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This oxygen duration chart from an airplane shows the amount of time a pilot can be on oxygen at a specified altitude (in 1000s of feet). For example, the chart shows two pilots able to cruise at a cabin altitude of 35,000 FT MSL for 182 minutes using a diluter demand system or 192 minutes using 100% oxygen.
I have one question.
- Why does the oxygen duration chart show increasing times above 30,000 FT MSL?
This is related to the diluter demand system, O2 present in the cabin, and tracheal pressure.
The diluter demand system is designed to compensate for the short-comings of the continuous flow system. It gives the user oxygen on-demand (during inhalation) and stops the flow when the demand ceases (during exhalation). This helps conserve oxygen. Additionally, the incoming oxygen is diluted with cabin air and provides the proper percentage of oxygen, depending on the altitude. This system is typically used at altitudes up to 40,000 feet.
Source: Oxygen Equipment: Use in General Aviation Operations - Federal Aviation Administration
When you get at altitudes higher than 35,000 feet you're more or less totally reliant on the oxygen provided by the diluter, that's why the diluter demand is very close to the cruise time. If there's low air pressure in the cabin above 35,000 feet there won't be enough oxygen for normal body function, and you run the risk of becoming hypoxic within half a minute.
Toe of Useful Consciousnees (TUC) per Effective Performance Time (EPT)
Look at the chart below:
Tracheal oxygen partial pressure starts at 149mm. Hg for sea level and can drop to 20 at 40,000 feet. If oxygen is given according to the % supplement O2 required for inspired air, the tracheal pressure stabilizes back to what it is at sea level. Above 30,000 feet, tracheal oxygen partial pressure cannot be maintained at 149mm. Hg. Therefore you need to use the diluter longer to at least maintain it close to 149mm. Hg. Or at level where the mm. Hg. isn't extremely low.
The required mean tracheal oxygen partial pressure can be different at the same altitude depending on the liters of O2 per minute BTPS (Body Temperature and Pressure Saturated) being inspired.
Source: Introduction to Aviation Physiology
Fore example, according to 14CFR 23.1443:
(ii) At cabin pressure altitudes above 18,500 feet up to and including 40,000 feet, a mean tracheal oxygen partial pressure of 83.8 mm. Hg when breathing 30 liters per minute, BTPS, and with a tidal volume of 1,100 cc. with a constant time interval between respirations.
(2) For each flight crew member, the minimum mass flow may not be less than the flow required to maintain, during inspiration, a mean tracheal oxygen partial pressure of 149 mm. Hg when breathing 15 liters per minute, BTPS, and with a maximum tidal volume of 700 cc. with a constant time interval between respirations.
So, at above 30,00 feet you will use most of the diluter demand oxygen to preserve tracheal pressure until the plane has stabilized. At lower altitudes the diluter demand is lower because you can reach safer altitudes faster.
The stratosphere is a layer of Earth's atmosphere. It is the second layer of the atmosphere as you go upward. The troposphere, the lowest layer, is right below the stratosphere. The next higher layer above the stratosphere is the mesosphere.
The bottom of the stratosphere is around 10 km (6.2 miles or about 33,000 feet) above the ground at middle latitudes. The top of the stratosphere occurs at an altitude of 50 km (31 miles). The height of the bottom of the stratosphere varies with latitude and with the seasons. The lower boundary of the stratosphere can be as high as 20 km (12 miles or 65,000 feet) near the equator and as low as 7 km (4 miles or 23,000 feet) at the poles in winter. The lower boundary of the stratosphere is called the tropopause the upper boundary is called the stratopause.
Ozone, an unusual type of oxygen molecule that is relatively abundant in the stratosphere, heats this layer as it absorbs energy from incoming ultraviolet radiation from the Sun. Temperatures rise as one moves upward through the stratosphere. This is exactly the opposite of the behavior in the troposphere in which we live, where temperatures drop with increasing altitude. Because of this temperature stratification, there is little convection and mixing in the stratosphere, so the layers of air there are quite stable. Commercial jet aircraft fly in the lower stratosphere to avoid the turbulence which is common in the troposphere below.
The stratosphere is very dry air there contains little water vapor. Because of this, few clouds are found in this layer almost all clouds occur in the lower, more humid troposphere. Polar stratospheric clouds (PSCs) are the exception. PSCs appear in the lower stratosphere near the poles in winter. They are found at altitudes of 15 to 25 km (9.3 to 15.5 miles) and form only when temperatures at those heights dip below -78° C. They appear to help cause the formation of the infamous holes in the ozone layer by "encouraging" certain chemical reactions that destroy ozone. PSCs are also called nacreous clouds.
Air is roughly a thousand times thinner at the top of the stratosphere than it is at sea level. Because of this, jet aircraft and weather balloons reach their maximum operational altitudes within the stratosphere.
Due to the lack of vertical convection in the stratosphere, materials that get into the stratosphere can stay there for long times. Such is the case for the ozone-destroying chemicals called CFCs (chlorofluorocarbons). Large volcanic eruptions and major meteorite impacts can fling aerosol particles up into the stratosphere where they may linger for months or years, sometimes altering Earth's global climate. Rocket launches inject exhaust gases into the stratosphere, producing uncertain consequences.
Various types of waves and tides in the atmosphere influence the stratosphere. Some of these waves and tides carry energy from the troposphere upward into the stratosphere others convey energy from the stratosphere up into the mesosphere. The waves and tides influence the flows of air in the stratosphere and can also cause regional heating of this layer of the atmosphere.
A rare type of electrical discharge, somewhat akin to lightning, occurs in the stratosphere. These "blue jets" appear above thunderstorms, and extend from the bottom of the stratosphere up to altitudes of 40 or 50 km (25 to 31 miles).
© 2011 UCAR with portions adapted from Windows to the Universe (© 2009 NESTA)
Aircraft fly high because it puts them above the weather. This is at least the historical reason why aviation has desired higher flying aircraft over the years and subsequently driven design that way. When it comes to weather altitude gives you diversion options, avoidance possibilities and in some cases the ability to simply fly over a system instead of through it.
Jet engines are more efficient at high altitudes which makes it beneficial to fly them up there (you can find the full explanation of that in this Q/A) but piston planes can fly quite high as well jets have prevailed for lots of reasons and that is a different discussion all together.
Altitude, in some cases also provides a safety margin for things like loss of engine power. With sufficient altitude you can have an outcome like this instead of this.
As for cabin depressurization that is not really a huge issue. Aircraft are equipped with oxygen masks to keep everyone safe in the event of a depressurization and all aircraft are certified to be able to do a decent from cruising altitude to 10,000ft. (non supplemental Oxygen altitude) in a specified time. Some newer systems will even bring the aircraft down automatically in the event of a depressurization.
The two parvorders, baleen whales (Mysticeti) and toothed whales (Odontoceti), are thought to have diverged around thirty-four million years ago. 
Baleen whales have bristles made of keratin instead of teeth. The bristles filter krill and other small invertebrates from seawater. Grey whales feed on bottom-dwelling mollusks. Rorqual family (balaenopterids) use throat pleats to expand their mouths to take in food and sieve out the water. Balaenids (right whales and bowhead whales) have massive heads that can make up 40% of their body mass. Most mysticetes prefer the food-rich colder waters of the Northern and Southern Hemispheres, migrating to the Equator to give birth. During this process, they are capable of fasting for several months, relying on their fat reserves.
The parvorder of Odontocetes – the toothed whales – include sperm whales, beaked whales, killer whales, dolphins and porpoises. Generally the teeth are designed for catching fish, squid or other marine invertebrates, not for chewing them, so prey is swallowed whole. Teeth are shaped like cones (dolphins and sperm whales), spades (porpoises), pegs (belugas), tusks (narwhals) or variable (beaked whale males). Female beaked whales' teeth are hidden in the gums and are not visible, and most male beaked whales have only two short tusks. Narwhals have vestigial teeth other than their tusk, which is present on males and 15% of females and has millions of nerves to sense water temperature, pressure and salinity. A few toothed whales, such as some killer whales, feed on mammals, such as pinnipeds and other whales.
Toothed whales have well-developed senses – their eyesight and hearing are adapted for both air and water, and they have advanced sonar capabilities using their melon. Their hearing is so well-adapted for both air and water that some blind specimens can survive. Some species, such as sperm whales, are well adapted for diving to great depths. Several species of toothed whales show sexual dimorphism, in which the males differ from the females, usually for purposes of sexual display or aggression.
Cetacean bodies are generally similar to that of fish, which can be attributed to their lifestyle and the habitat conditions. Their body is well-adapted to their habitat, although they share essential characteristics with other higher mammals (Eutheria). 
They have a streamlined shape, and their forelimbs are flippers. Almost all have a dorsal fin on their backs that can take on many forms depending on the species. A few species, such as the beluga whale, lack them. Both the flipper and the fin are for stabilization and steering in the water.
