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74-514: Rose Atoll , sometimes called Rose Island or Motu O Manu ("Bird Island") by people of the Manu'a Islands , is an oceanic atoll within the U.S. territory of American Samoa . An uninhabited wildlife refuge, it is the southernmost point belonging to the United States , about 170 miles (150 nmi; 270 km) to the east of Tutuila , the principal island of American Samoa. The land area

148-426: A heterocercal caudal fin in which the dorsal portion is usually noticeably larger than the ventral portion. This is because the shark's vertebral column extends into that dorsal portion, providing a greater surface area for muscle attachment. This allows more efficient locomotion among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a homocercal caudal fin. Tiger sharks have

222-523: A breeding population of some 400,000 sooty terns , as estimated in 1974. Manu%27a Islands Manu'a was the political centre of the Tui Manu’a Empire for many centuries, until the rise of the Tu'i Tonga maritime empire, which led to a shift in power from the eastern islands of Samoa to its western islands. All three islands are volcanic islands : volcanic remnants rising out of the sea 14° south of

296-415: A cell similar to hair cells present in the vertebrate ear that interact with the surrounding aquatic environment. This helps sharks distinguish between the currents around them, obstacles off on their periphery, and struggling prey out of visual view. The shark can sense frequencies in the range of 25 to 50  Hz . Shark lifespans vary by species. Most live 20 to 30 years. The spiny dogfish has one of

370-418: A constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species. The respiratory and circulatory process begins when deoxygenated venous blood travels to

444-499: A few known exceptions, such as the bull shark and the river sharks , which can be found in both seawater and freshwater, and the Ganges shark , which lives only in freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics . They have numerous sets of replaceable teeth. Several species are apex predators , which are organisms that are at

518-482: A heavy "k" sound that is usually reserved for non-biblical traditional oratory and everyday conversation. There are three elementary schools in Manu'a: Faleasao Elementary, Fitiuta Elementary, and 'Olosega Elementary. The high school is on Taʻū Island, called Manuʻa High School, and was designed to serve all of Manuʻa in 1966. Students seeking higher education go to American Samoa Community College on Tutuila Island where

592-525: A hurricane, both the U.S. Congress and the American Red Cross sent financial aid to American Samoa for the first time. The hurricane, which hit the islands on January 9, 1915, caused widespread destruction in the Manuʻa Islands. The storm severed all forms of communication with the outside world, isolating the islands. In the aftermath, no vessels on the Manuʻa Islands were capable of making

666-423: A large upper lobe , which allows for slow cruising and sudden bursts of speed. The tiger shark must be able to twist and turn in the water easily when hunting to support its varied diet, whereas the porbeagle shark , which hunts schooling fish such as mackerel and herring , has a large lower lobe to help it keep pace with its fast-swimming prey. Other tail adaptations help sharks catch prey more directly, such as

740-438: A long surface area, requiring food to circulate inside the short gut until fully digested, when remaining waste products pass into the cloaca . A few sharks appear fluorescent under blue light, such as the swell shark and the chain catshark , where the fluorophore derives from a metabolite of kynurenic acid . Sharks have keen olfactory senses, located in the short duct (which is not fused, unlike bony fish) between

814-445: A row behind the head. A modified slit called a spiracle lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active pelagic sharks. While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure

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888-405: A similar mechanism for maintaining an elevated body temperature. Larger species, like the whale shark, are able to conserve their body heat through sheer size when they dive to colder depths, and the scalloped hammerhead close its mouth and gills when they dives to depths of around 800 metres, holding its breath till it reach warmer waters again. In contrast to bony fish, with the exception of

962-555: A single type of cone photoreceptor sensitive to green and, seeing only in shades of grey and green, are believed to be effectively colorblind. The study indicates that an object's contrast against the background, rather than colour, may be more important for object detection. Although it is hard to test the hearing of sharks, they may have a sharp sense of hearing and can possibly hear prey from many miles away. The hearing sensitivity for most shark species lies between 20 and 1000 Hz. A small opening on each side of their heads (not

1036-400: A tissue called tapetum lucidum . This tissue is behind the retina and reflects light back to it, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Many sharks can contract and dilate their pupils , like humans, something no teleost fish can do. Sharks have eyelids, but they do not blink because

1110-497: Is also an atoll, but only politically part of American Samoa, not geographically.) Rose Atoll is quite isolated, the closest island to it being Taʻū , 140 km (87 mi.) to the WNW. The earliest Western sighting was June 13, 1722, during the voyage of Jacob Roggeveen , who called it Vuil Eiland "useless island." The name Rose Island comes from its sighting by Louis de Freycinet in 1819. He named it after his wife Rose . While

