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Some rubies show a three-point or six-point asterism or "star". These rubies are cut into cabochons to display the effect properly. Asterisms are best visible with a single-light source and move across the stone as the light moves or the stone is rotated. Such effects occur when light is reflected off the "silk" (the structurally oriented rutile needle inclusions) in a certain way. This is one example where inclusions increase the value of a gemstone. Furthermore, rubies can show color changes—though this occurs very rarely—as well as chatoyancy or the "cat's eye" effect.
Versus pink sapphire
Generally, gemstone-quality corundum in all shades of red, including pink, are called rubies. However, in the United States, a minimum color saturation must be met to be called a ruby; otherwise, the stone will be called a pink sapphire. Drawing a distinction between rubies and pink sapphires is relatively new, having arisen sometime in the 20th century. Often, the distinction between ruby and pink sapphire is not clear and can be debated. As a result of the difficulty and subjectiveness of such distinctions, trade organizations such as the International Colored Gemstone Association (ICGA) have adopted the broader definition for ruby which encompasses its lighter shades, including pink.
Occurrence and mining
Historically, rubies have been mined in Thailand, in the Pailin and Samlout District of Cambodia, as well as in Afghanistan, Australia, Brazil, Colombia, India, Namibia, Japan, and Scotland. After the Second World War, ruby deposits were found in Madagascar, Mozambique, Nepal, Pakistan, Tajikistan, Tanzania, and Vietnam.
The Republic of North Macedonia is the only country in mainland Europe to have naturally occurring rubies. They can mainly be found around the city of Prilep. Macedonian rubies have a unique raspberry color.
A few rubies have been found in the U.S. states of Montana, North Carolina, South Carolina and Wyoming. | Ruby | Wikipedia | 418 | 43551 | https://en.wikipedia.org/wiki/Ruby | Physical sciences | Mineral gemstones | null |
Spinel, another red gemstone, is sometimes found along with rubies in the same gem gravel or marble. Red spinels may be mistaken for rubies by those lacking experience with gems. However, the finest red spinels, now heavily sought, can have values approaching all but the finest examples of ruby.
The Mogok Valley in Upper Myanmar (Burma) was for centuries the world's main source for rubies. That region has produced some exceptional rubies; however, in recent years few good rubies have been found. In central Myanmar, the area of Mong Hsu began producing rubies during the 1990s and rapidly became the world's main ruby mining area. The most recently found ruby deposit in Myanmar is in Namya (Namyazeik) located in the northern state of Kachin.
In Pakistani Kashmir there are vast proven reserves of millions of rubies, worth up to half a billion dollars. However, as of 2017 there was only one mine (at Chitta Katha) due to lack of investment. In Afghanistan, rubies are mined at Jegdalek. In 2017 the Aappaluttoq mine in Greenland began running.
The rubies in Greenland are said to be among the oldest in the world at approximately 3 billion years old. The Aappaluttoq mine in Greenland is located 160 kilometers south of Nuuk, the capital of Greenland. The rubies are traceable from mine to market.
The Montepuez ruby mine in northeastern Mozambique is situated on one of the most significant ruby deposits in the world, although, rubies were only discovered here for the first time in 2009. In less than a decade, Mozambique has become the world's most productive source for gem-quality ruby.
Factors affecting value
Rubies, as with other gemstones, are graded using criteria known as the four Cs, namely color, cut, clarity and carat weight. Rubies are also evaluated on the basis of their geographic origin. | Ruby | Wikipedia | 400 | 43551 | https://en.wikipedia.org/wiki/Ruby | Physical sciences | Mineral gemstones | null |
Color
In the evaluation of colored gemstones, color is the most important factor. Color divides into three components: hue, saturation and tone. Hue refers to color as we normally use the term. Transparent gemstones occur in the pure spectral hues of red, orange, yellow, green, blue, violet. In nature, there are rarely pure hues, so when speaking of the hue of a gemstone, we speak of primary and secondary and sometimes tertiary hues. Ruby is defined to be red. All other hues of the gem species corundum are called sapphire. Ruby may exhibit a range of secondary hues, including orange, purple, violet, and pink.
Clarity
Because rubies host many inclusions, their clarity is evaluated by the inclusions’ size, number, location, and visibility. Rubies with the highest clarity grades are known as “eye-clean,” because their inclusions are the least visible to the naked human eye. Rubies may also have thin, intersecting inclusions called silk. Silk can scatter light, brightening the gem's appearance, and the presence of silk can also show whether a ruby has been previously heat treated, since intense heat will degrade a ruby's silk.
Treatments and enhancements
Improving the quality of gemstones by treating them is common practice. Some treatments are used in almost all cases and are therefore considered acceptable. During the late 1990s, a large supply of low-cost materials caused a sudden surge in supply of heat-treated rubies, leading to a downward pressure on ruby prices.
Improvements used include color alteration, improving transparency by dissolving rutile inclusions, healing of fractures (cracks) or even completely filling them.
The most common treatment is the application of heat. Most rubies at the lower end of the market are heat treated to improve color, remove purple tinge, blue patches, and silk. These heat treatments typically occur around temperatures of 1800 °C (3300 °F). Some rubies undergo a process of low tube heat, when the stone is heated over charcoal of a temperature of about 1300 °C (2400 °F) for 20 to 30 minutes. The silk is partially broken, and the color is improved.
Another treatment, which has become more frequent in recent years, is lead glass filling. Filling the fractures inside the ruby with lead glass (or a similar material) dramatically improves the transparency of the stone, making previously unsuitable rubies fit for applications in jewelry. The process is done in four steps: | Ruby | Wikipedia | 508 | 43551 | https://en.wikipedia.org/wiki/Ruby | Physical sciences | Mineral gemstones | null |
The rough stones are pre-polished to eradicate all surface impurities that may affect the process
The rough is cleaned with hydrogen fluoride
The first heating process during which no fillers are added. The heating process eradicates impurities inside the fractures. Although this can be done at temperatures up to 1400 °C (2500 °F) it most likely occurs at a temperature of around 900 °C (1600 °F) since the rutile silk is still intact.
The second heating process in an electrical oven with different chemical additives. Different solutions and mixes have shown to be successful; however, mostly lead-containing glass-powder is used at present. The ruby is dipped into oils, then covered with powder, embedded on a tile and placed in the oven where it is heated at around 900 °C (1600 °F) for one hour in an oxidizing atmosphere. The orange colored powder transforms upon heating into a transparent to yellow-colored paste, which fills all fractures. After cooling the color of the paste is fully transparent and dramatically improves the overall transparency of the ruby.
If a color needs to be added, the glass powder can be "enhanced" with copper or other metal oxides as well as elements such as sodium, calcium, potassium etc.
The second heating process can be repeated three to four times, even applying different mixtures. When jewelry containing rubies is heated (for repairs) it should not be coated with boracic acid or any other substance, as this can etch the surface; it does not have to be "protected" like a diamond.
The treatment can be identified by noting bubbles in cavities and fractures using a 10× loupe.
Synthesis and imitation
In 1837, Gaudin made the first synthetic rubies by fusing potash alum at a high temperature with a little chromium as a pigment. In 1847, Ebelmen made white sapphire by fusing alumina in boric acid. In 1877, Edmond Frémy and industrial glass-maker Charles Feil made crystal corundum from which small stones could be cut. In 1887, Fremy and Auguste Verneuil manufactured artificial ruby by fusing BaF and AlO with a little chromium at red heat.
In 1903, Verneuil announced he could produce synthetic rubies on a commercial scale using this flame fusion process, later also known as the Verneuil process. By 1910, Verneuil's laboratory had expanded into a 30 furnace production facility, with annual gemstone production having reached in 1907. | Ruby | Wikipedia | 511 | 43551 | https://en.wikipedia.org/wiki/Ruby | Physical sciences | Mineral gemstones | null |
Other processes in which synthetic rubies can be produced are through Czochralski's pulling process, flux process, and the hydrothermal process. Most synthetic rubies originate from flame fusion, due to the low costs involved. Synthetic rubies may have no imperfections visible to the naked eye but magnification may reveal curved striae and gas bubbles. The fewer the number and the less obvious the imperfections, the more valuable the ruby is; unless there are no imperfections (i.e., a perfect ruby), in which case it will be suspected of being artificial. Dopants are added to some manufactured rubies so they can be identified as synthetic, but most need gemological testing to determine their origin.
Synthetic rubies have technological uses as well as gemological ones. Rods of synthetic ruby are used to make ruby lasers and masers. The first working laser was made by Theodore H. Maiman in 1960. Maiman used a solid-state light-pumped synthetic ruby to produce red laser light at a wavelength of 694 nanometers (nm). Ruby lasers are still in use.
Rubies are also used in applications where high hardness is required such as at wear-exposed locations in mechanical clockworks, or as scanning probe tips in a coordinate measuring machine.
Imitation rubies are also marketed. Red spinels, red garnets, and colored glass have been falsely claimed to be rubies. Imitations go back to Roman times and already in the 17th century techniques were developed to color foil red—by burning scarlet wool in the bottom part of the furnace—which was then placed under the imitation stone. Trade terms such as balas ruby for red spinel and rubellite for red tourmaline can mislead unsuspecting buyers. Such terms are therefore discouraged from use by many gemological associations such as the Laboratory Manual Harmonisation Committee (LMHC).
Records and famous examples | Ruby | Wikipedia | 393 | 43551 | https://en.wikipedia.org/wiki/Ruby | Physical sciences | Mineral gemstones | null |
The Smithsonian's National Museum of Natural History in Washington, D.C. has some of the world's largest and finest ruby gemstones. The Burmese ruby, set in a platinum ring with diamonds, was donated by businessman and philanthropist Peter Buck in memory of his late wife Carmen Lúcia. This gemstone displays a richly saturated red color combined with an exceptional transparency. The finely proportioned cut provides vivid red reflections. The stone was mined from the Mogok region of Burma (now Myanmar) in the 1930s.
In 2007, the London jeweler Garrard & Co featured a heart-shaped 40.63-carat ruby on their website.
On 13/14 December 2011, Elizabeth Taylor's complete jewelry collection was auctioned by Christie's. Several ruby-set pieces were included in the sale, notably a ring set with an 8.24 ct gem that broke the 'price-per-carat' record for rubies (US$512,925 per carat – i.e., over US$4.2 million in total), and a necklace that sold for over US$3.7 million.
The Liberty Bell Ruby is the largest mined ruby in the world. It was stolen in a heist in 2011.
The Sunrise Ruby was the world's most expensive ruby, most expensive colored gemstone, and most expensive gemstone other than a diamond when it sold at auction in Switzerland to an anonymous buyer for US$30 million In May 2015.
A synthetic ruby crystal became the gain medium in the world's first optical laser, conceived, designed and constructed by Theodore H. "Ted" Maiman, on 16 May 1960 at Hughes Research Laboratories.
The concept of electromagnetic radiation amplification through the mechanism of stimulated emission had already been successfully demonstrated in the laboratory by way of the maser, using other materials such as ammonia and, later, ruby, but the ruby laser was the first device to work at optical (694.3 nm) wavelengths. Maiman's prototype laser is still in working order. | Ruby | Wikipedia | 416 | 43551 | https://en.wikipedia.org/wiki/Ruby | Physical sciences | Mineral gemstones | null |
Historical and cultural references
The Old Testament of the Bible mentions ruby many times in the Book of Exodus, and many times in the Book of Proverbs, as well as various other times. It is not certain that the Biblical words mean 'ruby' as distinct from other jewels.
An early recorded transport and trading of rubies arises in the literature on the North Silk Road of China, wherein about 200 BC rubies were carried along this ancient trackway moving westward from China.
Rubies have always been held in high esteem in Asian countries. They were used to ornament armor, scabbards, and harnesses of noblemen in India and China. Rubies were laid beneath the foundation of buildings to secure good fortune to the structure.
A traditional Hindu astrological belief holds rubies as the "gemstone of the Sun and also the heavenly deity Surya, the leader of the nine heavenly bodies (Navagraha)." The belief is that worshiping and wearing rubies causes the Sun to be favorable to the wearer.
In the Marvel comic books, the Godstone is a ruby that the son of J. Jonah Jameson, John Jameson found on the Moon that becomes activated by moonlight, grafts itself to his chest which turns him into the Man-Wolf. | Ruby | Wikipedia | 259 | 43551 | https://en.wikipedia.org/wiki/Ruby | Physical sciences | Mineral gemstones | null |
Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.
The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 4 as fluorite.
Pure fluorite is colourless and transparent, both in visible and ultraviolet light, but impurities usually make it a colorful mineral and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses and enamels. The purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals. Optically clear transparent fluorite has anomalous partial dispersion, that is, its refractive index varies with the wavelength of light in a manner that differs from that of commonly used glasses, so fluorite is useful in making apochromatic lenses, and particularly valuable in photographic optics. Fluorite optics are also usable in the far-ultraviolet and mid-infrared ranges, where conventional glasses are too opaque for use. Fluorite also has low dispersion, and a high refractive index for its density.
History and etymology
The word fluorite is derived from the Latin verb fluere, meaning to flow. The mineral is used as a flux in iron smelting to decrease the viscosity of slag. The term flux comes from the Latin adjective fluxus, meaning flowing, loose, slack. The mineral fluorite was originally termed fluorspar and was first discussed in print in a 1530 work Bermannvs sive de re metallica dialogus [Bermannus; or dialogue about the nature of metals], by Georgius Agricola, as a mineral noted for its usefulness as a flux. Agricola, a German scientist with expertise in philology, mining, and metallurgy, named fluorspar as a Neo-Latinization of the German Flussspat from Fluss (stream, river) and Spat (meaning a nonmetallic mineral akin to gypsum, spærstān, spear stone, referring to its crystalline projections). | Fluorite | Wikipedia | 490 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
In 1852, fluorite gave its name to the phenomenon of fluorescence, which is prominent in fluorites from certain locations, due to certain impurities in the crystal. Fluorite also gave the name to its constitutive element fluorine. Currently, the word "fluorspar" is most commonly used for fluorite as an industrial and chemical commodity, while "fluorite" is used mineralogically and in most other senses.
In archeology, gemmology, classical studies, and Egyptology, the Latin terms murrina and myrrhina refer to fluorite. In book 37 of his Naturalis Historia, Pliny the Elder describes it as a precious stone with purple and white mottling, and noted that the Romans prized objects carved from it.
Structure
Fluorite crystallizes in a cubic motif. Crystal twinning is common and adds complexity to the observed crystal habits. Fluorite has four perfect cleavage planes that help produce octahedral fragments. The structural motif adopted by fluorite is so common that the motif is called the fluorite structure. Element substitution for the calcium cation often includes strontium and certain rare-earth elements (REE), such as yttrium and cerium.
Occurrence and mining
Fluorite forms as a late-crystallizing mineral in felsic igneous rocks typically through hydrothermal activity. It is particularly common in granitic pegmatites. It may occur as a vein deposit formed through hydrothermal activity particularly in limestones. In such vein deposits it can be associated with galena, sphalerite, barite, quartz, and calcite. Fluorite can also be found as a constituent of sedimentary rocks either as grains or as the cementing material in sandstone.
It is a common mineral mainly distributed in South Africa, China, Mexico, Mongolia, the United Kingdom, the United States, Canada, Tanzania, Rwanda and Argentina.
The world reserves of fluorite are estimated at 230 million tonnes (Mt) with the largest deposits being in South Africa (about 41 Mt), Mexico (32 Mt) and China (24 Mt). China is leading the world production with about 3 Mt annually (in 2010), followed by Mexico (1.0 Mt), Mongolia (0.45 Mt), Russia (0.22 Mt), South Africa (0.13 Mt), Spain (0.12 Mt) and Namibia (0.11 Mt). | Fluorite | Wikipedia | 510 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
One of the largest deposits of fluorspar in North America is located on the Burin Peninsula, Newfoundland, Canada. The first official recognition of fluorspar in the area was recorded by geologist J.B. Jukes in 1843. He noted an occurrence of "galena" or lead ore and fluoride of lime on the west side of St. Lawrence harbour. It is recorded that interest in the commercial mining of fluorspar began in 1928 with the first ore being extracted in 1933. Eventually, at Iron Springs Mine, the shafts reached depths of . In the St. Lawrence area, the veins are persistent for great lengths and several of them have wide lenses. The area with veins of known workable size comprises about .
In 2018, Canada Fluorspar Inc. commenced mine production again in St. Lawrence; in spring 2019, the company was planned to develop a new shipping port on the west side of Burin Peninsula as a more affordable means of moving their product to markets, and they successfully sent the first shipload of ore from the new port on July 31, 2021. This marks the first time in 30 years that ore has been shipped directly out of St. Lawrence.
Cubic crystals up to 20 cm across have been found at Dalnegorsk, Russia. The largest documented single crystal of fluorite was a cube 2.12 meters in size and weighing approximately 16 tonnes.
In Asturias (Spain) there are several fluorite deposits known internationally for the quality of the specimens they have yielded. In the area of Berbes, Ribadesella, fluorite appears as cubic crystals, sometimes with dodecahedron modifications, which can reach a size of up to 10 cm of edge, with internal colour zoning, almost always violet in colour. It is associated with quartz and leafy aggregates of baryte. In the Emilio mine, in Loroñe, Colunga, the fluorite crystals, cubes with small modifications of other figures, are colourless and transparent. They can reach 10 cm of edge. In the Moscona mine, in Villabona, the fluorite crystals, cubic without modifications of other shapes, are yellow, up to 3 cm of edge. They are associated with large crystals of calcite and barite.
"Blue John" | Fluorite | Wikipedia | 465 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
One of the most famous of the older-known localities of fluorite is Castleton in Derbyshire, England, where, under the name of "Derbyshire Blue John", purple-blue fluorite was extracted from several mines or caves. During the 19th century, this attractive fluorite was mined for its ornamental value. The mineral Blue John is now scarce, and only a few hundred kilograms are mined each year for ornamental and lapidary use. Mining still takes place in Blue John Cavern and Treak Cliff Cavern.
Recently discovered deposits in China have produced fluorite with coloring and banding similar to the classic Blue John stone.
Fluorescence
George Gabriel Stokes named the phenomenon of fluorescence from fluorite, in 1852.
Many samples of fluorite exhibit fluorescence under ultraviolet light, a property that takes its name from fluorite. Many minerals, as well as other substances, fluoresce. Fluorescence involves the elevation of electron energy levels by quanta of ultraviolet light, followed by the progressive falling back of the electrons into their previous energy state, releasing quanta of visible light in the process. In fluorite, the visible light emitted is most commonly blue, but red, purple, yellow, green, and white also occur. The fluorescence of fluorite may be due to mineral impurities, such as yttrium and ytterbium, or organic matter, such as volatile hydrocarbons in the crystal lattice. In particular, the blue fluorescence seen in fluorites from certain parts of Great Britain responsible for the naming of the phenomenon of fluorescence itself, has been attributed to the presence of inclusions of divalent europium in the crystal. Natural samples containing rare earth impurities such as erbium have also been observed to display upconversion fluorescence, in which infrared light stimulates emission of visible light, a phenomenon usually only reported in synthetic materials.
