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Post by elosha11 on Apr 5, 2013 20:19:54 GMT 5
 Adult female captured, tagged, and released off of Guadalupe Island in 2012. Nicknamed "Arden Grace." Biological profile taken primarily from the Florida Museum of Natural History Ichthyology DeptWHITE SHARK Order - Lamniformes Family - Lamnidae Genus - Carcharodon Species - carcharias Carcharodon carcharias Taxonomy and Evolution The white shark was not always known as Carcharodon carcharias. Since 1758, when it was named Squalus carcharias, this species has been afforded a variety of scientific names, including Carcharias lamnia Rafinesque 1810, Carcharias verus Cloquet 1817, Carcharodon smithii Bonaparte 1838, Carcharodon rondeletii Müller & Henle 1839, Carcharias atwoodi Storer 1848, Carcharias maso Morris 1898, and Carcharodon albimors Whitley 1939. The genus name Carcharodon is derived from the Greek "karcharos" = sharpen and "odous" = teeth. The species name carcharias, also translated from Greek, means point or type of shark, leading to its common name in Australia of the white pointer. Cladograms of proposed generic relationships in the family Lamnidae, adapted from Klimley & Ainley (1996) Proposed generic relationships in the family Lamnidae The relationships between the white shark and the other genera of its family are controversial. Two phyletic arrangements have been proposed. One suggests it is more closely related to the mako sharks (genus Isurus) (figure A), while the other proposes it remains closer to the porbeagle and salmon sharks (genus Lamna) (figure B). Recent studies indicate that the first hypothesis is best supported but does not refute the second one.  Studies indicate that the white shark and the other genera of its family may have originated in the Paleocene or early Eocene. Fossil registers indicate that, in the late Cretaceous and Paleocene, the lamnid sharks (sharks from the family Lamnidae) were abundant and diverse. The evolution of the white shark also presents various theories. One proposes that it evolved from the megatoothed line of sharks, and another suggests that it evolved from a Miocene mako shark. A recent 2013 published study of a Peruvian prehistoric great white fossilized skull and associated teeth strongly suggests the latter theory. Common Name The white shark, also known as "great white", and "white pointer", is believed to have received its name from the appearance of dead specimens lying on deck, ventral side up with stark white underbelly revealed. Other common English language names are man eater, shark, and white death. Common names in other languages include anequim (Portuguese), devorador de hombres (Spanish), grand requin blanc (French), hohojirozame (Japanese), hvithai (Norwegian), jaquentón blanco (Spanish), kalb bahr (Arabic), kelb il - bahar abjad (Maltese), manzo de mar (Italian), menschenhai (German), niuhi (Hawaiian), peshkagen njeringrenes (Albanian), rechin mancator de oameni (Rumanian), requin blanc (French), sbrillias (Greek), squalo bianco (Italian), tiburón blanco (Spanish), valkohai (Finnish), vithaj (Swedish), weißer hai (German), witdoodshaai (Afrikaans), and zarlacz ludojad (Polish). Geographical Distribution The white shark is cosmopolitan but occurs mostly in temperate seas, with large individuals known to penetrate tropical waters. It makes sporadic movements to cold, boreal waters and has been recorded off Alaskan and Canadian coasts. It occurs in the western Atlantic from Newfoundland to Florida, the northern Gulf of Mexico, the Bahamas and Cuba as well from Brazil to Argentina and in the eastern Atlantic from France to South Africa, including the Mediterranean. In the Indian Ocean, it occurs in the Red Sea, off South Africa and the Seychelles Islands, as well as Reunion and Mauritius. In the western Pacific, it ranges from Siberia to New Zealand and the Marshall Islands, off the Hawaiian Islands in the central Pacific and from Alaska to the Gulf of California and Panama to Chile in the eastern Pacific.  World distribution map for the white shark HabitatThe white shark is principally an epipelagic (living in the upper part of the water column) dweller of neritic (nearshore) waters. However, it ranges from the surfline to well offshore and from the surface and to depths over 250 m (775 ft). This shark commonly patrols small coastal archipelagos inhabited by pinnipeds (seal, sea lions and walruses), offshore reefs, banks and shoals and rocky headlands where deepwater lies close to shore. The white shark usually cruises in a purposeful manner, either just off the bottom or near the surface, but spends very little time at midwater depths. Biology · Distinctive FeaturesBody fusiform, snout conical and relatively short, long gill slits not encircling the head. Large first dorsal fin with the origin over pectoral fin inner margins. Second dorsal and anal fins minute. Caudal fin homocercal (crescent shaped), without a secondary keel below extension of caudal keel. · ColorationDorsal surface blue-grey to grey-brown, often bronzy. Ventral surface is white. Boundary between these tones is generally abrupt. Small, irregular dark spots may be present on the flanks posterior to the last gill slit. Most specimens exhibit a black oval blotch in the axil of the pectoral fin. · DentitionTeeth large, erect, triangular and serrated. More slender in lower jaw. In juveniles under 1.8 m (5.5 ft), the teeth have small lateral cusplets and in neonates, the lower teeth may actually lack marginal serration.  