1184-648: Is debated. Some believe that electro- and chemoreception are more significant, while others point to the nictating membrane as evidence that sight is important, since presumably the shark would not protect its eyes were they unimportant. The use of sight probably varies with species and water conditions. The shark's field of vision can swap between monocular and stereoscopic at any time. A micro-spectrophotometry study of 17 species of sharks found 10 had only rod photoreceptors and no cone cells in their retinas giving them good night vision while making them colorblind . The remaining seven species had in addition to rods

1258-676: Is divided into the superorders Galea (or Galeomorphii ), and Squalea (or Squalomorphii ). The Galeans are the Heterodontiformes , Orectolobiformes , Lamniformes , and Carcharhiniformes . Lamnoids and Carcharhinoids are usually placed in one clade , but recent studies show that Lamnoids and Orectoloboids are a clade. Some scientists now think that Heterodontoids may be Squalean. The Squaleans are divided into Hexanchiformes and Squalomorpha. The former includes cow shark and frilled shark , though some authors propose that both families be moved to separate orders. The Squalomorpha contains

1332-409: Is high, species of sharks from the family Carcharhinidae have smaller olfactory bulbs. Sharks found in deeper waters also have larger olfactory bulbs. Sharks have the ability to determine the direction of a given scent based on the timing of scent detection in each nostril. This is similar to the method mammals use to determine direction of sound. They are more attracted to the chemicals found in

1406-435: Is just 0.05 km (12 acres) at high tide. The total area of the atoll, including lagoon and reef flat amounts to 6.33 km (1,560 acres). Just west of the northernmost point is a channel into the lagoon, about 80 metres (260 ft) wide. There are two islets on the northeastern rim of the reef, larger Rose Island, 3.5 metres (11 ft) high, in the east and the non-vegetated Sand Island, 1.5 metres (5 ft) high, in

1480-581: Is limited, so sharks employ dynamic lift to maintain depth while swimming. Sand tiger sharks store air in their stomachs, using it as a form of swim bladder. Bottom-dwelling sharks, like the nurse shark , have negative buoyancy, allowing them to rest on the ocean floor. Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility . Researchers use this condition to handle sharks safely. Like other fish, sharks extract oxygen from seawater as it passes over their gills . Unlike other fish, shark gill slits are not covered, but lie in

1554-434: Is observed in the cookiecutter shark . Tooth shape depends on the shark's diet: those that feed on mollusks and crustaceans have dense and flattened teeth used for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey such as mammals have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. The teeth of plankton-feeders such as

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1628-496: Is still evidential in several species termed " dogfish ," or the porbeagle . The etymology of the word shark is uncertain. The most likely etymology states that the original sense of the word was that of "predator, one who preys on others" from the Dutch schurk , meaning 'villain, scoundrel' ( cf. card shark , loan shark , etc.), which was later applied to the fish due to its predatory behaviour. A now disproven theory

1702-775: Is that it derives from the Yucatec Maya word xook ( pronounced [ʃoːk] ), meaning 'shark'. Evidence for this etymology came from the Oxford English Dictionary , which notes that shark first came into use after Sir John Hawkins ' sailors exhibited one in London in 1569 and posted " sharke " to refer to the large sharks of the Caribbean Sea . However, the Middle English Dictionary records an isolated occurrence of

1776-683: The Devonian Period (419–359 million years), though some fossilized chondrichthyan-like scales are as old as the Late Ordovician (458–444 million years ago). The earliest confirmed modern sharks (selachimorphs) are known from the Early Jurassic around 200  million years ago , with the oldest known member being Agaleus , though records of true sharks may extend back as far as the Permian . Sharks range in size from

1850-633: The Devonian . Anachronistidae , the oldest probable representatives of Neoselachii, the group containing modern sharks (Selachimorpha) and rays (Batoidea) to the exclusion of most extinct elasmobranch groups, date to the Carboniferous . Selachiimorpha and Batoidea are suggested by some to have diverged during the Triassic . Fossils of the earliest true sharks may have appeared during the Permian , based on remains of " synechodontiforms " found in

1924-651: The National Marine Sanctuary of American Samoa in 2014; they are co-managed by the Fish and Wildlife Service and the Office of National Marine Sanctuaries , a component of the National Oceanic and Atmospheric Administration (NOAA). Rose Atoll contains the largest populations of giant clams , nesting seabirds and rare reef fish in all of American Samoa. The fish population is different from

