| Whale | |
|---|---|
| North Atlantic right whales, mother and calf | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Subclass: | Eutheria |
| Order: | Cetacea |
Whale (origin Old English hwæl) 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,[2] 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[3] at 30 m (98 ft) and 180 tonnes (180 long tons; 200 short tons), to various pygmy species, such as the pygmy sperm whale at 3.5 m (11 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% to 13%.[4] 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.
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Cetaceans are divided into two suborders:
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.[5]
All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulates). Both are related to the Indohyus (an extinct semi-aquatic deer-like ungulate) from which they split around 54 million years ago.[6][7] Primitive whales probably first took to the sea about 50 million years ago and became fully aquatic about 5–10 million years later.[8]
Like all mammals, whales breathe air, are warm-blooded, nurse their young with milk from mammary glands, and have body hair.
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.
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.
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.
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.[9]
Instead of teeth, Baleen whales have a row of plates on the upper side of their jaws that resemble the "teeth" of a comb.
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.[10] The whale ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. [11]
Males are called 'bulls', females, 'cows' and newborns, 'calves'. Most species do not maintain fixed partnerships and females have several mates each season.[12][13]
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.
Whales are known to teach, learn, cooperate, scheme, and even grieve.[14] The neocortex of many species of whale is home to elongated spindle neurons that, prior to 2007, were known only in hominids.[15] In humans these cells are involved in social conduct, emotions, judgment, and theory of mind.[16] Whale spindle neurons are found in areas of the brain homologous to where they are found in humans, suggesting that they perform a similar function. [17]
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.[18]
Many whales exhibit behaviors such as breaching and tail slapping that expose large parts of their bodies to the air.
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.[19] 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.[20] 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.[21][22] The accuracy of this technique has been questioned because racemization did not correlate well with other dating methods.[23]
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 (+73 dBm or +43 dBw[24]) and be heard for many miles. Whale vocalization is likely to serve many purposes, including echolocation, mating, and identification.
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]
A recent discovery of a positive influence on the productivity of ocean fisheries has been attributed to whales 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 the assumption of some scientists that whales accelerate the loss of nutrients to the bottom. They note that this nitrogen input in the Gulf of Maine is "more than the input of all rivers combined," some 23,000 metric tons each year." [25][26]
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 17th century.[27] At its peak in 1846, the American whaling industry employed more than 70,000 people and 736 vessels.[28] More than 2 million were taken in the 20th century,[29] and by the middle of the century, many populations were severely depleted.
The International Whaling Commission banned commercial whaling in 1986.[30] The ban is not absolute, however, and some whaling continues under the auspices of scientific research[30] (sometimes not proved[31]) or aboriginal rights; current whaling nations are Norway, Iceland and Japan and the aboriginal communities of Siberia, Alaska and northern Canada.
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.
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.[32] Responses in Nature the following year discounted the explanation.[33]
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 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.[14]
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 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.
Whales were little understood for most of human history as they spend up to 90% of their lives underwater, only surfacing briefly to breathe.[34] They also include the largest animals on the planet. 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.[35]
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.[35]
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.[36] 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.[37]
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.[37]
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.[37]
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.[37]
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.[38][39][40][41] The whale is a revered creature to Vietnamese fishermen. They are respectfully addressed as "Lord". If one finds a stranded whale corpse, one is in charge of holding the funeral for the "Lord" as if it was one's own parent.
The story of Jonah being swallowed by a whale also is told in the Qur'an.[42]
The Bible, 1611 Authorized Version, expressly mentions whales four times:
The translators in that latter verse above thereby identified the "great fish" of the book of Jonah as a whale. It is apparent that Jeremiah recognized that some great fish are mammals. The English word "monster", (used in the ordinary sense of a "huge animal",) is used in the Bible in Jeremiah's Lamentations to refer to whales: