According to
modern terminology, whales are the larger members of the order Cetacea. This order of
aquatic mammals is divided into three suborders: the Mysticeti, the baleen whales; the
Odontoceti, the toothed whales; and the Archaeoceti, an extinct group known only through
fossils. The toothed whales (Odontoceti) also include the smaller DOLPHIN and PORPOISE.
The large
baleen whales comprise three families and about a dozen species. All these species lack
teeth except as vestiges in the embryos. Instead, they possess a row of fringed plates of
baleen (whalebone), which is a keratinaceous (horny) material developed from the gums. The
fringed plates of baleen act as a filter, or sieve, straining small marine organisms from
the water. The baleen whales are primarily plankton feeders and derive most of their
nourishment from marine organisms that may be only a few millimeters (several hundredths
of an inch) in length. Their principal food in the polar regions consists of small,
shrimplike crustaceans collectively known as "krill." Commonly known baleen
whales include the right whales, Balaena; the gray whale, Eschrichtius gibbosus; the blue
whale, Balaenoptera musculus; the fin whale, B. physalus; and the humpback whale,
Megaptera novaeanglia. The largest species, and the largest animal that has ever lived, is
the blue whale. Specimens up to 30 m (100 ft) in length have been recorded, with weights
estimated at more than 130 metric tons.
The toothed whales are all predators, feeding actively on fish and squid. They possess
sharp teeth, usually in both jaws, used to catch their prey. The odontocetes that are
commonly called whales comprise five families and about 30 species, including such forms
as pilot whales, Globicephala; beaked whales, Mesoplodon; the beluga or white whale,
Delphinapterus leucas; the killer whale, Orcinus orca; the pygmy sperm whale, Kogia; and
the species best known through Melville's novel Moby-Dick, the sperm whale, Physeter
catodon. Sperm whales have been recorded up to 19 m (62 ft) in length. This species is
recognizable by the large, oblong head and the relatively tiny, narrow lower jaw.
General Characteristics
The general form of whales is torpedo-shaped, and their bodies are smooth and streamlined.
The front limbs are modified into a pair of flippers and are used primarily as stabilizers
or steering mechanisms. The hind limbs are represented only by a few bony vestiges. A
dorsal fin is usually present, and the tail fin consists of a pair of horizontal flukes.
The primary thrust in locomotion is derived from up-and-down movements of the tail and
flukes.
Some baleen whales--including the blue, fin, and humpback--have longitudinal furrows on
their undersides; they are known as rorquals. The skin of whales is smooth and hairless,
except for the stiff bristles, or vibrissae, in the head region of some whales, such as
the fin whale and other rorquals, and the vestiges of hair and hair follicles in the
embryos of the sperm whale and certain other species. The humpback whale commonly
possesses many large, rough-surfaced growths on parts of its head. The function of these
is unknown. Underneath the whale's skin is a thick layer of dense fatty tissue, the
blubber, the primary function of which appears to be as an aid in maintaining the body
temperature of these warm-blooded mammals at 34 degrees-37 degrees C (93 degrees-99
degrees F). Because they are air-breathing mammals, all whales must rise to the surface to
breathe. Some species, such as the sperm whale, are capable of diving to depths of more
than 1,000 m (3,300 ft) and remaining underwater for 50 minutes or more. A single breath
of a whale consists of a rapid expulsion of air, mainly produced through the elasticity of
the thoracic tissues. The exhalation is followed immediately by a slower inhalation. The
spout of a whale is often erroneously thought to be water. Because the exhaled air is
normally warmer than the outside atmosphere, a rapid condensation of water occurs, giving
the spout the appearance of a jet of steam. It emerges from the top of the head, from the
blowhole. In reality, the blowhole is the nostril, single in odontocetes and double in
mysticetes.
Reproduction
In common with all mammals except the monotremes, whales bear living young, with usually a
single calf per pregnancy. Only fragmentary evidence is available on the reproductive
behavior of whales, and much of it is derived from studies on small cetaceans, such as
porpoises, in captivity. Among the baleen whales, some data are available on courtship and
other aspects of reproductive behavior in the gray whale. This species spends its breeding
season in bays and lagoons along the Baja California peninsula of Mexico, and it thus
becomes approachable for observation. The gestation period for cetaceans in general is
about 10 to 12 months, including even the gigantic blue whales. Some estimates give as
long as a 16-month gestation period for the sperm and killer whales. The young are nursed
from about 5 to 7 months in the blue and fin whales and up to about a year in most
odontocetes. Life spans for cetacean species are estimated from about 30 years in the
smaller odontocetes to perhaps 90 or even 100 years for the large baleen whales.
Distribution
Whales can be found in all oceans and seas of the world and at any latitude. Gray whales
follow migration paths along the Pacific coasts of Asia and North America, some of them
undertaking the longest round-trip migration of any mammal, up to 22,000 km (14,500 mi).
The blue whale, the sperm whale, and possibly other species have a circumpolar
distribution, and there appear to be distinct noninterbreeding populations in the Northern
and Southern hemispheres. Migratory paths of many species have been well tracked by
whalers, and the animals evidently follow ocean currents, planktonic movements,
temperature gradients, and other environmental and climatic factors.
Behavior
Although little is known directly of the social behavior of whales, it is clear that most
are gregarious, traveling in schools, also called pods or gams. Occasionally, whales
thrust themselves completely out of the water, leaping into the air, and falling back with
a huge splash. This "breaching" is thought to be associated with some aspects of
reproduction or courtship, but may be only incidental to some other behavior as yet
undetermined.
Virtually all species of cetaceans are known to produce sounds, and these sounds may serve
as an important means of interaction and communication. All odontocetes thus far
investigated produce short, pulse-type sounds that function in echolocation. In addition,
most species are also known to emit high-pitched squeals and whistles that appear to be
used as part of social behavior. Although there is no evidence that these sounds represent
anything comparable to a true language, there is little doubt that they are used to denote
specific emotional states, for example, fright, hunger, or sexual readiness. For the
mysticetes, there is much less evidence available on the function of sounds because none
have yet survived in captivity for study. Some baleen whales, particularly the gray whale,
are known to produce pulse-type sounds, or clicks, but it has not yet been shown that
these sounds are utilized in echolocation. Baleen whales commonly emit low-pitched groans
and moans. The fin whale has been identified as a source of extremely low-pitched and
powerful pulses at frequencies of about 20 Hz (cycles per second). By contrast to these
rather monotonous tones, the humpback produces an enormous variety of sounds that can be
described as groans, yelps, squeaks, and growls in repetitive patterns. Although these
baleen whale sounds are probably associated in some way with social behavior and
communication, possible over distances of many kilometers, there are no data available to
show a specific function.