1998-792: The Squaliformes and the Hypnosqualea. The Hypnosqualea may be invalid. It includes the Squatiniformes , and the Pristorajea, which may also be invalid, but includes the Pristiophoriformes and the Batoidea . There are more than 500 species of sharks split across thirteen orders , including several orders of sharks that have gone extinct: Shark teeth are embedded in the gums rather than directly affixed to

2072-630: The United States Fish and Wildlife Service . Rose Atoll Marine National Monument is a United States National Monument covering 8,571,633 acres (13,393.18 sq mi; 10,113.45 sq nmi; 34,688.17 km). It was established in 2009. At the signing of the order establishing the monument, President George W. Bush noted that "the waters surrounding the atoll are the home of many rare species, including giant clams and reef sharks—as well as an unusual abundance of rose-colored corals". The monument's marine areas were incorporated into

2146-753: The University of Hawaiʻi offers a teachers' college, and several mainline churches offer seminaries. Such as the Kanana Fou Seminary and the Wayland Baptist University. Some students opt to attend the National University of Samoa on ʻUpolu Island, or elsewhere on the US mainland. Shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton , five to seven gill slits on

2220-463: The bull shark , which has developed a way to change its kidney function to excrete large amounts of urea. When a shark dies, the urea is broken down to ammonia by bacteria, causing the dead body to gradually smell strongly of ammonia. Research in 1930 by Homer W. Smith showed that sharks' urine does not contain sufficient sodium to avoid hypernatremia , and it was postulated that there must be an additional mechanism for salt secretion. In 1960 it

2294-511: The clade Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes . The Elasmobranchii also include rays and skates ; the Chondrichthyes also include Chimaeras . It was thought that the sharks form a polyphyletic group: some sharks are more closely related to rays than they are to some other sharks, but current molecular studies support monophyly of both groups of sharks and batoids. The clade Selachimorpha

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2368-441: The coelacanth , the blood and other tissue of sharks and Chondrichthyes is generally isotonic to their marine environments because of the high concentration of urea (up to 2.5% ) and trimethylamine N-oxide (TMAO), allowing them to be in osmotic balance with the seawater. This adaptation prevents most sharks from surviving in freshwater, and they are therefore confined to marine environments. A few exceptions exist, such as

2442-461: The cranium . The jaw's surface (in comparison to the shark's vertebrae and gill arches) needs extra support due to its heavy exposure to physical stress and its need for strength. It has a layer of tiny hexagonal plates called " tesserae ", which are crystal blocks of calcium salts arranged as a mosaic. This gives these areas much of the same strength found in the bony tissue found in other animals. Generally sharks have only one layer of tesserae, but

2516-456: The electric fields they produce. Ocean currents moving in the magnetic field of the Earth also generate electric fields that sharks can use for orientation and possibly navigation. This system is found in most fish, including sharks. It is a tactile sensory system which allows the organism to detect water speed and pressure changes near by. The main component of the system is the neuromast,

2590-414: The great white shark ) are homeothermic and maintain a higher body temperature than the surrounding water. In these sharks, a strip of aerobic red muscle located near the center of the body generates the heat, which the body retains via a countercurrent exchange mechanism by a system of blood vessels called the rete mirabile ("miraculous net"). The common thresher and bigeye thresher sharks have

2664-573: The 12 bird species is federally protected. Red-footed boobies and greater and lesser frigate birds nest in the buka trees. Black noddies and white terns nest in the middle and lower branches. The root system is used by reef herons and red-tailed tropic birds . Other birds can be found in the Pisonia forest, the only one left in Samoa. The atoll has been recognised as an Important Bird Area (IBA) by BirdLife International because it supports

2738-838: The Crown residence of the Tuimanuʻa (called the Faleula ) in Lalopua (according to official documents of the Tuimanuʻa government (Office of the Governor, 2004). Around this time, as of 1903, Manu'a had a total population of approximately 2,000 residents. Since that time, the Manuʻa Island Group has officially been part of the US Protectorate of American Samoa . In 1915, in response to the destruction caused to Manu'a that year by

