whale

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.

Origins and taxonomy

All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulate animals). Both cetaceaos 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. Whales entered the water roughly 50 million years ago.

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

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.

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.

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.

Anatomy of the ear

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.

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.

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.

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, 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.

Intelligence

An often used, but discredited indicator of intelligence is overall brain size, 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, there is a theory that, in mammals, intelligence should be measured in the brain mass to body mass ratio, and that most of the extra brain capacity is used to manage the larger body. Only here do humans have an 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 cattle brain is four times as large as a whale's by this criterion. 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. Also the brain size of animals does not increase at the same rate as body size. However, because cetacean brains function quite differently from the human brain, even if whales had matching body/brain weight ratio to humans, it is not a conclusive indication of high intelligence. Simply, "overall" brain size is not a decisive criterion because it is now known that different parts of the brain regulate different functions, mostly physiological. Hummingbirds have an even higher brain-to-body ratio than humans, as do some dolphins. 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, much like that of some present-day insectivores. 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. However, even if this is true, it does not follow that this older design of brain is any less efficient.

Many people, particularly in the West, believe that cetaceans in general, and whales in particular, are highly intelligent animals. This belief has become one of a central argument against whaling (killing whales for commercial reasons). Proponents of whale and dolphin intelligence cite the social behaviour of whales and dolphins and their apparent capacity for communication as evidence of a sophisticated intellect, though scientists often carefully point out the difference between the social traits and intelligence of animals, which laymen often confuse. 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.

Human impacts

Whaling

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 , 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. 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.

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.

See also

• 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
• whale watching

References

General references

• Carwardine, M. (2000). Whales, Dolphins and Porpoises, Dorling Kindersley. ISBN 0-7513-2781-6.

External links

• Whale Evolution
• images and movies of Whales and Dolphins, text in French
• Greenpeace work defending whales
• Save the Whales, founded in 1977
• AquaNetwork Marine Mammal Project
• Oldest whale fossil confirms amphibious origins
• The Oceania Project - Caring for whales and dolphins
• Research on dolphins and whales from Science Daily
• Whale and Dolphin Conservation Society - latest news and information on whales and dolphins

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