Right side upper and lower teeth of the white shark ex RadCliffe (1916) Bull. Bur. Fish. Circ. 822 White shark dentition · Dermal Denticles A Top view of white shark denticles (magnified) and B Side view of a single denticle ex RadCliffe (1916) Bull. Bur. Fish. Circ. 822 Dermal denticles of the white shark Denticles minute, tightly packed with three ridges and very flat blades. Skin of the white shark is relatively smooth in comparison with many other species. · Size, Age & Growth The maximum size attained by white sharks has been the target of many debates and spurious information. Scientists now suggest that the maximum total length of this species is about 680 cm (22.3 ft). Males mature at about 350 cm (10.5 ft) and females at about 450 cm (14 ft). White sharks are 120-150 cm (47-59 in) in length at birth. Studies have indicated that white sharks live at least 14 years. However, in reality, this number is likely much higher. Growth rates of the white shark are also largely unclear, although one recent study included a tagged specimen that had grown 69 cm (27 in) in a period of 2.6 yrs. · Spatial BehaviorAlthough information about its movements is limited by the rarity of the white shark, some data has been gathered through tag-and-release programs in the United States, South Africa and Australia. These studies reveal that the white shark is capable of making movements on localized, regional and intercontinental scales. Generally, larger individuals undertake long journeys across the great ocean basins. Observations of two white sharks cruising in open water, apparently not feeding, revealed a strong tendency to ascend and descend slowly and steadily. The white shark is also capable of short, high-speed pursuits and launching itself clear from the surface. The white shark has been recorded and estimated to reach speeds of up to 25 miles per hour in attack mode. Patterns in movement and abundance within some areas appear to be linked with seasonal variations in surface temperature. However, this may only have a minimal effect on the distribution of the white shark. · Food HabitsIn most areas where white sharks occur, pinnipeds such as California sea lions (Zalophus californianus), make up the bulk of the white shark's diet. The white shark is a macropredator, known to be active during the daytime. Its most important prey items are marine mammals (including, seals, sea lions, elephant seals, dolphins and other cetaceans) and fishes (including other sharks and rays). Marine reptiles are sporadically ingested, mostly sea turtles. Marine birds and sea otters are almost exclusively rejected as prey. These animals are commonly found having suffered injuries from encounters with white sharks, but are rarely ingested. Predatory behavior is usually divided into five stages; detection, identification, approach, subjugation, and consumption. However, these stages, especially the first and second, are poorly understood in white sharks. The patterns of prey detection and identification in white sharks have been investigated by the use of experimental targets, baits, and other objects in which they are "offered" to the sharks. The results of these experiments reveal that when white sharks have a choice between a square target and a fusiform, seal-shaped target, they select the shape that is more common in their natural environment. Indeed, the choice made in nature is usually whether to respond to a single potential prey item rather than choosing between two of them. When only a single object was presented, it was invariably investigated. Some scientists believe diver and surfer silhouettes, when viewed from below, resemble those of pinnipeds and that this misidentification on behalf of the shark is the cause of most white shark attacks on humans. However, the fact that white sharks attack inanimate objects of a variety of shapes, colors and sizes, none of which resemble those of a marine mammal, refute the well-known hypothesis of "mistaken identity". Researchers suggest that white sharks often strike unfamiliar objects to determine their potential as food. In this case, it would seem that grasping an unfamiliar object would be the shark's only reliable method of determining palatability. Based on underwater observations, scientists described some approach patterns. Most sharks used an "underwater approach" in which the shark swam just below the surface until it was approximately 1 m (3.3 ft) from its intended prey and then attacked by deflecting the head upward and emerging out of the water. The white shark also presented a "surface-charge" which consisted of a rapid rush with the body partially above the surface. In rare cases, whites performed an "inverted