2812-1065: The Early Permian of Russia, but if remains of "synechodontiformes" from the Permian and Triassic are true sharks, they only had low diversity. Modern shark orders first appeared during the Early Jurassic, and during the Jurassic true sharks underwent great diversification. Selachimorphs largely replaced the hybodonts , which had previously been a dominant group of shark-like fish during the Triassic and Early Jurassic. Batoidea [REDACTED] Heterodontiformes [REDACTED] Orectolobiformes [REDACTED] Carcharhiniformes [REDACTED] Lamniformes [REDACTED] Hexanchiformes [REDACTED] Squatiniformes [REDACTED] Pristiophoriformes [REDACTED] Squaliformes [REDACTED] Sharks belong to

2886-648: The Samoan Islands, giving the U.S. control of the eastern islands (including Tutuila and the Manuʻa Group), and giving European powers control of the western islands (including ʻUpolu and Savaiʻi). In 1901, Tutuila's leaders agreed to this arrangement. As a result, Manu'a was eventually forced to accept U.S. rule, and they formalized their acceptance in a Deed of Succession, signed by the Tui Manuʻa (supreme chief of Manuʻa) on July 16, 1904. The signing took place at

2960-567: The Tongans and the Samoans regarded Manuʻa as having sacred status. The last Tui Manuʻa was Tuimanuʻa Elisara (sometimes written Tui Manuʻa Elisala ), who held the title at the beginning of the 20th century. Before he died on July 2, 1909, he expressed the wish that the title die with him. At the time, the U.S. government took the position that Elisara's title had actually changed to “District Governor” nine years before his death, on June 5, 1900,

3034-478: The United States. The local diet was generally healthier than in Tutuila, with less reliance on imported tinned foods. However, with the declining population, fewer and fewer locals are fishing and farming, and the dependence on imported food has been exasperated by the lack of local produce, flailing plantations, and diminishing livestock. A few mom-and-pop stores are open, and some private rental homes contribute to

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3108-417: The anterior and posterior nasal openings, with some species able to detect as little as one part per million of blood in seawater. The size of the olfactory bulb varies across different shark species, with size dependent on how much a given species relies on smell or vision to find their prey. In environments with low visibility, shark species generally have larger olfactory bulbs. In reefs, where visibility

3182-568: The basking shark are small and non-functional. Shark skeletons are very different from those of bony fish and terrestrial vertebrates . Sharks and other cartilaginous fish ( skates and rays ) have skeletons made of cartilage and connective tissue . Cartilage is flexible and durable, yet is about half the normal density of bone. This reduces the skeleton's weight, saving energy. Because sharks do not have rib cages, they can easily be crushed under their own weight on land. The jaws of sharks, like those of rays and skates, are not attached to

3256-416: The body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses . From there venous blood re-enters the heart ventricle and the cycle repeats. Most sharks are "cold-blooded" or, more precisely, poikilothermic , meaning that their internal body temperature matches that of their ambient environment. Members of the family Lamnidae (such as the shortfin mako shark and

3330-481: The day that the U.S. flag had been hoisted at Taʻū (Office of the Governor, 2004). However, titles and holdings were not obliterated when the islands became a U.S. territory, and the title and estates of Tuimanuʻa remain in the custody of the Anoalo clan (the male Tuimanuʻa line). So the title Tui Manuʻa technically still exists, although no one is the holder of the title. The Tripartite Convention of 1899 partitioned

3404-485: The dolphin genus Stenella also use the waters. The atoll is a critical nesting habitat for the threatened green turtle and the endangered hawksbill turtle . The turtles migrate between American Samoa and other Pacific island nations. Their nesting season is between the months of August and February. It is a nesting site for rare species of petrels , shearwaters , and terns . Approximately 97% of American Samoa's seabird population resides on Rose Atoll. Each of

3478-468: The entire Samoan archipelago, as well as other nearby islands, including Tonga and Fiji . The traditional capital of Manuʻa is the village of Taʻū, on the island of Taʻū . The sovereign of Manuʻa was the Tui Manu'a , This title was the progenitor of many of the high titles used in other parts of the Samoan Islands. Manuʻa was the only part of Samoa that was never subjected to Tongan rule, because both

3552-414: The equator. The islands are elevated and mountainous. In contrast to most places in the world, the population of these islands has been decreasing steadily for decades. In the 1930s some 20% of the population of American Samoa lived in the Manuʻa Islands. By the 1980s, only 6% were located there. Emigration is the consequence of a lack of economic opportunities and a desire of young people to participate in