One fluorescent variety of fluorite is chlorophane, which is reddish or purple in color and fluoresces brightly in emerald green when heated (thermoluminescence), or when illuminated with ultraviolet light. | Fluorite | Wikipedia | 434 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
The color of visible light emitted when a sample of fluorite is fluorescing depends on where the original specimen was collected; different impurities having been included in the crystal lattice in different places. Neither does all fluorite fluoresce equally brightly, even from the same locality. Therefore, ultraviolet light is not a reliable tool for the identification of specimens, nor for quantifying the mineral in mixtures. For example, among British fluorites, those from Northumberland, County Durham, and eastern Cumbria are the most consistently fluorescent, whereas fluorite from Yorkshire, Derbyshire, and Cornwall, if they fluoresce at all, are generally only feebly fluorescent.
Fluorite also exhibits the property of thermoluminescence.
Color
Fluorite is allochromatic, meaning that it can be tinted with elemental impurities. Fluorite comes in a wide range of colors and has consequently been dubbed "the most colorful mineral in the world". Every color of the rainbow in various shades is represented by fluorite samples, along with white, black, and clear crystals. The most common colors are purple, blue, green, yellow, or colorless. Less common are pink, red, white, brown, and black. Color zoning or banding is commonly present. The color of the fluorite is determined by factors including impurities, exposure to radiation, and the absence of voids of the color centers.
Uses
Source of fluorine and fluoride
Fluorite is a major source of hydrogen fluoride, a commodity chemical used to produce a wide range of materials. Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid:
CaF2(s) + H2SO4 → CaSO4(s) + 2 HF(g)
The resulting HF is converted into fluorine, fluorocarbons, and diverse fluoride materials. As of the late 1990s, five billion kilograms were mined annually. | Fluorite | Wikipedia | 405 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
There are three principal types of industrial use for natural fluorite, commonly referred to as "fluorspar" in these industries, corresponding to different grades of purity. Metallurgical grade fluorite (60–85% CaF2), the lowest of the three grades, has traditionally been used as a flux to lower the melting point of raw materials in steel production to aid the removal of impurities, and later in the production of aluminium. Ceramic grade fluorite (85–95% CaF2) is used in the manufacture of opalescent glass, enamels, and cooking utensils. The highest grade, "acid grade fluorite" (97% or more CaF2), accounts for about 95% of fluorite consumption in the US where it is used to make hydrogen fluoride and hydrofluoric acid by reacting the fluorite with sulfuric acid.
Internationally, acid-grade fluorite is also used in the production of AlF3 and cryolite (Na3AlF6), which are the main fluorine compounds used in aluminium smelting. Alumina is dissolved in a bath that consists primarily of molten Na3AlF6, AlF3, and fluorite (CaF2) to allow electrolytic recovery of aluminium. Fluorine losses are replaced entirely by the addition of AlF3, the majority of which react with excess sodium from the alumina to form Na3AlF6.
Niche uses
Lapidary uses
Natural fluorite mineral has ornamental and lapidary uses. Fluorite may be drilled into beads and used in jewelry, although due to its relative softness it is not widely used as a semiprecious stone. It is also used for ornamental carvings, with expert carvings taking advantage of the stone's zonation.
Optics | Fluorite | Wikipedia | 376 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
In the laboratory, calcium fluoride is commonly used as a window material for both infrared and ultraviolet wavelengths, since it is transparent in these regions (about 0.15 μm to 9 μm) and exhibits an extremely low change in refractive index with wavelength. Furthermore, the material is attacked by few reagents. At wavelengths as short as 157 nm, a common wavelength used for semiconductor stepper manufacture for integrated circuit lithography, the refractive index of calcium fluoride shows some non-linearity at high power densities, which has inhibited its use for this purpose. In the early years of the 21st century, the stepper market for calcium fluoride collapsed, and many large manufacturing facilities have been closed. Canon and other manufacturers have used synthetically grown crystals of calcium fluoride components in lenses to aid apochromatic design, and to reduce light dispersion. This use has largely been superseded by newer glasses and computer-aided design. As an infrared optical material, calcium fluoride is widely available and was sometimes known by the Eastman Kodak trademarked name "Irtran-3", although this designation is obsolete. | Fluorite | Wikipedia | 237 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
Fluorite should not be confused with fluoro-crown (or fluorine crown) glass, a type of low-dispersion glass that has special optical properties approaching fluorite. True fluorite is not a glass but a crystalline material. Lenses or optical groups made using this low dispersion glass as one or more elements exhibit less chromatic aberration than those utilizing conventional, less expensive crown glass and flint glass elements to make an achromatic lens. Optical groups employ a combination of different types of glass; each type of glass refracts light in a different way. By using combinations of different types of glass, lens manufacturers are able to cancel out or significantly reduce unwanted characteristics; chromatic aberration being the most important. The best of such lens designs are often called apochromatic (see above). Fluoro-crown glass (such as Schott FK51) usually in combination with an appropriate "flint" glass (such as Schott KzFSN 2) can give very high performance in telescope objective lenses, as well as microscope objectives, and camera telephoto lenses. Fluorite elements are similarly paired with complementary "flint" elements (such as Schott LaK 10). The refractive qualities of fluorite and of certain flint elements provide a lower and more uniform dispersion across the spectrum of visible light, thereby keeping colors focused more closely together. Lenses made with fluorite are superior to fluoro-crown based lenses, at least for doublet telescope objectives; but are more difficult to produce and more costly.
The use of fluorite for prisms and lenses was studied and promoted by Victor Schumann near the end of the 19th century. Naturally occurring fluorite crystals without optical defects were only large enough to produce microscope objectives. | Fluorite | Wikipedia | 371 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
With the advent of synthetically grown fluorite crystals in the 1950s - 60s, it could be used instead of glass in some high-performance optical telescope and camera lens elements. In telescopes, fluorite elements allow high-resolution images of astronomical objects at high magnifications. Canon Inc. produces synthetic fluorite crystals that are used in their better telephoto lenses. The use of fluorite for telescope lenses has declined since the 1990s, as newer designs using fluoro-crown glass, including triplets, have offered comparable performance at lower prices. Fluorite and various combinations of fluoride compounds can be made into synthetic crystals which have applications in lasers and special optics for UV and infrared.
Exposure tools for the semiconductor industry make use of fluorite optical elements for ultraviolet light at wavelengths of about 157 nanometers. Fluorite has a uniquely high transparency at this wavelength. Fluorite objective lenses are manufactured by the larger microscope firms (Nikon, Olympus, Carl Zeiss and Leica). Their transparence to ultraviolet light enables them to be used for fluorescence microscopy. The fluorite also serves to correct optical aberrations in these lenses. Nikon has previously manufactured at least one fluorite and synthetic quartz element camera lens (105 mm f/4.5 UV) for the production of ultraviolet images. Konica produced a fluorite lens for their SLR cameras – the Hexanon 300 mm f/6.3.
Source of fluorine gas in nature
In 2012, the first source of naturally occurring fluorine gas was found in fluorite mines in Bavaria, Germany. It was previously thought that fluorine gas did not occur naturally because it is so reactive, and would rapidly react with other chemicals. Fluorite is normally colorless, but some varied forms found nearby look black, and are known as 'fetid fluorite' or antozonite. The minerals, containing small amounts of uranium and its daughter products, release radiation sufficiently energetic to induce oxidation of fluoride anions within the structure, to fluorine that becomes trapped inside the mineral. The color of fetid fluorite is predominantly due to the calcium atoms remaining. Solid-state fluorine-19 NMR carried out on the gas contained in the antozonite, revealed a peak at 425 ppm, which is consistent with F2.
Gallery | Fluorite | Wikipedia | 496 | 43589 | https://en.wikipedia.org/wiki/Fluorite | Physical sciences | Minerals | Earth science |
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications in physics. For transport phenomena, flux is a vector quantity, describing the magnitude and direction of the flow of a substance or property. In vector calculus flux is a scalar quantity, defined as the surface integral of the perpendicular component of a vector field over a surface.
Terminology
The word flux comes from Latin: fluxus means "flow", and fluere is "to flow". As fluxion, this term was introduced into differential calculus by Isaac Newton.
The concept of heat flux was a key contribution of Joseph Fourier, in the analysis of heat transfer phenomena. His seminal treatise Théorie analytique de la chaleur (The Analytical Theory of Heat), defines fluxion as a central quantity and proceeds to derive the now well-known expressions of flux in terms of temperature differences across a slab, and then more generally in terms of temperature gradients or differentials of temperature, across other geometries. One could argue, based on the work of James Clerk Maxwell, that the transport definition precedes the definition of flux used in electromagnetism. The specific quote from Maxwell is:
According to the transport definition, flux may be a single vector, or it may be a vector field / function of position. In the latter case flux can readily be integrated over a surface. By contrast, according to the electromagnetism definition, flux is the integral over a surface; it makes no sense to integrate a second-definition flux for one would be integrating over a surface twice. Thus, Maxwell's quote only makes sense if "flux" is being used according to the transport definition (and furthermore is a vector field rather than single vector). This is ironic because Maxwell was one of the major developers of what we now call "electric flux" and "magnetic flux" according to the electromagnetism definition. Their names in accordance with the quote (and transport definition) would be "surface integral of electric flux" and "surface integral of magnetic flux", in which case "electric flux" would instead be defined as "electric field" and "magnetic flux" defined as "magnetic field". This implies that Maxwell conceived of these fields as flows/fluxes of some sort. | Flux | Wikipedia | 483 | 43590 | https://en.wikipedia.org/wiki/Flux | Physical sciences | Basics_6 | null |
Given a flux according to the electromagnetism definition, the corresponding flux density, if that term is used, refers to its derivative along the surface that was integrated. By the Fundamental theorem of calculus, the corresponding flux density is a flux according to the transport definition. Given a current such as electric current—charge per time, current density would also be a flux according to the transport definition—charge per time per area. Due to the conflicting definitions of flux, and the interchangeability of flux, flow, and current in nontechnical English, all of the terms used in this paragraph are sometimes used interchangeably and ambiguously. Concrete fluxes in the rest of this article will be used in accordance to their broad acceptance in the literature, regardless of which definition of flux the term corresponds to.
Flux as flow rate per unit area
In transport phenomena (heat transfer, mass transfer and fluid dynamics), flux is defined as the rate of flow of a property per unit area, which has the dimensions [quantity]·[time]−1·[area]−1. The area is of the surface the property is flowing "through" or "across". For example, the amount of water that flows through a cross section of a river each second divided by the area of that cross section, or the amount of sunlight energy that lands on a patch of ground each second divided by the area of the patch, are kinds of flux.
General mathematical definition (transport)
Here are 3 definitions in increasing order of complexity. Each is a special case of the following. In all cases the frequent symbol j, (or J) is used for flux, q for the physical quantity that flows, t for time, and A for area. These identifiers will be written in bold when and only when they are vectors.
First, flux as a (single) scalar:
where
In this case the surface in which flux is being measured is fixed and has area A. The surface is assumed to be flat, and the flow is assumed to be everywhere constant with respect to position and perpendicular to the surface.
Second, flux as a scalar field defined along a surface, i.e. a function of points on the surface: | Flux | Wikipedia | 447 | 43590 | https://en.wikipedia.org/wiki/Flux | Physical sciences | Basics_6 | null |
As before, the surface is assumed to be flat, and the flow is assumed to be everywhere perpendicular to it. However the flow need not be constant. q is now a function of p, a point on the surface, and A, an area. Rather than measure the total flow through the surface, q measures the flow through the disk with area A centered at p along the surface.
Finally, flux as a vector field:
In this case, there is no fixed surface we are measuring over. q is a function of a point, an area, and a direction (given by a unit vector ), and measures the flow through the disk of area A perpendicular to that unit vector. I is defined picking the unit vector that maximizes the flow around the point, because the true flow is maximized across the disk that is perpendicular to it. The unit vector thus uniquely maximizes the function when it points in the "true direction" of the flow. (Strictly speaking, this is an abuse of notation because the "argmax" cannot directly compare vectors; we take the vector with the biggest norm instead.)
Properties
These direct definitions, especially the last, are rather unwieldy. For example, the argmax construction is artificial from the perspective of empirical measurements, when with a weathervane or similar one can easily deduce the direction of flux at a point. Rather than defining the vector flux directly, it is often more intuitive to state some properties about it. Furthermore, from these properties the flux can uniquely be determined anyway.
If the flux j passes through the area at an angle θ to the area normal , then the dot product
That is, the component of flux passing through the surface (i.e. normal to it) is jcosθ, while the component of flux passing tangential to the area is jsinθ, but there is no flux actually passing through the area in the tangential direction. The only component of flux passing normal to the area is the cosine component.
For vector flux, the surface integral of j over a surface S, gives the proper flowing per unit of time through the surface:
where A (and its infinitesimal) is the vector area combination of the magnitude of the area A through which the property passes and a unit vector normal to the area.
Unlike in the second set of equations, the surface here need not be flat. | Flux | Wikipedia | 485 | 43590 | https://en.wikipedia.org/wiki/Flux | Physical sciences | Basics_6 | null |
Finally, we can integrate again over the time duration t1 to t2, getting the total amount of the property flowing through the surface in that time (t2 − t1):
Transport fluxes
Eight of the most common forms of flux from the transport phenomena literature are defined as follows:
Momentum flux, the rate of transfer of momentum across a unit area (N·s·m−2·s−1). (Newton's law of viscosity)
Heat flux, the rate of heat flow across a unit area (J·m−2·s−1). (Fourier's law of conduction) (This definition of heat flux fits Maxwell's original definition.)
Diffusion flux, the rate of movement of molecules across a unit area (mol·m−2·s−1). (Fick's law of diffusion)
Volumetric flux, the rate of volume flow across a unit area (m3·m−2·s−1). (Darcy's law of groundwater flow)
Mass flux, the rate of mass flow across a unit area (kg·m−2·s−1). (Either an alternate form of Fick's law that includes the molecular mass, or an alternate form of Darcy's law that includes the density.)
Radiative flux, the amount of energy transferred in the form of photons at a certain distance from the source per unit area per second (J·m−2·s−1). Used in astronomy to determine the magnitude and spectral class of a star. Also acts as a generalization of heat flux, which is equal to the radiative flux when restricted to the electromagnetic spectrum.
Energy flux, the rate of transfer of energy through a unit area (J·m−2·s−1). The radiative flux and heat flux are specific cases of energy flux.
Particle flux, the rate of transfer of particles through a unit area ([number of particles] m−2·s−1)
These fluxes are vectors at each point in space, and have a definite magnitude and direction. Also, one can take the divergence of any of these fluxes to determine the accumulation rate of the quantity in a control volume around a given point in space. For incompressible flow, the divergence of the volume flux is zero.
Chemical diffusion
As mentioned above, chemical molar flux of a component A in an isothermal, isobaric system is defined in Fick's law of diffusion as: | Flux | Wikipedia | 511 | 43590 | https://en.wikipedia.org/wiki/Flux | Physical sciences | Basics_6 | null |
where the nabla symbol ∇ denotes the gradient operator, DAB is the diffusion coefficient (m2·s−1) of component A diffusing through component B, cA is the concentration (mol/m3) of component A.
This flux has units of mol·m−2·s−1, and fits Maxwell's original definition of flux.
For dilute gases, kinetic molecular theory relates the diffusion coefficient D to the particle density n = N/V, the molecular mass m, the collision cross section , and the absolute temperature T by
where the second factor is the mean free path and the square root (with the Boltzmann constant k) is the mean velocity of the particles.
In turbulent flows, the transport by eddy motion can be expressed as a grossly increased diffusion coefficient.
Quantum mechanics
In quantum mechanics, particles of mass m in the quantum state ψ(r, t) have a probability density defined as
So the probability of finding a particle in a differential volume element d3r is
Then the number of particles passing perpendicularly through unit area of a cross-section per unit time is the probability flux;
This is sometimes referred to as the probability current or current density, or probability flux density.
Flux as a surface integral
General mathematical definition (surface integral)
As a mathematical concept, flux is represented by the surface integral of a vector field,
where F is a vector field, and dA is the vector area of the surface A, directed as the surface normal. For the second, n is the outward pointed unit normal vector to the surface.
The surface has to be orientable, i.e. two sides can be distinguished: the surface does not fold back onto itself. Also, the surface has to be actually oriented, i.e. we use a convention as to flowing which way is counted positive; flowing backward is then counted negative.
The surface normal is usually directed by the right-hand rule.
Conversely, one can consider the flux the more fundamental quantity and call the vector field the flux density.
Often a vector field is drawn by curves (field lines) following the "flow"; the magnitude of the vector field is then the line density, and the flux through a surface is the number of lines. Lines originate from areas of positive divergence (sources) and end at areas of negative divergence (sinks). | Flux | Wikipedia | 473 | 43590 | https://en.wikipedia.org/wiki/Flux | Physical sciences | Basics_6 | null |
In physical geography, a fjord (also spelled fiord in New Zealand English; ) is a long, narrow sea inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Antarctica, the Arctic, and surrounding landmasses of the northern and southern hemispheres. Norway's coastline is estimated to be long with its nearly 1,200 fjords, but only long excluding the fjords.
Formation
A true fjord is formed when a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock. According to the standard model, glaciers formed in pre-glacial valleys with a gently sloping valley floor. The work of the glacier then left an overdeepened U-shaped valley that ends abruptly at a valley or trough end. Such valleys are fjords when flooded by the ocean. Thresholds above sea level create freshwater lakes. Glacial melting is accompanied by the rebounding of Earth's crust as the ice load and eroded sediment is removed (also called isostasy or glacial rebound). In some cases, this rebound is faster than sea level rise. Most fjords are deeper than the adjacent sea; Sognefjord, Norway, reaches as much as below sea level. Fjords generally have a sill or shoal (bedrock) at their mouth caused by the previous glacier's reduced erosion rate and terminal moraine. In many cases this sill causes extreme currents and large saltwater rapids (see skookumchuck). Saltstraumen in Norway is often described as the world's strongest tidal current. These characteristics distinguish fjords from rias (such as the Bay of Kotor), which are drowned valleys flooded by the rising sea. Drammensfjorden is cut almost in two by the Svelvik "ridge", a sandy moraine that was below sea level when it was covered by ice, but after the post-glacial rebound reaches above the fjord. | Fjord | Wikipedia | 397 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
In the 19th century, Jens Esmark introduced the theory that fjords are or have been created by glaciers and that large parts of Northern Europe had been covered by thick ice in prehistory. Thresholds at the mouths and overdeepening of fjords compared to the ocean are the strongest evidence of glacial origin, and these thresholds are mostly rocky. Thresholds are related to sounds and low land where the ice could spread out and therefore have less erosive force. John Walter Gregory argued that fjords are of tectonic origin and that glaciers had a negligible role in their formation. Gregory's views were rejected by subsequent research and publications. In the case of Hardangerfjord the fractures of the Caledonian fold has guided the erosion by glaciers, while there is no clear relation between the direction of Sognefjord and the fold pattern. This relationship between fractures and direction of fjords is also observed in Lyngen. Preglacial, tertiary rivers presumably eroded the surface and created valleys that later guided the glacial flow and erosion of the bedrock. This may in particular have been the case in Western Norway where the tertiary uplift of the landmass amplified eroding forces of rivers.
