Whale And Dolphin

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Whale (origin Old English hwæl) is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti (toothed whales). This suborder also includes the sperm whale, killer whale, pilot whale, and beluga whaleSONY PCG-8113M battery. The other Cetacean suborder Mysticeti (baleen whales) are filter feeders that eat small organisms caught by straining seawater through a comblike structure found in the mouth called baleen. This suborder includes the blue whale, the humpback whale, the bowhead whale and the minke whale. All Cetacea have forelimbs modified as fins, a tail with horizontal flukes, and nasal openings (blowholes) on top of the headSONY PCG-8112M battery .

Whales range in size from the blue whale, the largest animal known ever to have existed[3] at 30 m (98 ft) and 180 tonnes (180 long tons; 200 short tons), to various pygmy species, such as the pygmy sperm whale at 3.5 m (11 ft).

Whales collectively inhabit all the world's oceans and number in the millions, with annual population growth rate estimates for various species ranging from 3% to 13%.[4] For centuries, whales have been hunted for meat and as a source of raw materialsSONY PCG-7134M battery. By the middle of the 20th century, however, industrial whaling had left many species seriously endangered, leading to the end of whaling in all but a few countries.

Taxonomy

See also: List of whale species

Cetaceans are divided into two suborders:

The largest suborder, Mysticeti (baleen whales) are characterized by baleen, a sieve-like structure in the upper jaw made of keratin, which it uses to filter plankton from the water.

Odontoceti (toothed whales) bear sharp teeth for hunting. Odontoceti also include dolphins and porpoisesSONY PCG-7131M battery .

Both cetaceans and artiodactyl are now classified under the super-order Cetartiodactyla which includes both whales and hippopotamuses. Whales are the hippopotamus's closest living relatives.[5]

Evolution

Ambulocetus natans – a primitive cetacean

See also: Evolution of cetaceans

All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulates). Both are related to the Indohyus (an extinct semi-aquatic deer-like ungulate) from which they split around 54 million years ago. SONY PCG-7122M battery  These primitive cetaceans probably first took to the sea about 50 million years ago and became fully aquatic about 5–10 million years later.[8]

Anatomy

Like all mammals, whales breathe air, are warm-blooded, nurse their young with milk from mammary glands, and have body hair.[9] Beneath the skin lies a layer of fat called blubber, which stores energy and insulates the body. Whales have a spinal column, a vestigial pelvic bone, and a four-chambered heartSONY PCG-7121M battery. The neck vertebrae are typically fused, trading flexibility for stability during swimming.

Blowhole(s)

Features of a blue whale

Whales breathe via blowholes; baleen whales have two and toothed whales have one. These are located on the top of the head, allowing the animal to remain mostly submerged whilst breathing. Breathing involves expelling excess water from the blowhole, forming an upward spout, followed by inhaling air into the lungs. Spout shapes differ among species and can help with identificationSONY PCG-7113M battery .

Appendages

The body shape is fusiform and the modified forelimbs, or fins, are paddle-shaped. The end of the tail is composed of two flukes, which propel the animal by vertical movement, as opposed to the horizontal movement of a fish tail. Although whales do not possess fully developed hind limbs, some (such as sperm whales and baleen whales) possess discrete rudimentary appendagesSONY PCG-7112M battery , which may even have feet and digits. Most species have a dorsal fin.

Dentition

Toothed whales, such as the sperm whale, possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Only in larger whales, where the cementum has been worn away on the tip of the tooth, does enamel show. SONY PCG-8Z3M battery

Instead of teeth, Baleen whales have a row of plates on the upper side of their jaws that resemble the "teeth" of a comb.

Ears

The whale ear has specific adaptations to the marine 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 environmentsSONY PCG-8Z2M battery. Instead of sound passing through the outer ear to the middle ear, whales receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear.[11] The whale ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. SONY PCG-8Z1M battery

Life history and behavior

Reproduction

Males are called 'bulls', females, 'cows' and newborns, 'calves'. Most species do not maintain fixed partnerships and females have several mates each season.

The female delivers usually a single calf tail-first to minimize the risk of drowning. Whale cows nurse by actively squirting milk, so fatty that it has the consistency of toothpaste, into the mouths of their young.[13] Nursing continues for more than a year in many speciesSONY PCG-8Y3M battery, and is associated with a strong bond between mother and calf. Reproductive maturity occurs typically at seven to ten years. This mode of reproduction produces few offspring, but increases survival probability.

Socialization

Whales are known to teach, learn, cooperate, scheme, and even grieve.[15] The neocortex of many species of whale is home to elongated spindle neurons thatSONY PCG-8Y2M battery, prior to 2007, were known only in hominids. In humans these cells are involved in social conduct, emotions, judgment, and theory of mind. Whale spindle neurons are found in areas of the brain homologous to where they are found in humans, suggesting that they perform a similar function. SONY PCG-7Z1M battery

Sleep

A humpback whale breaching.

