From Wikipedia, the free encyclopedia
| North Atlantic right whales, mother and calf | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Subclass: | Eutheria |
| Order: | Cetacea |
Whale (origin Old English hwæl from Proto-Germanic *hwalaz) is the common name for various marine mammals of the order Cetacea.[1] The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to the suborder Odontoceti (toothed whales). This suborder includes the sperm whale, killer whale, pilot whale, and beluga whale. The other cetacean suborder, Mysticeti (baleen whales), comprises filter feeders who 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 cetaceans 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,[2] at 30 m (98 ft) and 180 tonnes (180 long tons; 200 short tons), to pygmy species such as the pygmy sperm whale at 3.5 m (11 ft). Whales inhabit all the world's oceans and number in the millions, with annual population growth rate estimates for various species ranging from 3% to 13%.[3] Whales are long-lived, humpback whales living for up to 77 years, while bowhead whales may live for more than a century.
Human hunting of whales from the seventeenth century until 1986 radically reduced the populations of some whale species.
Whales play a role in creation myths, for example among the Inuit, and they are revered by coastal people in countries such as Ghana and Vietnam.
Taxonomy
Cetaceans are divided into two suborders:- The largest suborder, Mysticeti (baleen whales), is characterized by the presence of 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 includes dolphins and porpoises. If they were not considered to be whales, this would mean that the informal grouping 'whale' is not a clade.
Evolution
These primitive cetaceans first took to the sea approximately 50 million years ago and became fully aquatic by 5–10 million years later.[7] Their features became adapted for living in the marine environment. Major anatomical changes include streamlining of the body, the migration of the nasal openings toward the top of the cranium, the shrinking and eventual disappearance of the hind limbs, the modification of the forelimbs into flippers, and the growth of flukes on the tail.
Anatomy
As with all mammals, whales breathe air, are warm-blooded, nurse their young with milk from mammary glands, and have body hair.[8] 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. Typically, the neck vertebrae are fused, an adaptation trading flexibility for stability during swimming.[9][10]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 almost completely submerged while breathing. Breathing involves expelling stale air (which is warm and moist), as well as some mucus and excess water from the blowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs.[11] Spout shapes differ among species, which facilitates 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 contain feet and digits. Most species have a dorsal fin.[12][13]During March 2014 in Japan a bottle-nosed dolphin with hind fins about as large as a human hand, was captured.[14]
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 is worn away on the tip of the tooth, does enamel show.[15]Instead of teeth, baleen whales have a row of baleen 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 equalizer 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.[16] The whale ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.[17]Life history and behavior
Reproduction
Males are called 'bulls', females, 'cows' and all newborns, 'calves'. Most species do not maintain fixed reproductive partnerships. Females have several mates each season.[18][19]The female usually delivers a single calf, which is birthed tail-first to minimize the risk of drowning. Whale cows nurse by squirting milk into the mouths of their young. This milk is so rich in fat that it has the consistency of toothpaste.[18] In many species, nursing continues for more than a year and is associated with a strong bond between mother and calf. Reproductive maturity typically occurs at seven to ten years. This mode of reproduction produces few offspring, but increases the survival probability of each one.