approach" in which they swam with the ventral side up. Although the majority of approaches are horizontally oriented, vertical approaches are nonetheless common. White sharks readily engage in vertical swimming during feeding activities, sometimes swimming perpendicular to the surface in direct and rapid pursuit of floating objects. There are benefits of using the vertical approach to capture prey positioned near the surface. Firstly, a predator attacking from below is more difficult for the prey to see, while at the same time, the shark has a better view of its prey positioned overhead. In addition, fleeing (rapid movement away from an approaching predator) is probably the most common escape tactic used by animals under attack. Considering these situations, extended escape in the direction opposite the vertically approaching shark is virtually impossible. The propensity for vertical swimming was observed in small white sharks approximately 220 cm (86 in) in length. Scientists believe that the development of this behavior precedes physical changes, such as broadening of the teeth, believed to be adaptations for feeding on large marine mammals. Few hypotheses about the consumption patterns of white sharks have been made based on observations under natural conditions. One of these hypotheses, the "bite, spit and wait" theory, is composed of three elements. Initially, the white shark seizes its prey and releases it intact; secondly, the shark waits until the prey lapses into a state of shock or bleeds to death; finally, the white shark returns to feed on the dead or dying animal. However, recent studies do not support this hypothesis. Scientists believe that these sharks may not release potential prey to permit them to die but, rather, let them go in response to their defensive behavior or unsuitability as food. Some evidence suggests that white sharks decide a prey's palatability while it is lodged in the shark's mouth. Researchers also believe that white sharks may prefer animals rich in energy, such as marine mammals, in favor of less fatty, energy-poor prey. This is supported by some observations of aggregations of white sharks selectively feeding on the blubber but not the muscle layers of mysticete whales. This behavior seems based upon a size-hierarchy, where large sharks dominate in the feeding. A behavior pattern described as "repetitive aerial gaping" was observed in white sharks of southern Australia. The sharks were seen with their heads out of the water, mouths at or above the surface, rolling onto their side and opening and closing their mouth in a moderately slow, rhythmic, partial gape while swimming slowly along the surface. The most notable difference between this behavior and normal surface feeding is that the repetitive aerial gaping is not oriented toward food or possible targets. White sharks also scavenge from fishermen's nets and longlines and take all manners of hooked fish. This propensity often results in their own accidental entrapment. · Social BehaviorSome of the white's swimming modes, such as a cautiously timed turn away between two animals on reciprocal approaching courses, are interpreted as ensuring avoidance of conspecifics and maintenance of individual space. A parallel swim mode, whereby two sharks heading in the same direction at an unfluctuating distance from each other, also seems to be a result of the shark preserving its space from others. When two white sharks attempt to feed on the same prey, it is disadvantageous for one to discourage the other from further feeding by biting it and inflicting a wound. Such an injury might reduce either shark's future ability to catch prey. For this reason, scientists believe that white sharks sometimes use displays in order to discourage other sharks. White sharks have been observed with their caudal fin out of the water and slapping the surface, propelling water usually in the direction of a second shark. The recipient shark probably perceives the sign with its vision, lateral line (related with mechanical stimulation), and sense of hearing. This behavior is called a "tail slap" and is the most common avoidance display shown by white sharks. These sharks also present other types of displays. White sharks have been observed rolling on their sides and directing exaggerated tail beats in one direction, a phenomenon know as "tilting behavior". Sometimes a white shark will position itself between prey and another shark, preventing the second shark from feeding. White sharks have also been known to propel two-thirds of their body out of the water and land flat against the surface, causing a large splash. This behavior is called a "pattern breach" and may represent a similar, but more intense sign than the tail slap. This specific behavior might also be used to help remove external parasites, attract a mate during courtship or may be the result of a vertical charge approach pattern toward a prey item. · ReproductionWhite sharks are viviparous (embryos hatching in uteri, with the female giving birth to live young). Embryos are nourished through oophagy (ingestion of unfertilized eggs). While