Unlike most animals, whales are conscious breathers. All mammals sleep, but whales cannot afford to become unconscious for long because they may drown. It is thought that only one hemisphere of the whale's brain sleeps at a time, so they rest but are never completely asleep. SONY PCG-6W2M battery

Surfacing behavior

Main article: Whale surfacing behaviour

Many whales exhibit behaviors such as breaching and tail slapping that expose large parts of their bodies to the air.

Lifespan

Whale lifespans vary among species and are not well characterized. Whaling left few older individuals to observe directly. R.M. Nowak of Johns Hopkins University estimated that humpback whales may live as long as 77 years.SONY PCG-5J5M battery  In 2007, a 19th century lance fragment was found in a bowhead whale off Alaska, suggesting the individual could be between 115 and 130 years old.[21] Aspartic acid racemization in the whale eye, combined with a harpoon fragment, indicated an age of 211 years for another male, which, if true would make bowheads the longest-lived extant mammal speciesSONY PCG-5K2M battery . The accuracy of this technique has been questioned because racemization did not correlate well with other dating methods.[24]

Vocalization

Humpback Whale "Song"

Recording of Humpback Whales singing and Clicking.

Problems listening to this file? See media help.

Some species, such as the humpback whale, communicate using melodic sounds, known as whale song. These sounds can be extremely loud, depending on the species. Sperm whales have only been heard making clicks, while toothed whales (Odontoceti) SONY PCG-5K1M battery use echolocation that can generate about 20,000 watts of sound (+73 dBm or +43 dBw[25]) and be heard for many miles. Whale vocalization is likely to serve many purposes, including echolocation, mating, and identification.[citation needed]

Ecology

Whales are generally classed as predators, but their food ranges from microscopic plankton to very large animalsSONY PCG-5J4M battery.

Toothed whales eat fish and squid which they hunt by use of echolocation. Killer whales sometimes eat other marine mammals, including whales.

Baleen whales such as humpbacks and blues, when feeding in higher latitudes (such as the Southern Ocean), eat mostly krill. They imbibe enormous amounts of seawater which they expel through their baleen platesSONY PCG-5J1M battery . The water is then expelled and the krill is retained on the plates and then swallowed.[13] Whales do not drink seawater but indirectly extract water from their food by metabolizing fat.

Whale pump

A study in 2010 has attributed to whales a positive influence on the productivity of ocean fisheries, in what has been termed a "whale pump." Whales carry nutrients such as nitrogen from the depths back to the surfaceSONY PCG-5G2M battery. This functions as an upward biological pump, reversing the assumption of some scientists that whales accelerate the loss of nutrients to the bottom. They note that this nitrogen input in the Gulf of Maine is "more than the input of all rivers combined," some 23,000 metric tons each year."

Relation to humans

Whaling

Main article: Whaling

Dutch whalers near Spitsbergen. Abraham Storck, 1690

World map of International Whaling Commission (IWC) members/non-members(member countries in blue) Sony VAIO PCG-8131M battery

World population graph of Blue Whales (Balaenoptera musculus)

Some species of large whales are listed as endangered by multinational organizations such as CITES along with governments and advocacy groups primarily due to whaling's impacts. They have been hunted commercially for whale oil, meat, baleen and ambergris (a perfume ingredient from the intestine of sperm whales) since the 17th century. Sony VAIO PCG-8152M battery At its peak in 1846, the American whaling industry employed more than 70,000 people and 736 vessels.[29] More than 2 million were taken in the 20th century,[30] and by the middle of the century, many populations were severely depleted.

The International Whaling Commission banned commercial whaling in 1986.[31] The ban is not absolute, however, and some whaling continues under the auspices of scientific researchSony VAIO PCG-31311M battery (sometimes not proved[32]) or aboriginal rights; current whaling nations are Norway, Iceland and Japan and the aboriginal communities of Siberia, Alaska and northern Canada.

Bycatch

Several species of small whales are caught as bycatch in fisheries for other species. In the Eastern Tropical Pacific tuna fishery, thousands of dolphins drowned in purse-seine nets, until preventive measures were introduced. Gear and deployment modifications, and eco-labelling (dolphin-safe or dolphin-friendly brands of tuna), have contributed to a reduction in dolphin mortality by tuna vesselsSony VAIO PCG-31111M battery.

Naval sonar

See also: Marine Mammals and Sonar

Environmentalists speculate that advanced naval sonar endangers some cetaceans, including whales. In 2003 British and Spanish scientists suggested in Nature that the effects of sonar trigger whale beachings and to signs that such whales have experienced decompression sickness.[33] Responses in Nature the following year discounted the explanation. Sony VAIO PCG-8112M battery

Mass beachings occur in many species, mostly beaked whales that use echolocation 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, have been used to estimate the population of various whale species by assuming that the proportion of the total whale population beaching in any one year is constantSony VAIO PCG-7186M battery. Beached whales can give other clues about population conditions, especially health problems. For example, bleeding around ears, internal lesions, and nitrogen bubbles in organ tissue suggest decompression sickness.[15]

Following public concern, the U.S. Defense department was ordered by the 9th Circuit Court to strictly limit use of its Low Frequency Active Sonar during peacetimeSony VAIO PCG-7171M battery. 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) failed as of 2008. The European Parliament has requested that EU members refrain from using the powerful sonar system until an environmental impact study has been carried outSony VAIO PCG-9Z1M battery.

Other environmental disturbances

See also: Cetacean bycatch

Other human activities have been suggested by marine biologists to adversely impact whale populations, such as collisions with ships and propellers, poisoning by waste contaminants and the unregulated use of fishing gear that catches anything that swims into it.[citation needed]

In mythology

Whale weather-vane atop the Nantucket Historical Association Whaling Museum displaying a Sperm WhaleSony VAIO PCG-5S1M battery.

Whales were little understood for most of human history as they spend up to 90% of their lives underwater, only surfacing briefly to breathe.[35] They also include the largest animals on the planet. Many cultures, even those that have hunted them, hold them in awe and feature them in their mythologiesSony VAIO PCG-5P1M battery.

In China, Yu-kiang, a whale with the hands and feet of a man was said to rule the ocean.[36]

In the Tyrol region of Austria it was said that if a sunbeam were to fall on a maiden entering womanhood, she would be carried away in the belly of a whale.[36]

Paikea, the youngest and favourite son of the chief Uenuku from the island of Mangaia in the present day Cook Islands in New Zealand was said by the Kati Kuri people of Kaikoura to have come from the Pacific Islands on the back of a whale many centuries before. Sony VAIO PCG-5N2M battery The novel and movie Whale Rider follow the trials of a girl named Paikia, who lives in such a culture.

The whale features in Inuit creation myths. When ‘Big Raven', a deity in human form, found a stranded whale, he was told by the Great Spirit where to find special mushrooms that would give him the strength to drag the whale back to the sea and thus return order to the world.[38]

The Tlingit people of northern Canada said that the Orcas were created when the hunter Natsihlane carved eight fish from yellow cedar, Sony VAIO PCG-3C2M battery sang his most powerful spirit song and commanded the fish to leap into the water.[38]

In Icelandic legend a man threw a stone at a fin whale and hit the blowhole, causing the whale to burst. The man was told not to go to sea for twenty years but in the nineteenth year he went fishing and a whale came and killed him. Sony VAIO PCG-8161M battery

In East African legend King Sulemani asked God that He might permit him to feed all the beings on earth. A whale came and ate until there was no corn left and then told Sulemani that he was still hungry and that there were 70,000 more in his tribe. Sulemani then prayed to God for forgiveness and thanked the creature for teaching him a lesson in humility.Sony VAIO PCG-8141M battery

Some cultures associate divinity with whales, such as among Ghanaians and Vietnamese, who occasionally hold funerals for beached whales, a throwback to Vietnam's ancient sea-based Austro-asiatic culture. The whale is a revered creature to Vietnamese fishermen. They are respectfully addressed as "Lord". If one finds a stranded whale corpse, one is in charge of holding the funeral for the "Lord" as if it was one's own parentSony VAIO PCG-3J1M battery.

The story of Jonah being swallowed by a whale also is told in the Qur'an.[43]

Whales in the Bible

The Bible, 1611 Authorized Version, expressly mentions whales four times:

Genesis 1:21 And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that it was good. Sony VAIO PCG-3H1M battery

Job 7:12 Am I a sea, or a whale, that thou settest a watch over me?

Ezekiel 32:2 Son of man, take up a lamentation for Pharaoh king of Egypt, and say unto him, Thou art like a young lion of the nations, and thou art as a whale in the seas: and thou camest forth with thy rivers, and troubledst the waters with thy feet, and fouledst their rivers.

Matthew 12:40 For as Jonas 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 earthSony VAIO PCG-3F1M battery.

The translators in that latter verse above thereby identified the "great fish" of the book of Jonah as a whale. It is apparent that Jeremiah recognized that some great fish are mammals. The English word "monster", (used in the ordinary sense of a "huge animal",) is used in the Bible in Jeremiah's Lamentations to refer to whales
Sony VAIO PCG-3C1M battery
:

Lamentations 4:3 Even the sea monsters draw out the breast, they give suck to their young ones: the daughter of my people is become cruel, like the ostriches in the wilderness.

Dolphins are marine mammals closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from 1.2 m (4 ft) and 40 kg (90 lb) (Maui's dolphin), up to 9.5 m (30 ft) and 10 tonnesSony VAIO PCG-9Z2L battery (9.8 long tons; 11 short tons) (the orca or killer whale). They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, eating mostly fish and squid. The family Delphinidae is the largest in the Cetacean order, and evolved relatively recently, about ten million years ago, during the Miocene. Dolphins are among the most intelligent animals, and their often friendly appearance and seemingly playful attitude have made them very popular in human cultureSony VAIO PCG-9Z1L battery.

Etymology

The name is originally from Greek δελφίς (delphís), "dolphin",[1] which was related to the Greek δελφύς (delphus), "womb".[2] The animal's name can therefore be interpreted as meaning "a 'fish' with a womb".[3] The name was transmitted via the Latin delphinus[4] (the romanization of the later Greek δελφῖνος – delphinos[5]), which in Medieval Latin became dolfinus and in Old French daulphinSony VAIO PCG-9131L battery, which reintroduced the ph into the word. The term mereswine (that is, "sea pig") has also historically been used.[6]

The word is used in a few different ways. It can mean:

any member of the family Delphinidae (oceanic dolphins),

any member of the family Delphinidae or the superfamily Platanistoidea (oceanic and river dolphins),

any member of the suborder Odontoceti (toothed whales; these include the above families and some others) Sony VAIO PCG-8161L battery,

and is used casually as a synonym for bottlenose dolphin, the most common and familiar species of dolphin.

This article uses the second definition and does not describe porpoises (suborder Odontoceti, family Phocoenidae). Orcas and some closely related species belong to the Delphinidae family and therefore qualify as dolphins, even though they are called whales in common languageSony VAIO PCG-8152L battery.

A group of dolphins is called a "school" or a "pod". Male dolphins are called "bulls", females "cows" and young dolphins are called "calves".[7]

Hybridization

In 1933, three strange dolphins beached off the Irish coast; they appeared to be hybrids between Risso's and bottlenose dolphins.[9] This mating was later repeated in captivity, producing a hybrid calf. In captivity, a bottlenose and a rough-toothed dolphin produced hybrid offspring.[10] A common-bottlenose hybrid lives at SeaWorld California. Sony VAIO PCG-8141L battery Other dolphin hybrids live in captivity around the world or have been reported in the wild, such as a bottlenose-Atlantic spotted hybrid.[12] The best known hybrid is the wolphin, a false killer whale-bottlenose dolphin hybrid. The wolphin is a fertile hybrid. Two wolphins currently live at the Sea Life Park in Hawaii; the first was born in 1985 from a male false killer whale and a female bottlenose. Wolphins have also been observed in the wild.Sony VAIO PCG-8131L battery

Evolution and anatomy

The anatomy of a dolphin, showing its skeleton, major organs, tail, and body shape

Pacific white-sided dolphin skeleton (missing pelvic bones), on exhibit at The Museum of Osteology, Oklahoma City, Oklahoma

Evolution

See also: Evolution of cetaceans

Dolphins, along with whales and porpoises, are descendants of terrestrial mammals, most likely of the Artiodactyl order. The ancestors of the modern-day dolphins entered the water roughly 50 million years ago, in the Eocene epochSony VAIO PCG-81312L battery.

Hind limb buds are apparent on an embryo of a spotted dolphin in the fifth week of development as small bumps (hind limb buds) near the base of the tail. The pin is approximately 2.5 cm (1.0 in) long.

Modern dolphin skeletons have two small, rod-shaped pelvic bones thought to be vestigial hind limbs. In October 2006, an unusual bottlenose dolphin was captured in Japan; it had small fins on each side of its genital slitSony VAIO PCG-81214L battery, which scientists believe to be a more pronounced development of these vestigial hind limbs.[14]

Anatomy

Dolphins have a streamlined fusiform body, adapted for fast swimming. The tail fin, called the fluke, is used for propulsion, while the pectoral fins together with the entire tail section provide directional control. The dorsal fin, in those species that have one, provides stability while swimming. Though it varies by speciesSony VAIO PCG-81115L battery, basic coloration patterns are shades of grey, usually with a lighter underside, often with lines and patches of different hue and contrast.

The head contains the melon, a round organ used for echolocation. In many species, elongated jaws form a distinct beak; species such as the bottlenose have a curved mouth which looks like a fixed smile. Some species have up to 250 teeth. Dolphins breathe through a blowhole on top of their head. The trachea is anterior to the brainSony VAIO PCG-81114L battery. The dolphin brain is large and highly complex, and is different in structure from that of most land mammals.

Unlike most mammals, dolphins do not have hair, except for a few hairs around the tip of their rostrum which they lose shortly before or after birth.[15] The only exception to this is the Boto river dolphin, which has persistent small hairs on the rostrum. Sony VAIO PCG-81113L battery

Dolphins' reproductive organs are located on the underside of the body. Males have two slits, one concealing the penis and one further behind for the anus. The female has one genital slit, housing the vagina and the anus. Two mammary slits are positioned on either side of the female's genital slitSony VAIO PCG-7142L battery.

Though the exact methods used to achieve this are not known, dolphins can tolerate and recover from extreme injuries, such as shark bites. The healing process is rapid and even very deep wounds do not cause dolphins to hemorrhage to death. Furthermore, even gaping wounds restore in such a way that the animal's body shape is restored, and infection of such large wounds seems rare. Sony VAIO PCG-7141L battery

A study at the U.S. National Marine Mammal Foundation revealed that dolphins, like humans, develop a natural form of type 2 diabetes, which may lead to a better understanding of the disease and new treatments for both humans and dolphins.[18]