Confluence of tributary fjords led to excavation of the deepest fjord basins. Near the very coast, the typical West Norwegian glacier spread out (presumably through sounds and low valleys) and lost their concentration and reduced the glaciers' power to erode leaving bedrock thresholds. Bolstadfjorden is deep with a threshold of only , while the deep Sognefjorden has a threshold around deep. Hardangerfjord is made up of several basins separated by thresholds: The deepest basin Samlafjorden between Jonaneset (Jondal) and Ålvik with a distinct threshold at Vikingneset in Kvam Municipality. | Fjord | Wikipedia | 373 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Hanging valleys are common along glaciated fjords and U-shaped valleys. A hanging valley is a tributary valley that is higher than the main valley and was created by tributary glacier flows into a glacier of larger volume. The shallower valley appears to be 'hanging' above the main valley or a fjord. Often, waterfalls form at or near the outlet of the upper valley. Small waterfalls within these fjords are also used as freshwater resources. Hanging valleys also occur underwater in fjord systems. The branches of Sognefjord are for instance much shallower than the main fjord. The mouth of Fjærlandsfjord is about deep while the main fjord is nearby. The mouth of Ikjefjord is only deep while the main fjord is around at the same point.
Features and variations
Hydrology
During the winter season, there is usually little inflow of freshwater. Surface water and deeper water (down to or more) are mixed during winter because of the steady cooling of the surface and wind. In the deep fjords, there is still fresh water from the summer with less density than the saltier water along the coast. Offshore wind, common in the fjord areas during winter, sets up a current on the surface from the inner to the outer parts. This current on the surface in turn pulls dense salt water from the coast across the fjord threshold and into the deepest parts of the fjord. Bolstadfjorden has a threshold of only and strong inflow of freshwater from Vosso river creates a brackish surface that blocks circulation of the deep fjord. The deeper, salt layers of Bolstadfjorden are deprived of oxygen and the seabed is covered with organic material. The shallow threshold also creates a strong tidal current. | Fjord | Wikipedia | 352 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
During the summer season, there is usually a large inflow of river water in the inner areas. This freshwater gets mixed with saltwater creating a layer of brackish water with a slightly higher surface than the ocean which in turn sets up a current from the river mouths towards the ocean. This current is gradually more salty towards the coast and right under the surface current there is a reverse current of saltier water from the coast. In the deeper parts of the fjord the cold water remaining from winter is still and separated from the atmosphere by the brackish top layer. This deep water is ventilated by mixing with the upper layer causing it to warm and freshen over the summer. In fjords with a shallow threshold or low levels of mixing this deep water is not replaced every year and low oxygen concentration makes the deep water unsuitable for fish and animals. In the most extreme cases, there is a constant barrier of freshwater on the surface and the fjord freezes over such that there is no oxygen below the surface. Drammensfjorden is one example. The mixing in fjords predominantly results from the propagation of an internal tide from the entrance sill or internal seiching.
The Gaupnefjorden branch of Sognefjorden is strongly affected by freshwater as a glacial river flows in. Velfjorden has little inflow of freshwater.
Coral reefs
In 2000, some coral reefs were discovered along the bottoms of the Norwegian fjords. These reefs were found in fjords from the north of Norway to the south. The marine life on the reefs is believed to be one of the most important reasons why the Norwegian coastline is such a generous fishing ground. Since this discovery is fairly new, little research has been done. The reefs are host to thousands of lifeforms such as plankton, coral, anemones, fish, several species of shark, and many more. Most are specially adapted to life under the greater pressure of the water column above it, and the total darkness of the deep sea.
New Zealand's fjords are also host to deep-water corals, but a surface layer of dark fresh water allows these corals to grow in much shallower water than usual. An underwater observatory in Milford Sound allows tourists to view them without diving. | Fjord | Wikipedia | 460 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Skerries
In some places near the seaward margins of areas with fjords, the ice-scoured channels are so numerous and varied in direction that the rocky coast is divided into thousands of island blocks, some large and mountainous while others are merely rocky points or rock reefs, menacing navigation. These are called skerries. The term skerry is derived from the Old Norse , which means a rock in the sea.
Skerries most commonly formed at the outlet of fjords where submerged glacially formed valleys perpendicular to the coast join with other cross valleys in a complex array. The island fringe of Norway is such a group of skerries (called a ); many of the cross fjords are so arranged that they parallel the coast and provide a protected channel behind an almost unbroken succession of mountainous islands and skerries. By this channel, one can travel through a protected passage almost the entire route from Stavanger to North Cape, Norway. The Blindleia is a skerry-protected waterway that starts near Kristiansand in southern Norway and continues past Lillesand. The Swedish coast along Bohuslän is likewise skerry guarded. The Inside Passage provides a similar route from Seattle, Washington, and Vancouver, British Columbia, to Skagway, Alaska. Yet another such skerry-protected passage extends from the Straits of Magellan north for .
Phytoplankton
Fjords provide unique environmental conditions for phytoplankton communities. In polar fjords, glacier and ice sheet outflow add cold, fresh meltwater along with transported sediment into the body of water. Nutrients provided by this outflow can significantly enhance phytoplankton growth. For example, in some fjords of the West Antarctic Peninsula (WAP), nutrient enrichment from meltwater drives diatom blooms, a highly productive group of phytoplankton that enable such fjords to be valuable feeding grounds for other species. It is possible that as climate change reduces long-term meltwater output, nutrient dynamics within such fjords will shift to favor less productive species, destabilizing the food web ecology of fjord systems.
In addition to nutrient flux, sediment carried by flowing glaciers can become suspended in the water column, increasing turbidity and reducing light penetration into greater depths of the fjord. This effect can limit the available light for photosynthesis in deeper areas of the water mass, reducing phytoplankton abundance beneath the surface. | Fjord | Wikipedia | 500 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Overall, phytoplankton abundance and species composition within fjords is highly seasonal, varying as a result of seasonal light availability and water properties that depend on glacial melt and the formation of sea ice. The study of phytoplankton communities within fjords is an active area of research, supported by groups such as FjordPhyto, a citizen science initiative to study phytoplankton samples collected by local residents, tourists, and boaters of all backgrounds.
Epishelf lakes
An epishelf lake forms when meltwater is trapped behind a floating ice shelf and the freshwater floats on the denser saltwater below. Its surface may freeze forming an isolated ecosystem.
Etymology
The word fjord is borrowed from Norwegian, where it is pronounced , , or in various dialects and has a more general meaning, referring in many cases to any long, narrow body of water, inlet or channel (for example, see Oslofjord).
The Norwegian word is inherited from Old Norse , a noun which refers to a 'lake-like' body of water used for passage and ferrying and is closely related to the noun "travelling, ferrying, journey". Both words go back to Indo-European "crossing", from the root "cross". The words and ferry are of the same origin.
The Scandinavian fjord, Proto-Scandinavian *, is the origin for similar Germanic words: Icelandic , Faroese , Swedish (for Baltic waterbodies), Scots (for marine waterbodies, mainly in Scotland and northern England). The Norse noun was adopted in German as , used for the narrow long bays of Schleswig-Holstein, and in English as firth "fjord, river mouth". The English word ford (compare German , Low German or , in Dutch names such as Vilvoorde, Ancient Greek , , and Latin ) is assumed to originate from Germanic and Indo-European root * meaning "crossing point". Fjord/firth/Förde as well as ford/Furt/Vörde/voorde refer to a Germanic noun for a travel: North Germanic or and of the verb to travel, Dutch , German ; English to fare. | Fjord | Wikipedia | 441 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
As a loanword from Norwegian, it is one of the few words in the English language to start with the sequence fj. The word was for a long time normally spelled fiord, a spelling preserved in place names such as Grise Fiord. The fiord spelling mostly remains only in New Zealand English, as in the place name Fiordland.
Scandinavian usage
The use of the word fjord in Norwegian, Danish and Swedish is more general than in English and in international scientific terminology. In Scandinavia, fjord is used for a narrow inlet of the sea in Norway, Denmark and western Sweden, but this is not its only application. In Norway and Iceland, the usage is closest to the Old Norse, with fjord used for both a firth and for a long, narrow inlet. In eastern Norway, the term is also applied to long narrow freshwater lakes (Randsfjorden and Tyrifjorden) and sometimes even to rivers (for instance in Flå Municipality in Hallingdal, the Hallingdal river is referred to as ). In southeast Sweden, the name fjard is a subdivision of the term 'fjord' used for bays, bights and narrow inlets on the Swedish Baltic Sea coast, and in most Swedish lakes. This latter term is also used for bodies of water off the coast of Finland where Finland Swedish is spoken. In Danish, the word may even apply to shallow lagoons. In modern Icelandic, is still used with the broader meaning of firth or inlet. In Faroese is used both about inlets and about broader sounds, whereas a narrower sound is called . In the Finnish language, a word is used although there is only one fjord in Finland.
In old Norse genitive was fjarðar whereas dative was firði. The dative form has become common place names like Førde (for instance Førde), Fyrde or Førre (for instance Førre).
The German use of the word for long narrow bays on their Baltic Sea coastline, indicates a common Germanic origin of the word. The landscape consists mainly of moraine heaps. The and some "fjords" on the east side of Jutland, Denmark are also of glacial origin. But while the glaciers digging "real" fjords moved from the mountains to the sea, in Denmark and Germany they were tongues of a huge glacier covering the basin of which is now the Baltic Sea. See Förden and East Jutland Fjorde. | Fjord | Wikipedia | 502 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Whereas fjord names mostly describe bays (though not always geological fjords), straits in the same regions typically are named Sund, in Scandinavian languages as well as in German. The word is related to "to sunder" in the meaning of "to separate". So the use of Sound to name fjords in North America and New Zealand differs from the European meaning of that word.
The name of Wexford in Ireland is originally derived from ("inlet of the mud flats") in Old Norse, as used by the Viking settlers—though the inlet at that place in modern terms is an estuary, not a fjord. Similarly the name of Milford (now Milford Haven) in Wales is derived from ("sandbank fjord/inlet"), though the inlet on which it is located is actually a ria.
Before or in the early phase of Old Norse was another common noun for fjords and other inlets of the ocean. This word has survived only as a suffix in names of some Scandinavian fjords and has in same cases also been transferred to adjacent settlements or surrounding areas for instance Hardanger, Stavanger, and Geiranger.
Differences in definitions
The differences in usage between the English and the Scandinavian languages have contributed to confusion in the use of the term fjord. Bodies of water that are clearly fjords in Scandinavian languages are not considered fjords in English; similarly bodies of water that would clearly not be fjords in the Scandinavian sense have been named or suggested to be fjords. Examples of this confused usage follow.
In the Danish language some inlets are called a fjord, but are, according to the English language definition, technically not a fjord, such as Roskilde Fjord. Limfjord in English terminology is a sound, since it separates the North Jutlandic Island (Vendsyssel-Thy) from the rest of Jutland. However, the Limfjord once was a fjord until the sea broke through from the west. Ringkøbing Fjord on the western coast of Jutland is a lagoon. The long narrow fjords of Denmark's Baltic Sea coast like the German were dug by ice moving from the sea upon land, while fjords in the geological sense were dug by ice moving from the mountains down to the sea. However, some definitions of a fjord is: "A long narrow inlet consisting of only one inlet created by glacial activity". Examples of Danish fjords are: Kolding Fjord, Vejle Fjord and Mariager Fjord. | Fjord | Wikipedia | 502 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
The fjords in Finnmark in Norway, which are fjords in the Scandinavian sense of the term, are not universally considered to be fjords by the scientific community, because although glacially formed, most Finnmark fjords lack the steep-sided valleys of the more southerly Norwegian fjords. The glacial pack was deep enough to cover even the high grounds when they were formed. The Oslofjord, on the other hand, is a rift valley, and not glacially formed.
The indigenous Māori people of New Zealand see a fjord as a kind of sea () that runs by a bluff (, altogether "bluff sea"). | Fjord | Wikipedia | 129 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
"Fjords" not created by glaciers
The term "fjord" is sometimes applied to steep-sided inlets which were not created by glaciers. Most such inlets are drowned river canyons or rias. Examples include:
In Acapulco, Mexico, the calanques (narrow, rocky inlets) on the western side of the city, where the famous cliff-divers perform daily, are described in the city's tourist literature as being fjords.
The calanques of Parc national des Calanques, Provence, France, are also referred to as fjords.
Camel Estuary at Padstow, Cornwall, England, is sometimes referred to as a fjord. despite being classified as a ria.
The Fiordo di Furore in Italy is actually a ria.
Golfo Dulce in Puntarenas, Costa Rica. Like the Saco de Mamangua below, it is sometimes described as a "tropical fjord".
The Khor ash Sham in the Musandam Peninsula in Oman, and other "khors" or inlets in the deeply indented coast of Musandam, are often described as "fjords". They were formed by the subduction of the Arabian tectonic plate beneath the Eurasian plate.
Bay of Kotor in Montenegro
the Lim bay in Istria, Croatia, is sometimes called "Lim fjord" although it is a ria dug by the river Pazinčica. The Croats call it , which does not translate precisely to the English equivalent either.
Milford Haven Waterway in Pembrokeshire, Wales. This inlet is a ria. The place-name is derived from Old Norse Melrfjordr meaning "sandbank fjord".
Port Davey in Tasmania, Australia is popularly believed to be a "fjord", but is now thought to be part of a drowned river valley system.
in Paraty, Rio de Janeiro, Brazil. Colloquially, it's been labeled the world's "only tropical fjord".
Freshwater fjords | Fjord | Wikipedia | 405 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Some Norwegian freshwater lakes that have formed in long glacially carved valleys with sill thresholds, ice front deltas or terminal moraines blocking the outlet follow the Norwegian naming convention; they are frequently named fjords. Ice front deltas developed when the ice front was relatively stable for long time during the melting of the ice shield. The resulting landform is an isthmus between the lake and the saltwater fjord, in Norwegian called "eid" as in placename Eidfjord or Nordfjordeid. The post-glacial rebound changed these deltas into terraces up to the level of the original sea level. In Eidfjord, Eio has dug through the original delta and left a terrace while lake is only above sea level. Such deposits are valuable sources of high-quality building materials (sand and gravel) for houses and infrastructure. Eidfjord village sits on the eid or isthmus between Eidfjordvatnet lake and Eidfjorden branch of Hardangerfjord. Nordfjordeid is the isthmus with a village between Hornindalsvatnet lake and Nordfjord. Such lakes are also denoted fjord valley lakes by geologists.
One of Norway's largest is Tyrifjorden at above sea level and an average depth at most of the lake is under sea level. Norway's largest lake, Mjøsa, is also referred to as "the fjord" by locals. Another example is the freshwater fjord Movatnet (Mo lake) that until 1743 was separated from Romarheimsfjorden by an isthmus and connected by a short river. During a flood in November 1743, the river bed eroded and sea water could flow into the lake at high tide. Eventually, Movatnet became a saltwater fjord and renamed Mofjorden (). Like fjords, freshwater lakes are often deep. For instance Hornindalsvatnet is at least deep and water takes an average of 16 years to flow through the lake. Such lakes created by glacial action are also called fjord lakes or moraine-dammed lakes. | Fjord | Wikipedia | 432 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Some of these lakes were salt after the ice age but later cut off from the ocean during the post-glacial rebound. At the end of the ice age Eastern Norway was about lower (the marine limit). When the ice cap receded and allowed the ocean to fill valleys and lowlands, and lakes like Mjøsa and Tyrifjorden were part of the ocean while Drammen valley was a narrow fjord. At the time of the Vikings Drammensfjord was still higher than today and reached the town of Hokksund, while parts of what is now the city of Drammen was under water. After the ice age the ocean was about at Notodden. The ocean stretched like a fjord through Heddalsvatnet all the way to Hjartdal. Post-glacial rebound eventually separated Heddalsvatnet from the ocean and turned it into a freshwater lake. In neolithic times Heddalsvatnet was still a saltwater fjord connected to the ocean, and was cut off from the ocean around 1500 BC.
Some freshwater fjords such as Slidrefjord are above the marine limit.
Like freshwater fjords, the continuation of fjords on land are in the same way denoted as fjord-valleys. For instance Flåmsdal (Flåm valley) and Måbødalen. | Fjord | Wikipedia | 267 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Outside of Norway, the three western arms of New Zealand's Lake Te Anau are named North Fiord, Middle Fiord and South Fiord. Another freshwater "fjord" in a larger lake is Western Brook Pond, in Newfoundland's Gros Morne National Park; it is also often described as a fjord, but is actually a freshwater lake cut off from the sea, so is not a fjord in the English sense of the term. Locally they refer to it as a "landlocked fjord". Such lakes are sometimes called "fjord lakes". Okanagan Lake was the first North American lake to be so described, in 1962. The bedrock there has been eroded up to below sea level, which is below the surrounding regional topography. Fjord lakes are common on the inland lea of the Coast Mountains and Cascade Range; notable ones include Lake Chelan, Seton Lake, Chilko Lake, and Atlin Lake. Kootenay Lake, Slocan Lake and others in the basin of the Columbia River are also fjord-like in nature, and created by glaciation in the same way. Along the British Columbia Coast, a notable fjord-lake is Owikeno Lake, which is a freshwater extension of Rivers Inlet. Quesnel Lake, located in central British Columbia, is claimed to be the deepest fjord formed lake on Earth.
Great Lakes
A family of freshwater fjords are the embayments of the North American Great Lakes. Baie Fine is located on the northwestern coast of Georgian Bay of Lake Huron in Ontario, and Huron Bay is located on the southern shore of Lake Superior in Michigan.
Locations
The principal mountainous regions where fjords have formed are in the higher middle latitudes and the high latitudes reaching to 80°N (Svalbard, Greenland), where, during the glacial period, many valley glaciers descended to the then-lower sea level. The fjords develop best in mountain ranges against which the prevailing westerly marine winds are orographically lifted over the mountainous regions, resulting in abundant snowfall to feed the glaciers. Hence coasts having the most pronounced fjords include the west coast of Norway, the west coast of North America from Puget Sound to Alaska, the southwest coast of New Zealand, and the west and to south-western coasts of South America, chiefly in Chile. | Fjord | Wikipedia | 467 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Principal fjord regions
West coast of Europe
Faroe Islands
Westfjords of Iceland
Eastern Region of Iceland
West Highlands of Scotland
Norway, the whole coast including Svalbard
Kola Peninsula in Russia
West coast of New Zealand
Fiordland, in the southwest of the South Island
Northwest coast of North America
Coast of Alaska, United States: Lynn Canal, Glacier Bay, etc.
