Whale
This article is about the animal. For other uses, see Whale (disambiguation).Whales are the largest
species of exclusively aquatic
mammals, members of the
order Cetacea, which also includes
dolphins and
porpoises. They include the largest animals known to have ever existed.
The term
whale is ambiguous: it can refer to all cetaceans, to just the larger ones, or only to members of particular
families within the order Cetacea. The last definition is the one followed here. Whales are those cetaceans which are neither dolphins (i.e. members of the families
Delphinidae or
Platanistoidea) nor
porpoises. This can lead to some confusion because
Orcas ("Killer Whales") and
Pilot Whales have "whale" in their name, but they are dolphins for the purpose of classification.
Whales, along with most dolphins and porpoises, are descendants of land-living mammals, most likely of the
Artiodactyl order. They entered the water roughly 50 million years ago. See
Evolution of cetaceans for the details [
1].
Cetaceans are divided into two suborders:
*The
baleen whales are characterized by the
baleen, a sieve-like structure in the upper jaw made of
keratin, which they use to filter
plankton from the water. They are the largest species of whale.
*The
toothed whales have teeth and prey on fish, squid, or both. An outstanding ability of this group is to sense their surrounding environment through
echolocation.
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, breast-feed their young, and have some (although very little) hair. A young scientist, Eric Alexander Ivanov, in 1911, was the first to discover that the whale's ancestors lived on land, and that whales have adapted to a fully aquatic life. At first his findings were not accepted by the scientific community, but were later proved correct. Ivanov worked with others to stop whaling in the United States. Eric Ivanov died shortly after his goal was achieved. The body is fusiform, resembling the streamlined form of a fish. The forelimbs, also called flippers, are paddle-shaped. The end of the tail holds the fluke, or tail fins, which provide propulsion by vertical movement. Although whales generally do not possess hind limbs, some whales (such as
sperm whales and
baleen whales) sometimes have rudimentary hind limbs; some even with feet and digits. Most species of whale bear a fin on their backs known as a
dorsal fin.
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 have one. The shapes of whales' spouts when exhaling after a dive, when seen from the right angle, differ between species. Whales have a unique respiratory system that lets them stay underwater for long periods of time without taking in oxygen. Some whales, such as the
Sperm Whale, can stay underwater for up to two hours holding a single breath. The
Blue Whale is the largest known animal that has ever lived, at up to 30 m (93ft) long and 180 tons.
Their skin has evolved hydrophilic properties. Its surface is covered with microscopic pores surrounded by nanoridges. Between these ridges there is a rubber-like gel which is excreted from the gaps between the skin cells. This gel contains enzymes that attack microbes, and the edge of the ridges makes it hard for smaller organisms to get attached.
Whale flukes often can be used as identifying markings, as is the case for
humpback whales. This is the method by which the publicized errant
Humphrey the whale was identified in three separate sightings.
|
Humpback whale tail flip off coast of Moloka'i, Hawaii, 2005 |
Main article: Whale behaviour
Whales are broadly classed as
predators, but their food ranges from microscopic plankton to very large fish. Males are called bulls; females, cows. The young are called calves.
Because of their environment (and unlike many animals), whales are conscious breathers: they decide when to breathe. All mammals
sleep, including whales, but they cannot afford to fall into an unconscious state for too long, since they need to be conscious in order to breathe. It is thought that only one hemisphere of their brains sleeps at a time, so that whales are never completely asleep, but still get the rest they need. Whales are thought to sleep around 8 hours a day.
Whales also communicate with each other using lyrical sounds. Being so large and powerful these sounds are also extremely loud and can be heard for many miles. They have been known to generate about 20,000 acoustic watts of sound at 163 decibels. See
Table of sound decibel levels.
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, but provides each 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 minimized. Whale mothers nurse the young by actively squirting the fatty milk into their mouths, a milk that according to German naturalist
Dieffenbach, bears great similarities to cow's milk. Biologists compare the consistency of whale milk to cottage cheese; it must be thick, or else it will dissipate into the surrounding water.
For more material in this area, focusing more on dolphins, see cetacean intelligence.