The male genitals and mammary glands of females are sunken into the body.  
The body is wrapped in a thick layer of fat, known as blubber, used for thermal insulation and gives cetaceans their smooth, streamlined body shape. In larger species, it can reach a thickness up to half a meter (1.6 ft).
Sexual dimorphism evolved in many toothed whales. Sperm whales, narwhals, many members of the beaked whale family, several species of the porpoise family, killer whales, pilot whales, eastern spinner dolphins and northern right whale dolphins show this characteristic.  Males in these species developed external features absent in females that are advantageous in combat or display. For example, male sperm whales are up to 63% percent larger than females, and many beaked whales possess tusks used in competition among males.   Hind legs are not present in cetaceans, nor are any other external body attachments such as a pinna and hair. 
Whales have an elongated head, especially baleen whales, due to the wide overhanging jaw. Bowhead whale plates can be 9 metres (30 ft) long. Their nostril(s) make up the blowhole, with one in toothed whales and two in baleen whales.
The nostrils are located on top of the head above the eyes so that the rest of the body can remain submerged while surfacing for air. The back of the skull is significantly shortened and deformed. By shifting the nostrils to the top of the head, the nasal passages extend perpendicularly through the skull.  The teeth or baleen in the upper jaw sit exclusively on the maxilla. The braincase is concentrated through the nasal passage to the front and is correspondingly higher, with individual cranial bones that overlap.
In toothed whales, connective tissue exists in the melon as a head buckle. This is filled with air sacs and fat that aid in buoyancy and biosonar. The sperm whale has a particularly pronounced melon this is called the spermaceti organ and contains the eponymous spermaceti, hence the name "sperm whale". Even the long tusk of the narwhal is a vice-formed tooth. In many toothed whales, the depression in their skull is due to the formation of a large melon and multiple, asymmetric air bags.
River dolphins, unlike most other cetaceans, can turn their head 90°. Most other cetaceans have fused neck vertebrae and are unable to turn their head at all.
The baleen of baleen whales consists of long, fibrous strands of keratin. Located in place of the teeth, it has the appearance of a huge fringe and is used to sieve the water for plankton and krill.
The neocortex of many cetaceans is home to elongated spindle neurons that, prior to 2019, were known only in hominids.  In humans, these cells are thought to be involved in social conduct, emotions, judgment and theory of mind.  Cetacean spindle neurons are found in areas of the brain homologous to where they are found in humans, suggesting they perform a similar function. 
Brain size was previously considered a major indicator of intelligence. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for cognitive tasks. Allometric analysis indicates that mammalian brain size scales at approximately two-thirds or three-quarter exponent of the body mass.  Comparison of a particular animal's brain size with the expected brain size based on such an analysis provides an encephalization quotient that can be used as an indication of animal intelligence. Sperm whales have the largest brain mass of any animal on earth, averaging 8,000 cm 3 (490 in 3 ) and 7.8 kg (17 lb) in mature males.  The brain to body mass ratio in some odontocetes, such as belugas and narwhals, is second only to humans.  In some whales, however, it is less than half that of humans: 0.9% versus 2.1%.
The cetacean skeleton is largely made up of cortical bone, which stabilizes the animal in the water. For this reason, the usual terrestrial compact bones, which are finely woven cancellous bone, are replaced with lighter and more elastic material. In many places, bone elements are replaced by cartilage and even fat, thereby improving their hydrostatic qualities. The ear and the muzzle contain a bone shape that is exclusive to cetaceans with a high density, resembling porcelain. This conducts sound better than other bones, thus aiding biosonar.
The number of vertebrae that make up the spine varies by species, ranging from forty to ninety-three. The cervical spine, found in all mammals, consists of seven vertebrae which, however, are reduced or fused. This fusion provides stability during swimming at the expense of mobility. The fins are carried by the thoracic vertebrae, ranging from nine to seventeen individual vertebrae. The sternum is cartilaginous. The last two to three pairs of ribs are not connected and hang freely in the body wall. The stable lumbar and tail include the other vertebrae. Below the caudal vertebrae is the chevron bone.
The front limbs are paddle-shaped with shortened arms and elongated finger bones, to support movement. They are connected by cartilage. The second and third fingers display a proliferation of the finger members, a so-called hyperphalangy. The shoulder joint is the only functional joint in all cetaceans except for the Amazon river dolphin. The collarbone is completely absent.
They have a cartilaginous fluke at the end of their tails that is used for propulsion. The fluke is set horizontally on the body, unlike fish, which have vertical tails.
Cetaceans have powerful hearts. Blood oxygen is distributed effectively throughout the body. They are warm-blooded, i.e., they hold a nearly constant body temperature.
Cetaceans have lungs, meaning they breathe air. An individual can last without a breath from a few minutes to over two hours depending on the species. Cetacea are deliberate breathers who must be awake to inhale and exhale. When stale air, warmed from the lungs, is exhaled, it condenses as it meets colder external air. As with a terrestrial mammal breathing out on a cold day, a small cloud of 'steam' appears. This is called the 'spout' and varies across species in shape, angle and height. Species can be identified at a distance using this characteristic.
The structure of the respiratory and circulatory systems is of particular importance for the life of marine mammals. The oxygen balance is effective. Each breath can replace up to 90% of the total lung volume. For land mammals, in comparison, this value is usually about 15%. During inhalation, about twice as much oxygen is absorbed by the lung tissue as in a land mammal. As with all mammals, the oxygen is stored in the blood and the lungs, but in cetaceans, it is also stored in various tissues, mainly in the muscles. The muscle pigment, myoglobin, provides an effective bond. This additional oxygen storage is vital for deep diving, since beyond a depth around 100 m (330 ft), the lung tissue is almost completely compressed by the water pressure.
The stomach consists of three chambers. The first region is formed by a loose gland and a muscular forestomach (missing in beaked whales), which is then followed by the main stomach and the pylorus. Both are equipped with glands to help digestion. A bowel adjoins the stomachs, whose individual sections can only be distinguished histologically. The liver is large and separate from the gall bladder. 
The kidneys are long and flattened. The salt concentration in cetacean blood is lower than that in seawater, requiring kidneys to excrete salt. This allows the animals to drink seawater. 
Cetacean eyes are set on the sides rather than the front of the head. This means only species with pointed 'beaks' (such as dolphins) have good binocular vision forward and downward. Tear glands secrete greasy tears, which protect the eyes from the salt in the water. The lens is almost spherical, which is most efficient at focusing the minimal light that reaches deep water. Cetaceans are known to possess excellent hearing. 
At least one species, the tucuxi or Guiana dolphin, is able to use electroreception to sense prey. 
The external ear has lost the pinna (visible ear), but still retains a narrow external auditory meatus. To register sounds, instead, the posterior part of the mandible has a thin lateral wall (the pan bone) fronting a concavity that houses a fat pad. The pad passes anteriorly into the greatly enlarged mandibular foramen to reach in under the teeth and posteriorly to reach the thin lateral wall of the ectotympanic. The ectotympanic offers a reduced attachment area for the tympanic membrane. The connection between this auditory complex and the rest of the skull is reduced—to a single, small cartilage in oceanic dolphins.
In odontocetes, the complex is surrounded by spongy tissue filled with air spaces, while in mysticetes, it is integrated into the skull as with land mammals. In odontocetes, the tympanic membrane (or ligament) has the shape of a folded-in umbrella that stretches from the ectotympanic ring and narrows off to the malleus (quite unlike the flat, circular membrane found in land mammals.) In mysticetes, it also forms a large protrusion (known as the "glove finger"), which stretches into the external meatus and the stapes are larger than in odontocetes. In some small sperm whales, the malleus is fused with the ectotympanic.
The ear ossicles are pachyosteosclerotic (dense and compact) and differently shaped from land mammals (other aquatic mammals, such as sirenians and earless seals, have also lost their pinnae). T semicircular canals are much smaller relative to body size than in other mammals. 
The auditory bulla is separated from the skull and composed of two compact and dense bones (the periotic and tympanic) referred to as the tympanoperiotic complex. This complex is located in a cavity in the middle ear, which, in the Mysticeti, is divided by a bony projection and compressed between the exoccipital and squamosal, but in the odontoceti, is large and completely surrounds the bulla (hence called "peribullar"), which is, therefore, not connected to the skull except in physeterids. In the Odontoceti, the cavity is filled with a dense foam in which the bulla hangs suspended in five or more sets of ligaments. The pterygoid and peribullar sinuses that form the cavity tend to be more developed in shallow water and riverine species than in pelagic Mysticeti. In Odontoceti, the composite auditory structure is thought to serve as an acoustic isolator, analogous to the lamellar construction found in the temporal bone in bats. 
Cetaceans use sound to communicate, using groans, moans, whistles, clicks or the 'singing' of the humpback whale. 