in uteri, the embryonic white sharks swallow their own sets of shedded teeth, perhaps to reutilize calcium and other minerals. Size at birth ranges from 120-150 cm (47-59 in) in total length. It is possible that any one female only reproduces biennually, mating soon after giving birth, but this remains to be confirmed. Gestation time is also unknown, but is thought to be quite long, possibly up to one year. Some bite-marks observed on the dorsum, flanks and particularly the pectoral fins of mature female white sharks have been interpreted as results of mating activity. As in other species of sharks, the male white shark most likely grabs the female during copulation. Some records suggest that parturition occurs in temperate shelf waters during the spring to late summer. · PredatorsThe white shark is an apex predator (atop the food chain) and as such, has very few predators. Killer whales (Orcinus orca) and larger sharks pose the only real threats for an adult white shark. · ParasitesParasites of the white shark include the Pandarus sinuatus and Pandarus smithii. These copepods parasitize the body surface of this shark. Importance to HumansDespite its relative sparseness, the white shark's rate of capture by humans is alarmingly high. This is due in part to the increasing monetary value of its jaws and teeth. Entire specimens, some attaining more than 5m in length have been preserved by freezing or taxidermy for permanent public display or as private trophies or curios. Also, the flesh is utilized for human consumption, the skin for leather, the liver for oil, the carcass for fishmeal and the fins for shark-fin soup. Worldwide, specimens are reported annually from gill nets, trammels, herring weirs, purse seines, tuna enclosures as well as surface hooks, bottom longlines and set-lines. Danger to HumansThe white shark has been credited with more fatal attacks on humans than any other species of shark. This is due primarily to its size, power and feeding behavior. Click here for statistics on white shark attacks on humans. Conservation This 2080 lb white shark was caught on a longline off Cape Fear, NC in 1984 © S.W. Ross Overall population estimates for this species are unknown and even regional and localized estimates are questionable. It has been proposed that white sharks should be afforded protection for the same reasons as other top carnivores. In addition to being rare, they are important participants in a complicated food web. As with most species of shark, white sharks are slow-growing animals with low productivity and are therefore highly vulnerable to overfishing. Fortunately, the threat of habitat loss appears minimal to white sharks. They are adaptable predators capable of shifting diet as conditions dictate and may simply cease to inhabit an area with little food. The most significant problem in applying definitive measures in favor of the white shark remains the lack of data, such as fecundity, age, growth, and population numbers. Considering the lack of data, it has been proposed that protective measures should be based on a precautionary principle, until more biological information has been collected. Researchers do know that shark populations, including the white shark, will inevitably dwindle unless careful measures are implemented. Some governments, such as those in South Africa, Australia and the United States, have already afforded protection to the white shark. At present, the white shark is listed as "Vulnerable" by the World Conservation Union (IUCN) throughout its range, and is now protected in some regions. In 2004, the Convention on International Trade in Endangered Species (CITES) placed this shark on its Appendix II list, which demands tighter regulations and requires a series of permits that will control the trade in white shark products. |
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Post by elosha11 on Apr 5, 2013 20:45:13 GMT 5
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Post by creature386 on Apr 7, 2013 17:53:57 GMT 5
About Teeth and Size:As great white sharks mature, their teeth become broader, more triangular and more serrated. This change starts at lengths of 3-4 m when the sharks stop primarily feeding on fish. Below is a table about tooth height, width, serrations the corresponding TL:  Citation: Hubbel, G. Using tooth structure to Determine the Evolutionary History of the White Shark In: Klimley, A. P., Ainley D. G. (1998). Great White Sharks: The Biology of Carcharodon Carcharias. Academic Press, San Diego (p. 15) The reason for that adaptation may be the fact that the bite force increases as well when getting older, so the teeth have to survive more stress: news.discovery.com/animals/great-white-shark-bites.htmlNow about the size. According to Compagno (1984), the largest verified great white shark is 6.4 m long. The average size is in the ballpark of 3-5 m, as the table above indicates. Overall, adutls range in size from 3.8-6 m (see the quote below). There are some specimen larger than 6 m (they are rare tough), but they are often difficult to measure, leading to a lot of speculation. The largest great white shark ever captured is believed to be around o 7 m long, with a possible maximum of 7,7 m (measured along the curve). Citation: Mollet, H. F., Cailliet, G. M., Klimley, A. P., Ebert, D. A., Testi, A. D., Compagno, L. J. V.: A review of length validation methods and protocols to measure large white sharks In: Klimley, A. P., Ainley D. G. (1998). Great White Sharks: The Biology of Carcharodon Carcharias. Academic Press, San Diego (p. 91-108) Diagnostic Criteria of Carcharodon:Citation: Compagno, L. J. V. (2001): Sharks of the world. An annotated and illustrated catalogue of shark species known to date (= FAO Species Catalogue for Fishery Purposes. Vol. 2, FAO, Rome (91-107); weblink: www.fao.org/3/x9293e/X9293E06.pdf