Socialization
Whales are known to teach, learn, cooperate, scheme, and even grieve.[20] The neocortex of many species of whale is home to elongated spindle neurons that, prior to 2007, were known only in hominids.[21] In humans these cells are involved in social conduct, emotions, judgment, and theory of mind.[22] Whale spindle neurons are found in areas of the brain that are homologous to where they are found in humans, suggesting that they perform a similar function.[23]Sleep
Unlike most animals, whales are conscious breathers. All mammals sleep, but whales cannot afford to become unconscious for long because they may drown. While knowledge of sleep in wild cetaceans is limited, toothed cetaceans in captivity have been recorded to sleep with one side of their brain at a time, ostensibly so that they may swim, breathe consciously, avoid both predators and social contact during their period of rest. It is thought that only one hemisphere of the whale's brain sleeps at a time, so that they rest, but are never completely asleep.[24]
A 2008 study found that wild sperm whales (Physeter macrocephalus) sleep in vertical postures just under the surface in passive shallow 'drift-dives', generally during the day, during which whales do not respond to passing vessels unless they are in contact, leading to the suggestion that whales possibly sleep during such dives.[25]
Surfacing behavior
Many whales exhibit behaviors that expose large parts of their bodies to the air, such as breaching and tail slapping.Sounding
Sounding is a term used for whales diving. Typically it is only used for longer dives. Before sounding, whales typically stay close to the surface for a series of short, shallow dives while building their oxygen reserves. They then make a sounding dive.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.[26] In 2007, a nineteenth-century lance fragment was found in a bowhead whale off Alaska, which suggests the individual could be between 115 and 130 years old.[27] 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.[28][29] The accuracy of this age determination method has been questioned because racemization does not correlate well with other dating methods.[30]Vocalization
 |
|
| Problems playing this file? See media help. | |
Some species, such as the humpback whale, communicate using melodic sounds, known as whale song. These sounds may be extremely loud, depending on the species. Sperm whales only have been heard making clicks, while toothed whales (Odontoceti) use echolocation that may generate approximately 20,000 watts of sound (+73 dBm or +43 dBw)[31] and be heard for many miles. Whale vocalization is likely to serve many purposes, including echolocation, mating, and identification.[32]
Captive whales occasionally have been known to mimic human speech. Scientists have suggested this indicates a strong desire on behalf of the whales to communicate with humans, as whales have a very different vocal mechanism, so producing human speech likely takes considerable effort.[33]
Ecology
Whales are considered as "marine ecosystem engineers" for the following reasons:[34]
- Whales are major consumers of fish and oceanic invertebrates.
- Whales act as reservoirs of nutrients, such as iron and nitrogen, and they recycle them both horizontally and vertically in the water column.
- Whale detritus provides energy and habitat for deep sea organisms.
Feeding
Whales generally are classed as predators. Their food ranges from microscopic plankton to very large animals.Toothed whales eat fish and squid, which they hunt by the use of echolocation. Killer whales sometimes eat other marine mammals, including whales.
Baleen whales, such as humpbacks and blues, mainly eat krill when feeding in the higher latitudes (such as the Southern Ocean). They take in enormous amounts of seawater that they expel through their baleen plates; the krill in the seawater are retained on the plates and then swallowed.[18] Whales do not drink seawater. They extract water indirectly from their food by metabolizing fat.[18]
Whale pump
A 2010 study considered whales to be a positive influence to the productivity of ocean fisheries, in what has been termed a "whale pump." Whales carry nutrients such as nitrogen from the depths back to the surface. This functions as an upward biological pump, reversing an earlier presumption that whales accelerate the loss of nutrients to the bottom. This nitrogen input in the Gulf of Maine is "more than the input of all rivers combined" emptying into the gulf, some 23,000 metric tons each year.[35][36] Whales defecate at the oceans surface and this excrement is important for fisheries because it is rich in iron and nitrogen. The whale feces are liquid and instead of sinking, they stay at the surface where phytoplankton feed off it.[37]Whale fall
Upon death, whale carcasses fall to the deep ocean and being massive, with body weights of the range 30 to 160 tonnes (30,000 to 160,000 kg), provide a substantial habitat for marine creatures. Evidence of whale falls in present day and fossil records shows that deep sea whale falls support a rich assemblage of creatures, with a global diversity of 407 species as per Smith & Baco (2003), comparable to other neritic biodiversity hotspots, such as cold seeps and hydrothermal vents.[38]Deterioration of whale carcasses happens though a series of three stages. Initially, moving organisms such as sharks and hagfish, scavenge the soft tissues at a rapid rate over a period of months, and as long as two years. This is followed by the colonisation of bones and surrounding sediments (which contain organic matter) by enrichment opportunists, such as crustaceans and polychaetes, throughout a period of years. Finally, sulfophilic bacteria reduce the bones releasing hydrogen sulfide enabling the growth of chemoautotrophic organisms, which in turn, support other organisms such as mussels, clams, limpets, and sea snails. This stage may last for decades and supports a rich assemblage of species, averaging 185 species per site as per Smith & Baco (2003).[38]
Interaction with humans
Whaling
.jpg)
Dutch whalers near Spitsbergen, Abraham Storck, 1690
Some species of large whales are listed as endangered by multinational organizations, such as CITES, as well as governments and advocacy groups. This status is due primarily to the impact of whaling. Whales have been hunted commercially since the seventeenth century for whale oil, meat, baleen, and ambergris (a perfume ingredient from the intestine of sperm whales).[39] More than two million whales were taken during the twentieth century,[40] and by the middle of that century, many populations were severely depleted.