Odontoceti are generally capable of echolocation.  They can discern the size, shape, surface characteristics, distance and movement of an object. They can search for, chase and catch fast-swimming prey in total darkness. Most Odontoceti can distinguish between prey and nonprey (such as humans or boats) captive Odontoceti can be trained to distinguish between, for example, balls of different sizes or shapes. Echolocation clicks also contain characteristic details unique to each animal, which may suggest that toothed whales can discern between their own click and that of others. 
Mysticeti have exceptionally thin, wide basilar membranes in their cochleae without stiffening agents, making their ears adapted for processing low to infrasonic frequencies. 
The initial karyotype includes a set of chromosomes from 2n = 44. They have four pairs of telocentric chromosomes (whose centromeres sit at one of the telomeres), two to four pairs of subtelocentric and one or two large pairs of submetacentric chromosomes. The remaining chromosomes are metacentric—the centromere is approximately in the middle—and are rather small. Sperm whales, beaked whales and right whales converge to a reduction in the number of chromosomes to 2n = 42. 
Range and habitat Edit
Cetaceans are found in many aquatic habitats. While many marine species, such as the blue whale, the humpback whale and the killer whale, have a distribution area that includes nearly the entire ocean, some species occur only locally or in broken populations. These include the vaquita, which inhabits a small part of the Gulf of California and Hector's dolphin, which lives in some coastal waters in New Zealand. River dolphin species live exclusively in fresh water.
Many species inhabit specific latitudes, often in tropical or subtropical waters, such as Bryde's whale or Risso's dolphin. Others are found only in a specific body of water. The southern right whale dolphin and the hourglass dolphin live only in the Southern Ocean. The narwhal and the beluga live only in the Arctic Ocean. Sowerby's beaked whale and the Clymene dolphin exist only in the Atlantic and the Pacific white-sided dolphin and the northern straight dolphin live only in the North Pacific.
Cosmopolitan species may be found in the Pacific, Atlantic and Indian Oceans. However, northern and southern populations become genetically separated over time. In some species, this separation leads eventually to a divergence of the species, such as produced the southern right whale, North Pacific right whale and North Atlantic right whale.  Migratory species' reproductive sites often lie in the tropics and their feeding grounds in polar regions.
Thirty-two species are found in European waters, including twenty-five toothed and seven baleen species.
Whale migration Edit
Many species of whales migrate on a latitudinal basis to move between seasonal habitats. For example, the gray whale migrates 10,000 miles round trip. The journey begins at winter birthing grounds in warm lagoons along Baja California, and traverses 5,000-7,000 miles of coastline to summer feeding grounds in the Bering, Chuckchi and Beaufort seas off the coast of Alaska. 
Conscious breathing cetaceans sleep but cannot afford to be unconscious for long, because they may drown. While knowledge of sleep in wild cetaceans is limited, toothed cetaceans in captivity have been recorded to exhibit unihemispheric slow-wave sleep (USWS), which means they sleep with one side of their brain at a time, so that they may swim, breathe consciously and avoid both predators and social contact during their period of rest. 
A 2008 study found that sperm whales sleep in vertical postures just under the surface in passive shallow 'drift-dives', generally during the day, during which whales do not respond to passing vessels unless they are in contact, leading to the suggestion that whales possibly sleep during such dives. 
While diving, the animals reduce their oxygen consumption by lowering the heart activity and blood circulation individual organs receive no oxygen during this time. Some rorquals can dive for up to 40 minutes, sperm whales between 60 and 90 minutes and bottlenose whales for two hours. Diving depths average about 100 m (330 ft). Species such as sperm whales can dive to 3,000 m (9,800 ft), although more commonly 1,200 metres (3,900 ft).  
Social relations Edit
Most cetaceans are social animals, although a few species live in pairs or are solitary. A group, known as a pod, usually consists of ten to fifty animals, but on occasion, such as mass availability of food or during mating season, groups may encompass more than one thousand individuals. Inter-species socialization can occur. 
Pods have a fixed hierarchy, with the priority positions determined by biting, pushing or ramming. The behavior in the group is aggressive only in situations of stress such as lack of food, but usually it is peaceful. Contact swimming, mutual fondling and nudging are common. The playful behavior of the animals, which is manifested in air jumps, somersaults, surfing, or fin hitting, occurs more often than not in smaller cetaceans, such as dolphins and porpoises. 
Whale song Edit
Males in some baleen species communicate via whale song, sequences of high pitched sounds. These "songs" can be heard for hundreds of kilometers. Each population generally shares a distinct song, which evolves over time. Sometimes, an individual can be identified by its distinctive vocals, such as the 52-hertz whale that sings at a higher frequency than other whales. Some individuals are capable of generating over 600 distinct sounds.  In baleen species such as humpbacks, blues and fins, male-specific song is believed to be used to attract and display fitness to females. 
Pod groups also hunt, often with other species. Many species of dolphins accompany large tunas on hunting expeditions, following large schools of fish. The killer whale hunts in pods and targets belugas and even larger whales. Humpback whales, among others, form in collaboration bubble carpets to herd krill or plankton into bait balls before lunging at them. 
Cetacea are known to teach, learn, cooperate, scheme and grieve. 
Smaller cetaceans, such as dolphins and porpoises, engage in complex play behavior, including such things as producing stable underwater toroidal air-core vortex rings or "bubble rings". The two main methods of bubble ring production are rapid puffing of air into the water and allowing it to rise to the surface, forming a ring, or swimming repeatedly in a circle and then stopping to inject air into the helical vortex currents thus formed. They also appear to enjoy biting the vortex rings, so that they burst into many separate bubbles and then rise quickly to the surface. Whales produce bubble nets to aid in herding prey. 
Larger whales are also thought to engage in play. The southern right whale elevates its tail fluke above the water, remaining in the same position for a considerable time. This is known as "sailing". It appears to be a form of play and is most commonly seen off the coast of Argentina and South Africa.  Humpback whales also display this behaviour.
Self-awareness appears to be a sign of abstract thinking. Self-awareness, although not well-defined, is believed to be a precursor to more advanced processes such as metacognitive reasoning (thinking about thinking) that humans exploit. Cetaceans appear to possess self-awareness.  The most widely used test for self-awareness in animals is the mirror test, in which a temporary dye is placed on an animal's body and the animal is then presented with a mirror. Researchers then explore whether the animal shows signs of self-recognition. 
Critics claim that the results of these tests are susceptible to the Clever Hans effect. This test is much less definitive than when used for primates. Primates can touch the mark or the mirror, while cetaceans cannot, making their alleged self-recognition behavior less certain. Skeptics argue that behaviors said to identify self-awareness resemble existing social behaviors, so researchers could be misinterpreting self-awareness for social responses. Advocates counter that the behaviors are different from normal responses to another individual. Cetaceans show less definitive behavior of self-awareness, because they have no pointing ability. 
In 1995, Marten and Psarakos used video to test dolphin self-awareness.  They showed dolphins real-time footage of themselves, recorded footage and another dolphin. They concluded that their evidence suggested self-awareness rather than social behavior. While this particular study has not been replicated, dolphins later "passed" the mirror test. 
Reproduction and brooding Edit
Most cetaceans sexually mature at seven to 10 years. An exception to this is the La Plata dolphin, which is sexually mature at two years, but lives only to about 20. The sperm whale reaches sexual maturity within about 20 years and a lifespan between 50 and 100 years. 
For most species, reproduction is seasonal. Ovulation coincides with male fertility. This cycle is usually coupled with seasonal movements that can be observed in many species. Most toothed whales have no fixed bonds. In many species, females choose several partners during a season. Baleen whales are largely monogamous within each reproductive period.
Gestation ranges from 9 to 16 months. Duration is not necessarily a function of size. Porpoises and blue whales gestate for about 11 months. As with all mammals other than marsupials and monotremes, the embryo is fed by the placenta, an organ that draws nutrients from the mother’s bloodstream. Mammals without placentas either lay minuscule eggs (monotremes) or bear minuscule offspring (marsupials).
Cetaceans usually bear one calf. In the case of twins, one usually dies, because the mother cannot produce sufficient milk for both. The fetus is positioned for a tail-first delivery, so that the risk of drowning during delivery is minimal. After birth, the mother carries the infant to the surface for its first breath. At birth they are about one-third of their adult length and tend to be independently active, comparable to terrestrial mammals.
Like other placental mammals, cetaceans give birth to well-developed calves and nurse them with milk from their mammary glands. When suckling, the mother actively splashes milk into the mouth of the calf, using the muscles of her mammary glands, as the calf has no lips. This milk usually has a high fat content, ranging from 16 to 46%, causing the calf to increase rapidly in size and weight. 
In many small cetaceans, suckling lasts for about four months. In large species, it lasts for over a year and involves a strong bond between mother and offspring.
The mother is solely responsible for brooding. In some species, so-called "aunts" occasionally suckle the young.
