The term whale 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.
Origins and taxonomy
- See also: Evolution of
cetaceans
All cetaceans, including whales, dolphins and porpoises, are descendants of land-living
mammals of the Artiodactyl order (even-toed ungulate animals). Both cetaceans and artiodactyl are now classified under the
super-order Cetartiodactyla which includes both whales and hippos. In fact, whales are the closest living relatives of hippos; they evolved from a common ancestor at around 54 million years ago.[1] Whales entered the water roughly 50 million years ago.[2]
Cetaceans are divided into two suborders:
- The baleen whales are characterized by 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.
Anatomy
Physical characteristics of a baleen whale.
Like all mammals, whales breathe air into lungs, are warm-blooded, feed their young milk from mammary
glands, and have some (although very little) hair.
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. They have a pelvis bone, which is a vestigial structure.
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
mammal that has ever lived, and the largest living animal, at up to 35 m (105ft) long and 150 tons.
Whales generally live for 40-200 years, depending on their species, but it is rare to find one that lives over a century.
Recently a fragment of a lance used by commercial whalers in the 19th century has been found in a bowhead whale caught off
Alaska. The fragment showed the whale is between 115 and 130 years old. [3] "No other finding has been this precise," said John Bockstoce, an adjunct curator of the New Bedford
Whaling Museum.[4]
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.
Anatomy of the ear
- See also: Evolution of
cetaceans
While there are direct similarities between the ears of whales and humans, whales’ ears have specific adaptations to their underwater 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 outer
ear to middle ear, whales receive sound through their lower jaw, where it passes through a
low-impedance, fat-filled cavity.[5]
Behaviour
-
Whales are widely 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.[citation needed]
Whales also communicate with each other using lyrical sounds. Being so large and powerful these sounds are also extremely loud
(depending on the species; sperm whales have only been heard making clicks, as all toothed whales (Odontoceti) use echolocation and can be heard for many miles.
They have been known to generate about 20,000 acoustic watts of sound at 163 decibels. [6]
Delta the whale, who swam to
Sacramento River 70 miles from the ocean in May,
2007
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
mode of reproduction spawns few offspring, but provides each with a high
probability of survival in the wild.
The male genitals 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 milk
into their mouths, a milk that according to German naturalist Dieffenbach[citation needed], bears great similarities to cow's
milk, except with a much higher concentration of fat. Biologists compare the consistency of whale milk to cottage cheese; it must be thick, or else it will dissipate into the surrounding water.
Human effects
Whaling
-
World map of International Whaling Commission (IWC) members/non-members(member countries in blue).
World population graph of
Blue Whales (Balaenoptera musculus).
Some 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 a six year
moratorium on all commercial whaling in 1986, which has been extended to the present day. 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 were drowned 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 a
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.
Sonar interference
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. [7] 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 U.S. Defense department has been ordered by the U.S. 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.
Other environmental disturbances
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. [8]
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, collisions with ships,
toxins and the combination of toxins POPs among other threats.
Whales are also threatened by climate change and global warming. As the Antarctic Ocean warms, krill populations, that are the main food source of some species of whales, reduce dramatically, being replaced by
jelly like salps.[citation needed]
Whales in culture
Whale weather-vane atop the Nantucket Historical Association Whaling Museum.
- 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 symposia.
- In the British series Hitchhiker's Guide to the Galaxy a whale,
alongside a bowl of petunias, is created by the use of the Infinite Improbability Drive
See also
References
- General references
- Carwardine, M. (2000). Whales, Dolphins and Porpoises. Dorling
Kindersley. ISBN 0-7513-2781-6.
External links
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