British Columbia Coast, Canada: from the Alaskan Border along the Portland Canal to Indian Arm; Kingcome Inlet is a typical West Coast fjord.
Hood Canal in Washington, United States and various of the arms of Puget Sound
Northeast coast of North America
Labrador: Saglek Fjord, Nachvak Fjord, Hebron Fjord
The east coast of Ungava Bay.
Baffin Island
Ellesmere Island
Greenland: Kangerlussuaq, Ilulissat Icefjord, Scoresby Sund, Disko Island
Southwest coast of South America
Fjords and channels of Chile
Isla de los Estados, Argentina
Other glaciated or formerly glaciated regions
Other regions have fjords, but many of these are less pronounced due to more limited exposure to westerly winds and less pronounced relief. Areas include:
Europe
Ireland
Lough Swilly
Carlingford Lough
Killary Harbour
Russia (see also List of fjords of Russia)
Chukchi Peninsula
Kola Peninsula
Scotland (where they are called firths, the Scots language cognate of fjord; lochs or sea lochs). Notable examples are:
Loch Long
Loch Fyne, Scotland's longest fjord at 65 km
Loch Etive
Sweden
Gullmarsfjorden, in Bohuslän, Sweden
Wales
Mawddach Estuary, a fjord in-filled by glacial deposits.
North America
Canada:
the west and south coasts of Newfoundland, particularly:
Facheux Bay
Bonne Bay in Gros Morne National Park
Aviron Bay
La Hune Bay
Bay de Vieux
White Bear Bay
Baie d'Espoir
La Poile Bay
Bay Le Moine
the Canadian Arctic Archipelago
Quebec, Saguenay Fjord
United States:
Somes Sound, Acadia National Park, Maine
Hudson River
most clearly seen at The Palisades
Puget Sound
South America
Argentina:
Isla de los Estados
Arctic
Arctic islands
Novaya Zemlya
Severnaya Zemlya
Antarctica
South Georgia (UK)
Kerguelen Islands (France)
particularly the Antarctic Peninsula
Sub-Antarctic islands | Fjord | Wikipedia | 484 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Extreme fjords
The longest fjords in the world are:
Nansen Sound/Greely Fiord/Tanquary Fiord in Canada—
Chatham Strait/Lynn Canal in United States—
Scoresby Sund in Greenland—
Concepción Channel-Puerto Simpson in Chile—
Sognefjord in Norway—
Independence Fjord in Greenland—
Matochkin Shar, Novaya Zemlya, Russia— (a strait with a fjord structure)
Deep fjords include:
Skelton Inlet in Antarctica—
Sognefjord in Norway— (the mountains then rise to up to and more, Hurrungane reaches )
Messier Channel in Tortel, Chile—
Baker Channel in Tortel, Chile—
Heritage fjords
Norway has several heritage fjords, including UNESCO World Heritage Sites and other notable fjords, these will require visiting ships to be low-emission by 2026 and zero-emission by 2032
Geirangerfjord
Nærøyfjord
Hardangerfjord
Trollfjord
Urnes Stave Church
Hjørundfjord | Fjord | Wikipedia | 211 | 43598 | https://en.wikipedia.org/wiki/Fjord | Physical sciences | Glacial landforms | null |
Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some species are found in brooks and streams, where fresh water is running, while others thrive in swamps, ditches, and paddy fields. Most crayfish cannot tolerate polluted water, although some species, such as Procambarus clarkii, are hardier. Crayfish feed on animals and plants, either living or decomposing, and detritus.
The term "crayfish" is applied to saltwater species in some countries.
Terminology
The name "crayfish" comes from the Old French word (Modern French ). The word has been modified to "crayfish" by association with "fish" (folk etymology). The largely American variant "crawfish" is similarly derived.
Some kinds of crayfish are known locally as lobsters, crawdads, mudbugs, and yabbies. In the Eastern United States, "crayfish" is more common in the north, while "crawdad" is heard more in central and southwestern regions, and "crawfish" farther south, although considerable overlaps exist.
The study of crayfish is called astacology.
Anatomy
The body of a decapod crustacean, such as a crab, lobster, or prawn (shrimp), is made up of twenty body segments grouped into two main body parts, the cephalothorax and the abdomen. Each segment may possess one pair of appendages, although in various groups, these may be reduced or missing. On average, crayfish grow to in length. Walking legs have a small claw at the end.
Diet
Crayfish are opportunistic omnivorous scavengers, with the ability to filter and process mud. In aquaculture ponds using isotope analysis they were shown to build body tissue selectively from the animal protein portion of pelleted food and not the other components of the pellet.
They have the potential to eat most foods, even nutrient poor material such as grass, leaves, and paper, but can be highly selective and need variety to balance their diet. The personalities of the individual crayfish can be a key determinant in the food preference behaviour in aquaria. | Crayfish | Wikipedia | 506 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
Crayfish all over the world can be seen in an ecological role of benthic dwellers, so this is where most of their food is obtained - at the sediment/water interface in ponds, lakes, swamps, or burrows. When the gut contents are analysed, most of the contents is mud: fine particulate organic matter (FPOM) and mixed particles of lignin and cellulose (roots, leaves, bark, wood). Some animal material can also be identified, but this only contributes a small portion of the diet by volume.
They feed on submerged vegetable material at times, but their ability to catch large living animal material is restricted. They can feed on interstitial organisms if they can be grasped in the small feeding claws. They can be lured into traps with an array of baits from dog biscuits, fish heads, meat, etc., all of which reinforces the fact that they are generalist feeders.
On a day-to-day basis, they consume what they can acquire in their immediate environment in limited space and time available - detritus. At a microbial level, the FPOM has a high surface area of organic particles and consists of a plethora of substrate and bacteria, fungi, micro-algae, meiofauna, partially decomposed organic material and mucus. This mucus or "slime" is a biofilm and can be felt on the surface of leaves and sticks. Also crayfish have been shown to be coprophagic - eating their own faeces, they also eat their own exuviae (moulted carapace) and each other. They have even been observed leaving the water to graze.
Detritus or mud is a mixture of dead plankton (plant and animal), organic wastes from the water column, and debris derived from the aquatic and terrestrial environments. Mostly detritus is in the end phase of decomposition and is recognised as black organic mud. The crayfish usually ingest the material in only a few minutes, as distinct from grazing for many hours. The material is mixed with digestive fluids and sorted by size. The finer particles follow a slower and more exacting route through to the hindgut, compared to the coarser material. The coarser material is eliminated first and often reappears in approximately 10 to 12 hours, whereas the finer material is usually eliminated from 16 to 26 hours after ingestion. | Crayfish | Wikipedia | 501 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
All waste products coming out through the hindgut are wrapped in a peritrophic membrane, so they look like a tube. Such an investment in the wrapping of the microbial free faeces in a protein rich membrane is most likely the reason they are coprophagic. Such feeding behaviour based on selection, ingestion, and extreme processing ensures periodic feeding, as distinct from continuous grazing. They tend to eat to satiation and then take many hours to process the material, leaving minimal chance of having more room to ingest other items. Crayfish usually have limited home range and so they rest, digest, and eliminate their waste, most commonly in the same location each day.
Feeding exposes the crayfish to risk of predation, and so feeding behaviour is often rapid and synchronised with feeding processes that reduce such risks — eat, hide, process and eliminate.
Knowledge of the diet of these creatures was considered too complex since the first book ever written in the field of zoology, The Crayfish by T.H. Huxley (1879), where they were described as "detritivores". This is why most researchers have not attempted to understand the diet of freshwater crayfish. The most complex study which matched the structure and function of the whole digestive tract with ingested material was performed in the 1990s by Brett O'Brien on marron, the least aggressive of the larger freshwater crayfish with aquaculture potential, similar to redclaw and yabbies.
Classification and geographical distribution
Crayfish are closely related to lobsters, and together they belong to the infraorder Astacidea. Their phylogeny can be shown in the simplified cladogram below:
Four extant (living) families of crayfish are described, three in the Northern Hemisphere and one in the Southern Hemisphere. The Southern Hemisphere (Gondwana-distributed) family Parastacidae, with 14 extant genera and two extinct genera, live(d) in South America, Madagascar, and Australasia. They are distinguished by the absence of the first pair of pleopods. Of the other three Northern Hemisphere families (grouped in the superfamily Astacoidea), the four genera of the family Astacidae live in western Eurasia and western North America, the 15 genera of the family Cambaridae live in eastern North America, and the single genus of Cambaroididae live in eastern Asia.
North America | Crayfish | Wikipedia | 501 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
The greatest diversity of crayfish species is found in southeastern North America, with over 330 species in 15 genera, all in the family Cambaridae. A further genus of astacid crayfish is found in the Pacific Northwest and the headwaters of some rivers east of the Continental Divide. Many crayfish are also found in lowland areas where the water is abundant in calcium, and oxygen rises from underground springs. Crayfish are also found in some non-coastal wetlands; eight species of crayfish live in Iowa, for example.
In 1983, Louisiana designated the crayfish, or crawfish as they are commonly called, as its official state crustacean. Louisiana produces of crawfish per year with the red swamp and white river crawfish being the main species harvested. Crawfish are a part of Cajun culture dating back hundreds of years. A variety of cottage industries have developed as a result of commercialized crawfish iconography. Their products include crawfish attached to wooden plaques, T-shirts with crawfish logos, and crawfish pendants, earrings, and necklaces made of gold or silver.
Australia
Australia has over 100 species in a dozen genera. It is home to the world's three largest freshwater crayfish:
the Tasmanian giant freshwater crayfish Astacopsis gouldi, which can achieve a mass over and is found in rivers of northern Tasmania
the Murray crayfish Euastacus armatus, which can reach , although reports of animals up to have been made. It is found in much of the southern Murray-Darling basin.
the marron from Western Australia (now believed to be two species, Cherax tenuimanus and C. cainii) which may reach
Many of the better-known Australian crayfish are of the genus Cherax, and include the common yabby (C. destructor), western yabby (C. preissii), and red-claw crayfish (C. quadricarinatus).
The marron species C. tenuimanus is critically endangered, while other large Australasian crayfish are threatened or endangered.
New Zealand
In New Zealand, two species of Paranephrops are endemic, and are known by the Māori name .
Other animals | Crayfish | Wikipedia | 471 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
In Australia, New Zealand, and South Africa, the term "crayfish" or "cray" generally refers to a saltwater spiny lobster, of the genus Jasus that is indigenous to much of southern Oceania, while the freshwater species are usually called yabbies or , from the indigenous Australian and Māori names for the animal, respectively, or by other names specific to each species. Exceptions include western rock lobster (of the Palinuridae family) found on the west coast of Australia (it is a spiny lobster, but not of Jasus); the Tasmanian giant freshwater crayfish (from the Parastacidae family and therefore a true crayfish) found only in Tasmania; and the Murray crayfish found along Australia's Murray River.
In Singapore, the term crayfish typically refers to Thenus orientalis, a seawater crustacean from the slipper lobster family. True crayfish are not native to Singapore, but are commonly found as pets, or as an invasive species (Cherax quadricarinatus) in the many water catchment areas, and are alternatively known as freshwater lobsters.
In the United Kingdom and Ireland, the terms crayfish or crawfish commonly refer to the European spiny lobster, a saltwater species found in much of the East Atlantic and Mediterranean. The only true crayfish species native to the British Isles is the endangered white clawed crayfish.
Fossil record | Crayfish | Wikipedia | 294 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
Fossil burrows very similar in construction to those of modern crayfish and likely produced by early crayfish are known from the Early Permian (~300-270 million years ago) of equatorial Pangea, in what is now North America (Washington Formation), and Europe (Sardinia). The oldest body fossils assigned to crayfish are known from the Late Triassic (~230-200 million years ago) Chinle Formation of North America, assigned to the species "Enoploclytia" porteri and Camborygma eumekenomos, which are not assigned to any modern families. An indeterminate member of the modern family Cambaridae is known from the Late Jurassic Morrison Formation of North America. The earliest records of other modern families date to the Early Cretaceous, including the parastacid Palaeoechinastacus from Australia which is 115 million years old, the cambaroidid Palaeocambarus from the Yixian Formation of China which is likely around 120 million years old (Barremian-Aptian), and the astacid "Austropotamobius" llopisi from the Las Hoyas site in Spain (Barremian).
Threats to crayfish
Crayfish are susceptible to infections such as crayfish plague and to environmental stressors including acidification. In Europe, they are particularly threatened by crayfish plague, which is caused by the North American water mold Aphanomyces astaci. This water mold was transmitted to Europe when North American species of crayfish were introduced. Species of the genus Astacus are particularly susceptible to infection, allowing the plague-coevolved signal crayfish (native to western North America) to invade parts of Europe.
Acid rain can cause problems for crayfish across the world. In whole-ecosystem experiments simulating acid rain at the Experimental Lakes Area in Ontario, Canada, crayfish populations crashed – probably because their exoskeletons are weaker in acidified environments.
Invasive pest
In several countries, particularly in Europe, native species of crayfish are under threat by imported species, particularly the signal crayfish (Pacifastacus leniusculus). Crayfish are also considered an invasive predatory species, endangering native European species such as the Italian agile frog and the painted frog in Malta.
Uses
Culinary use | Crayfish | Wikipedia | 484 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
Crayfish are eaten worldwide. Like other edible crustaceans, only a small portion of the body of a crayfish is eaten. In most prepared dishes, such as soups, bisques and étouffées, only the tail portion is served. At crawfish boils or other meals where the entire body of the crayfish is presented, other portions, such as the claw meat, may be eaten.
Research shows that crayfish do not die immediately when boiled alive, and respond to pain in a similar way to mammals. Then the stress hormone cortisol is released and this leads to the formation of lactic acid in the muscles, which makes the meat taste sour. Crayfish can be cooked more humanely by first freezing them unconscious for a few hours, then destroying the central nervous system along their abdomen by cutting the crayfish lengthwise with a long knife down the center of the crayfish before cooking it.
Global crayfish production is centered in Asia, primarily China. In 2018, Asian production accounted for 95% of the world's crawfish supply.
Crayfish is part of Swedish cuisine and is usually eaten in August at special crayfish parties (). Documentation of the consumption of crayfish dates to at least the 16th century. On the Swedish west coast, Nephrops norvegicus (, ) is more commonly eaten while various freshwater crayfish are consumed in the rest of the country. Prior to the 1960s, crayfish was largely inaccessible to the urban population in Sweden and consumption was largely limited to the upper classes or farmers holding fishing rights in fresh water lakes. With the introduction of import of frozen crayfish the crayfish party is now widely practiced across all spheres in Sweden and among the Swedish-speaking population of Finland. | Crayfish | Wikipedia | 372 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
In the United States, crayfish production is strongly centered in Louisiana, with 93% of crayfish farms located in the state as of 2018. In 1987, Louisiana produced 90% of the crayfish harvested in the world, 70% of which were consumed locally. In 2007, the Louisiana crayfish harvest was about 54,800 tons, almost all of it from aquaculture. About 70–80% of crayfish produced in Louisiana are Procambarus clarkii (red swamp crawfish), with the remaining 20–30% being Procambarus zonangulus (white river crawfish). Optimum dietary nutritional requirement of freshwater crayfish, or crayfish nutrient specifications are now available for aquaculture feed producers
Like all crustaceans, crayfish are not kosher because they are aquatic animals that do not have both fins and scales. They are therefore not eaten by observant Jews.
Bait
Crayfish are preyed upon by a variety of ray-finned fishes, and are commonly used as bait, either live or with only the tail meat. They are a popular bait for catching catfish, largemouth bass, smallmouth bass, striped bass, perch, pike and muskie. When using live crayfish as bait, anglers prefer to hook them between the eyes, piercing through their hard, pointed beak which causes them no harm; therefore, they remain more active.
When using crayfish as bait, it is important to fish in the same environment where they were caught. An Illinois State University report that focused on studies conducted on the Fox River and Des Plaines River watershed stated that rusty crayfish, initially caught as bait in a different environment, were dumped into the water and "outcompeted the native clearwater crayfish". Other studies confirmed that transporting crayfish to different environments has led to various ecological problems, including the elimination of native species. Transporting crayfish as live bait has also contributed to the spread of zebra mussels in various waterways throughout Europe and North America, as they are known to attach themselves to exoskeleton of crayfishes.
Pets | Crayfish | Wikipedia | 444 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
Crayfish are kept as pets in freshwater aquariums. They prefer foods like shrimp pellets or various vegetables, but will also eat tropical fish food, regular fish food, algae wafers, and small fish that can be captured with their claws. A report by the National Park Service as well as video and anecdotal reports by aquarium owners indicate that crayfish will eat their moulted exoskeleton "to recover the calcium and phosphates contained in it." As omnivores, crayfish will eat almost anything; therefore, they may explore the edibility of aquarium plants in a fish tank. However, most species of dwarf crayfish, such as Cambarellus patzcuarensis, will not destructively dig or eat live aquarium plants.
In some nations, such as the United Kingdom, United States, Australia, and New Zealand, imported alien crayfish are a danger to local rivers. The three most widespread American species invasive in Europe are Faxonius limosus, Pacifastacus leniusculus and Procambarus clarkii. Crayfish may spread into different bodies of water because specimens captured for pets in one river are often released into a different catchment. There is a potential for ecological damage when crayfish are introduced into non-native bodies of water: e.g., crayfish plague in Europe, or the introduction of the common yabby (Cherax destructor) into drainages east of the Great Dividing Range in Australia.
Education
Some public schools in the United States keep live crayfish in the classroom and have the students take care of them in order to give the students a greater understanding of the creatures.
Sentinel species
The Protivin brewery in the Czech Republic uses crayfish outfitted with sensors to detect any changes in their bodies or pulse activity in order to monitor the purity of the water used in their product. The creatures are kept in a fish tank that is fed with the same local natural source water used in their brewing. If three or more of the crayfish have changes to their pulses, employees know there is a change in the water and examine the parameters.
Scientists also monitor crayfish in the wild in natural bodies of water to study the levels of pollutants there. | Crayfish | Wikipedia | 468 | 43600 | https://en.wikipedia.org/wiki/Crayfish | Biology and health sciences | Crustaceans | null |
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on 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 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 , 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 the small dwarf lanternshark (Etmopterus perryi), a deep sea species that is only in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately in length. They are found in all seas and are common to depths up to . They generally do not live in freshwater, although there are 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 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. | Shark | Wikipedia | 478 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Etymology
Until the 16th century, sharks were known to mariners as "sea dogs". This 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 , 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 is that it derives from the Yucatec Maya word (), 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 the word shark (referring to a sea fish) in a letter written by Thomas Beckington in 1442, which rules out a New World etymology.
Evolutionary history
Fossil record
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 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 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.