Senses

Most dolphins have acute eyesight, both in and out of the water, and they can hear frequencies ten times or more above the upper limit of adult human hearingSony VAIO PCG-71111L battery.[19] Though they have a small ear opening on each side of their head, it is believed hearing underwater is also, if not exclusively, done with the lower jaw, which conducts sound to the middle ear via a fat-filled cavity in the lower jaw bone. Hearing is also used for echolocation, which all dolphins have. Dolphin teeth are believed to function as antennae to receive incoming sound and to pinpoint the exact location of an object. Sony VAIO PCG-61411L batteryBeyond locating an object, echolocation also provides the animal with an idea on the object's shape and size, though how exactly this works is not yet understood.[21] The Indus Dolphin is effectively blind. This may be because not much light penetrates the waters of the Indus river (due to suspended sediments), making eyes futile. Sony VAIO PCG-61112L battery

The dolphin's sense of touch is also well-developed, with free nerve endings densely packed in the skin, especially around the snout, pectoral fins and genital area. However, dolphins lack an olfactory nerve and lobes, and thus are believed to have no sense of smell.[23] They do have a sense of taste and show preferences for certain kinds of fishSony VAIO PCG-61111L battery. Since dolphins spend most of their time below the surface, tasting the water could function like smelling, in that substances in the water can signal the presence of objects that are not in the dolphin’s mouth.

Though most dolphins do not have hair, they do have hair follicles that may perform some sensory function.[24] The small hairs on the rostrum of the Boto river dolphin are believed to function as a tactile sense possibly to compensate for the Boto's poor eyesight. Sony VAIO PCG-5T4L battery

Behavior

A pod of Indo-Pacific bottlenose dolphins in the Red Sea.

See also: Whale surfacing behaviour

Dolphins are often regarded as one of Earth's most intelligent animals, though it is hard to say just how intelligent. Comparing species' relative intelligence is complicated by differences in sensory apparatus, response modes, and nature of cognition. Furthermore, the difficulty and expense of experimental work with large aquatic animals has so far prevented some tests and limited sample size and rigor in othersSony VAIO PCG-5T3L battery. Compared to many other species, however, dolphin behavior has been studied extensively, both in captivity and in the wild. See cetacean intelligence for more details.

Social behavior

Dolphins surfing at Snapper Rocks, Queensland, Australia

Dolphins are social, living in pods of up to a dozen individuals. In places with a high abundance of food, pods can merge temporarily, forming a superpod; such groupings may exceed 1,000 dolphins. Individuals communicate using a variety of clicks, whistles-like sounds and other vocalizationsSony VAIO PCG-5T2L battery. Membership in pods is not rigid; interchange is common. However, dolphins can establish strong social bonds; they will stay with injured or ill individuals, even helping them to breathe by bringing them to the surface if needed.[26] This altruism does not appear to be limited to their own species however. The dolphin Moko in New Zealand has been observed guiding a female Pygmy Sperm Whale together with her calf out of shallow water where they had stranded several timesSony VAIO PCG-5S3L battery.[27] They have also been seen protecting swimmers from sharks by swimming circles around the swimmers[28][29] or charging the sharks to make them go away.[30]

Dolphins also display culture, something long believed to be unique to humans (and possibly other primate species). In May 2005, a discovery in Australia found Indo-Pacific bottlenose dolphins (Tursiops aduncus) teaching their young to use tools. They cover their snouts with sponges to protect them while foragingSony VAIO PCG-5S2L battery. This knowledge is mostly transferred by mothers to daughters, unlike simian primates, where knowledge is generally passed on to both sexes. Using sponges as mouth protection is a learned behavior.[31] Another learned behavior was discovered among river dolphins in Brazil, where some male dolphins use weeds and sticks as part of a sexual display.Sony VAIO PCG-5S1L battery

Dolphins engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is to be covered with bite scars. Male dolphins engage in such acts of aggression apparently for the same reasons as humans: disputes between companions and competition for females. Acts of aggression can become so intense that targeted dolphins sometimes go into exile as a result of losing a fightSony VAIO PCG-5R2L battery.

Male bottlenose dolphins have been known to engage in infanticide. Dolphins have also been known to kill porpoises for reasons which are not fully understood, as porpoises generally do not share the same diet as dolphins, and are therefore not competitors for food supplies. Sony VAIO PCG-5R1L battery

Reproduction and sexuality

See also: Bottlenose dolphin#Reproduction

Dolphin copulation happens belly to belly; though many species engage in lengthy foreplay, the actual act is usually brief, but may be repeated several times within a short timespan. The gestation period varies with species; for the small Tucuxi dolphin, this period is around 11 to 12 months, while for the orca, the gestation period is around 17 monthsSony VAIO PCG-5P4L battery. Typically dolphins give birth to a single calf, which is, unlike most other mammals, born tail first in most cases.[34] They usually become sexually active at a young age, even before reaching sexual maturity. The age of sexual maturity varies by species and gender.

Dolphins are known to have sex for reasons other than reproduction[citation needed], sometimes also engaging in homosexual behaviorSony VAIO PCG-5P2L battery. Various species sometimes engage in sexual behavior including copulation with other dolphin species. Sexual encounters may be violent, with male dolphins sometimes showing aggressive behavior towards both females and other males.[35] Occasionally, dolphins behave sexually towards other animals, including humans. Sony VAIO PCG-5N4L battery

Feeding

Various methods of feeding exist among and within species, some apparently exclusive to a single population. Fish and squid are the main food, but the false killer whale and the orca also feed on other marine mammals.