This reproductive strategy provides a few offspring that have a high survival rate.
Among cetaceans, whales are distinguished by an unusual longevity compared to other higher mammals. Some species, such as the bowhead whale (Balaena mysticetus), can reach over 200 years. Based on the annual rings of the bony otic capsule, the age of the oldest known specimen is a male determined to be 211 years at the time of death. 
Upon death, whale carcasses fall to the deep ocean and provide a substantial habitat for marine life. Evidence of whale falls in present-day and fossil records shows that deep-sea whale falls support a rich assemblage of creatures, with a global diversity of 407 species, comparable to other neritic biodiversity hotspots, such as cold seeps and hydrothermal vents. 
Deterioration of whale carcasses happens through three stages. Initially, organisms such as sharks and hagfish scavenge the soft tissues at a rapid rate over a period of months and as long as two years. This is followed by the colonization of bones and surrounding sediments (which contain organic matter) by enrichment opportunists, such as crustaceans and polychaetes, throughout a period of years. Finally, sulfophilic bacteria reduce the bones releasing hydrogen sulfide enabling the growth of chemoautotrophic organisms, which in turn, support organisms such as mussels, clams, limpets and sea snails. This stage may last for decades and supports a rich assemblage of species, averaging 185 per site.  
Brucellosis affects almost all mammals. It is distributed worldwide, while fishing and pollution have caused porpoise population density pockets, which risks further infection and disease spreading. Brucella ceti, most prevalent in dolphins, has been shown to cause chronic disease, increasing the chance of failed birth and miscarriages, male infertility, neurobrucellosis, cardiopathies, bone and skin lesions, strandings and death. Until 2008, no case had ever been reported in porpoises, but isolated populations have an increased risk and consequentially a high mortality rate. 
Molecular biology and immunology show that cetaceans are phylogenetically closely related with the even-toed ungulates (Artiodactyla). Whales direct lineage began in the early Eocene, around 55.8 million years ago, with early artiodactyls.  Fossil discoveries at the beginning of the 21st century confirmed this.
Most molecular biological evidence suggests that hippos are the closest living relatives. Common anatomical features include similarities in the morphology of the posterior molars, and the bony ring on the temporal bone (bulla) and the involucre, a skull feature that was previously associated only with cetaceans.  The fossil record, however, does not support this relationship, because the hippo lineage dates back only about 15 million years.    The most striking common feature is the talus, a bone in the upper ankle. Early cetaceans, archaeocetes, show double castors, which occur only in even-toed ungulates. Corresponding findings are from Tethys Sea deposits in northern India and Pakistan. The Tethys Sea was a shallow sea between the Asian continent and northward-bound Indian plate.
Mysticetes evolved baleen around 25 million years ago and lost their teeth.
The direct ancestors of today's cetaceans are probably found within the Dorudontidae whose most famous member, Dorudon, lived at the same time as Basilosaurus. Both groups had already developed the typical anatomical features of today's whales, such as hearing. Life in the water for a formerly terrestrial creature required significant adjustments such as the fixed bulla, which replaces the mammalian eardrum, as well as sound-conducting elements for submerged directional hearing. Their wrists were stiffened and probably contributed to the typical build of flippers. The hind legs existed, however, but were significantly reduced in size and with a vestigial pelvis connection. 
Transition from land to sea Edit
The fossil record traces the gradual transition from terrestrial to aquatic life. The regression of the hind limbs allowed greater flexibility of the spine. This made it possible for whales to move around with the vertical tail hitting the water. The front legs transformed into flippers, costing them their mobility on land.
One of the oldest members of ancient cetaceans (Archaeoceti) is Pakicetus from the Middle Eocene. This is an animal the size of a wolf, whose skeleton is known only partially. It had functioning legs and lived near the shore. This suggests the animal could still move on land. The long snout had carnivorous dentition. 
The transition from land to sea dates to about 49 million years ago, with the Ambulocetus ("running whale"), discovered in Pakistan. It was up to 3 m (9.8 ft) long. The limbs of this archaeocete were leg-like, but it was already fully aquatic, indicating that a switch to a lifestyle independent from land happened extraordinarily quickly.  The snout was elongated with overhead nostrils and eyes. The tail was strong and supported movement through water. Ambulocetus probably lived in mangroves in brackish water and fed in the riparian zone as a predator of fish and other vertebrates. 
Dating from about 45 million years ago are species such as Indocetus, Kutchicetus, Rodhocetus and Andrewsiphius, all of which were adapted to life in water. The hind limbs of these species were regressed and their body shapes resemble modern whales. Protocetidae family member Rodhocetus is considered the first to be fully aquatic. The body was streamlined and delicate with extended hand and foot bones. The merged pelvic lumbar spine was present, making it possible to support the floating movement of the tail. It was likely a good swimmer, but could probably move only clumsily on land, much like a modern seal. 
Marine animals Edit
Since the late Eocene, about 40 million years ago, cetaceans populated the subtropical oceans and no longer emerged on land. An example is the 18-m-long Basilosaurus, sometimes referred to as Zeuglodon. The transition from land to water was completed in about 10 million years. The Wadi Al-Hitan ("Whale Valley") in Egypt contains numerous skeletons of Basilosaurus, as well as other marine vertebrates.
Molecular findings and morphological indications suggest that artiodactyls as traditionally defined are paraphyletic with respect to cetaceans. Cetaceans are deeply nested within the former the two groups together form a monophyletic taxon, for which the name Cetartiodactyla is sometimes used. Modern nomenclature divides Artiodactyla (or Cetartiodactyla) in four subordinate taxa: camelids (Tylopoda), pigs and peccaries (Suina), ruminants (Ruminantia), and hippos plus whales (Whippomorpha).
Cetacea's presumed location within Artiodactyla can be represented in the following cladogram:     
Within Cetacea, the two parvorders are baleen whales (Mysticeti) which owe their name to their baleen, and toothed whales (Odontoceti), which have teeth shaped like cones, spades, pegs or tusks, and can perceive their environment through biosonar.
The terms whale and dolphin are informal:
- , with four families: Balaenidae (right and bowhead whales), Cetotheriidae (pygmy right whales), Balaenopteridae (rorquals), Eschrichtiidae (grey whales)
- : with four families: Monodontidae (belugas and narwhals), Physeteridae (sperm whales), Kogiidae (dwarf and pygmy sperm whales), and Ziphiidae (beaked whales) , with five families: Delphinidae (oceanic dolphins), Platanistidae (South Asian river dolphins), Lipotidae (old world river dolphins) Iniidae (new world river dolphins), and Pontoporiidae (La Plata dolphins) , with one family: Phocoenidae
The term 'great whales' covers those currently regulated by the International Whaling Commission:  the Odontoceti families Physeteridae (sperm whales), Ziphiidae (beaked whales), and Kogiidae (pygmy and dwarf sperm whales) and all the Mysticeti families Balaenidae (right and bowhead whales), Cetotheriidae (pygmy right whales), Eschrichtiidae (grey whales), and some of the Balaenopteridae (minke, Bryde's, sei, blue and fin not Eden's and Omura's whales). 
