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.
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.
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 1800s has been found in a huge bowhead whale caught off Alaska. The fragment showed the whale is estimated between 115 and 130 years old. "No other finding has been this precise," said John Bockstoce, an adjunct curator of the New Bedford Whaling Museum.
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 attach themselves.
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.
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.
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.
Delta the whale, who swam to Sacramento River 70 miles from the ocean in May, 2007Females 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.
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, the moratorium was due to be lifted in 1992 but has been extended till 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-labeling (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. 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.
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.
The Orca or Killer Whale (Orcinus
orca), less commonly, Blackfish or Seawolf, is the largest
species of the oceanic dolphin family (Delphinidae). It is found
in all the world's oceans, from the frigid Arctic and Antarctic
regions to warm, tropical seas.
Orcas are versatile and opportunistic predators. Some populations feed mostly on fish, and other populations hunt marine mammals, including sea lions, seals, and even large whales. There are up to five distinct Orca types, some of which may be separate subspecies or even species. Orcas are highly social; some populations are composed of matrilineal family groups which are the most stable of any animal species. The sophisticated social behavior, hunting techniques, and vocal behaviors of Orcas have been described as manifestations of culture.
Although Orcas are not an endangered species, some local populations are considered threatened or endangered due to pollution, depletion of prey species, conflicts with fishing activities and vessels, habitat loss, and whaling. Wild Orcas are usually not considered a threat to humans. There have, however, been isolated reports of captive Orcas attacking their handlers at marine theme parks.
a yellowish or orange tint, which fades to white. Orcas have
a heavy and stocky body and a large dorsal fin with a dark grey
"saddle patch" at the fin's rear. Males normally grow from 6.5-8
m long (20-25 ft) and weigh in excess of 6 tones; it has been
reported that especially large males have reached nearer 8
tones. Females are smaller, growing from 5.7-7m (18-22 ft) and a
weight of about 5 tones. The longest Orca ever recorded was a
male off the coast of Japan, measuring 9.8 m (32 ft). Calves at
birth weigh about 180 kg and are about 2.4 m long (8 ft). The
Orca's large size and strength make them the fastest marine
mammals, often reaching speeds in excess of 56 km/h (35mph).
Unlike most dolphins, the pectoral fin of an Orca is large and rounded — more of a paddle than other dolphin species. Males have significantly larger pectoral fins than females. At about 1.8 m (6 ft), the dorsal fin of the male is more than twice the size of the female's, and is more of a triangle shape — a tall, elongated isosceles triangle, whereas the dorsal fin of the female is shorter and generally more curved.
Adult male Orcas are very distinctive and are unlikely to be confused with any other sea creature. When seen from a distance in temperate waters, adult females and juveniles can be confused with various other species, such as the False Killer Whale or Risso's Dolphin.
Individual Orcas can be identified from a good photograph of the animal's dorsal fin and saddle patch, taken when it surfaces. Variations such as nicks, scratches, and tears on the dorsal fin, and the pattern of white or grey in the saddle patch, are sufficient to distinguish Orcas from each other. For the well-studied Orcas of the northeast Pacific, catalogues have been published with the photograph and name of each Orca. Photo-identification has enabled the local population of Orcas to be counted each year rather than estimated, and has enabled great insight into Orca lifecycles and social structures.
Females become mature at around 15 years of age. Then they have periods of polyestrous cycling with non-cycling periods of between three and sixteen months. The gestation period varies from fifteen to eighteen months. Mothers calve, with a single offspring, about once every five years. In analyzed resident pods, birth occurs at any time of year, with the most popular months being those in winter. Newborn mortality is very high — one survey suggested that nearly half of all calves fail to reach the age of six months. Calves nurse for up to two years, but will start to take solid food at about twelve months. All resident Orca pod members, including males of all ages, participate in the care of young whales.
Cows breed until the age of 40, meaning that on average they raise five offspring. Typically, females live to the age of fifty, but may survive well into their eighties or nineties in exceptional cases. Males become sexually mature at the age of 15, but do not typically reproduce until age 21. Males live to about 45 on average, and up to 90 in exceptional cases. The lifespan of captive Orcas are significantly shorter, usually less than 25 years.
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