Taxonomy | Shark | Wikipedia | 510 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Sharks belong to 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 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 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 | Wikipedia | 358 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Carcharhiniformes: Commonly known as ground sharks, the order includes the blue, tiger, bull, grey reef, blacktip reef, Caribbean reef, blacktail reef, whitetip reef, and oceanic whitetip sharks (collectively called the requiem sharks) along with the houndsharks, catsharks, and hammerhead sharks. They are distinguished by an elongated snout and a nictitating membrane which protects the eyes during an attack.
Heterodontiformes: They are generally referred to as the bullhead or horn sharks.
Hexanchiformes: Examples from this group include the cow sharks and frilled sharks, which somewhat resembles a marine snake.
Lamniformes: They are commonly known as the mackerel sharks. They include the goblin shark, basking shark, megamouth shark, the thresher sharks, shortfin and longfin mako sharks, and great white shark. They are distinguished by their large jaws and ovoviviparous reproduction. The Lamniformes also include the extinct megalodon, Otodus megalodon.
Orectolobiformes: They are commonly referred to as the carpet sharks, including zebra sharks, nurse sharks, wobbegongs, and the whale shark.
Pristiophoriformes: These are the sawsharks, with an elongated, toothed snout that they use for slashing their prey.
Squaliformes: This group includes the dogfish sharks and roughsharks.
Squatiniformes: Also known as angel sharks, they are flattened sharks with a strong resemblance to stingrays and skates.
Echinorhiniformes: This group includes the prickly shark and bramble shark. Phylogenetic placement of this group has been ambiguous in scientific studies. They are sometimes given their own order, Echinorhiniformes.
Anatomy
Teeth
Shark teeth are embedded in the gums rather than directly affixed to 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 is observed in the cookiecutter shark. | Shark | Wikipedia | 493 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
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 the basking shark are small and non-functional.
Skeleton
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.
Jaw
The jaws of sharks, like those of rays and skates, are not attached to 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 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.
Fins
Fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling 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.
Dermal denticles | Shark | Wikipedia | 454 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
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
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 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 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 the thresher shark's usage of its powerful, elongated upper lobe to stun fish and squid.
Physiology | Shark | Wikipedia | 383 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Buoyancy
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 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.
Respiration
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 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 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 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 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. | Shark | Wikipedia | 501 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Thermoregulation
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 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 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.
Osmoregulation
In contrast to bony fish, with the exception of 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 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 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. | Shark | Wikipedia | 468 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Digestion
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 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 a long surface area, requiring food to circulate inside the short gut until fully digested, when remaining waste products pass into the cloaca.
Fluorescence
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.
Senses
Smell
Sharks have keen olfactory senses, located in the short duct (which is not fused, unlike bony fish) between 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 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 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.
Sight | Shark | Wikipedia | 421 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
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 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 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 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 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. | Shark | Wikipedia | 393 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Hearing
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 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 the inner ear has been lost.
Electroreception
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 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.
Lateral line
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, 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.
Life history
Shark lifespans vary by species. Most live 20 to 30 years. The spiny dogfish has one of 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 specimen was 392 ± 120 years old (i.e., at least 272 years old), making it the longest-lived vertebrate known. | Shark | Wikipedia | 475 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Reproduction
Unlike most bony fish, sharks are K-selected reproducers, meaning that they produce a small number of well-developed young as opposed to a large number of poorly developed young. Fecundity in sharks ranges from 2 to over 100 young per reproductive cycle. Sharks mature slowly relative to many other fish. For example, lemon sharks reach sexual maturity at around age 13–15.
Sexual
Sharks practice internal fertilization. The posterior part of a male shark's pelvic fins are modified into a pair of intromittent organs called claspers, analogous to a mammalian penis, of which one is used to deliver sperm into the female.
Mating has rarely been observed in sharks. The smaller catsharks often mate with the male curling around the female. In less flexible species the two sharks swim parallel to each other while the male inserts a clasper into the female's oviduct. Females in many of the larger species have bite marks that appear to be a result of a male grasping them to maintain position during mating. The bite marks may also come from courtship behavior: the male may bite the female to show his interest. In some species, females have evolved thicker skin to withstand these bites.
Asexual
There have been a number of documented cases in which a female shark who has not been in contact with a male has conceived a pup on her own through parthenogenesis. The details of this process are not well understood, but genetic fingerprinting showed that the pups had no paternal genetic contribution, ruling out sperm storage. The extent of this behavior in the wild is unknown. Mammals are now the only major vertebrate group in which asexual reproduction has not been observed.
Scientists say that asexual reproduction in the wild is rare, and probably a last-ditch effort to reproduce when a mate is not present. Asexual reproduction diminishes genetic diversity, which helps build defenses against threats to the species. Species that rely solely on it risk extinction. Asexual reproduction may have contributed to the blue shark's decline off the Irish coast.
Brooding
Sharks display three ways to bear their young, varying by species, oviparity, viviparity and ovoviviparity. | Shark | Wikipedia | 457 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Ovoviviparity
Most sharks are ovoviviparous, meaning that the eggs hatch in the oviduct within the mother's body and that the egg's yolk and fluids secreted by glands in the walls of the oviduct nourishes the embryos. The young continue to be nourished by the remnants of the yolk and the oviduct's fluids. As in viviparity, the young are born alive and fully functional. Lamniforme sharks practice oophagy, where the first embryos to hatch eat the remaining eggs. Taking this a step further, sand tiger shark pups cannibalistically consume neighboring embryos. The survival strategy for ovoviviparous species is to brood the young to a comparatively large size before birth. The whale shark is now classified as ovoviviparous rather than oviparous, because extrauterine eggs are now thought to have been aborted. Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs. They choose such areas for protection from predators (mainly other sharks) and the abundance of food. Dogfish have the longest known gestation period of any shark, at 18 to 24 months. Basking sharks and frilled sharks appear to have even longer gestation periods, but accurate data are lacking.
Oviparity
Some species are oviparous, laying their fertilized eggs in the water. In most oviparous shark species, an egg case with the consistency of leather protects the developing embryo(s). These cases may be corkscrewed into crevices for protection. The egg case is commonly called a mermaid's purse. Oviparous sharks include the horn shark, catshark, Port Jackson shark, and swellshark.
Viviparity
Viviparity is the gestation of young without the use of a traditional egg, and results in live birth. Viviparity in sharks can be placental or aplacental. Young are born fully formed and self-sufficient. Hammerheads, the requiem sharks (such as the bull and blue sharks), and smoothhounds are viviparous. | Shark | Wikipedia | 467 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Behavior
The classic view describes a solitary hunter, ranging the oceans in search of food. However, this applies to only a few species. Most live far more social, sedentary, benthic lives, and appear likely to have their own distinct personalities. Even solitary sharks meet for breeding or at rich hunting grounds, which may lead them to cover thousands of miles in a year. Shark migration patterns may be even more complex than in birds, with many sharks covering entire ocean basins.
Sharks can be highly social, remaining in large schools. Sometimes more than 100 scalloped hammerheads congregate around seamounts and islands, e.g., in the Gulf of California. Cross-species social hierarchies exist. For example, oceanic whitetip sharks dominate silky sharks of comparable size during feeding.
When approached too closely some sharks perform a threat display. This usually consists of exaggerated swimming movements, and can vary in intensity according to the threat level.
Speed
In general, sharks swim ("cruise") at an average speed of , but when feeding or attacking, the average shark can reach speeds upwards of . The shortfin mako shark, the fastest shark and one of the fastest fish, can burst at speeds up to . The great white shark is also capable of speed bursts. These exceptions may be due to the warm-blooded, or homeothermic, nature of these sharks' physiology. Sharks can travel 70 to 80 km in a day.
Intelligence
Sharks possess brain-to-body mass ratios that are similar to mammals and birds, and have exhibited apparent curiosity and behavior resembling play in the wild.
There is evidence that juvenile lemon sharks can use observational learning in their investigation of novel objects in their environment.
Sleep
All sharks need to keep water flowing over their gills in order for them to breathe; however, not all species need to be moving to do this. Those that are able to breathe while not swimming do so by using their spiracles to force water over their gills, thereby allowing them to extract oxygen from the water. It has been recorded that their eyes remain open while in this state and actively follow the movements of divers swimming around them and as such they are not truly asleep. | Shark | Wikipedia | 445 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Species that do need to swim continuously to breathe go through a process known as sleep swimming, in which the shark is essentially unconscious. It is known from experiments conducted on the spiny dogfish that its spinal cord, rather than its brain, coordinates swimming, so spiny dogfish can continue to swim while sleeping, and this also may be the case in larger shark species. In 2016 a great white shark was captured on video for the first time in a state researchers believed was sleep swimming.
Ecology
Feeding
Most sharks are carnivorous. Basking sharks, whale sharks, and megamouth sharks have independently evolved different strategies for filter feeding plankton: basking sharks practice ram feeding, whale sharks use suction to take in plankton and small fishes, and megamouth sharks make suction feeding more efficient by using the luminescent tissue inside of their mouths to attract prey in the deep ocean. This type of feeding requires gill rakers—long, slender filaments that form a very efficient sieve—analogous to the baleen plates of the great whales. The shark traps the plankton in these filaments and swallows from time to time in huge mouthfuls. Teeth in these species are comparatively small because they are not needed for feeding.
Other highly specialized feeders include cookiecutter sharks, which feed on flesh sliced out of other larger fish and marine mammals. Cookiecutter teeth are enormous compared to the animal's size. The lower teeth are particularly sharp. Although they have never been observed feeding, they are believed to latch onto their prey and use their thick lips to make a seal, twisting their bodies to rip off flesh.
Some seabed–dwelling species are highly effective ambush predators. Angel sharks and wobbegongs use camouflage to lie in wait and suck prey into their mouths. Many benthic sharks feed solely on crustaceans which they crush with their flat molariform teeth.
Other sharks feed on squid or fish, which they swallow whole. The viper dogfish has teeth it can point outwards to strike and capture prey that it then swallows intact. The great white and other large predators either swallow small prey whole or take huge bites out of large animals. Thresher sharks use their long tails to stun shoaling fishes, and sawsharks either stir prey from the seabed or slash at swimming prey with their tooth-studded rostra. | Shark | Wikipedia | 478 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
The bonnethead shark is the only known omnivorous species. Its main prey is crustaceans and mollusks, but it also eats a large amount of seagrass, and is able to digest and extract nutrients from about 50% of the seagrass it consume.
Many sharks, including the whitetip reef shark are cooperative feeders and hunt in packs to herd and capture elusive prey. These social sharks are often migratory, traveling huge distances around ocean basins in large schools. These migrations may be partly necessary to find new food sources.
Range and habitat
Sharks are found in all seas. They generally do not live in fresh water, with a few exceptions such as the bull shark and the river shark which can swim both in seawater and freshwater. Sharks are common down to depths of , and some live even deeper, but they are almost entirely absent below . The deepest confirmed report of a shark is a Portuguese dogfish at .
Relationship with humans
Attacks
In 2006 the International Shark Attack File (ISAF) undertook an investigation into 96 alleged shark attacks, confirming 62 of them as unprovoked attacks and 16 as provoked attacks. The average number of fatalities worldwide per year between 2001 and 2006 from unprovoked shark attacks is 4.3.
Contrary to popular belief, only a few sharks are dangerous to humans. Out of more than 470 species, only four have been involved in a significant number of fatal, unprovoked attacks on humans: the great white, oceanic whitetip, tiger, and bull sharks. These sharks are large, powerful predators, and may sometimes attack and kill people. Despite being responsible for attacks on humans they have all been filmed without using a protective cage.
The perception of sharks as dangerous animals has been popularized by publicity given to a few isolated unprovoked attacks, such as the Jersey Shore shark attacks of 1916, and through popular fictional works about shark attacks, such as the Jaws film series. Jaws author Peter Benchley, as well as Jaws director Steven Spielberg, later attempted to dispel the image of sharks as man-eating monsters.
To help avoid an unprovoked attack, humans should not wear jewelry or metal that is shiny and refrain from splashing around too much. | Shark | Wikipedia | 446 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
In general, sharks show little pattern of attacking humans specifically, part of the reason could be that sharks prefer the blood of fish and other common preys. Research indicates that when humans do become the object of a shark attack, it is possible that the shark has mistaken the human for species that are its normal prey, such as seals. This was further proven in a recent study conducted by researchers at the California State University's Shark Lab. According to footage caught by the Lab's drones, juveniles swam right up to humans in the water without any bites incidents. The lab stated that the results showed that humans and sharks can co-exist in the water.
In captivity
Until recently, only a few benthic species of shark, such as hornsharks, leopard sharks and catsharks, had survived in aquarium conditions for a year or more. This gave rise to the belief that sharks, as well as being difficult to capture and transport, were difficult to care for. More knowledge has led to more species (including the large pelagic sharks) living far longer in captivity, along with safer transportation techniques that have enabled long-distance transportation. The great white shark had never been successfully held in captivity for long periods of time until September 2004, when the Monterey Bay Aquarium successfully kept a young female for 198 days before releasing her.
Most species are not suitable for home aquaria, and not every species sold by pet stores are appropriate. Some species can flourish in home saltwater aquaria. Uninformed or unscrupulous dealers sometimes sell juvenile sharks like the nurse shark, which upon reaching adulthood is far too large for typical home aquaria. Public aquaria generally do not accept donated specimens that have outgrown their housing. Some owners have been tempted to release them. Species appropriate to home aquaria represent considerable spatial and financial investments as they generally approach adult lengths of and can live up to 25 years.
In culture | Shark | Wikipedia | 386 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
In Hawaii
Sharks figure prominently in Hawaiian mythology. Stories tell of men with shark jaws on their back who could change between shark and human form. A common theme was that a shark-man would warn beach-goers of sharks in the waters. The beach-goers would laugh and ignore the warnings and get eaten by the shark-man who warned them. Hawaiian mythology also includes many shark gods. Among a fishing people, the most popular of all aumakua, or deified ancestor guardians, are shark aumakua. Kamaku describes in detail how to offer a corpse to become a shark. The body transforms gradually until the kahuna can point the awe-struck family to the markings on the shark's body that correspond to the clothing in which the beloved's body had been wrapped. Such a shark aumakua becomes the family pet, receiving food, and driving fish into the family net and warding off danger. Like all aumakua it had evil uses such as helping kill enemies. The ruling chiefs typically forbade such sorcery. Many Native Hawaiian families claim such an aumakua, who is known by name to the whole community.
Kamohoali'i is the best known and revered of the shark gods, he was the older and favored brother of Pele, and helped and journeyed with her to Hawaii. He was able to assume all human and fish forms. A summit cliff on the crater of Kilauea is one of his most sacred spots. At one point he had a heiau (temple or shrine) dedicated to him on every piece of land that jutted into the ocean on the island of Molokai. Kamohoali'i was an ancestral god, not a human who became a shark and banned the eating of humans after eating one herself. In Fijian mythology, Dakuwaqa was a shark god who was the eater of lost souls. | Shark | Wikipedia | 394 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
In American Samoa
On the island of Tutuila in American Samoa (a U.S. territory), there is a location called Turtle and Shark (Laumei ma Malie) which is important in Samoan culture—the location is the site of a legend called O Le Tala I Le Laumei Ma Le Malie, in which two humans are said to have transformed into a turtle and a shark. According to the U.S. National Park Service, "Villagers from nearby Vaitogi continue to reenact an important aspect of the legend at Turtle and Shark by performing a ritual song intended to summon the legendary animals to the ocean surface, and visitors are frequently amazed to see one or both of these creatures emerge from the sea in apparent response to this call."
In popular culture
In contrast to the complex portrayals by Hawaiians and other Pacific Islanders, the European and Western view of sharks has historically been mostly of fear and malevolence. Sharks are used in popular culture commonly as eating machines, notably in the Jaws novel and the film of the same name, along with its sequels. Sharks are threats in other films such as Deep Blue Sea, The Reef, and others, although they are sometimes used for comedic effect such as in Finding Nemo and the Austin Powers series. Sharks tend to be seen quite often in cartoons whenever a scene involves the ocean. Such examples include the Tom and Jerry cartoons, Jabberjaw, and other shows produced by Hanna-Barbera. They also are used commonly as a clichéd means of killing off a character that is held up by a rope or some similar object as the sharks swim right below them, or the character may be standing on a plank above shark infested waters.
Popular misconceptions
A popular myth is that sharks are immune to disease and cancer, but this is not scientifically supported. Sharks have been known to get cancer. Both diseases and parasites affect sharks. The evidence that sharks are at least resistant to cancer and disease is mostly anecdotal and there have been few, if any, scientific or statistical studies that show sharks to have heightened immunity to disease.
Other apparently false claims are that fins prevent cancer and treat osteoarthritis. No scientific proof supports these claims; at least one study has shown shark cartilage of no value in cancer treatment.
Threats to sharks | Shark | Wikipedia | 478 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Fishery
In 2008, it was estimated that nearly 100 million sharks were being killed by people every year, due to commercial and recreational fishing. In 2021, it was estimated that the population of oceanic sharks and rays had dropped by 71% over the previous half-century.
Shark finning yields are estimated at for 2000, and for 2010. Based on an analysis of average shark weights, this translates into a total annual mortality estimate of about 100 million sharks in 2000, and about 97 million sharks in 2010, with a total range of possible values between 63 and 273 million sharks per year. Sharks are a common seafood in many places, including Japan and Australia. In southern Australia, shark is commonly used in fish and chips, in which fillets are battered and deep-fried or crumbed and grilled. In fish and chip shops, shark is called flake. In India, small sharks or baby sharks (called sora in Tamil language, Telugu language) are sold in local markets. Since the flesh is not developed, cooking the flesh breaks it into powder, which is then fried in oil and spices (called sora puttu/sora poratu). The soft bones can be easily chewed, they are considered a delicacy in coastal Tamil Nadu. Icelanders ferment Greenland sharks to produce a delicacy called hákarl. During a four-year period from 1996 to 2000, an estimated 26 to 73 million sharks were killed and traded annually in commercial markets.
Sharks are often killed for shark fin soup. Fishermen capture live sharks, fin them, and dump the finless animal back into the water. Shark finning involves removing the fin with a hot metal blade. The resulting immobile shark soon dies from suffocation or predators. Shark fin has become a major trade within black markets all over the world. Fins sell for about $300/lb in 2009. Poachers illegally fin millions each year. Few governments enforce laws that protect them. In 2010 Hawaii became the first U.S. state to prohibit the possession, sale, trade or distribution of shark fins. From 1996 to 2000, an estimated 38 million sharks had been killed per year for harvesting shark fins. It is estimated by TRAFFIC that over 14,000 tonnes of shark fins were exported into Singapore between 2005–2007 and 2012–2014. | Shark | Wikipedia | 470 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
Shark fin soup is a status symbol in Asian countries and is erroneously considered healthy and full of nutrients. Scientific research has revealed, however, that high concentrations of BMAA are present in shark fins. Because BMAA is a neurotoxin, consumption of shark fin soup and cartilage pills, therefore, may pose a health risk. BMAA is under study for its pathological role in neurodegenerative diseases such as ALS, Alzheimer's disease, and Parkinson's disease.