The current classification of living species is as follows:   
- INFRAORDER CETACEA
- Parvorder Mysticeti: baleen whales
- Superfamily Balaenoidea: right whales
- Family Balaenidae
- Genus Balaena
- , Balaena mysticetus
- , Eubalaena glacialis , Eubalaena japonica , Eubalaena australis
- Genus Balaena
- Genus Caperea
- , Caperea marginata
- Family Balaenopteridae: rorquals
- Subfamily Balaenopterinae
- Genus Balaenoptera: slender rorquals
- , Balaenoptera acutorostrata , Balaenoptera bonaerensis , Balaenoptera borealis , Balaenoptera brydeiBalaenoptera edeniBalaenoptera ricei , Balaenoptera omurai , Balaenoptera musculus , Balaenoptera physalus
- Genus Megaptera
- , Megaptera novaeangliae
- Genus Eschrichtius
- , Eschrichtius robustus
- Superfamily Delphinoidea
- Family Delphinidae: oceanic dolphins (though Orcaella & Sotalia can live in fresh water)
- Genus Cephalorhynchus: blunt-nosed dolphins
- , Cephalorhynchus commersonii , Cephalorhynchus eutropia , Cephalorhynchus heavisidii , Cephalorhynchus hectori
- , Delphinus capensis , Delphinus delphis , Delphinus tropicalis
- Genus Cephalorhynchus: blunt-nosed dolphins
- , Feresa attenuata
- Family Delphinidae: oceanic dolphins (though Orcaella & Sotalia can live in fresh water)
- , Globicephala macrorhyncus , Globicephala melas
- Genus Balaenoptera: slender rorquals
- , Grampus griseus
- Subfamily Balaenopterinae
- , Lagenodelphis hosei
- Family Balaenidae
- , Lagenorhynchus acutus , Lagenorhynchus albirostris , Lagenorhynchus australis , Lagenorhynchus cruciger , Lagenorhynchus obliquidens , Lagenorhynchus obscurus
- Superfamily Balaenoidea: right whales
- , Lissodelphis borealis , Lissodelphis peronii
- Parvorder Mysticeti: baleen whales
- Genus Delphinapterus
- , Delphinapterus leucas
- Genus Neophocaena
- , Neophocaena phocaenoides
- Family Physeteridae
- Genus Physeter
- , Physeter catodon (syn. P. macrocephalus)
- Genus Kogia
- , Kogia breviceps , Kogia sima
- Family Platanistidae
- Genus Platanista
- , Platanista gangetica
- Family Lipotidae
- Genus Lipotes
- , Lipotes Vexillifer
- Family Iniidae
- Genus Inia
- , Inia geoffrensis , Inia boliviensis , Inia araguaiaensis
- Genus Pontoporia
- , Pontoporia blainvillei
- Family Ziphiidae
- Genus Berardius: giant beaked whales
- , Berardius arnuxii (North Pacific bottlenose whale), Berardius bairdii
- Berardius minimus
- Genus Hyperoodon: bottlenose whales
- , Hyperoodon ampullatus , Hyperoodon planifrons
- (Longman's beaked whale), Indopacetus pacificus
- Genus Berardius: giant beaked whales
- , Mesoplodon bidens , Mesoplodon bowdoini , Mesoplodon carlhubbsi , Mesoplodon densirostris , Mesoplodon europaeus , Mesoplodon ginkgodens , Mesoplodon grayi , Mesoplodon hectori , Mesoplodon layardii , Mesoplodon mirus , Mesoplodon perrini , Mesoplodon peruvianus , Mesoplodon stejnegeri , Mesoplodon traversii , Mesoplodon hotaula
- Genus Inia
- , Tasmacetus shepherdi
- Genus Lipotes
- , Ziphius cavirostris
- Genus Platanista
- toxic contaminants
- debilitating parasites (in the respiratory tract, brain or middle ear)
- infections (bacterial or viral)
- flight from predators (including humans)
- social bonds within a group, so that the pod follows a stranded animal
- disturbance of their magnetic senses by natural anomalies in the Earth's magnetic field
- injuries by shipping traffic, seismic surveys and military sonar experiments
- breathing normally, this adds air to their lungs every time they inhale
- adding air to their mask by breathing out their nose
- adding air to their ears and sinuses by using one of several ear equalization techniques
- breathing normally, this releases extra air from their lungs every time they exhale
- ascending slowly and allowing the extra air in their ears, sinuses and mask to bubble out on its own
The primary threats to cetaceans come from people, both directly from whaling or drive hunting and indirect threats from fishing and pollution. 
Whaling is the practice of hunting whales, mainly baleen and sperm whales. This activity has gone on since the Stone Age.
In the Middle Ages, reasons for whaling included their meat, oil usable as fuel and the jawbone, which was used in house construction. At the end of the Middle Ages, early whaling fleets aimed at baleen whales, such as bowheads. In the 16th and 17th centuries, the Dutch fleet had about 300 whaling ships with 18,000 crewmen.
In the 18th and 19th centuries, baleen whales especially were hunted for their baleen, which was used as a replacement for wood, or in products requiring strength and flexibility such as corsets and crinoline skirts. In addition, the spermaceti found in the sperm whale was used as a machine lubricant and the ambergris as a material for pharmaceutical and perfume industries. In the second half of the 19th century, the explosive harpoon was invented, leading to a massive increase in the catch size.
Large ships were used as "mother" ships for the whale handlers. In the first half of the 20th century, whales were of great importance as a supplier of raw materials. Whales were intensively hunted during this time in the 1930s, 30,000 whales were killed. This increased to over 40,000 animals per year up to the 1960s, when stocks of large baleen whales collapsed.
Most hunted whales are now threatened, with some great whale populations exploited to the brink of extinction. Atlantic and Korean gray whale populations were completely eradicated and the North Atlantic right whale population fell to some 300-600. The blue whale population is estimated to be around 14,000.
The first efforts to protect whales came in 1931. Some particularly endangered species, such as the humpback whale (which then numbered about 100 animals), were placed under international protection and the first protected areas were established. In 1946, the International Whaling Commission (IWC) was established, to monitor and secure whale stocks. Whaling of 14 large species for commercial purposes was prohibited worldwide by this organization from 1985 to 2005, though some countries do not honor the prohibition.
The stocks of species such as humpback and blue whales have recovered, though they are still threatened. The United States Congress passed the Marine Mammal Protection Act of 1972 sustain the marine mammal population. It prohibits the taking of marine mammals except for several hundred per year taken in Alaska. Japanese whaling ships are allowed to hunt whales of different species for ostensibly scientific purposes.
Aboriginal whaling is still permitted. About 1,200 pilot whales were taken in the Faroe Islands in 2017,  and about 900 narwhals and 800 belugas per year are taken in Alaska, Canada, Greenland, and Siberia. About 150 minke are taken in Greenland per year, 120 gray whales in Siberia and 50 bowheads in Alaska, as aboriginal whaling, besides the 600 minke taken commercially by Norway, 300 minke and 100 sei taken by Japan and up to 100 fin whales taken by Iceland.  Iceland and Norway do not recognize the ban and operate commercial whaling. Norway and Japan are committed to ending the ban.
Dolphins and other smaller cetaceans are sometimes hunted in an activity known as dolphin drive hunting. This is accomplished by driving a pod together with boats, usually into a bay or onto a beach. Their escape is prevented by closing off the route to the ocean with other boats or nets. Dolphins are hunted this way in several places around the world, including the Solomon Islands, the Faroe Islands, Peru and Japan (the most well-known practitioner). Dolphins are mostly hunted for their meat, though some end up in dolphinaria. Despite the controversy thousands of dolphins are caught in drive hunts each year.
Dolphin pods often reside near large tuna shoals. This is known to fishermen, who look for dolphins to catch tuna. Dolphins are much easier to spot from a distance than tuna, since they regularly breathe. The fishermen pull their nets hundreds of meters wide in a circle around the dolphin groups, in the expectation that they will net a tuna shoal. When the nets are pulled together, the dolphins become entangled under water and drown. Line fisheries in larger rivers are threats to river dolphins.
A greater threat than by-catch for small cetaceans is targeted hunting. In Southeast Asia, they are sold as fish-replacement to locals, since the region's edible fish promise higher revenues from exports. In the Mediterranean, small cetaceans are targeted to ease pressure on edible fish. 
A stranding is when a cetacean leaves the water to lie on a beach. In some cases, groups of whales strand together. The best known are mass strandings of pilot whales and sperm whales. Stranded cetaceans usually die, because their as much as 90 metric tons (99 short tons) body weight compresses their lungs or breaks their ribs. Smaller whales can die of heatstroke because of their thermal insulation.
The causes are not clear. Possible reasons for mass beachings are: 
Since 2000, whale strandings frequently occurred following military sonar testing. In December 2001, the US Navy admitted partial responsibility for the beaching and the deaths of several marine mammals in March 2000. The coauthor of the interim report stated that animals killed by active sonar of some Navy ships were injured. Generally, underwater noise, which is still on the increase, is increasingly tied to strandings because it impairs communication and sense of direction. 
Climate change influences the major wind systems and ocean currents, which also lead to cetacean strandings. Researchers studying strandings on the Tasmanian coast from 1920–2002 found that greater strandings occurred at certain time intervals. Years with increased strandings were associated with severe storms, which initiated cold water flows close to the coast. In nutrient-rich, cold water, cetaceans expect large prey animals, so they follow the cold water currents into shallower waters, where the risk is higher for strandings. Whales and dolphins who live in pods may accompany sick or debilitated pod members into shallow water, stranding them at low tide. [ citation needed ]
Environmental hazards Edit
—Rear Admiral Lawrence Rice
Heavy metals, residues of many plant and insect venoms and plastic waste flotsam are not biodegradable. Sometimes, cetaceans consume these hazardous materials, mistaking them for food items. As a result, the animals are more susceptible to disease and have fewer offspring. 
Damage to the ozone layer reduces plankton reproduction because of its resulting radiation. This shrinks the food supply for many marine animals, but the filter-feeding baleen whales are most impacted. Even the Nekton is, in addition to intensive exploitation, damaged by the radiation. 
Food supplies are also reduced long-term by ocean acidification due to increased absorption of increased atmospheric carbon dioxide. The CO2 reacts with water to form carbonic acid, which reduces the construction of the calcium carbonate skeletons of food supplies for zooplankton that baleen whales depend on. 