3626-1168: The horny keratin in hair and feathers. Most sharks have eight fins. Sharks can only drift away from objects directly in front of them because their fins do not allow them to move in the tail-first direction. Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body. This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy. Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming. Some species of shark have pigmented denticles that form complex patterns like spots (e.g. Zebra shark ) and stripes (e.g. Tiger shark ). These markings are important for camouflage and help sharks blend in with their environment, as well as making them difficult for prey to detect. For some species, dermal patterning returns to healed denticles even after they have been removed by injury. Tails provide thrust, making speed and acceleration dependent on tail shape. Caudal fin shapes vary considerably between shark species, due to their evolution in separate environments. Sharks possess

3700-418: The inner ear has been lost. The ampullae of Lorenzini are the electroreceptor organs. They number in the hundreds to thousands. Sharks use the ampullae of Lorenzini to detect the electromagnetic fields that all living things produce. This helps sharks (particularly the hammerhead shark ) find prey. The shark has the greatest electrical sensitivity of any animal. Sharks find prey hidden in sand by detecting

3774-402: The intestines of many species, and as a result often linger near or in sewage outfalls. Some species, such as nurse sharks , have external barbels that greatly increase their ability to sense prey. Shark eyes are similar to the eyes of other vertebrates , including similar lenses , corneas and retinas , though their eyesight is well adapted to the marine environment with the help of

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3848-451: The jaw, and are constantly replaced throughout life. Multiple rows of replacement teeth grow in a groove on the inside of the jaw and steadily move forward in comparison to a conveyor belt ; some sharks lose 30,000 or more teeth in their lifetime. The rate of tooth replacement varies from once every 8 to 10 days to several months. In most species, teeth are replaced one at a time as opposed to the simultaneous replacement of an entire row, which

3922-453: The jaws of large specimens, such as the bull shark, tiger shark, and the great white shark, have two to three layers or more, depending on body size. The jaws of a large great white shark may have up to five layers. In the rostrum (snout), the cartilage can be spongy and flexible to absorb the power of impacts. Fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling

3996-425: The journey to Tutuila . It took 22 days for the first contact to be reestablished between Tutuila and Manuʻa. This was achieved when Pele Scoles repaired a longboat and rowed from Ofu to Tutuila. Manu'a District was first recorded beginning with the 1900 U.S. Census. No census was taken in 1910, but a special census was taken in 1912. Regular decennial censuses were taken beginning in 1920. Its population zenith

4070-569: The local economy. Yet, the American Samoa Government (ASG) is the largest employer in the islands, with branch offices of each government department: Agriculture, Education, Department of Health, Public Safety & Fire, Port Administration, ASPA, ASTCA, Marine Wildlife Resources, and M&O. In 2010, the Manuʻa District had a per capita income of $ 5,441 — this makes the Manuʻa District the county / county-equivalent with

4144-543: The longest lifespans at more than 100 years. Whale sharks ( Rhincodon typus ) may also live over 100 years. Earlier estimates suggested the Greenland shark ( Somniosus microcephalus ) could reach about 200 years, but a recent study found that a 5.02-metre-long (16.5 ft) specimen was 392 ± 120 years old (i.e., at least 272 years old), making it the longest-lived vertebrate known. Unlike most bony fish , sharks are K-selected reproducers, meaning that they produce

4218-550: The lowest-per capita income in the entire United States. Traditionally, the people of Manuʻa spoke the Samoan language with a unique "t" sound. The ancient sound was between a light spoken "t" with a puff of air and a gentle "d" sound. By the 1830s, missionaries transcribed the Holy Bible into the native tongue, adding the letters h, k, and r to accommodate the new sounds from the scriptures. The spoken language has since adopted

4292-570: The more modern lifestyle offered on Tutuila (Office of Tourism, 2005). All the land of Manuʻa is owned communally by Samoan families of Manuʻa. This includes the National Parks lands which are only leased to the US National Parks system for 50 years. Manu'a District is further divided into five counties. According to historical Samoan oral tradition, Manu'a was formerly the ruling center of a large Polynesian empire that included

4366-467: The north. The Rose Atoll Marine National Monument that lies on the two outstanding islands of the atoll is managed cooperatively between the U.S. Fish and Wildlife Service and the government of American Samoa . The nearly square atoll is one of the smallest in the world, measuring only 2.6 × 2.7 km (1.62 × 1.68 mi.). It is also the only atoll of the Samoan Islands . ( Swains Island

4440-502: The ocean near Rose Atoll on May 26, 1969. The three astronauts were treated to a lavish welcome at Pago Pago International Airport before being flown to Hawai’i. The island was protected as the Rose Atoll National Wildlife Refuge in 1973 with 39,066 acres (61.04 sq mi; 46.09 sq nmi; 158.09 km), only 20 acres (8.1 ha) of which is emergent. The wildlife refuge is managed by