The International Whaling Commission banned commercial whaling in 1986.[41] The ban is not absolute, however, and some whaling continues under the auspices of scientific research[41] (sometimes not proved[42]) or aboriginal rights. Current whaling nations are Norway, Iceland, and Japan as well as the aboriginal communities of Siberia, Alaska, and northern Canada.
Captivity
Most current captives were caught in the wild, since captive breeding has had limited success.[55] There is controversy over captivity,[46][56] with limited enrichment activities and tank sizes, though defenders say easy access for research[49][56][57][58] and public viewing are beneficial.[59] The whales have far larger family groups and ranges in the wild[60] than in captivity.
Whale watching
Bycatch
Several species of small whales are caught as bycatch while fishing 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.[65]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 they point to signs that such whales have experienced decompression sickness.[66]
Responses in Nature the following year discounted the explanation.[67]Mass beachings occur in many species, mostly beaked whales that use echolocation for deep diving. The frequency and size of beachings around the world, recorded throughout the last thousand 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.[20]
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.[citation needed]
Whales were little understood for most of human history as little of their lives could be seen from the surface of the ocean.[70] Many cultures, even those that have hunted them, hold whales in awe and feature them in their mythologies. In China, Yu-kiang, a whale with the hands and feet of a human was said to rule the ocean.[71] In the Tyrol region of Austria, it was said that if a sunbeam were to fall on a girl entering puberty, she would be carried away in the belly of a whale.[72] Paikea, the youngest and favourite son of the chief Uenuku from the island of Mangaia (Cook Islands), was said by the Kati Kuri people of Kaikoura to have traveled from the Pacific Islands on the back of a whale many centuries before.[73] 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.[71] 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.[74] In an 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 during the nineteenth year he went fishing and a whale came and killed him.[75] 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 still was 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.[71]
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.[76][77][78][79]
The Bible mentions whales in Genesis 1:21, Job 7:12, Ezekiel and 32:2. The "sea monsters" in Lamentations 4:3 have been taken by some commentators to refer to marine mammals, in particular whales, although most modern versions use the word "jackals" instead.[80] The story of Jonah being swallowed by a "big Fish" is told both in the Qur'an and in the Bible.[81] The Old Testament contains the Book of Jonah and in the New Testament, Jesus mentions this story in Matthew 12:40.[82]
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.[citation needed]
In fiction
The 1851 American novel, Moby-Dick by Herman Melville concerns a vexed captain's hunt for a gigantic white whale. Rudyard Kipling's 1902 Just So Stories includes the tale of "How the Whale got his Throat".[68] The film Whale Rider directed by Niki Caro has a Maori girl ride a whale in her quest to be a suitable heir to the chiefship.[69] An enormous whale called Monstro is the final antagonist featured in Walt Disney's 1940 animated film Pinocchio.In mythology
Whale weather-vane atop the Nantucket Historical Association Whaling Museum displaying a sperm whale
Whales were little understood for most of human history as little of their lives could be seen from the surface of the ocean.[70] Many cultures, even those that have hunted them, hold whales in awe and feature them in their mythologies. In China, Yu-kiang, a whale with the hands and feet of a human was said to rule the ocean.[71] In the Tyrol region of Austria, it was said that if a sunbeam were to fall on a girl entering puberty, she would be carried away in the belly of a whale.[72] Paikea, the youngest and favourite son of the chief Uenuku from the island of Mangaia (Cook Islands), was said by the Kati Kuri people of Kaikoura to have traveled from the Pacific Islands on the back of a whale many centuries before.[73] 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.[71] 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.[74] In an 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 during the nineteenth year he went fishing and a whale came and killed him.[75] 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 still was 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.[71]
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.[76][77][78][79]
The Bible mentions whales in Genesis 1:21, Job 7:12, Ezekiel and 32:2. The "sea monsters" in Lamentations 4:3 have been taken by some commentators to refer to marine mammals, in particular whales, although most modern versions use the word "jackals" instead.[80] The story of Jonah being swallowed by a "big Fish" is told both in the Qur'an and in the Bible.[81] The Old Testament contains the Book of Jonah and in the New Testament, Jesus mentions this story in Matthew 12:40.[82]
The engraving by William van der Gouwen shows a 20 m (65.6 ft) long whale, stranded on the Dutch coast between Scheveningen and Katwijk on 3 February 1598
_Wolf.png)