The military and resource extraction industries operate strong sonar and blasting operations. Marine seismic surveys use loud, low-frequency sound that show what is lying underneath the Earth's surface.  Vessel traffic also increases noise in the oceans. Such noise can disrupt cetacean behavior such as their use of biosonar for orientation and communication. Severe instances can panic them, driving them to the surface. This leads to bubbles in blood gases and can cause decompression sickness.  Naval exercises with sonar regularly results in fallen cetaceans that wash up with fatal decompression. Sounds can be disruptive at distances of more than 100 kilometres (62 mi). Damage varies across frequency and species.
Research history Edit
In Aristotle's time, the 4th century BCE, whales were regarded as fish due to their superficial similarity. Aristotle, however, observed many physiological and anatomical similarities with the terrestrial vertebrates, such as blood (circulation), lungs, uterus and fin anatomy. [ citation needed ] His detailed descriptions were assimilated by the Romans, but mixed with a more accurate knowledge of the dolphins, as mentioned by Pliny the Elder in his Natural history. In the art of this and subsequent periods, dolphins are portrayed with a high-arched head (typical of porpoises) and a long snout. The harbour porpoise was one of the most accessible species for early cetologists because it could be seen close to land, inhabiting shallow coastal areas of Europe. Much of the findings that apply to all cetaceans were first discovered in porpoises.  One of the first anatomical descriptions of the airways of a harbor porpoise dates from 1671 by John Ray. It nevertheless referred to the porpoise as a fish.  
The tube in the head, through which this kind fish takes its breath and spitting water, located in front of the brain and ends outwardly in a simple hole, but inside it is divided by a downward bony septum, as if it were two nostrils but underneath it opens up again in the mouth in a void.
In the 10th edition of Systema Naturae (1758), Swedish biologist and taxonomist Carl Linnaeus asserted that cetaceans were mammals and not fish. His groundbreaking binomial system formed the basis of modern whale classification.
Cetaceans play a role in human culture.
Stone Age petroglyphs, such as those in Roddoy and Reppa (Norway), and the Bangudae Petroglyphs in South Korea, depict them.   Whale bones were used for many purposes. In the Neolithic settlement of Skara Brae on Orkney sauce pans were made from whale vertebrae.
The whale was first mentioned in ancient Greece by Homer. There, it is called Ketos, a term that initially included all large marine animals. From this was derived the Roman word for whale, Cetus. Other names were phálaina (Aristotle, Latin form of ballaena) for the female and, with an ironic characteristic style, musculus (Mouse) for the male. North Sea whales were called Physeter, which was meant for the sperm whale Physter macrocephalus. Whales are described in particular by Aristotle, Pliny and Ambrose. All mention both live birth and suckling. Pliny describes the problems associated with the lungs with spray tubes and Ambrose claimed that large whales would take their young into their mouth to protect them.
In the Bible especially, the leviathan plays a role as a sea monster. The essence, which features a giant crocodile or a dragon and a whale, was created according to the Bible by God  and should again be destroyed by him.   In the Book of Job, the leviathan is described in more detail.  
In Jonah there is a more recognizable description of a whale alongside the prophet Jonah, who, on his flight from the city of Nineveh is swallowed by a whale.
Dolphins are mentioned far more often than whales. Aristotle discusses the sacred animals of the Greeks in his Historia Animalium and gives details of their role as aquatic animals. The Greeks admired the dolphin as a "king of the aquatic animals" and referred to them erroneously as fish. Its intelligence was apparent both in its ability to escape from fishnets and in its collaboration with fishermen.
River dolphins are known from the Ganges and – erroneously – the Nile. In the latter case it was equated with sharks and catfish. Supposedly they attacked even crocodiles.
Dolphins appear in Greek mythology. Because of their intelligence, they rescued multiple people from drowning. They were said to love music – probably not least because of their own song – they saved, in the legends, famous musicians such as Arion of Lesbos from Methymna or Kairanos from Miletus. Because of their mental faculties, dolphins were considered for the god Dionysus.
Dolphins belong to the domain of Poseidon and led him to his wife Amphitrite. Dolphins are associated with other gods, such as Apollo, Dionysus and Aphrodite. The Greeks paid tribute to both whales and dolphins with their own constellation. The constellation of the Whale (Ketos, lat. Cetus) is located south of the Dolphin (Delphi, lat. Delphinus) north of the zodiac.
Ancient art often included dolphin representations, including the Cretan Minoans. Later they appeared on reliefs, gems, lamps, coins, mosaics and gravestones. A particularly popular representation is that of Arion or the Taras (mythology) riding on a dolphin. In early Christian art, the dolphin is a popular motif, at times used as a symbol of Christ.
Middle Ages to the 19th century Edit
St. Brendan described in his travel story Navigatio Sancti Brendani an encounter with a whale, between the years 565–573. He described how he and his companions entered a treeless island, which turned out to be a giant whale, which he called Jasconicus. He met this whale seven years later and rested on his back.
Most descriptions of large whales from this time until the whaling era, beginning in the 17th century, were of beached whales, which resembled no other animal. This was particularly true for the sperm whale, the most frequently stranded in larger groups. Raymond Gilmore documented seventeen sperm whales in the estuary of the Elbe from 1723 to 1959 and thirty-one animals on the coast of Great Britain in 1784. In 1827, a blue whale beached itself off the coast of Ostend. Whales were used as attractions in museums and traveling exhibitions.
Whalers from the 17th to 19th centuries depicted whales in drawings and recounted tales of their occupation. Although they knew that whales were harmless giants, they described battles with harpooned animals. These included descriptions of sea monsters, including huge whales, sharks, sea snakes, giant squid and octopuses.
Among the first whalers who described their experiences on whaling trips was Captain William Scoresby from Great Britain, who published the book Northern Whale Fishery, describing the hunt for northern baleen whales. This was followed by Thomas Beale, a British surgeon, in his book Some observations on the natural history of the sperm whale in 1835 and Frederick Debell Bennett's The tale of a whale hunt in 1840. Whales were described in narrative literature and paintings, most famously in the novels Moby Dick by Herman Melville and 20,000 Leagues Under the Sea by Jules Verne.
Baleen was used to make vessel components such as the bottom of a bucket in the Scottish National Museum. The Norsemen crafted ornamented plates from baleen, sometimes interpreted as ironing boards.
In the Canadian Arctic (east coast) in Punuk and Thule culture (1000–1600 C.E.),  baleen was used to construct houses in place of wood as roof support for winter houses, with half of the building buried under the ground. The actual roof was probably made of animal skins that were covered with soil and moss. 
Modern culture Edit
In the 20th century perceptions of cetaceans changed. They transformed from monsters into creatures of wonder, as science revealed them to be intelligent and peaceful animals. Hunting was replaced by whale and dolphin tourism. This change is reflected in films and novels. For example, the protagonist of the series Flipper was a bottle-nose dolphin. The TV series SeaQuest DSV (1993–1996), the movies Free Willy, Star Trek IV: The Voyage Home and the book series The Hitchhiker's Guide to the Galaxy by Douglas Adams are examples. 
The study of whale song also produced a popular album, Songs of the Humpback Whale.
Whales and dolphins have been kept in captivity for use in education, research and entertainment since the 19th century.
Beluga whales were the first whales to be kept in captivity. Other species were too rare, too shy or too big. The first was shown at Barnum's Museum in New York City in 1861.  For most of the 20th century, Canada was the predominant source.  They were taken from the St. Lawrence River estuary until the late 1960s, after which they were predominantly taken from the Churchill River estuary until capture was banned in 1992.  Russia then became the largest provider.  Belugas are caught in the Amur Darya delta and their eastern coast and are transported domestically to aquaria or dolphinaria in Moscow, St. Petersburg and Sochi, or exported to countries such as Canada.  They have not been domesticated. 
As of 2006, 30 belugas lived in Canada and 28 in the United States. 42 deaths in captivity had been reported.  A single specimen can reportedly fetch up to US$100,000 (GB£64,160). The beluga's popularity is due to its unique color and its facial expressions. The latter is possible because while most cetacean "smiles" are fixed, the extra movement afforded by the beluga's unfused cervical vertebrae allows a greater range of apparent expression. 
Killer whales Edit
The killer whale's intelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquaria and aquatic theme parks. From 1976 to 1997, fifty-five whales were taken from the wild in Iceland, nineteen from Japan and three from Argentina. These figures exclude animals that died during capture. Live captures fell dramatically in the 1990s and by 1999, about 40% of the forty-eight animals on display in the world were captive-born. 
Organizations such as World Animal Protection and the Whale and Dolphin Conservation campaign against the practice of keeping them in captivity.
In captivity, they often develop pathologies, such as the dorsal fin collapse seen in 60–90% of captive males. Captives have reduced life expectancy, on average only living into their 20s, although some live longer, including several over 30 years old and two, Corky II and Lolita, in their mid-40s. In the wild, females who survive infancy live 46 years on average and up to 70–80 years. Wild males who survive infancy live 31 years on average and can reach 50–60 years. 