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Post by elosha11 on Apr 10, 2013 10:04:28 GMT 5
White Shark Summary Carcharodon carcharias (Linnaeus, 1758)
Besides a huge number of photographic evidence of different sized great whites, he also includes many links to his research, such as his paper regarding the size estimates of the Manga and Kanga specimens, (each thought to have approached or exceeded 7 meters), papers on the reproductive strategies of the great white, and detailed morphometric graphs. His elasmollet.org site in general gives a vast amount of information and pictures specimens of many other types of sharks and rays and is a wonderful resource. I am in communication with Dr. Mollet and one of his colleagues about the recent large Taiwan sharks caught in Taiwan recently and will post our conversations later after we have finished them.
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Post by elosha11 on Apr 12, 2013 21:11:27 GMT 5
Great white sharks scavenging on dead whales
Many terrestrial animals are frequently observed scavenging on other animals- whether it is a hyena stealing a lion kill in the Serengeti or a buzzard swooping down on a dead animal. However, documenting this sort of activity in the oceans is especially difficult, and often overlooked in marine food web studies.
In a new study published in PLOS ONE titled, "White sharks (Carcharodon carcharias) scavenging on whales and its potential role in further shaping the ecology of an apex predator," Captain Chris Fallows from Apex Expeditions collaborated with University of Miami (UM) scientists Dr. Neil Hammerschlag and Austin Gallagher, to explore the behaviors of Great white sharks scavenging on dead whales in South Africa. The team documented as many as 40 different sharks scavenging on a carcass over the course of a single day, revealing unique social interactions among sharks. The study summarized observations based on four scavenging events opportunistically observed over a 10 year period. In each multi-day observation, the team recorded daily evidence of social, aggregative and feeding behaviors observed in the waters off South Africa. They suggest that although the occurrence of coming upon a whale carcass may be sporadic, the shark populations are likely prepared to scavenge on them, and may even rely on their scavenging activities to supplement their regular feeding activities. "Although rarely seen, we suspect that as white sharks mature, scavenging on whales becomes more prevalent and significant to these species than previously thought," said Hammerschlag, who is director of the R.J. Dunlap Marine Conservation Program at UM. The team found that sharks showed a clear preference for scavenging on the blubber, probably because these high calorie meals can sustain the sharks for longer periods of time. Interestingly, though, the study also found that sharks showed an initial preference for feeding on the whale's fluke before moving on to feed on the rest of the carcass. The team also found that while scavenging on whales, they ceased hunting and feeding on seals, one of their primary natural prey. "While scavenging on the whale, the sharks clearly showed a size-based pecking order," said Fallows. "The biggest sharks came right in, targeting areas of highest blubber content, while smaller sharks fed on areas with less blubber or kept their distance from the whale, mostly scavenging on pieces of blubber that drifted away from the carcass."The paper reveals how the social and size structure of sharks at the carcass appeared to be influenced by environmental patterns. "The cues, such as the oils, emanating from this pulse of food are likely attracting much larger sharks over 4.5 meters from long distances to scavenge," said Gallagher. "These data provide some credence to the hypothesis that large white sharks may be swimming known ocean corridors looking for dead, dying, or vulnerable whales.""By attracting many large white sharks together to scavenge, we suspect that the appearance of a whale carcass can play a role in shaping the behaviors, movements, and the ecosystem impacts of white sharks" said Hammerschlag. "These patterns may shed some light into the ecology of this often studied -- yet still highly enigmatic -- marine predator."----- Research article: White Sharks (Carcharodon carcharias) Scavenging on Whales and Its Potential Role in Further Shaping the Ecology of an Apex Predator