4514-433: The rest of the region due to a high concentration of carnivorous fish and low concentration of herbivorous fish . Almost 270 different species of fish have been recorded in the last 15 years. Tuna , mahi-mahi , billfish , barracuda and sharks reside outside the lagoon. In deeper waters, tunicates and stalked crinoids have been spotted by scuba expeditions. Sea mammals such as the endangered humpback whale and

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4588-399: The second woman to circumnavigate the globe, Rose de Freycinet was the first to tell her tale. In his official report Louis de Freycinet records that 'I named Rose Island, from the name of someone who is extremely dear to me'. Soon afterwards, in 1824, it was seen by the expedition under Otto von Kotzebue , who named it Kordinkov after his First Lieutenant. Apollo 10 returned to Earth in

4662-403: The shark's two-chambered heart . Here, the shark pumps blood to its gills via the ventral aorta where it branches into afferent branchial arteries . Gas exchange takes place in the gills and the reoxygenated blood flows into the efferent branchial arteries, which come together to form the dorsal aorta . The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from

4736-484: The sides of the head , and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii ) and are the sister group to the Batoidea ( rays and kin). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts . Shark-like chondrichthyans such as Cladoselache and Doliodus first appeared in

4810-410: The small dwarf lanternshark ( Etmopterus perryi ), a deep sea species that is only 17 centimetres (6.7 in) in length, to the whale shark ( Rhincodon typus ), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length. They are found in all seas and are common to depths up to 2,000 metres (6,600 ft). They generally do not live in freshwater, although there are

4884-413: The spiracle) leads directly into the inner ear through a thin channel. The lateral line shows a similar arrangement, and is open to the environment via a series of openings called lateral line pores . This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fish and tetrapods the external opening into

4958-414: The stomach, and instead the shark either vomits or turns its stomachs inside out and ejects unwanted items from its mouth. One of the biggest differences between the digestive systems of sharks and mammals is that sharks have much shorter intestines. This short length is achieved by the spiral valve with multiple turns within a single short section instead of a long tube-like intestine. The valve provides

5032-465: The sun, and it sets at Falealupo the westernmost village on the island of Savaiʻi in Samoa. This journey of the sun is strongly related to traditional beliefs and defines the uniformity of cultural identity across both Samoas. The term Fa'asamoa describes "The Samoan Way", or traditional Samoan way of life Today, many families of Manuʻa rely on income from family members working in Tutuila and in

5106-423: The surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes . This membrane covers the eyes while hunting and when the shark is being attacked. However, some species, including the great white shark ( Carcharodon carcharias ), do not have this membrane, but instead roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunting behavior

5180-403: The thresher shark's usage of its powerful, elongated upper lobe to stun fish and squid. Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver filled with oil that contains squalene , and their cartilage, which is about half the normal density of bone. Their liver constitutes up to 30% of their total body mass. The liver's effectiveness

5254-456: The top of their food chain . Select examples include the bull shark , tiger shark , great white shark , mako sharks , thresher sharks , and hammerhead sharks . Sharks are caught by humans for shark meat or shark fin soup . Many shark populations are threatened by human activities. Since 1970, shark populations have been reduced by 71%, mostly from overfishing . Until the 16th century, sharks were known to mariners as "sea dogs". This

5328-548: The word shark (referring to a sea fish) in a letter written by Thomas Beckington in 1442, which rules out a New World etymology. The oldest total-group chondrichthyans, known as acanthodians or "spiny sharks", appeared during the Early Silurian , around 439 million years ago. The oldest confirmed members of Elasmobranchii sensu lato (the group containing all cartilaginous fish more closely related to modern sharks and rays than to chimaeras ) appeared during

5402-576: Was discovered at the Mount Desert Island Biological Laboratory in Salsbury Cove, Maine that sharks have a type of salt gland located at the end of the intestine, known as the "rectal gland", whose function is the secretion of chlorides. Digestion can take a long time. The food moves from the mouth to a J-shaped stomach, where it is stored and initial digestion occurs. Unwanted items may never get past

5476-471: Was in 1950. As of 2000–10, it had a population lower than when first recorded in 1900. The history of Manuʻa is said in Samoan oratory to contain the origins of Samoan and Polynesian culture, and the genealogy of Polynesians east of Samoa is said to have originated in Manuʻa. In traditional belief the sun rises over Samoa at Saua on the island of Taʻū, where the coral reef is supposed to be always yellow from

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