Captivity usually bears little resemblance to wild habitat and captive whales' social groups are foreign to those found in the wild. Critics claim captive life is stressful due to these factors and the requirement to perform circus tricks that are not part of wild killer whale behavior. Wild killer whales may travel up to 160 kilometres (100 mi) in a day and critics say the animals are too big and intelligent to be suitable for captivity.  Captives occasionally act aggressively towards themselves, their tankmates, or humans, which critics say is a result of stress.  Killer whales are well known for their performances in shows, but the number of orcas kept in captivity is small, especially when compared to the number of bottlenose dolphins, with only forty-four captive orcas being held in aquaria as of 2012. 
Each country has its own tank requirements in the US, the minimum enclosure size is set by the Code of Federal Regulations, 9 CFR E § 3.104, under the Specifications for the Humane Handling, Care, Treatment and Transportation of Marine Mammals. 
Aggression among captive killer whales is common. They attack each other and their trainers as well. In 2013, SeaWorld's treatment of killer whales in captivity was the basis of the movie Blackfish, which documents the history of Tilikum, a killer whale at SeaWorld Orlando, who had been involved in the deaths of three people.  The film led to proposals by some lawmakers to ban captivity of cetaceans, and led SeaWorld to announce in 2016 that it would phase out its killer whale program after various unsuccessful attempts to restore its revenues, reputation, and stock price. 
Dolphins and porpoises are kept in captivity. Bottlenose dolphins are the most common, as they are relatively easy to train, have a long lifespan in captivity and have a friendly appearance. Bottlenose dolphins live in captivity across the world, though exact numbers are hard to determine. Other species kept in captivity are spotted dolphins, false killer whales and common dolphins, Commerson's dolphins, as well as rough-toothed dolphins, but all in much lower numbers. There are also fewer than ten pilot whales, Amazon river dolphins, Risso's dolphins, spinner dolphins, or tucuxi in captivity. Two unusual and rare hybrid dolphins, known as wolphins, are kept at Sea Life Park in Hawaii, which is a cross between a bottlenose dolphin and a false killer whale. Also, two common/bottlenose hybrids reside in captivity at Discovery Cove and SeaWorld San Diego.
In repeated attempts in the 1960s and 1970s, narwhals kept in captivity died within months. A breeding pair of pygmy right whales were retained in a netted area. They were eventually released in South Africa. In 1971, SeaWorld captured a California gray whale calf in Mexico at Scammon's Lagoon. The calf, later named Gigi, was separated from her mother using a form of lasso attached to her flukes. Gigi was displayed at SeaWorld San Diego for a year. She was then released with a radio beacon affixed to her back however, contact was lost after three weeks. Gigi was the first captive baleen whale. JJ, another gray whale calf, was kept at SeaWorld San Diego. JJ was an orphaned calf that beached itself in April 1997 and was transported two miles to SeaWorld. The 680 kilograms (1,500 lb) calf was a popular attraction and behaved normally, despite separation from his mother. A year later, the then 8,164.7 kilograms (18,000 lb) whale though smaller than average, was too big to keep in captivity, and was released on April 1, 1998. A captive Amazon river dolphin housed at Acuario de Valencia is the only trained river dolphin in captivity.  
Here is a list of all the cetaceans that have been taken into captivity for either conservation or human entertainment purposes currently or in the past, temporarily or permanently.
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Up, up and away
Somehow, these high flyers can exert themselves at exceptional altitudes. But what allows them to navigate the air up there? While these birds vary in size, they have one thing in common: a longer wingspan relative to their bodies, compared with birds that fly lower.
"That's something we consistently see," Scott said. "Longer wings are better for generating lift to keep the body aloft."
But it takes more than longer wings to navigate high altitudes, which come with enormous physical trials, Scott added.
"The first big challenge is that the air gets less dense," he said. "As they go higher, they have to flap harder to stay aloft, so their metabolic demands increase. The oxygen levels become more limited. At high altitudes, it gets colder, and they need to keep their bodies warm. And the air gets drier — they're more likely to lose water from breathing and evaporation, and be thirsty."
So what keeps these high fliers going? There are certainly physical adaptations that allow birds to reach exceptional heights, said Charles Bishop, a senior lecturer in zoology at the School of Biological Sciences at Bangor University in the United Kingdom.
Bishop, who studies high-flying bar-headed geese, told Live Science in an email that the geese do not appear to suffer from altitude sickness or from cerebral or pulmonary edema, "so that, unlike humans they do not feel ill when at high altitude."
The geese also hyperventilate to increase their oxygen intake while flying. This rapid breathing makes their blood more alkaline, a change that in humans affects circulation to the brain (which is why hyperventilating makes people feel dizzy or faint).
But geese are very tolerant of high pH (alkaline conditions), Bishop explained, so blood flow to the animals' brains and bodies remains healthy.
"Finally, the hemoglobin in their blood has quite a high affinity for oxygen binding," Bishop told Live Science. "Again, this maximizes oxygen uptake." [Quest for Survival: Photos of Incredible Animal Migrations]
Pressure Affects Many Aspects of Diving
Now that you understand the basics, let's look at how pressure affects four basic aspects of diving.
As a diver descends, the pressure increase causes the air in their body's air spaces to compress. The air spaces in their ears, mask, and lungs become like vacuums as the compressing air creates a negative pressure. Delicate membranes, like the ear drum, can get sucked into theses air spaces, causing pain and injury. This is one of the reasons that a diver must equalize their ears for scuba diving.
On ascent, the reverse happens. Decreasing pressure causes the air in a diver's air spaces to expand. The air spaces in their ears and lungs experience a positive pressure as they become overfull of air, leading to pulmonary barotrauma or a reverse block. In a worst-case scenario, this could burst a diver's lungs or eardrums.
To avoid a pressure-related injury (such as an ear barotrauma) a diver must equalize the pressure in their body's air spaces with the pressure around them.
To equalize their air spaces on descent a diver adds air to their body airspaces to counteract the "vacuum" effect by
To equalize their air spaces on ascent a diver releases air from their body air spaces so that they do not become overfull by
Divers control their buoyancy (whether they sink, float up, or remain “neutrally buoyant” without floating or sinking) by adjusting their lung volume and buoyancy compensator (BCD).
As a diver descends, the increased pressure causes the air in their BCD and wetsuit (there are small bubbles trapped in neoprene) to compress. They become negatively buoyant (sinks). As they sink, the air in their dive gear compresses more and they sink more quickly. If they do not add air to his BCD to compensate for their increasingly negative buoyancy, a diver can quickly find themselves fighting an uncontrolled descent.
In the opposite scenario, as a diver ascends, the air in their BCD and wetsuit expands. The expanding air makes the diver positively buoyant, and they begin to float up. As they float towards the surface, the ambient pressure decreases and the air in their dive gear continues to expand. A diver must continuously vent air from their BCD during ascent or they risk an uncontrolled, rapid ascent (one of the most dangerous things a diver can do).
A diver must add air to their BCD as they descend and release air from their BCD as they ascend. This may seem counterintuitive until a diver understands how pressure changes affect buoyancy.
Bottom time refers to the amount of time a diver can stay underwater before beginning their ascent. Ambient pressure affects bottom time in two important ways.
Increased Air Consumption Reduces Bottom Times
The air that a diver breathes is compressed by the surrounding pressure. If a diver descends to 33 feet, or 2 ATA of pressure, the air they breathe is compressed to half of its original volume. Each time the diver inhales, it takes twice as much air to fill their lungs than it does at the surface. This diver will use their air up twice as quickly (or in half the time) as they would at the surface. A diver will use up their available air more quickly the deeper they go.
Increased Nitrogen Absorption Reduces Bottom Times
The greater the ambient pressure, the more rapidly a diver's body tissues will absorb nitrogen. Without getting into specifics, a diver can only allow their tissues a certain amount of nitrogen absorption before they begin their ascent, or they run an unacceptable risk of decompression illness without mandatory decompression stops. The deeper a diver goes, the less time they have before their tissues absorb the maximum allowable amount of nitrogen.
Because pressure becomes greater with depth, both air consumption rates and nitrogen absorption increase the deeper a diver goes. One of these two factors will limit a diver's bottom time.
Rapid Pressure Changes Can Cause Decompression Sickness (the Bends)
Increased pressure underwater causes a diver's body tissues to absorb more nitrogen gas than they would normally contain at the surface. If a diver ascends slowly, this nitrogen gas expands bit by bit and the excess nitrogen is safely eliminated from the diver's tissues and blood and released from their body when they exhale.
However, the body can only eliminate nitrogen so quickly. The faster a diver ascends, the faster nitrogen expands and must be removed from their tissues. If a diver goes through too great of pressure change too quickly, their body cannot eliminate all of the expanding nitrogen and the excess nitrogen forms bubbles in their tissues and blood.