Abstract Scavenging, a result of a temporary pulse of resources, occurs in virtually all ecosystems containing carnivores, and is an important energy transfer pathway that can impact ecosystem structure and function, and this ecological significance has largely been considered from a terrestrial standpoint; however, little is known about the role of scavenging in shaping the behavioral ecology of marine species, specifically apex predators. Here we present findings from multiple opportunistic observations of white sharks scavenging on whale carcasses in False Bay, South Africa. Observations of white sharks scavenging over successive days provided evidence of strategic and selective scavenging by this species. Moreover, extended daily observations permitted recordings of unique social, aggregative, and feeding behaviors. We further compare these data against observations of natural predation by sharks on seals in the study area. We discuss these data in relation to environmental conditions, shark social interactions, migration patterns, whale biology, and behaviorally-mediated trophic cascades. While the appearance of a whale carcass is largely a stochastic event, we propose that white shark scavenging on whales may represent an underestimated, yet significant component to the overall foraging ecology of this species, especially as individuals attain sexual maturity.
Citation: Fallows, C., Gallagher, A. J., & Hammerschlag, N. (2013). White sharks (Carcharodon carcharias) scavenging on whales and its potential role in further shaping the ecology of an apex predator. PloS One, 8(4), e60797.
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Post by elosha11 on Apr 12, 2013 21:15:15 GMT 5
Travels of Pregnant Great White Sharks Revealed A great white shark cruises underwater in search of prey. (Image credit: Neil Hammerschlag)
For the first time, migrating great white sharks have been tagged and their movements around the oceans tracked for years, as opposed to the few months they have previously been tracked, according to a researcher. Scientists used special satellite tags that tracked several sharks from a specific great white population for up to three years off the coast of Mexico. The study found that adult female sharks complete a two-year breeding cycle and avoid male sharks whenever possible, said study author Michael Domeier, a researcher and the president of the Marine Conservation Science Institute. Published recently in the journal Animal Biotelemetry, the study followed four female great white sharks from their mating grounds off Mexico's Guadalupe Island until they returned 24 months later, Domeier said. During the first 18 months, the females followed an ambling path through the open ocean, he said. They then arrived in off Baja California to give birth to shark pups, putting themselves at risk of running into shipping traffic on their voyage along the shore, the study found. "During the time the females are giving birth along the Baja Peninsula they are exposed to an array of commercial fishing activities that put them at risk," Domeier told OurAmazingPlanet in an email. "Of course, the baby white sharks are at even more risk since they spend the first years of their life in coastal waters and their small size makes them even more susceptible to capture." Once the young sharks are born, the females return to Guadalupe Island to mate again. The study found a high prevalence of bite marks on the sharks. Male sharks "bite the head, flank or pectoral fin of females during the mating ritual, but certainly these sharks are biting each other out of aggression as well," Domeier added. "Males may be battling it out for access to females or preferred hunting grounds."While the females return to mate every two years, the males only return every other year. When they're not mating, both males and females may range as far afield as the waters off Hawaii, Domeier said. The researchers tag the great white sharks by affixing the device to the tip of the animal's dorsal fin, during which time they are very close to the predators. "It's surreal and humbling," Domeier said. "It is also stressful since the shark's life is in our hands during the short time it takes us to capture and tag each individual." ----- Research article: Two-year migration of adult female white sharks (Carcharodon carcharias) reveals widely separated nursery areas and conservation concerns
Abstract
Background
Satellite tagging programs have provided detailed information about the migratory patterns of northeastern Pacific white sharks, revealing a seasonal migration between a vast offshore region and coastal aggregation sites. Although adult males undergo annual round-trip migrations, photo-identification programs have noted that sexually mature females may only visit coastal aggregation sites once every 2 years, a behavior that is presumably linked to an estimated 18-month gestation period. The whereabouts of females during their full 2-year migration were previously unknown, because of the limited battery capacity of satellite pop-up tags.