One common feeding method is herding, where a pod squeezes a school of fish into a small volume, known as a bait ballSony VAIO PCG-5N2L battery. Individual members then take turns plowing through the ball, feeding on the stunned fish. Coralling is a method where dolphins chase fish into shallow water to catch them more easily. In South Carolina, the Atlantic bottlenose dolphin takes this further with "strand feeding", driving prey onto mud banks for easy access.[37] In some places, orcas come to the beach to capture sea lionsSony VAIO PCG-51513L battery. Some species also whack fish with their flukes, stunning them and sometimes knocking them out of the water.

Reports of cooperative human-dolphin fishing date back to the ancient Roman author and natural philosopher Pliny the Elder.[38] A modern human-dolphin partnership currently operates in Laguna, Santa Catarina, BrazilSony VAIO PCG-51511L battery. Here, dolphins drive fish towards fishermen waiting along the shore and signal the men to cast their nets. The dolphins’ reward is the fish that escape the nets.

Vocalizations

Spectrogram of dolphin vocalizations. Whistles, whines, and clicks are visible as upside down V's, horizontal striations, and vertical lines, respectively.

Dolphins are capable of making a broad range of sounds using nasal airsacs located just below the blowhole. Roughly three categories of sounds can be identified: frequency modulated whistles, burst-pulsed sounds and clicksSony VAIO PCG-51412L battery. Dolphins communicate with whistle-like sounds produced by vibrating connective tissue, similar to the way human vocal cords function,[41] and through burst-pulsed sounds, though the nature and extent of that ability is not known. The clicks are directional and are for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interestSony VAIO PCG-51411L battery. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals.[42]

In 2011 researchers in the United States and Great Britain, using a CymaScope — an instrument which produces visible patterns from sound — have found that part of dolphin communication consists of receiving and transmitting sound pictures. It is almost certain that to some extent this ability is shared by the entire dolphin familySony VAIO PCG-51312L battery.

Jumping and playing

Pacific white-sided dolphins porpoising

Dolphins occasionally leap above the water surface, and sometimes perform acrobatic figures (for example, the spinner dolphin). Scientists are not certain about the purpose(s) of the acrobatics. Possibilities include locating schools of fish by looking at above-water signs like feeding birds, communicating with other dolphins, dislodging parasites or simple amusementSony VAIO PCG-51311L battery.

Play is an important part of dolphin culture. Dolphins play with seaweed and play-fight with other dolphins. At times they harass other local creatures, like seabirds and turtles. Dolphins enjoy riding waves and frequently surf coastal swells and the bow waves of boats, at times “leaping” between the dual bow waves of a moving catamaranSony VAIO PCG-51211L battery. Occasionally, they playfully interact with swimmers. Captive dolphins have been observed in aquariums engaging in complex play behavior which involves the creation and manipulation of bubble rings.

Sleeping

Further information: Sleep (non-human)

Sleeping dolphin in captivity: a tail kick reflex keeps the dolphin's blowhole above the water

GenerallySony VAIO PCG-41112L battery, dolphins sleep with only one brain hemisphere in slow-wave sleep at a time, thus maintaining enough consciousness to breathe and to watch for possible predators and other threats. Earlier sleep stages can occur simultaneously in both hemispheres. In captivity, dolphins seemingly enter a fully asleep state where both eyes are closed and there is no response to mild external stimuliSony VAIO PCG-3A4L battery. In this case, respiration is automatic; a tail kick reflex keeps the blowhole above the water if necessary. Anesthetized dolphins initially show a tail kick reflex.[51] Though a similar state has been observed with wild sperm whales, it is not known if dolphins in the wild reach this state.[52] The Indus river dolphin has a sleep method that is different from that of other dolphin speciesSony VAIO PCG-3A3L battery. Living in water with strong currents and potentially dangerous floating debris, it must swim continuously to avoid injury. As a result, this species sleeps in very short bursts which last between 4 and 60 seconds.[53]

Threats

Natural threats

Except for humans (discussed below), dolphins have few natural enemies. Some species or specific populations have none, making them apex predators. For most of the smaller species of dolphins, only a few of the larger sharks, such as the bull sharkSony VAIO PCG-3A2L battery, dusky shark, tiger shark and great white shark, are a potential risk, especially for calves. Some of the larger dolphinic species, especially orcas (killer whales), may also prey on smaller dolphins, but this seems rare. Dolphins also suffer from a wide variety of diseases and parasites.

Human threats

See also: Dolphin drive hunting and Cetacean bycatch

Dead Atlantic white-sided dolphins in Hvalba on the Faroe Islands, killed in a drive huntSony VAIO PCG-3A1L battery

Some dolphin species face an uncertain future, especially some river dolphin species such as the Amazon river dolphin, and the Ganges and Yangtze river dolphin, which are critically or seriously endangered. A 2006 survey found no individuals of the Yangtze river dolphin, which now appears to be functionally extinct. Sony VAIO PCG-394L battery

Pesticides, heavy metals, plastics, and other industrial and agricultural pollutants that do not disintegrate rapidly in the environment concentrate in predators such as dolphins.[55] Injuries or deaths due to collisions with boats, especially their propellers, are also common.

