whale
, any of the larger species of aquatic mammals belonging to the order
Cetacea
. The term
whale
can be used in reference to any cetacean, including
porpoises
and
dolphins
, but in general it is applied to those more than 3 metres (10 feet) long. An exception is the 2.7-metre
dwarf sperm whale
(
Kogia simus
), so called for its otherwise striking resemblance to its larger namesake. Whales are the heaviest known animals, living or fossil, reaching a maximum size in the
blue whale
(
Balaenoptera musculus
) of perhaps more than 30 metres and 200 metric tons (220 short [U.S.] tons). Large predatory whales, including the
killer whale
, are often considered to be the
apex predators
(meaning they have no natural predators or enemies) of their
marine
environments
.
Whales are distributed throughout the world’s oceans and seas, from the Equator to the polar ice, except for the landlocked Caspian and Aral seas. They are
mammals
, and they share the defining traits of that group: they breathe air, are warm-blooded, give
live birth
, suckle their young on milk, and have hair. All are entirely aquatic, with specialized
adaptations
such as flippers and tail flukes for living in water. Whales must surface regularly to breathe, evacuating their lungs more completely than most mammals in an almost explosive breath known as a
blow
. Blows are visible because water vapour in the whale’s hot breath condenses when the blow is released.
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Despite living in a medium that has much greater
thermal conduction
characteristics than air, whales, like other mammals, must regulate their body temperature. Hair, however, is restricted to the head, appearing mainly as isolated whiskers (vibrissae) near the mouth and blowhole.
Blubber
serves as an insulating layer to protect small whales from
hypothermia
. Large whales have the opposite problem in that they can produce too much heat; they possess elaborate thermoregulation mechanisms to prevent overheating.
Because of the restricted utility of vision underwater, whales use
sound
to perceive and interpret their
environment
and to communicate, sometimes over vast distances. Biologists have computed that the 10-hertz sounds of
fin whales
(
Balaenoptera physalus
), for example, can travel over 1,800 km (1,100 miles).
Toothed whales
can produce sounds and interpret their reflections via active
echolocation
. The extent to which
baleen whales
have this ability is unknown.
Following internal fertilization, female whales are pregnant for about a year. The young are relatively large when born?one-third to one-half the length of the mother. They are nursed for about six months on extremely rich milk containing almost 50 percent fat. Whales have one pair of nipples located at the rear of the abdomen near the genital opening.
The first fossil whales are known from rocks approximately 50 million years old (Early
Eocene Epoch
). These members of the extinct suborder
Archaeoceti
are the primitive whales from which modern whales are derived. They show many similarities to terrestrial mammals, including a
differentiated
dentition (heterodonty) consisting of incisors, canines, premolars, and molars. Archaeocetes gave rise to the living suborders: the baleen whales (suborder Mysticeti) and the toothed whales (suborder Odontoceti).
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Mysticetes have baleen plates and take small prey by the mouthful, mainly in the form of drifting (planktonic)
crustaceans
such as
copepods
and
krill
, but they also occasionally consume small schooling fish or
squid
. One interesting departure from this pattern is the
gray whale
(
Eschrichtius robustus
), which commonly eats
shrimp
and other bottom-dwelling creatures: it scoops up mud and strains it through the baleen plates, retaining its food. Odontocetes have simple teeth (homodonty) and pursue individual squid, fish, and other prey. The largest odontocete, the
sperm whale
(
Physeter macrocephalus
), occasionally feeds on
giant squid
.
Humans have long utilized stranded whales as a food resource, and historically whales were hunted for
whale oil
and
baleen
. In the early 20th century, as demand increased and technology enabled meat to be frozen at sea, whales began to be taken in larger numbers for human
consumption
and for specialty products. Scientific concern over the increased
catch
of whales in the Southern Hemisphere in the 1930s led to the ratification of the International Whaling Convention and the founding of the
International Whaling Commission
in 1946. Through the years this agency has acted to moderate
whaling
, and it instituted a
moratorium
on commercial whaling in the late 1980s. Some whaling still occurs under special permit. Native peoples are also allowed to continue traditional whale hunting that has been a part of their
culture
.