Sharks are also killed for meat. European diners consume dogfishes, smoothhounds, catsharks, makos, porbeagle and also skates and rays. However, the U.S. FDA lists sharks as one of four fish (with swordfish, king mackerel, and tilefish) whose high mercury content is hazardous to children and pregnant women.
Sharks generally reach sexual maturity only after many years and produce few offspring in comparison to other harvested fish. Harvesting sharks before they reproduce severely impacts future populations. Capture induced premature birth and abortion (collectively called capture-induced parturition) occurs frequently in sharks/rays when fished. Capture-induced parturition is rarely considered in fisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).
The majority of shark fisheries have little monitoring or management. The rise in demand for shark products increases pressure on fisheries. Major declines in shark stocks have been recorded—some species have been depleted by over 90% over the past 20–30 years with population declines of 70% not unusual. A study by the International Union for Conservation of Nature suggests that one quarter of all known species of sharks and rays are threatened by extinction and 25 species were classified as critically endangered.
Shark culling
In 2014, a shark cull in Western Australia killed dozens of sharks (mostly tiger sharks) using drum lines, until it was cancelled after public protests and a decision by the Western Australia EPA; from 2014 to 2017, there was an "imminent threat" policy in Western Australia in which sharks that "threatened" humans in the ocean were shot and killed. This "imminent threat" policy was criticized by senator Rachel Siewart for killing endangered sharks. The "imminent threat" policy was cancelled in March 2017. In August 2018, the Western Australia government announced a plan to re-introduce drum lines (though, this time the drum lines are "SMART" drum lines). | Shark | Wikipedia | 501 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
From 1962 to the present, the government of Queensland has targeted and killed sharks in large numbers by using drum lines, under a "shark control" program—this program has also inadvertently killed large numbers of other animals such as dolphins; it has also killed endangered hammerhead sharks. Queensland's drum line program has been called "outdated, cruel and ineffective". From 2001 to 2018, a total of 10,480 sharks were killed on lethal drum lines in Queensland, including in the Great Barrier Reef. From 1962 to 2018, roughly 50,000 sharks were killed by Queensland authorities.
The government of New South Wales has a program that deliberately kills sharks using nets. The current net program in New South Wales has been described as being "extremely destructive" to marine life, including sharks. Between 1950 and 2008, 352 tiger sharks and 577 great white sharks were killed in the nets in New South Wales—also during this period, a total of 15,135 marine animals were killed in the nets, including dolphins, whales, turtles, dugongs, and critically endangered grey nurse sharks. There has been a very large decrease in the number of sharks in eastern Australia, and the shark-killing programs in Queensland and New South Wales are partly responsible for this decrease.
Kwazulu-Natal, an area of South Africa, has a shark-killing program using nets and drum lines—these nets and drum lines have killed turtles and dolphins, and have been criticized for killing wildlife. During a 30-year period, more than 33,000 sharks have been killed in KwaZulu-Natal's shark-killing program—during the same 30-year period, 2,211 turtles, 8,448 rays, and 2,310 dolphins were killed in KwaZulu-Natal. Authorities on the French island of Réunion kill about 100 sharks per year.
Killing sharks negatively affects the marine ecosystem. Jessica Morris of Humane Society International calls shark culling a "knee-jerk reaction" and says, "sharks are top order predators that play an important role in the functioning of marine ecosystems. We need them for healthy oceans." | Shark | Wikipedia | 425 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
George H. Burgess, the former director of the International Shark Attack File, "describes [shark] culling as a form of revenge, satisfying a public demand for blood and little else"; he also said shark culling is a "retro-type move reminiscent of what people would have done in the 1940s and 50s, back when we didn't have an ecological conscience and before we knew the consequences of our actions." Jane Williamson, an associate professor in marine ecology at Macquarie University, says "There is no scientific support for the concept that culling sharks in a particular area will lead to a decrease in shark attacks and increase ocean safety."
Other threats
Other threats include habitat alteration, damage and loss from coastal development, pollution and the impact of fisheries on the seabed and prey species. The 2007 documentary Sharkwater exposed how sharks are being hunted to extinction.
Conservation
In 1991, South Africa was the first country in the world to declare Great White sharks a legally protected species (however, the KwaZulu-Natal Sharks Board is allowed to kill great white sharks in its "shark control" program in eastern South Africa).
Intending to ban the practice of shark finning while at sea, the United States Congress passed the Shark Finning Prohibition Act in 2000. Two years later the Act saw its first legal challenge in United States v. Approximately 64,695 Pounds of Shark Fins. In 2008 a Federal Appeals Court ruled that a loophole in the law allowed non-fishing vessels to purchase shark fins from fishing vessels while on the high seas. Seeking to close the loophole, the Shark Conservation Act was passed by Congress in December 2010, and it was signed into law in January 2011.
In 2003, the European Union introduced a general shark finning ban for all vessels of all nationalities in Union waters and for all vessels flying a flag of one of its member states. This prohibition was amended in June 2013 to close remaining loopholes.
In 2009, the International Union for Conservation of Nature's IUCN Red List of Endangered Species named 64 species, one-third of all oceanic shark species, as being at risk of extinction due to fishing and shark finning. | Shark | Wikipedia | 435 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
In 2010, the Convention on International Trade in Endangered Species (CITES) rejected proposals from the United States and Palau that would have required countries to strictly regulate trade in several species of scalloped hammerhead, oceanic whitetip and spiny dogfish sharks. The majority, but not the required two-thirds of voting delegates, approved the proposal. China, by far the world's largest shark market, and Japan, which battles all attempts to extend the convention to marine species, led the opposition. In March 2013, three endangered commercially valuable sharks, the hammerheads, the oceanic whitetip and porbeagle were added to Appendix 2 of CITES, bringing shark fishing and commerce of these species under licensing and regulation.
In 2010, Greenpeace International added the school shark, shortfin mako shark, mackerel shark, tiger shark and spiny dogfish to its seafood red list, a list of common supermarket fish that are often sourced from unsustainable fisheries. Advocacy group Shark Trust campaigns to limit shark fishing. Advocacy group Seafood Watch directs American consumers to not eat sharks.
Under the auspices of the Convention on the Conservation of Migratory Species of Wild Animals (CMS), also known as the Bonn Convention, the Memorandum of Understanding on the Conservation of Migratory Sharks was concluded and came into effect in March 2010. It was the first global instrument concluded under CMS and aims at facilitating international coordination for the protection, conservation and management of migratory sharks, through multilateral, intergovernmental discussion and scientific research.
In July 2013, New York state, a major market and entry point for shark fins, banned the shark fin trade joining seven other states of the United States and the three Pacific U.S. territories in providing legal protection to sharks.
In the United States, and as of January 16, 2019, 12 states including (Massachusetts, Maryland, Delaware, California, Illinois, Hawaii, Oregon, Nevada, Rhode Island, Washington, New York and Texas) along with 3 U.S. territories (American Samoa, Guam and the Northern Mariana Islands) have passed laws against the sale or possession of shark fins.
Several regions now have shark sanctuaries or have banned shark fishing—these regions include American Samoa, the Bahamas, the Cook Islands, French Polynesia, Guam, the Maldives, the Marshall Islands, Micronesia, the Northern Mariana Islands, and Palau. | Shark | Wikipedia | 480 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
In April 2020 researchers reported to have traced the origins of shark fins of endangered hammerhead sharks from a retail market in Hong Kong back to their source populations and therefore the approximate locations where the sharks were first caught using DNA analysis.
In July 2020 scientists reported results of a survey of 371 reefs in 58 nations estimating the conservation status of reef sharks globally. No sharks have been observed on almost 20% of the surveyed reefs and shark depletion was strongly associated with both socio-economic conditions and conservation measures. Sharks are considered to be a vital part of the ocean ecosystem.
According to a 2021 study in Nature, overfishing has resulted in a 71% global decline in the number of oceanic sharks and rays over the preceding 50 years. The oceanic whitetip, and both the scalloped hammerhead and great hammerheads are now classified as critically endangered. Sharks in tropical waters have declined more rapidly than those in temperate zones during the period studied. A 2021 study published in Current Biology found that overfishing is currently driving over one-third of sharks and rays to extinction. | Shark | Wikipedia | 216 | 43617 | https://en.wikipedia.org/wiki/Shark | Biology and health sciences | Sharks | null |
The great white shark (Carcharodon carcharias), also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark which can be found in the coastal surface waters of all the major oceans. It is the only known surviving species of its genus Carcharodon. The great white shark is notable for its size, with the largest preserved female specimen measuring in length and around in weight at maturity. However, most are smaller; males measure , and females measure on average. According to a 2014 study, the lifespan of great white sharks is estimated to be as long as 70 years or more, well above previous estimates, making it one of the longest lived cartilaginous fishes currently known. According to the same study, male great white sharks take 26 years to reach sexual maturity, while the females take 33 years to be ready to produce offspring. Great white sharks can swim at speeds of 25 km/h (16 mph) for short bursts and to depths of .
The great white shark is arguably the world's largest-known extant macropredatory fish, and is one of the primary predators of marine mammals, such as pinnipeds and dolphins. The great white shark is also known to prey upon a variety of other animals, including fish, other sharks, and seabirds. It has only one recorded natural predator, the orca.
The species faces numerous ecological challenges which has resulted in international protection. The International Union for Conservation of Nature lists the great white shark as a vulnerable species, and it is included in Appendix II of CITES. It is also protected by several national governments, such as Australia (as of 2018). Due to their need to travel long distances for seasonal migration and extremely demanding diet, it is not logistically feasible to keep great white sharks in captivity; because of this, while attempts have been made to do so in the past, there are no known aquariums in the world believed to house a live specimen.
The great white shark is depicted in popular culture as a ferocious man-eater, largely as a result of the novel Jaws by Peter Benchley and its subsequent film adaptation by Steven Spielberg. Humans are not a preferred prey, but nevertheless it is responsible for the largest number of reported and identified fatal unprovoked shark attacks on humans. However, attacks are rare, typically occurring fewer than 10 times per year globally. | Great white shark | Wikipedia | 490 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Taxonomy
The great white is the sole recognized extant species in the genus Carcharodon, and is one of five extant species belonging to the family Lamnidae. Other members of this family include the mako sharks, porbeagle, and salmon shark. The family belongs to the Lamniformes, the order of mackerel sharks.
Etymology and naming history
The English name 'white shark' and its Australian variant 'white pointer' is thought to have come from the shark's stark white underside, a characteristic feature most noticeable in beached sharks lying upside down with their bellies exposed. Colloquial use favours the name 'great white shark', with 'great' perhaps stressing the size and prowess of the species, and "white shark" having historically been used to describe the much smaller oceanic white-tipped shark, later referred to for a time as the "lesser white shark". Most scientists prefer 'white shark', as the name "lesser white shark" is no longer used, while some use 'white shark' to refer to all members of the Lamnidae.
The scientific genus name Carcharodon literally means "jagged tooth", a reference to the large serrations that appear in the shark's teeth. It is a portmanteau of two Ancient Greek words: the prefix carchar- is derived from κάρχαρος (kárkharos), which means "jagged" or "sharp". The suffix -odon is a romanization of ὀδών (odṓn), a which translates to "tooth". The specific name carcharias is a Latinization of καρχαρίας (karkharías), the Ancient Greek word for shark.
The great white shark was one of the species originally described by Carl Linnaeus in his 1758 10th edition of Systema Naturae, in which it was identified as an amphibian and assigned the scientific name Squalus carcharias, Squalus being the genus that he placed all sharks in. By the 1810s, it was recognized that the shark should be placed in a new genus, but it was not until 1838 when Sir Andrew Smith coined the name Carcharodon as the new genus. | Great white shark | Wikipedia | 464 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
There have been a few attempts to describe and classify the great white before Linnaeus. One of its earliest mentions in literature as a distinct type of animal appears in Pierre Belon's 1553 book De aquatilibus duo, cum eiconibus ad vivam ipsorum effigiem quoad ejus fieri potuit, ad amplissimum cardinalem Castilioneum. In it, he illustrated and described the shark under the name Canis carcharias based on the jagged nature of its teeth and its alleged similarities with dogs. Another name used for the great white around this time was Lamia, first coined by Guillaume Rondelet in his 1554 book Libri de Piscibus Marinis, who also identified it as the fish that swallowed the prophet Jonah in biblical texts. Linnaeus recognized both names as previous classifications.
Fossil ancestry
Molecular clock studies published between 1988 and 2002 determined the closest living relative of the great white to be the mako sharks of the genus Isurus, which diverged some time between 60 and 43 million years ago. Tracing this evolutionary relationship through fossil evidence, however, remains subject to further paleontological study.
The original hypothesis of the great white shark's origin held that it is a descendant of a lineage of mega-toothed sharks, and is closely related to the prehistoric megalodon. These sharks were considerably larger in size, with megalodon attaining an estimated length of up to . Similarities between the teeth of great white and mega-toothed sharks, such as large triangular shapes, serrated blades, and the presence of dental bands, led the primary evidence of a close evolutionary relationship. As a result, scientists classified the ancient forms under the genus Carcharodon. Although weaknesses in the hypothesis existed, such as uncertainty over exactly which species evolved into the modern great white and multiple gaps in the fossil record, palaeontologists were able to chart the hypothetical lineage back to a 60-million-year-old shark known as Cretalamna as the common ancestor of all sharks within the Lamnidae. | Great white shark | Wikipedia | 423 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
However, it is now understood that the great white shark holds closer ties to the mako sharks and is descended from a separate lineage as a chronospecies unrelated to the mega-toothed sharks. This was proven with the discovery of a transitional species that connected the great white to an unserrated shark known as Carcharodon hastalis. This transitional species, which was named Carcharodon hubbelli in 2012, demonstrated a mosaic of evolutionary transitions between the great white and C. hastalis, namely the gradual appearance of serrations, in a span of between 8 and 5 million years ago. The progression of C. hubbelli characterized shifting diets and niches; by 6.5 million years ago, the serrations were developed enough for C. hubbelli to handle marine mammals. Although both the great white and C. hastalis were known worldwide, C. hubbelli is primarily found in California, Peru, Chile, and surrounding coastal deposits, indicating that the great white had Pacific origins. C. hastalis continued to thrive alongside the great white until its last appearance around one million years ago and is believed to have possibly sired a number of additional species, including Carcharodon subserratus and Carcharodon plicatilis.
However, Yun argued that the tooth fossil remains of C. hastalis and Great White Shark "have been documented from the same deposits, hence the former cannot be a chronospecific ancestor of the latter." He also criticized that the C. hastalis "morphotype has never been tested through phylogenetic analyses," and denoted that as of 2021, the argument that the modern Carcharodon lineage with narrow, serrated teeth evolved from C. hastalis with a broad, unserrated teeth is uncertain.
Tracing beyond C. hastalis, another prevailing hypothesis proposes that the great white and mako lineages shared a common ancestor in a primitive mako-like species. The identity of this ancestor is still debated, but a potential species includes Isurolamna inflata, which lived between 65 and 55 million years ago. It is hypothesized that the great white and mako lineages split with the rise of two separate descendants, the one representing the great white shark lineage being Macrorhizodus praecursor.
Distribution and habitat | Great white shark | Wikipedia | 490 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Great white sharks live in almost all coastal and offshore waters which have water temperature between , with greater concentrations in the United States (Northeast and California), South Africa, Japan, Oceania, Chile, and the Mediterranean including the Sea of Marmara and Bosphorus. One of the densest-known populations is found around Dyer Island, South Africa. Juvenile great white sharks inhabit a more narrow band of temperatures, between , in shallow coastal nurseries. Increased observation of young sharks in areas they were not previously common, such as Monterey Bay on the Central California coast, suggest climate change may be reducing the range of juvenile great white sharks and shifting it toward the poles.
The great white is an epipelagic fish, observed mostly in the presence of rich game, such as fur seals (Arctocephalus ssp.), sea lions, cetaceans, other sharks, and large bony fish species. In the open ocean, it has been recorded at depths as great as . These findings challenge the traditional notion that the great white is a coastal species.
According to a recent study, California great whites have migrated to an area between Baja California Peninsula and Hawaii known as the White Shark Café to spend at least 100 days before migrating back to Baja. On the journey out, they swim slowly and dive down to around . After they arrive, they change behaviour and do short dives to about for up to ten minutes. Another white shark that was tagged off the South African coast swam to the southern coast of Australia and back within the year. A similar study tracked a different great white shark from South Africa swimming to Australia's northwestern coast and back, a journey of in under nine months.
These observations argue against traditional theories that white sharks are coastal territorial predators, and open up the possibility of interaction between shark populations that were previously thought to have been discrete. The reasons for their migration and what they do at their destination is still unknown. Possibilities include seasonal feeding or mating. | Great white shark | Wikipedia | 398 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
In the Northwest Atlantic, the white shark populations off the New England coast were nearly eradicated due to over-fishing. In recent years, the populations have grown greatly, largely due to the increase in seal populations on Cape Cod, Massachusetts since the enactment of the Marine Mammal Protection Act in 1972. Currently very little is known about the hunting and movement patterns of great whites off Cape Cod, but ongoing studies hope to offer insight into this growing shark population. The Massachusetts Division of Marine Fisheries (part of the Department of Fish and Game) began a population study in 2014; since 2019, this research has focused on how humans can avoid conflict with sharks. Scientists believe all North Atlantic great white sharks spend their first year of life near New York City, off the coast of Long Island.
A 2018 study indicated that white sharks prefer to congregate deep in anticyclonic eddies in the North Atlantic Ocean. The sharks studied tended to favour the warm-water eddies, spending the daytime hours at depths of and coming to the surface at night.
Anatomy and appearance
The great white shark has a robust, large, conical snout. The upper and lower lobes on the tail fin are approximately the same size which is similar to some mackerel sharks. A great white displays countershading, by having a white underside and a grey dorsal area (sometimes in a brown or blue shade) that gives an overall mottled appearance. The coloration makes it difficult for prey to spot the shark because it breaks up the shark's outline when seen from the side. From above, the darker shade blends with the sea and from below it exposes a minimal silhouette against the sunlight.
Leucism is extremely rare in this species, but has been documented at least three times; in a pup that washed ashore in Australia and died, in another pup in South Africa, and a third six-metre adult male in Indonesia. Great white sharks, like many other sharks, have rows of serrated teeth behind the main ones, ready to replace any that break off. When the shark bites, it shakes its head side-to-side, helping the teeth saw off large chunks of flesh. Great white sharks, like other mackerel sharks, have larger eyes than other shark species in proportion to their body size. The iris of the eye is a deep blue instead of black.
Size | Great white shark | Wikipedia | 475 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
In great white sharks, sexual dimorphism is present, and females are generally larger than males. Male great whites on average measure in length, while females measure . Adults of this species weigh on average; however, mature females can have an average mass of . The largest females have been verified up to in length and an estimated in weight, perhaps up to . The maximum size is subject to debate because some reports are rough estimations or speculations performed under questionable circumstances. Among living cartilaginous fish, only the whale shark (Rhincodon typus), the basking shark (Cetorhinus maximus) and the giant manta ray (Manta birostris), in that order, are on average larger and heavier. These three species are generally quite docile in disposition and given to passively filter-feeding on very small organisms. This makes the great white shark the largest extant macropredatory fish. Great white sharks measure approximately when born, and grow about every year.