Many people believe that cetaceans in general, and whales in particular, are highly
intelligent animals. This belief has become a central argument against
whaling (killing whales for food or other commercial reasons).
There is no universally agreed definition of "intelligence." One commonly used definition is "the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience." Proponents of whale intelligence cite the social behavior of whales and their apparent capacity for language as evidence of a sophisticated intellect. Given the radically different environment of whales and humans, and the size of whales compared to
dolphins or
chimpanzees, for instance, it is extremely difficult to test these views experimentally.
One traditional indicator of intelligence is
brain capacity, since humans have bigger brains than most other animals. Whales have the largest brain of any animal. A typical sperm whale brain weighs about 7.8 kg, whereas a typical human brain weighs about 1.5 kg. While it may seem that this would indicate that five times greater intelligence, in mammals brain size is in approximate ratio to body size, and most of the extra capacity is used to manage the larger body.
A more precise indicator is the brain-body ratio: the size of the brain compared to body mass. Here humans have a decisive advantage. A human brain comprises about 2% of the human body mass, while the sperm whale's brain comprises only 0.02% of its body mass. A
cow's brain is four times as large as a whale's on this measurement. On the other hand, a large proportion of a whale's body mass is
blubber, which requires no brain power, and this distorts the ratio somewhat. Nevertheless, it is clear that brain size is not a decisive criterion.
Hummingbirds have an even higher brain-to-body ratio than humans.
The next consideration is the structure of the brain. It is generally agreed that the growth of the
neocortex, both absolutely and relative to the rest of the brain, during human evolution, has been responsible for the evolution of intelligence, however defined. In most mammals the neocortex has six layers, and its different functional areas (vision, hearing, etc) are sharply differentiated. The whale neocortex, on the other hand, has only five layers, and there is little differentiation of these layers according to function. This has led some to argue that the whale brain has not significantly evolved since the distant ancestors of the whale took to a marine lifestyle about 50 million years ago.
From an evolutionary point of view, this is consistent with the principles of
natural selection. Intelligence does not arise spontaneously: like any other animal capacity, it evolves under the pressure of the animal's environment. The human brain has evolved under the pressure of natural selection in a hostile terrestrial environment. The key primate characteristics -
bipedalism and the
opposable thumb - gave the early
hominids the ability to manipulate their environment through the use of
technology (by making tools). This unique adaptation created a
virtuous cycle: tool-making gave those hominids with larger brains a decisive evolutionary advantage, leading to larger and more sophisticated brains, and thus to more tool-making. This process is one of the proposed explanations of the exponential growth of
hominid intelligence over the past million years.
By contrast, the whale has faced no such environmental stimuli to brain evolution. Whales live in an unchanging and benign environment with few natural
predators. Their sole adaptation to their marine environment has been increasing size. The whale's lifestyle consists of swimming and eating, tasks which
fish perform perfectly competently with very small brains. From an evolutionary point of view, there is no reason for whales to have evolved intelligence, since their survival does not require them to perform any tasks for which intelligence is necessary.
Some whale species have a sophisticated
social system. Their communication system may contain some of the elements of true
language, although our knowledge of whale communications is not very advanced. Many other animals, including
insects, have complex social systems, and many others, such as birds, have sophisticated communications. Whales also have very acute hearing, which gives them advanced echo-location capacities analogous to
sonar - but so do bats. All this has led many (though far from all) zoologists to the conclusion that there is no convincing evidence for whale intelligence. A better understanding of whale communications and
whale behaviour may solve this problem eventually.
Most species of large whales are endangered as a result of large-scale
whaling during the nineteenth and twentieth centuries. For centuries large whales have been hunted for oil, meat, baleen and
ambergris (a perfume ingredient from the intestine of
sperm whales). By the middle of the 20th century, whaling left many populations severely depleted. The
International Whaling Commission introduced an open-ended moratorium on all commercial whaling in 1986. For various reasons some exceptions to this moratorium exist; current whaling nations are
Norway,
Iceland and
Japan and the aboriginal communities of
Siberia,
Alaska and northern
Canada. For details, see
whaling.