These nitrogen bubbles can cause decompression sickness (DCS) by blocking blood flow to various parts of the body, causing strokes, paralysis, and other life-threatening problems. Rapid pressure changes are one of the most common causes of DCS.
Water Pressures at Ocean Depths
Water pressures in the deep is one of the many phenomena researchers must content with when exploring deep-sea sites. The ocean is deep. If we shaved off all the continents and filled the trenches in the oceans with the earth from the continents, the entire globe would be covered with water about 2 miles in depth. The average ocean depth is 12,566 feet about 3800 meters. The greatest ocean depth is 36,200 feet over 11,000 meters! What effect does this great depth of water have on things living in the ocean? The answer depends upon where in the ocean it lives. A fish or a plant near the surface feels little effect from the great depths. It matters little if there is six feet or six thousand feet beneath a swimming fish. An animal living at 10,000 feet depth, however, is greatly influenced by the depth of the water over it.
We often speak of pressure in terms of atmospheres. One atmosphere is equal to the weight of the earth's atmosphere at sea level, about 14.6 pounds per square inch. If you are at sea level, each square inch of your surface is subjected to a force of 14.6 pounds.
The pressure increases about one atmosphere for every 10 meters of water depth. At a depth of 5,000 meters the pressure will be approximately 500 atmospheres or 500 times greater than the pressure at sea level. That's a lot of pressure.
Research equipment must be designed to deal with the enormous pressures encountered in the depths. Submarines must have reinforced walls to with stand pressures. Instruments that work well at the surface may be collapsed or rendered useless by the pressure.
Calculate how much pressure (pounds per square inch) the equipment used on NeMO cruise must withstand.
Depth of Axial Caldera - 1540 Meters
(One atmosphere of pressure on one square inch of surface is subjected to a force of 14.6 inches. Pressures increase about one atmosphere for every 10 meters of water depth)
How many pounds of pressure per square inch will the NeMO cruise equipment experience.
- "It was apparent that something was very wrong, and as the bathysphere swung clear I saw a needle of water shooting across the face of the port window. Weighing much more than she should have, she came over the side and was lowered to the deck. Looking through one of the good windows I could see that she was almost full of water. There were curious ripples on the top of the water, and I knew that the space above was filled with air, but such air as no human being could tolerate for a moment. Unceasingly the thin stream of water and air drove obliquely across the outer face of the quartz. I began to unscrew the giant wingbolt in the center of the door and after the first few turns, a strange high singing came forth, then a fine mist, steam -like in consistency, shot out, a needle of steam, then another and another. This warned me that I should have sensed when I looked through the window that the contents of the bathysphere were under terrific pressure. I cleared the deck in front of the door of everyone, staff and crew. One motion picture camera was placed on the upper deck and a second one close to, but well to one side of the bathysphere. Carefully, little by little, two of us turned the brass handles, soaked with the spray, and I listened as the high, musical tone of impatient confined elements gradually descended the scale, a quarter tone or less at each slight turn. Realizing what might happen we leaned back as far as possible from the line of fire. Suddenly without the slightest warning, the bolt was torn from our hands and the mass of heavy metal shot across the deck like a shell from a gun. The trajectory was almost straight and the brass bolt hurtled into the steel winch thirty feet across the deck and sheared a half-inch notch gouged out by the harder metal. This was followed by a solid cylinder of water, which slackened after a while to a cataract, pouring out of the hole in the door, some air mingled with the water looking like hot steam. Instead of compressed air shooting through ice-cold water. If I had been in the way, I would have been decapitated. "
The pressures are great, indeed.
From: Half Mile Down by William Beebe, Published by Duell Sloan Pearch (New York) 1951.
Creatures who live at great depths do not have air in their bodies such as the swim bladders found in fish that live in more shallow waters. Without air in their bodies, the pressure problem is solved. Fish, crab, octopus, worms, limpets and clams are just some of the creatures found in the depths of the oceans.
When man enters the world of water he encounters a number of problems. The average scuba diver becomes incapacitated at 250 feet of depth. This is a far cry from the 11,500 foot depth at which deep sea fishes have been found.
Scuba divers need oxygen to survive. Oxygen makes up 21% of the air we breathe. About 78% of the air we breathe is nitrogen gas. Nitrogen is relatively inert it is more or less chemically inactive. The oxygen and nitrogen are carried in the bloodstream. At sea level the nitrogen presents no problem for man. But what happens to these gases as we descend into the ocean depths.
The increased pressure allows more oxygen and more nitrogen to dissolve into the blood. At about 100 feet the pressure will cause enough nitrogen to dissolve in the blood for the nitrogen to become a danger. Nitrogen narcosis results from too much nitrogen being forced into the blood stream. It will eventually result in stupor and sleep, not a good condition 100 feet below the surface. Before the stupor stage, divers become dizzy, their ability to make even simple mental decisions (like tell time) is reduced. Sometimes they decide they no longer need to breathe through their mouthpiece. The precise symptoms and the depths to which the symptoms appear vary with each individual and with each dive. Diving below 100 feet requires special skills and is dangerous. Returning to the surface reduces the nitrogen content and reduces the symptoms.
If one atmosphere equals about 14.6 pounds per square inch pressure, and the pressure increases 1 atmosphere for every 10 meters of depth. How many atmospheres are forcing the nitrogen into the blood stream at 30 meters (about 100 feet) and at 75 meters (about 250 feet)?
Divers limiting the time and depth of their dives can avoid nitrogen narcosis. Coming to the surface in stages with a pause at each stage allows the nitrogen to diffuse out of the blood.
How to Pressure-Can Hamburger Meat
Canning Pressure: 10 lbs under 1000 ft elevation (See notes for high elevation)
Processing Time: Pints – 75 minutes, Quarts – 90 minutes
Begin by browning the meat in a pan in small batches with a little oil or fat of your choice. While the meat can be packed into jars raw, quickly browning it will greatly improve flavor and texture. A 10-inch cast iron can comfortably brown 1 pound of meat in 2-3 minutes, so work in batches until all the meat is just barely browned. A little raw still is ideal, so that it doesn’t toughen as it fully cooks in the canning process.
Season the meat to taste using salt and spices, but avoid using any recipes that include a starch or binder such as flour, egg, or bread crumbs. These ingredients can affect the canning process and cannot be used.
A pint jar can hold 3/4 to 1 pound of meat for canning, and a quart holds 1.5 to 2 pounds of meat. Try to have enough meat on hand to completely fill your pressure-canner, as it’s much more efficient to can a full batch.
Add water to your pressure-canner and bring the water to a boil. Generally, instructions say add around 2 inches of water to the bottom, but this can vary based on your canner model.
Pack the browned meat into canning jars, pints or quarts, leaving 1 inch of head space below the rim. Fill the jars with boiling stock or water, still leaving 1 inch of headspace.
Cap the jars with clean, new canning lids, and attach a canning ring to each jar. The canning ring should be “finger tight.” If the ring is too lose, you’ll lose fluid into the canner and have partially filled jars, if the lid is too tight air can’t escape and the jars have a small risk of braking in the canner. Ideally, set the jar on the counter and tighten the lid as tight as it will go with one hand.
Once the band is tight enough that the jar itself begins to spin without the other hand holding it, it’s called “finger tight.” This part sounds scary, but really, there’s a huge range that’s acceptable, just don’t crank them down too tight.
Arrange the jars in your pressure-canner according to the instructions. If you have a large double-decker pressure-canner, be sure to insert the divider between layers and stagger the jars so that they’re not directly on top of each other.
Seal the canner lid and for a weighted gauge canner, allow steam to escape from the valve for 7-10 minutes before adding the weighted pressure gauge. Use 10 pounds of pressure with a weighted gauge, or be sure to keep a dial pressure canner at or just above 11 pounds of pressure.
Once the canner is up to pressure, begin timing. Process for 75 minutes for pint jars and 90 minutes for quarts. When the processing time is over, turn off the heat and leave the canner in place until it is back down to 0 pounds of pressure. Once it’s at 0 pounds, remove the weighted gauge to allow the last little bit of steam to escape before unscrewing the lid.
Remove the jars and allow them to cool to room temperature before storing.
Be sure to remove the canning rings. Canning rings are only necessary during the canning process, and after the jars have cooled the vacuum from the seal itself will keep the canning lid sealed. Leaving rings on jars in storage can result in the rings rusting shut.
Notes: While many pressure-canners can accommodate a half gallon jar, the USDA does not approve canning meat in half gallon jars and does not provide canning timetables.
While some places on line will give you instructions for “dry canned” hamburger meat without using water or stock, this is not an approved method and will not guarantee food safety.
Above 1000 ft of elevation, canning pressure increases to make up for lower atmospheric pressure at high altitude. For high elevation pressure canning instructions, see in the All American Pressure Canning Instruction Manual .
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