A complete female great white shark specimen in the Museum of Zoology in Lausanne, and claimed by De Maddalena et al. (2003) as the largest preserved specimen, measured in total body length with the caudal fin in its depressed position, and is estimated to have weighed . According to J. E. Randall, the largest white shark reliably measured was a specimen reported from Ledge Point, Western Australia in 1987, but it is unclear whether that length was measured with the caudal fin in its depressed or natural position. Another great white specimen of similar size was a female caught in August 1988 in the Gulf of St. Lawrence, off Prince Edward Island, by David McKendrick of Alberton, Prince Edward Island. This female great white was long, as verified by the Canadian Shark Research Center.
A report of a specimen reportedly measuring in length and with a body mass estimated at caught in 1945 off the coast of Cuba was at the time considered reliable by some experts. However, later studies revealed this particular specimen to be around in length, i.e. a specimen within the typical maximum size range.
The largest great white recognized by the International Game Fish Association (IGFA) is one caught by Alf Dean in southern Australian waters in 1959, weighing . | Great white shark | Wikipedia | 461 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Examples of large unconfirmed great whites
A number of very large unconfirmed great white shark specimens have been recorded. For decades, many ichthyological works, as well as the Guinness Book of World Records, listed two great white sharks as the largest individuals: In the 1870s, a great white captured in southern Australian waters, near Port Fairy, and an shark trapped in a herring weir in New Brunswick, Canada, in the 1930s. However, these measurements were not obtained in a rigorous, scientifically valid manner, and researchers have questioned the reliability of these measurements for a long time, noting they were much larger than any other accurately reported sighting. Later studies proved these doubts to be well-founded. This New Brunswick shark may have been a misidentified basking shark, as the two have similar body shapes. The question of the Port Fairy shark was settled in the 1970s when J. E. Randall examined the shark's jaws and "found that the Port Fairy shark was of the order of in length and suggested that a mistake had been made in the original record, in 1870, of the shark's length". | Great white shark | Wikipedia | 228 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
While these measurements have not been confirmed, some great white sharks caught in modern times have been estimated to be more than long, but these claims have received some criticism. However, J. E. Randall believed that great white shark may have exceeded in length. A great white shark was captured near Kangaroo Island in Australia on 1 April 1987. This shark was estimated to be more than long by Peter Resiley, and has been designated as KANGA. Another great white shark was caught in Malta by Alfredo Cutajar on 16 April 1987. This shark was also estimated to be around long by John Abela and has been designated as MALTA. However, Cappo drew criticism because he used shark size estimation methods proposed by J. E. Randall to suggest that the KANGA specimen was long. In a similar fashion, I. K. Fergusson also used shark size estimation methods proposed by J. E. Randall to suggest that the MALTA specimen was long. However, photographic evidence suggested that these specimens were larger than the size estimations yielded through Randall's methods. Thus, a team of scientists—H. F. Mollet, G. M. Cailliet, A. P. Klimley, D. A. Ebert, A. D. Testi, and L. J. V. Compagno—reviewed the cases of the KANGA and MALTA specimens in 1996 to resolve the dispute by conducting a comprehensive morphometric analysis of the remains of these sharks and re-examination of photographic evidence in an attempt to validate the original size estimations and their findings were consistent with them. The findings indicated that estimations by P. Resiley and J. Abela are reasonable and could not be ruled out. A particularly large female great white nicknamed "Deep Blue", estimated measuring at was filmed off Guadalupe during shooting for the 2014 episode of Shark Week "Jaws Strikes Back". Deep Blue would also later gain significant attention when she was filmed interacting with researcher Mauricio Hoyas Pallida in a viral video that Mauricio posted on Facebook on 11 June 2015. Deep Blue was later seen off Oahu in January 2019 while scavenging a sperm whale carcass, whereupon she was filmed swimming beside divers including dive tourism operator and model Ocean Ramsey in open water. A particularly infamous great white shark, supposedly of record proportions, once patrolled the area that comprises False Bay, South Africa, was said to be well over during the early 1980s | Great white shark | Wikipedia | 498 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
This shark, known locally as the "Submarine", had a legendary reputation that was supposedly well-founded. Though rumours have stated this shark was exaggerated in size or non-existent altogether, witness accounts by the then young Craig Anthony Ferreira, a notable shark expert in South Africa, and his father indicate an unusually large animal of considerable size and power (though it remains uncertain just how massive the shark was as it escaped capture each time it was hooked). Ferreira describes the four encounters with the giant shark he participated in with great detail in his book Great White Sharks On Their Best Behavior | Great white shark | Wikipedia | 116 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
One contender in maximum size among the predatory sharks is the tiger shark (Galeocerdo cuvier). While tiger sharks, which are typically both a few feet smaller and have a leaner, less heavy body structure than white sharks, have been confirmed to reach at least in the length, an unverified specimen was reported to have measured in length and weighed , more than two times heavier than the largest confirmed specimen at . Some other macropredatory sharks such as the Greenland shark (Somniosus microcephalus) and the Pacific sleeper shark (S. pacificus) are also reported to rival these sharks in length (but probably weigh a bit less since they are more slender in build than a great white) in exceptional cases.
Reported sizes
Adaptations
Great white sharks, like all other sharks, have an extra sense given by the ampullae of Lorenzini which enables them to detect the electromagnetic field emitted by the movement of living animals. Great whites are so sensitive they can detect variations of half a billionth of a volt. At close range, this allows the shark to locate even immobile animals by detecting their heartbeat. Most fish have a less-developed but similar sense using their body's lateral line. | Great white shark | Wikipedia | 249 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
To more successfully hunt fast and agile prey such as sea lions, the great white has adapted to maintain a body temperature warmer than the surrounding water. One of these adaptations is a "rete mirabile" (Latin for "wonderful net"). This close web-like structure of veins and arteries, located along each lateral side of the shark, conserves heat by warming the cooler arterial blood with the venous blood that has been warmed by the working muscles. This keeps certain parts of the body (particularly the stomach) at temperatures up to above that of the surrounding water, while the heart and gills remain at sea temperature. When conserving energy, the core body temperature can drop to match the surroundings. A great white shark's success in raising its core temperature is an example of gigantothermy. Therefore, the great white shark can be considered an endothermic poikilotherm or mesotherm because its body temperature is not constant but is internally regulated. Great whites also rely on the fat and oils stored within their livers for long-distance migrations across nutrient-poor areas of the oceans. Studies by Stanford University and the Monterey Bay Aquarium published on 17 July 2013 revealed that in addition to controlling the sharks' buoyancy, the liver of great whites is essential in migration patterns. Sharks that sink faster during drift dives were revealed to use up their internal stores of energy quicker than those which sink in a dive at more leisurely rates.
Toxicity from heavy metals seems to have little negative effects on great white sharks. Blood samples taken from forty-three individuals of varying size, age and sex off the South African coast led by biologists from the University of Miami in 2012 indicates that despite high levels of mercury, lead, and arsenic, there was no sign of raised white blood cell count and granulate to lymphocyte ratios, indicating the sharks had healthy immune systems. This discovery suggests a previously unknown physiological defence against heavy metal poisoning. Great whites are known to have a propensity for "self-healing and avoiding age-related ailments". | Great white shark | Wikipedia | 426 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Bite force
A 2007 study from the University of New South Wales in Sydney, Australia, used CT scans of a shark's skull and computer models to measure the shark's maximum bite force. The study reveals the forces and behaviours its skull is adapted to handle and resolves competing theories about its feeding behaviour. In 2008, a team of scientists led by Stephen Wroe conducted an experiment to determine the great white shark's jaw power and findings indicated that a specimen massing could exert a bite force of .
Ecology and behaviour
This shark's behaviour and social structure are complex. In South Africa, white sharks have a dominance hierarchy where an individual's rank is primarily established by their size, and to a lesser extent, their sex and "squatter's rights"; larger sharks dominate smaller sharks, females dominate males, and established residents dominate newcomers. When hunting, great whites tend to separate and resolve conflicts with rituals and displays. White sharks rarely resort to combat, although some individuals have been found with bite marks that match those of other white sharks. This suggests that when a great white approaches too closely to another, they react with a warning bite. Another possibility is that white sharks bite to show their dominance. Data acquired from animal-borne telemetry receivers and published in 2022 via the journal Royal Society Publishing suggests that individual great whites may associate so that they can inadvertently share information on the whereabouts of prey or the location of the remains of animals that can be scavenged. As biologging can help to reveal social habits, it allows a better understanding to be made in future studies regarding the full extent of social interactions in large marine animals, including the great white shark. | Great white shark | Wikipedia | 341 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
The great white shark is one of only a few sharks known to regularly lift its head above the sea surface to gaze at other objects such as prey. This is known as spy-hopping. This behaviour has also been seen in at least one group of blacktip reef sharks, but this might be learned from interaction with humans (it is theorized that the shark may also be able to smell better this way because smell travels through air faster than through water). White sharks are generally very curious animals, display intelligence and may also turn to socializing if the situation demands it. At Seal Island, white sharks have been observed arriving and departing in stable "clans" of two to six individuals on a yearly basis. Whether clan members are related is unknown, but they get along peacefully enough. In fact, the social structure of a clan is probably most aptly compared to that of a wolf pack, in that each member has a clearly established rank and each clan has an alpha leader. When members of different clans meet, they establish social rank nonviolently through any of a variety of interactions. In 2022, research in South Africa suggested that the great white shark has the ability to change colours to camouflage itself depending on the hormones it gives off. Different hormones would change the colour of the skin from white to grey. Skin dosed with adrenaline would turn lighter, with melanocyte-stimulating hormone causing melanocyte cells to dissipate thus making the shark's skin a darker colour, although hormone mediated color change is not fully validated due to the limited number of test subjects (i.e. great whites). The camo shark hypothesis is supported by the fact that zebra sharks can change their colour as they age, and rainbow sharks can lose colour due to stress and ageing.
Diet | Great white shark | Wikipedia | 364 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Great white sharks are generalist carnivores, preying upon fish (e.g. tuna, rays, other sharks), cetaceans (i.e., dolphins, porpoises, whales), pinnipeds (e.g. seals, fur seals, and sea lions), squid, sea turtles, sea otters (Enhydra lutris) and seabirds. Great whites have also been known to eat objects that they are unable to digest. Juvenile white sharks predominantly prey on fish, including other elasmobranchs, as their jaws are not strong enough to withstand the forces required to attack larger prey such as pinnipeds and cetaceans until they reach a length of or more, at which point their jaw cartilage mineralizes enough to withstand the impact of biting into larger prey species. Upon approaching a length of nearly , great white sharks begin to target predominantly marine mammals for food, though individual sharks seem to specialize in different types of prey depending on their preferences. They seem to be highly opportunistic. These sharks prefer prey with a high content of energy-rich fat. Shark expert Peter Klimley used a rod-and-reel rig and trolled carcasses of a seal, a pig, and a sheep from his boat in the South Farallons. The sharks attacked all three baits but rejected the sheep carcass.
Off Seal Island, False Bay in South Africa, the sharks ambush brown fur seals (Arctocephalus pusillus) from below at high speeds, hitting the seal mid-body. They achieve high speeds that allow them to completely breach the surface of the water. The peak burst speed is estimated to be above . They have also been observed chasing prey after a missed attack. Prey is usually attacked at the surface. Shark attacks occur most often in the morning, within two hours of sunrise, when visibility is poor. Their success rate is 55% in the first two hours, falling to 40% in late morning after which hunting stops. | Great white shark | Wikipedia | 421 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Off California, sharks use different predation techniques depending on the prey species. They immobilize northern elephant seals (Mirounga angustirostris) with a large bite to the hindquarters (which is the main source of the seal's mobility) and wait for the seal to bleed to death. This technique is especially used on adult male elephant seals, which are typically larger than the shark, ranging between , and are potentially dangerous adversaries. However, juvenile elephant seals are the most frequently eaten at elephant seal colonies. Prey is normally attacked sub-surface. Harbor seals (Phoca vitulina) are taken from the surface and dragged down until they stop struggling. They are then eaten near the bottom. California sea lions (Zalophus californianus) are ambushed from below and struck mid-body before being dragged and eaten.
In the Northwest Atlantic mature great whites are known to feed on both harbor and grey seals. Unlike adults, juvenile white sharks in the area feed on smaller fish species until they are large enough to prey on marine mammals such as seals. | Great white shark | Wikipedia | 220 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
White sharks also attack dolphins and porpoises from above, behind or below to avoid being detected by their echolocation. Targeted species include dusky dolphins (Sagmatias obscurus), Risso's dolphins (Grampus griseus), bottlenose dolphins (Tursiops ssp.), humpback dolphins (Sousa ssp.), harbour porpoises (Phocoena phocoena), and Dall's porpoises (Phocoenoides dalli). Groups of dolphins have occasionally been observed defending themselves from sharks with mobbing behaviour. White shark predation on other species of small cetacean has also been observed. In August 1989, a juvenile male pygmy sperm whale (Kogia breviceps) was found stranded in central California with a bite mark on its caudal peduncle from a great white shark. In addition, white sharks attack and prey upon beaked whales. Cases where an adult Stejneger's beaked whale (Mesoplodon stejnegeri), with a mean mass of around , and a juvenile Cuvier's beaked whale (Ziphius cavirostris), an individual estimated at , were hunted and killed by great white sharks have also been observed. When hunting sea turtles, they appear to simply bite through the carapace around a flipper, immobilizing the turtle. The heaviest species of bony fish, the oceanic sunfish (Mola mola), has been found in great white shark stomachs. | Great white shark | Wikipedia | 323 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Whale carcasses comprise an important part of the diet of white sharks. However, this has rarely been observed due to whales dying in remote areas. It has been estimated that of whale blubber could feed a white shark for 1.5 months. Detailed observations were made of four whale carcasses in False Bay between 2000 and 2010. Sharks were drawn to the carcass by chemical and odour detection, spread by strong winds. After initially feeding on the whale caudal peduncle and fluke, the sharks would investigate the carcass by slowly swimming around it and mouthing several parts before selecting a blubber-rich area. During feeding bouts of 15–20 seconds the sharks removed flesh with lateral headshakes, without the protective ocular rotation they employ when attacking live prey. The sharks were frequently observed regurgitating chunks of blubber and immediately returning to feed, possibly in order to replace low energy yield pieces with high energy yield pieces, using their teeth as mechanoreceptors to distinguish them. After feeding for several hours, the sharks appeared to become lethargic, no longer swimming to the surface; they were observed mouthing the carcass but apparently unable to bite hard enough to remove flesh, they would instead bounce off and slowly sink. Up to eight sharks were observed feeding simultaneously, bumping into each other without showing any signs of aggression; on one occasion a shark accidentally bit the head of a neighbouring shark, leaving two teeth embedded, but both continued to feed unperturbed. Smaller individuals hovered around the carcass eating chunks that drifted away. Unusually for the area, large numbers of sharks over five metres long were observed, suggesting that the largest sharks change their behaviour to search for whales as they lose the manoeuvrability required to hunt seals. The investigating team concluded that the importance of whale carcasses, particularly for the largest white sharks, has been underestimated. | Great white shark | Wikipedia | 393 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
In another documented incident, white sharks were observed scavenging on a whale carcass alongside tiger sharks. In 2020, marine biologists Sasha Dines and Enrico Gennari published a documented incident in the journal Marine and Freshwater Research of two great white sharks within an hour apart, successfully attacking and killing a live juvenile 7 m (23 ft) humpback whale. The sharks utilized the classic attack strategy used on pinnipeds when attacking the whale, even utilizing the bite-and-spit tactic they employ on smaller prey items. The whale was an entangled individual, heavily emaciated and thus more vulnerable to the sharks' attacks. The incident is the first known documentation of great whites actively killing a large baleen whale. A second incident regarding great white sharks killing humpback whales involving a single large female great white nicknamed Helen was documented off the coast of South Africa. Working alone, the shark attacked a emaciated and entangled humpback whale by attacking the whale's tail to cripple it before she managed to drown the whale by biting onto its head and pulling it underwater. The attack was witnessed via aerial drone by marine biologist Ryan Johnson, who said the attack went on for roughly 50 minutes before the shark successfully killed the whale. Johnson suggested that the shark may have strategized its attack in order to kill such a large animal.
Stomach contents of great whites also indicates that whale sharks both juvenile and adult may also be included on the animal's menu, though whether this is active hunting or scavenging is not known at present.
Reproduction
Great white sharks were previously thought to reach sexual maturity at around 15 years of age, but are now believed to take far longer; male great white sharks reach sexual maturity at age 26, while females take 33 years to reach sexual maturity. Maximum life span was originally believed to be more than 30 years, but a study by the Woods Hole Oceanographic Institution placed it at upwards of 70 years. Examinations of vertebral growth ring count gave a maximum male age of 73 years and a maximum female age of 40 years for the specimens studied. The shark's late sexual maturity, low reproductive rate, long gestation period of 11 months and slow growth make it vulnerable to pressures such as overfishing and environmental change. | Great white shark | Wikipedia | 464 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Little is known about the great white shark's mating habits, and mating behaviour had not been observed in this species until 1997 and properly documented in 2020. It was assumed previously to be possible that whale carcasses are an important location for sexually mature sharks to meet for mating. According to the testimony of fisherman Dick Ledgerwood, who observed two great white sharks mating in the area near Port Chalmers and Otago Harbor, in New Zealand, it is theorized that great white sharks mate in shallow water away from feeding areas and continually roll belly to belly during copulation. Birth has never been observed, but pregnant females have been examined. Great white sharks are ovoviviparous, which means eggs develop and hatch in the uterus and continue to develop until birth. The great white has an 11-month gestation period. The shark pup's powerful jaws begin to develop in the first month. The unborn sharks participate in oophagy, in which they feed on ova produced by the mother. Delivery is in spring and summer. The largest number of pups recorded for this species is 14 pups from a single mother measuring that was killed incidentally off Taiwan in 2019.
On 9 July 2023, the first footage of what was likely a newborn great white shark was filmed via aerial drone off of Southern California, off Carpinteria, after a large adult shark was seen diving to the bottom roughly from the shoreline, after which the smaller shark rose to the surface. The young shark, estimated up to long, was pale in colour, possibly due to what may be an embryonic covering, possibly intrauterine milk, was seen sloughing off the skin of the young shark. Adult sharks filmed in the area days prior suggest the area may be a birthing ground for pregnant females. This footage was published in the journal Environmental Biology of Fishes on 29 January 2024. A follow-up study in published in October, 2024 lends further support to the theory that the Carpinteria shark was a newborn; The description and examination of neonate porbeagles with a similar body covering to the young great white suggests that the body covering is not intrauterine milk (which ceases in production mid-gestation), but is instead embryonic epithelium that covers the shark's denticles and rubs off shortly after birth.