Several species of small whales are caught as
bycatch in fisheries for other species. In the tuna fishery in the Eastern Tropical Pacific thousands of dolphins would drown in purse-seine nets, until measures to prevent this were introduced. Fishing gear and deployment modifications, and eco-labelling (
dolphin-safe or
dolphin-friendly brands of canned tuna), have contributed to an estimated 96% reduction in the mortality of dolphins by tuna fishing vessels in recent years. In many countries, small whales are still hunted for food, oil, meat or bait.
Environmentalists have long argued that some cetaceans, including whales, are endangered by
sonar used by advanced navies. In 2003 British and Spanish scientists suggested in
Nature that 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. Mass
whale beachings occur in many species, mostly beaked whales that use echolocation systems 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, has been used to estimate the changing population size of various whale species by assuming that the proportion of the total whale population beaching in any one year is constant.
Despite the concerns raised about sonar which may invalidate this assumption, this population estimate technique is still popular today. Researchers in the area (
Talpalar & Grossman, 2005) support the view that it is the combination of the high pressure environment of deep-diving with the disturbing effect of the sonar which causes decompression sickness and stranding of whales. Thus, an exaggerated startle response occurring during deep diving may alter orientation cues and produce rapid ascent.
Following public concern, the US Defense department has been ordered by the US judiciary 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) have so far failed. The
European Parliament on the other hand has requested that EU members refrain from using the powerful sonar system until an environmental impact study has been carried out. [
2]
Conservationists are concerned that seismic testing used for oil and gas exploration may also damage the hearing and echolocation capabilities of whales. They also suggest that disturbances in magnetic fields caused by the testing may also be responsible for beaching.
See e.g. Seismic testing and the impacts of high intensity sound on whales, Lindy Weilgart, Department of Biology Dalhouise University (PDF format)Some scientists and environmentalists suggest that some whale species are also endangered due to a number of other human activities such as the unregulated use of fishing gear, that often catch anything that swims into them, whales collisions with ships, toxins and the combination of toxins
POPs among other threats.
A
kenning in
Beowulf refers to the
sea as the "whale-road"
Procopius mentions a whale, nicknamed
Porphyrio by the
Byzantines, who depleted fisheries in the
Sea of Marmara.
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).
Nevertheless, the passages in question do not unambiguously refer to whales; modern translations tend to use other terms; for example the
New International Version uses "creatures of the sea"; "monster of the deep"; "monster"; and "huge fish" respectively.
The story of
Jonah being swallowed by a whale is mentioned in the
Qur'an as well.
A
whaling voyage is the
plot of
Herman Melville's
novel Moby-Dick. In the book, Melville classed whales as "a spouting
fish with a horizontal
tail", this despite
science suggesting otherwise the
previous century. (His
narrator acknowledged "the grounds upon which
Linnaeus would fain have banished the whales from the waters" but writes 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." (Chapter 32)) Melville's book is a classic of
American literature: part
adventure novel, part
metaphysical allegory, and part
natural history; it is essentially a summary of
19th century knowledge about the
biology,
ecology and cultural significance of the whale.
Some cultures associate some level of divinity with the whale, such as in some places in
Ghana and the
Vietnamese, who occasionally hold funerals for beached whales, a throwback to Vietnam's ancient sea-based
Austro-asiatic culture.
Festivals celebrating whales have sprung in both
Sitka and
Kodiak Alaska. They feature speakers on marine biology and celebrate the creatures with art, music, whale-watching cruises, and symposiums.
*
Cetacea (contains a species list)
*
Baleen whale*
Toothed whale*
Dorsal fin*
Whaling*
International Whaling Commission*
Exploding whale*
Whale fall*
List of whale species*
Sitka Whale Fest*
River Thames whale*
Whale song* Carwardine, M. (2000).
Whales, Dolphins and Porpoises. Dorling Kindersley. ISBN 0751327816
* [Cetacea]Link Removed… website currently on hiatus.
*
Whale Evolution*
Greenpeace work defending whales*
Save the Whales, founded in 1977*
Oldest whale fossil confirms amphibious originszh-yue:鯨魚
