles in organ tissue suggest decompression sickness.[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) 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.

Other environmental disturbances

See also: Cetacean bycatch

Other human activities have been suggested by marine biologists to adversely impact whale populations, such as collisions with ships and propellers, poisoning by waste contaminants and the unregulated use of fishing gear that catches anything that swims into it.[citation needed]

In mythology

File:Nantucket historical assocation whaling museum weather vane.jpg
Whale weather-vane atop the Nantucket Historical Association Whaling Museum displaying a Sperm Whale.

Whales were little understood for most of human history as they spend up to 90% of the lives underwater, only surfacing briefly to breathe.[25] They also include the largest animals on the planet, so it is not surprising that many cultures, even those that have hunted them, hold them in awe and feature them in their mythologies.

In China, Yu-kiang, a whale with the hands and feet of a man was said to rule the ocean.[26]

In the Tyrol region of Austria it was said that if a sunbeam were to fall on a maiden entering womanhood, she would be carried away in the belly of a whale.[26]

Paikea, the youngest and favourite son of the chief Uenuku from the island of Mangaia in the present day Cook Islands in New Zealand was said by the Kati Kuri people of Kaikoura to have come from the Pacific Islands on the back of a whale many centuries before.[27] The novel and movie Whale Rider follow the trials of a girl named Paikia, who lives in such a culture.

The whale features in Inuit creation myths. When ‘Big Raven', a deity in human form, found a stranded whale, he was told by the Great Spirit where to find special mushrooms that would give him the strength to drag the whale back to the sea and thus return order to the world.[28]

The Tlingit people of northern Canada said that the Orcas were created when the hunter Natsihlane carved eight fish from yellow cedar, sang his most powerful spirit song and commanded the fish to leap into the water.[28]

In Icelandic legend a man threw a stone at a fin whale and hit the blowhole, causing the whale to burst. The man was told not to go to sea for twenty years but in the nineteenth year he went fishing and a whale came and killed him.[28]

In East African legend King Sulemani asked God that He might permit him to feed all the beings on earth. A whale came and ate until there was no corn left and then told Sulemani that he was still hungry and that there were 70,000 more in his tribe. Sulemani then prayed to God for forgiveness and thanked the creature for teaching him a lesson in humility.[28]

The King James Version of the Bible mentions whales four times: "And God created great whales" (Genesis 1:21); "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). The story of Jonah being swallowed by a whale also is told in the Qur'an.[29]

Some cultures associate divinity with whales, such as among Ghanaians and Vietnamese, who occasionally hold funerals for beached whales, a throwback to Vietnam's ancient sea-based Austro-asiatic culture.[citation needed]

Evolution

See also: Evolution of cetaceans
Reconstruction of Ambulocetus natans

All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulates). Both descended from a common ancestor, the Indohyus (an extinct semi-aquatic deer-like ungulate) from which they split around 54 million years ago.[30][31] Whales entered the water roughly 50 million years ago.[32]

See also

References

  1. ^ Mead, J. G.; Brownell, R. L. Jr. (2005). "Order Cetacea". In Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 723–743. ISBN 978-0-8018-8221-0. OCLC 62265494.
  2. ^ Brown, Lesley, ed. (2007). Shorter Oxford English Dictionary. Vol. II (Sixth ed.). Oxford: Oxford University press. p. 3611.
  3. ^ http://www.acsonline.org/education/taxonomy.html
  4. ^ "What is the biggest animal ever to exist on Earth?". How Stuff Works. Retrieved 2007-05-29.
  5. ^ "Whale Population Estimates". International Whaling Commission. March 2010. Retrieved March 2010. {{cite web}}: Check date values in: |accessdate= (help)
  6. ^ Anon (25 January 2005). "Scientists find missing link between the whale and its closest relative, the hippo". PhysOrg.com. PhysOrg.com. Retrieved 6 May 2010.
  7. ^ "Common Characteristics of Whale Teeth" here
  8. ^ "How is that whale listening?". Retrieved February 4, 2008.
  9. ^ "Table of sound decibel levels". Retrieved 2006-09-14.
  10. ^ "Blue Whale". Discovery Channel Blue Ocean. {{cite episode}}: |access-date= requires |url= (help); Missing or empty |series= (help)
  11. ^ "Milk". Modern Marvels. Season 14. 2008-01-07. The History Channel.
  12. ^ a b c "Blue Whale". Discovery Channel Blue Ocean. {{cite episode}}: |access-date= requires |url= (help); Missing or empty |series= (help)
  13. ^ a b Siebert, Charles (July 8, 2009). "Watching Whales Watching Us". New York Times Magazine.
  14. ^ Anon. "Do whales and dolphins sleep?". How Stuff Works. Discovery Communications. Retrieved 14 February 2010.
  15. ^ Anon (2005). "Humpback Whale". Animal Infor. Animal Info. Retrieved 25 February 2010.
  16. ^ Conroy, Erin (June, 2007). "Netted whale hit by lance a century ago". Associated Press. Retrieved 2009-10-05. {{cite web}}: Check date values in: |date= (help)
  17. ^ "Bowhead Whales May Be the World's Oldest Mammals". 2008-02-15. Retrieved 2008-03-25.
  18. ^ George, J.C.; et al. (1999). "Age and growth estimates of bowhead whales (Balaena mysticetus) via aspartic acid racemization". Can. J. Zool. 77 (4): 571–580. doi:10.1139/cjz-77-4-571. {{cite journal}}: Explicit use of et al. in: |author= (help)
  19. ^ Brignole, Edward. "Amino Acid Racemization". Today's chemist at work. American Chemical Society. Retrieved 25 February 2010. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. ^ http://www.whaling.jp/english/history.html
  21. ^ http://ca.encarta.msn.com/encyclopedia_761565254_6/Whale.html Whale. Microsoft Encarta Online Encyclopedia 2009.
  22. ^ a b Anon. "Revised Management Scheme Information on the background and progress of the Revised Management Scheme (RMS)". International Whaling Commission. Retrieved 14 March 2010.
  23. ^ "Sonar may cause Whale deaths". BBC News. 2003-10-08. Retrieved 2006-09-14.
  24. ^ Piantadosi CA, Thalmann ED (2004-04-15). "Pathology: whales, sonar and decompression sickness". Nature. 428 (6894): 716–718. PMID 15085881.
  25. ^ Bird, Jonathon. "Sperm Wales:The deep rivers of the ocena". The Wonders of the Seas. jonathon.bird.org. Retrieved 14 February 2010.
  26. ^ a b Jones, Adair. "In search of . . . whales in literature". Wordpress.com. wordpress. Retrieved 14 February 2010.
  27. ^ Anon. "Whales". Tinirau education resource. Retrieved 14 February 2010.
  28. ^ a b c d Anon. "Whale Mythology from around the World". The Creative Continuum. worldtrans.org. Retrieved 14 February 2010.
  29. ^ Qutb, Sayyid. "Jonah and the Whale". Arab news. Arab News. Retrieved 14 February 2010.
  30. ^ Northeastern Ohio Universities Colleges of Medicine and Pharmacy. "Whales Descended From Tiny Deer-like Ancestors". ScienceDaily. Retrieved 2007-12-21.
  31. ^ Dawkins, Richard (2004). The Ancestor's Tale. Boston: Houghton Mifflin Company. ISBN 0-618-00583-8. {{cite book}}: Text "The Ancestor's Tale, A Pilgrimage to the Dawn of Life" ignored (help)
  32. ^ "How whales learned to swim". BBC News. 2002-05-08. Retrieved 2006-08-20.

Further reading

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