Breaching behaviour | Great white shark | Wikipedia | 481 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
A breach is the result of a high-speed approach to the surface with the resulting momentum taking the shark partially or completely clear of the water. This is a hunting technique employed by great white sharks whilst hunting seals. This technique is often used on cape fur seals at Seal Island in False Bay, South Africa. Because the behaviour is unpredictable, it is very hard to document. It was first photographed by Chris Fallows and Rob Lawrence who developed the technique of towing a slow-moving seal decoy to trick the sharks to breach. Between April and September, scientists may observe around 600 breaches. The seals swim on the surface and the great white sharks launch their predatory attack from the deeper water below. They can reach speeds of up to and can at times launch themselves more than into the air. Just under half of observed breach attacks are successful. In 2011, a 3-m-long shark jumped onto a seven-person research vessel off Seal Island in Mossel Bay. The crew were undertaking a population study using sardines as bait, and the incident was judged not to be an attack on the boat but an accident.
Natural threats
Interspecific competition and predation by orcas
Interspecific competition between the great white shark and the orca is probable in regions where dietary preferences of both species may overlap. An incident was documented on 4 October 1997, in the Farallon Islands off California in the United States. An estimated female orca immobilized an estimated great white shark. The orca held the shark upside down to induce tonic immobility and kept the shark still for fifteen minutes, causing it to suffocate. The orca then proceeded to eat the dead shark's liver. It is believed that the scent of the slain shark's carcass caused all the great whites in the region to flee, forfeiting an opportunity for a great seasonal feed. Another similar attack apparently occurred there in 2000, but its outcome is not clear. After both attacks, the local population of about 100 great whites vanished. Following the 2000 incident, a great white with a satellite tag was found to have immediately submerged to a depth of and swam to Hawaii. | Great white shark | Wikipedia | 442 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
In 2015, a pod of orcas was recorded to have killed a great white shark off South Australia. In 2017, three great whites were found washed ashore near Gansbaai, South Africa, with their body cavities torn open and the livers removed by what is likely to have been orcas. Orcas also generally impact great white distribution. Studies published in 2019 of orca and great white shark distribution and interactions around the Farallon Islands indicate that the cetaceans impact the sharks negatively, with brief appearances by orcas causing the sharks to seek out new feeding areas until the next season. It is unclear whether this is an example of competitive exclusion or ecology of fear. Occasionally, however, some great whites have been seen to swim near orcas without fear.
Parasites
The great white shark is the definitive host of two species of tapeworms from the genus Clistobothrium, these being Clistobothrium carcharodoni and Clistobothrium tumidum, both of which infect the shark's spiral intestine. The former is believed to be transmitted to great whites through the consumption of infected cetacean prey, namely the spinner dolphin (Stenella longirostris), Risso's dolphin (Grampus griseus), and the common bottlenose dolphin (Tursiops truncatus), all of which serve as intermediary or paratenic hosts of the tapeworm. The latter species of tapeworm's transmission vector is currently unknown, but it is unlikely to share the same intermediary hosts as Clisbotherium carcharodoni. The intensity of Clistobothrium carcharodoni infestations in affected great whites is extremely high; in one case, up to 2,533 specimens were recovered from the spiral valve of a single great white.
There are two recorded instances of the ectoparasitic cookiecutter shark (Isistius brasiliensis) targeting subadult great whites off the coast of Guadalupe Island. However, the relative dearth of predation records indicates that great whites are not a common food source for cookiecutter sharks, and that cetaceans and pinnipeds - especially the Guadalupe fur seal (Arctocephalus townsendi) - are preferred over great whites; in part due to the higher caloric content of their blubber, and in part due to the higher risk of retaliation from victimized great whites. | Great white shark | Wikipedia | 511 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Relationship with humans
Shark bite incidents
Of all shark species, the great white shark is responsible for by far the largest number of recorded shark bite incidents on humans, with 351 documented unprovoked bite incidents on humans as of 2024.
More than any documented bite incident, Peter Benchley's best-selling novel Jaws and the subsequent 1975 film adaptation directed by Steven Spielberg provided the great white shark with the image of being a "man-eater" in the public mind. While great white sharks have killed humans in at least 74 documented unprovoked bite incidents, they typically do not target them: for example, in the Mediterranean Sea there have been 31 confirmed bite incidents against humans in the last two centuries, most of which were non-fatal. Many of the incidents seemed to be "test-bites". Great white sharks also test-bite buoys, flotsam, and other unfamiliar objects, and they might grab a human or a surfboard to identify what it is.
Many bite incidents occur in waters with low visibility or other situations which impair the shark's senses. The species appears to not like the taste of humans, or at least finds the taste unfamiliar. Further research shows that they can tell in one bite whether or not the object is worth predating upon. Humans, for the most part, are too bony for their liking. They much prefer seals, which are fat and rich in protein.
Studies published in 2021 by Ryan et al. in the Journal of the Royal Society Interface suggest that mistaken identity is in fact a case for many shark bite incidents perpetrated by great white sharks. Using cameras and footage of seals in aquariums as models and mounted cameras moving at the same speed and angle as a cruising great white shark looking up at the surface from below, the experiment suggests that the sharks are likely colorblind and cannot see in fine enough detail to determine whether the silhouette above them is a pinniped or a swimming human, potentially vindicating the hypothesis.
Humans are not appropriate prey because the shark's digestion is too slow to cope with a human's high ratio of bone to muscle and fat. Accordingly, in most recorded shark bite incidents, great whites broke off contact after the first bite. Fatalities are usually caused by blood loss from the initial bite rather than from critical organ loss or from whole consumption. , of the 351 recorded unprovoked attacks, 59 were fatal. | Great white shark | Wikipedia | 490 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
However, some researchers have hypothesized that the reason the proportion of fatalities is low is not that sharks do not like human flesh, but because humans are often able to escape after the first bite. In the 1980s, John McCosker, chair of aquatic biology at the California Academy of Sciences, noted that divers who dived solo and were bitten by great whites were generally at least partially consumed, while divers who followed the buddy system were generally rescued by their companion. McCosker and Timothy C. Tricas, an author and professor at the University of Hawaii, suggest that a standard pattern for great whites is to make an initial devastating attack and then wait for the prey to weaken before consuming the wounded animal. Humans' ability to move out of reach with the help of others, thus foiling the attack, is unusual for a great white's prey.
Shark culling
Shark culling is the deliberate killing of sharks by a government in an attempt to reduce shark attacks; shark culling is often called "shark control". These programs have been criticized by environmentalists and scientists—they say these programs harm the marine ecosystem; they also say such programs are "outdated, cruel, and ineffective". Many different species (dolphins, turtles, etc.) are also killed in these programs (because of their use of shark nets and drum lines)—15,135 marine animals were killed in New South Wales' nets between 1950 and 2008, and 84,000 marine animals were killed by Queensland authorities from 1962 to 2015.
Great white sharks are currently killed in both Queensland and New South Wales in "shark control" (shark culling) programs. Queensland uses shark nets and drum lines with baited hooks, while New South Wales only uses nets. From 1962 to 2018, Queensland authorities killed about 50,000 sharks, many of which were great whites. From 2013 to 2014 alone, 667 sharks were killed by Queensland authorities, including great white sharks. In Queensland, great white sharks found alive on the drum lines are shot. In New South Wales, between 1950 and 2008, a total of 577 great white sharks were killed in nets. Between September 2017 and April 2018, fourteen great white sharks were killed in New South Wales.
KwaZulu-Natal (an area of South Africa) also has a "shark control" program that kills great white sharks and other marine life. In a 30-year period, more than 33,000 sharks were killed in KwaZulu-Natal's shark-killing program, including great whites. | Great white shark | Wikipedia | 512 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
In 2014 the state government of Western Australia led by Premier Colin Barnett implemented a policy of killing large sharks. The policy, colloquially referred to as the Western Australian shark cull, was intended to protect users of the marine environment from shark bite incidents, following the deaths of seven people on the Western Australian coastline in the years 2010–2013. Baited drum lines were deployed near popular beaches using hooks designed to catch great white sharks, as well as bull and tiger sharks. Large sharks found hooked but still alive were shot and their bodies discarded at sea. The government claimed they were not culling the sharks, but were using a "targeted, localised, hazard mitigation strategy". Barnett described opposition as "ludicrous" and "extreme", and said that nothing could change his mind. This policy was met with widespread condemnation from the scientific community, which showed that species responsible for bite incidents were notoriously hard to identify, that the drum lines failed to capture white sharks, as intended, and that the government also failed to show any correlation between their drum line policy and a decrease in shark bite incidents in the region.
Attacks on boats
Great white sharks infrequently bite and sometimes even sink boats. Only five of the 108 authenticated unprovoked shark bite incidents reported from the Pacific Coast during the 20th century involved kayakers. In a few cases they have bitten boats up to in length. They have bumped or knocked people overboard, usually biting the boat from the stern. In one case in 1936, a large shark leapt completely into the South African fishing boat Lucky Jim, knocking a crewman into the sea. Tricas and McCosker's underwater observations suggest that sharks are attracted to boats by the electrical fields they generate, which are picked up by the ampullae of Lorenzini and confuse the shark about whether or not wounded prey might be nearby.
In captivity
Prior to August 1981, no great white shark in captivity lived longer than 11 days. In August 1981, a great white survived for 16 days at SeaWorld San Diego before being released. The idea of containing a live great white at SeaWorld Orlando was used in the 1983 film Jaws 3-D. | Great white shark | Wikipedia | 442 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Monterey Bay Aquarium first attempted to display a great white in 1984, but the shark died after 11 days because it did not eat. In July 2003, Monterey researchers captured a small female and kept it in a large netted pen near Malibu for five days. They had the rare success of getting the shark to feed in captivity before its release. Not until September 2004 was the aquarium able to place a great white on long-term exhibit. A young female, which was caught off the coast of Ventura, was kept in the aquarium's Outer Bay exhibit for 198 days before she was released in March 2005. She was tracked for 30 days after release. On the evening of 31 August 2006, the aquarium introduced a juvenile male caught outside Santa Monica Bay. His first meal as a captive was a large salmon steak on 8 September 2006, and as of that date, he was estimated to be in length and to weigh approximately . He was released on 16 January 2007, after 137 days in captivity.
Monterey Bay Aquarium housed a third great white, a juvenile male, for 162 days between 27 August 2007, and 5 February 2008. On arrival, he was long and weighed . He grew to and before release. A juvenile female came to the Outer Bay Exhibit on 27 August 2008. While she did swim well, the shark fed only once during her stay and was tagged and released on 7 September 2008. Another juvenile female was captured near Malibu on 12 August 2009, introduced to the Outer Bay exhibit on 26 August 2009, and was successfully released into the wild on 4 November 2009. The Monterey Bay Aquarium introduced a 1.4-m-long male into their redesigned "Open Sea" exhibit on 31 August 2011. He was exhibited for 55 days, and was released into the wild on 25 October the same year. However, the shark was determined to have died shortly after release via an attached electronic tag. The cause of death is not known.
The Monterey Bay Aquarium does not plan to exhibit any more great whites, as the main purpose of containing them was scientific. As data from captive great whites were no longer needed, the institute has instead shifted its focus to study wild sharks. | Great white shark | Wikipedia | 433 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
One of the largest adult great whites ever exhibited was at Japan's Okinawa Churaumi Aquarium in 2016, where a male was exhibited for three days before dying. Perhaps the most famous captive was a female named Sandy, which in August 1980 became the only great white to be housed at the California Academy of Sciences' Steinhart Aquarium in San Francisco, California. She was released because she would not eat and constantly bumped against the walls.
Due to the vast amounts of resources required and the subsequent cost to keep a great white shark alive in captivity, their dietary preferences, size, migratory nature, and the stress of capture and containment, permanent exhibition of a great white shark is likely to be unfeasible.
Shark tourism
Cage diving is most common at sites where great whites are frequent including the coast of South Africa, the Neptune Islands in South Australia, and Guadalupe Island in Baja California. The popularity of cage diving and swimming with sharks is at the focus of a booming tourist industry. A common practice is to chum the water with pieces of fish to attract the sharks. These practices may make sharks more accustomed to people in their environment and to associate human activity with food; a potentially dangerous situation. By drawing bait on a wire towards the cage, tour operators lure the shark to the cage, possibly striking it, exacerbating this problem. Other operators draw the bait away from the cage, causing the shark to swim past the divers.
At present, hang baits are illegal off Isla Guadalupe and reputable dive operators do not use them. Operators in South Africa and Australia continue to use hang baits and pinniped decoys. In South Australia, playing rock music recordings underwater, including the AC/DC album Back in Black has also been used experimentally to attract sharks.
Companies object to being blamed for shark bite incidents, pointing out that lightning tends to strike humans more often than sharks bite humans. Their position is that further research needs to be done before banning practices such as chumming, which may alter natural behaviour. One compromise is to only use chum in areas where whites actively patrol anyway, well away from human leisure areas. Also, responsible dive operators do not feed sharks. Only sharks that are willing to scavenge follow the chum trail and if they find no food at the end then the shark soon swims off and does not associate chum with a meal. It has been suggested that government licensing strategies may help enforce these responsible tourism. | Great white shark | Wikipedia | 494 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
Conservation status
It is unclear how much of a concurrent increase in fishing for great white sharks has caused the decline of great white shark populations from the 1970s to the present. No accurate global population numbers are available, but the great white shark is now considered vulnerable worldwide, and critically endangered in Europe and the Mediterranean. Sharks taken during the long interval between birth and sexual maturity never reproduce, making population recovery and growth difficult.
The International Union for Conservation of Nature notes that very little is known about the actual status of the great white shark, but as it appears uncommon compared to other widely distributed species, it is considered vulnerable. It is included in Appendix II of CITES, meaning that international trade in the species (including parts and derivatives) requires a permit. As of March 2010, it has also been included in Annex I of the CMS Migratory Sharks MoU, which strives for increased international understanding and coordination for the protection of certain migratory sharks. A February 2010 study by Barbara Block of Stanford University estimated the world population of great white sharks to be lower than 3,500 individuals, making the species more vulnerable to extinction than the tiger, whose population is in the same range. According to another study from 2014 by George H. Burgess, Florida Museum of Natural History, University of Florida, there are about 2,000 great white sharks near the California coast, which is 10 times higher than the previous estimate of 219 by Barbara Block.
Fishermen target many sharks for their jaws, teeth, and fins, and as game fish in general. The great white shark, however, is rarely an object of commercial fishing, although its flesh is considered valuable. If casually captured (it happens for example in some tonnare in the Mediterranean), it is misleadingly sold as smooth-hound shark.
In Australia
The great white shark was declared vulnerable by the Australian Government in 1999 because of significant population decline and is currently protected under the Environmental Protection and Biodiversity Conservation (EPBC) Act. The causes of decline prior to protection included mortality from sport fishing harvests as well as being caught in beach protection netting.
The national conservation status of the great white shark is reflected by all Australian states under their respective laws, granting the species full protection throughout Australia regardless of jurisdiction. Many states had prohibited the killing or possession of great white sharks prior to national legislation coming into effect. The great white shark is further listed as threatened in Victoria under the Flora and Fauna Guarantee Act, and as rare or likely to become extinct under Schedule 5 of the Wildlife Conservation Act in Western Australia. | Great white shark | Wikipedia | 505 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
In 2002, the Australian government created the White Shark Recovery Plan, implementing government-mandated conservation research and monitoring for conservation in addition to federal protection and stronger regulation of shark-related trade and tourism activities. An updated recovery plan was published in 2013 to review progress, research findings, and to implement further conservation actions. A study in 2012 revealed that Australia's white shark population was separated by Bass Strait into genetically distinct eastern and western populations, indicating a need for the development of regional conservation strategies.
Presently, human-caused shark mortality is continuing, primarily from accidental and illegal catching in commercial and recreational fishing as well as from being caught in beach protection netting, and the populations of great white shark in Australia are yet to recover.
In spite of official protections in Australia, great white sharks continue to be killed in state "shark control" programs within Australia. For example, the government of Queensland has a "shark control" program (shark culling) which kills great white sharks (as well as other marine life) using shark nets and drum lines with baited hooks. In Queensland, great white sharks that are found alive on the baited hooks are shot. The government of New South Wales also kills great white sharks in its "shark control" program. Partly because of these programs, shark numbers in eastern Australia have decreased.
The Australasian population of great white sharks is believed to be in excess of 8,000–10,000 individuals according to genetic research studies done by CSIRO, with an adult population estimated to be around 2,210 individuals in both Eastern and Western Australia. The annual survival rate for juveniles in these two separate populations was estimated in the same study to be close to 73 per cent, while adult sharks had a 93 per cent annual survival rate. Whether or not mortality rates in great white sharks have declined, or the population has increased as a result of the protection of this species in Australian waters is as yet unknown due to the slow growth rates of this species. | Great white shark | Wikipedia | 396 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
In New Zealand
The great white shark is one of the most commonly found in the waters of New Zealand. As of April 2007, great white sharks were fully protected within of New Zealand and additionally from fishing by New Zealand-flagged boats outside this range. The maximum penalty is a $250,000 fine and up to six months in prison. In June 2018 the New Zealand Department of Conservation classified the great white shark under the New Zealand Threat Classification System as "Nationally Endangered". The species meets the criteria for this classification as there exists a moderate, stable population of between 1000 and 5000 mature individuals. This classification has the qualifiers "Data Poor" and "Threatened Overseas".
In the United States
California
In addition to existing federal regulations, great white sharks have been protected under California state law since January 1st, 1994. Under this law, catching, hunting, pursuit, capturing, and/or killing of great whites in California waters is strictly prohibited up to offshore, though exceptions exist for great whites caught for scientific research or unintentionally caught as bycatch. In both cases, a special permit is required in order to legally take them.
In 2013, great white sharks were added to California's Endangered Species Act. From data collected, the population of great whites in the North Pacific was estimated to be fewer than 340 individuals. Research also reveals these sharks are genetically distinct from other members of their species elsewhere in Africa, Australia, and the east coast of North America, having been isolated from other populations.
A 2014 study estimated the population of great white sharks along the California coastline to be approximately 2,400.
In September 2019, California governor Gavin Newsom signed Assembly Bill 2109 into law, banning the use of shark bait, shark lures, and chumming to attract great whites in California waters, and prohibiting their usage within one nautical mile of any shoreline, pier, or jetty when a great white is visible or known to be present in the area.
Massachusetts
In June 2015, Massachusetts banned catching, cage diving, feeding, towing decoys, or baiting and chumming for its significant and highly predictable migratory great white population without an appropriate research permit. However, these restrictions apply to only activities within state waters, which extend three miles from shore. Therefore there are over a dozen tour operators offering cage diving and some do bait and/or chum. | Great white shark | Wikipedia | 475 | 43619 | https://en.wikipedia.org/wiki/Great%20white%20shark | Biology and health sciences | Sharks | null |
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