Various fishing methods, most notably purse seine fishing for tuna and the use of drift and gill nets, unintentionally kill many dolphinsSony VAIO PCG-393L battery. Accidental by-catch in gill nets and incidental captures in antipredator nets that protect marine fish farms are common and pose a risk for mainly local dolphin populations. In some parts of the world, such as Taiji in Japan and the Faroe Islands, dolphins are traditionally considered as food, and are killed in harpoon or drive hunts.[59] Dolphin meat is high in mercury, and may thus pose a health danger to humans when consumedSony VAIO PCG-391L battery.

Dolphin safe labels attempt to reassure consumers fish and other marine products have been caught in a dolphin-friendly way. The original deal with "Dolphin safe" labels was brokered in the 1980s between marine activists and the major tuna companies, and involved decreasing incidental dolphin kills by up to 50% by changing the type of nets being used to catch the tunaSony VAIO PCG-384L battery. It should be noted that the dolphins are netted only while fishermen are in pursuit of smaller tuna. Albacore are not netted this way, making albacore the only truly dolphin-safe tuna.

Loud underwater noises, such as those resulting from naval sonar use, live firing exercises, or certain offshore construction projects, such as wind farms, may be harmful to dolphins, increasing stress, damaging hearing, and causing decompression sickness by forcing them to surface too quickly to escape the noiseSony VAIO PCG-382L battery.

Relationships with humans

Mythology

Fresco of Dolphins, ca. 1600 BC, from Knossos, Crete.

See also: Dolphins in mythology

Dolphins have long played a role in human culture. Dolphins are common in Greek mythology and there are many coins from ancient Greece which feature a man or boy or deity riding on the back of a dolphin. The Ancient Greeks welcomed dolphins; spotting dolphins riding in a ship’s wake was considered a good omen.[64] In Hindu mythology, the Ganges River Dolphin is associated with Ganga, the deity of the Ganges riverSony VAIO PCG-381L battery.

Popular culture

Luke Halpin with one of the dolphin performers in the 1963 film, Flipper.

In more recent times, the 1963 film Flipper and the subsequent 1964 television series popularized dolphins in Western society. The series, created by Ivan Tors, portrayed a dolphin as a kind of seagoing version of Lassie, the collie made popular in the 1950s TV series. Flipper was a Bottlenose Dolphin who understood commands and always behaved heroicallySony VAIO PCG-7185L battery. Flipper was remade as a film in 1996.

The 1973 movie The Day of the Dolphin portrays kidnapped dolphins performing a naval military assassination using explosives. This was also explored in the similarly named The Simpsons Treehouse of Horror episode, "Night of the Dolphin", where Lisa frees a dolphin at an aquarium exhibit and unwittingly initiates their plan to overthrow the land-dwellers and live in their placeSony VAIO PCG-7184L battery. The 1990s science fiction television series seaQuest DSV featured a bottle-nose named Darwin who could communicate using a vocoder, a fictional invention which translated clicks and whistles to English and back.

The 1995 movie Johnny Mnemonic portrays an ex-military dolphin named Jones who tries to find a password for Johnny by decrypting data in the latter's headSony VAIO PCG-7183L battery.

Killer whales have also been portrayed in film, though to a lesser extent than bottlenosed dolphins. The 1977 horror movie Orca portrayed killer whales as intelligent and capable of pair-bonding and aggressive behavior. In the movie, a male killer whale takes revenge on fishermen after they kill his mate. The 1993 movie Free Willy made a star of the Orca playing Willy, KeikoSony VAIO PCG-7182L battery.

Dolphinaria

See also: Dolphinarium

The renewed popularity of dolphins in the 1960s resulted in the appearance of many dolphinaria around the world, making dolphins accessible to the public. Criticism and animal welfare laws forced many to close, although hundreds still exist around the world. In the United States, the best known are the SeaWorld marine mammal parksSony VAIO PCG-7181L battery.

Welfare

Organizations such as the Mote Marine Laboratory rescue and rehabilitate sick, wounded, stranded or orphaned dolphins, while others, such as the Whale and Dolphin Conservation Society and Hong Kong Dolphin Conservation Society, work on dolphin conservation and welfare. India has declared the Dolphin as its national aquatic animal in an attempt to protect the endangered Ganges River DolphinSony VAIO PCG-7174L battery. The Vikramshila Gangetic Dolphin Sanctuary has been created in the Ganges river for the protection of the animals.

Various scientists who have researched Dolphin behaviour have proposed that their unusually high intelligence compared to other animals means that dolphins should be seen as non-human persons that should have their own specific rights, and that it is morally unacceptable to keep them captive for entertainment purposesSony VAIO PCG-7173L battery, or to kill them; either intentionally for consumption or as by-catch.

Attack on humans

Tilikum at SeaWorld. In 2010 he attacked and killed his trainer Dawn Brancheau, in his third fatal incident.

Although dolphins generally interact well with humans, some attacks have occurred, most of them resulting in small injuries.[67] The attacks can occur both in the wild and captivity.

Orcas, the largest species of dolphin, have been involved in fatal attacks on humans in captivitySony VAIO PCG-7172L battery. The record-holder of documented orca fatal attacks is a male named Tilikum, that belongs to SeaWorld and has played a role in the death of three people in three different incidents (1991, 1999 and 2010).[68] There are documented incidents in the wild too, but none of them fatal.

Fatal attacks from other species are less common, but there is a registered occurrence in the coast of Brazil in 1994, when a man died after being attacked by a bottlenose dolphin named TiãoSony VAIO PCG-7171L battery. It should be noted that Tião had suffered harassment by human visitors, including attempts to stick ice cream sticks down his blowhole.[72] Non-fatal incidents occur more frequently, both in wild and captivity.

While dolphin attacks occur far less frequently than attacks by other sea animals, such as sharks, some scientists are worried about the careless programs of human-dolphin interaction. Dr. Andrew J. Read, a biologist at the Duke University Marine Laboratory who studies dolphin attacksSony VAIO PCG-7162L battery, points out that dolphins are large and wild predators, so people should be more careful when they interact with them.[67]

Therapy

Dolphins are an increasingly popular choice of animal-assisted therapy for psychological problems and developmental disabilities. For example, a 2005 study found dolphins an effective treatment for mild to moderate depression. Sony VAIO PCG-7161L battery However, this study was criticized on several grounds. For example, it is not known whether dolphins are more effective than common pets.[74] Reviews of this and other published dolphin-assisted therapy (DAT) studies have found important methodological flaws and have concluded that there is no compelling scientific evidence that DAT is a legitimate therapy or that it affords more than fleeting mood improvement. Sony VAIO PCG-7154L battery

Military

A military dolphin

See also: Military dolphin

A number of militaries have employed dolphins for various purposes from finding mines to rescuing lost or trapped humans. The military use of dolphins, however, drew scrutiny during the Vietnam War when rumors circulated that the United States Navy was training dolphins to kill Vietnamese divers. Sony VAIO PCG-7153L battery The United States Navy denies that at any point dolphins were trained for combat. Dolphins are still being trained by the United States Navy on other tasks as part of the U.S. Navy Marine Mammal Program. The Russian military is believed to have closed its marine mammal program in the early 1990s. In 2000 the press reported that dolphins trained to kill by the Soviet Navy had been sold to Iran. Sony VAIO PCG-7152L battery

Literature

Dolphins are also common in contemporary literature, especially science fiction novels. Dolphins play a military role in William Gibson's short story Johnny Mnemonic, in which cyborg dolphins find submarines and decode encrypted information. Dolphins play a role as sentient patrollers of the sea enhanced with a deeper empathy toward humans in Anne McCaffrey's The Dragonriders of Pern seriesSony VAIO PCG-7151L battery. In the Known Space universe of author Larry Niven, dolphins play a significant role as fully recognised "legal entities". More humorous is Douglas Adams’ The Hitchhiker's Guide to the Galaxy series of picaresque novels, in which dolphins are the second most intelligent creatures on Earth (after mice, followed by humans) and try in vain to warn humans of Earth’s impending destruction
Sony VAIO PCG-7148L battery
. Their story is told in So Long, and Thanks for All the Fish. Much more serious is their major role in David Brin's Uplift series. A talking Dolphin named "Howard" helps Hagbard Celine and his submarine crew fight the evil Illuminati in Robert Shea and Robert Anton Wilson's Illuminatus TrilogySony VPCW21M2E/WI battery.

Dolphins appear frequently in non-science fiction literature. In the book The Music of Dolphins by author Karen Hesse, dolphins raise a girl from the age of four until the coast guard eventually discovers her. Fantasy author Ken Grimwood wrote dolphins into his 1995 novel Into the Deep about a marine biologist struggling to crack the code of dolphin intelligence, including chapters written from a dolphinian viewpointSony VPCW21C7E battery.

Art

Dolphins are a popular artistic motif, dating back to ancient times. Examples include the Triton Fountain by Bernini and depictions of dolphins in the ruined Minoan palace at Knossos and on Minoan pottery.

Plate of dolphin sashimi.

Dolphin meat is consumed in a small number of countries world-wide, which include Japan[78] and Peru (where it is referred to as chancho marino, or "sea pork").[79] While Japan may be the best-known and most controversial example, only a very small minority of the population has ever sampled itSony VPCW12S1E/WZ battery.

Dolphin meat is dense and such a dark shade of red as to appear black. Fat is located in a layer of blubber between the meat and the skin. When dolphin meat is eaten in Japan, it is often cut into thin strips and eaten raw as sashimi, garnished with onion and either horseradish or grated garlic, much as with sashimi of whale or horse meat (basashi)Sony VPCW12S1E/W battery. When cooked, dolphin meat is cut into bite-size cubes and then batter-fried or simmered in a miso sauce with vegetables. Cooked dolphin meat has a flavor very similar to beef liver.

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