Results
Through the use of satellite-linked radio-telemetry tags with multi-year tracking capability, we describe the 2-year migratory pattern for four mature female white sharks tagged at Guadalupe Island, Mexico. The 2-year migration comprised four phases: 1) an Offshore Gestation Phase (which had an average duration of 15.5 months; 2) a Pupping Phase, which occurred along the Mexican coast between the months of April and August; 3) a Pre-Aggregation Phase (when the females were in transition between the Pupping Phase and Guadalupe Island; and 4) the Guadalupe Island Aggregation Phase, which began when the mature females arrived at Guadalupe Island between late September and early October.
Conclusions
Long-term satellite tracking of mature female white sharks highlighted the connectivity between a single presumed mating site at Guadalupe Island, and two widely separated pupping sites along the Mexican coast. The Offshore Gestation Phase provided evidence that the females remained offshore for up to 16 months during their 2-year migration cycle. The Pupping Phase along the Mexican coast coincided with the seasonal presence of young-of-the-year white sharks along the coast of North America, and with a presumed gestation period of 18 months, this placed mating between October and January, during the period when white sharks are known to be at Guadalupe Island. Tracking data during the time sharks were offshore showed that mature males and females are spatially segregated, except for their concurrent seasonal presence at Guadalupe Island. These discoveries provide important new details about the complete life history of northeastern Pacific white sharks while identifying crucial regions in which young-of-the-year, juveniles and adult females are most vulnerable.
Citation: Domeier, M. L., & Nasby-Lucas, N. (2013). Two-year migration of adult female white sharks (Carcharodon carcharias) reveals widely separated nursery areas and conservation concerns. Animal Biotelemetry, 1(1), 1-10.
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Post by elosha11 on Apr 12, 2013 21:23:40 GMT 5
New research shows white sharks have a larger appetite than originally thought
(Phys.org) —A ground-breaking new study challenges popular assumptions about the feeding behaviour of the world's largest predatory fish, the white shark.
The research, which has been published in the prestigious journal Scientific Reports, suggests that white sharks may have much higher energy needs than previously thought.
The study was conceived by Dr Jayson Semmens of the University of Tasmaniaâs Institute for Marine and Antarctic Studies (IMAS), along with collaborators at the University of New South Wales, South Australian Research and Development Institute/Flinders University, The Marine Biological Association of the UK/University of Southampton and CSIRO.
White sharks are the ocean's top predators and their natural range extends across the globe. However, like many marine predators, they are notoriously difficult to study.
"The energy requirements of large sharks in the wild are poorly documented and their prey intake rates are largely unknown," Dr Semmens said. "Research on how sharks interact with their ecosystems is needed because many shark species are highly vulnerable to overexploitation.
"Our study uses metabolic rates derived from swimming speed estimates to suggest that feeding requirements of the white shark are much higher than previously proposed," he said.
The only prior study of shark energy requirements had suggested that a large (one-tonne) white shark could survive on a 30kg meal for around one and a half months.
However, the new research indicates that such a meal would in fact only provide energy for between 12 and 15 days - three to four times less than previously suggested. Quantifying the energy requirements of animals in their natural habitat, particularly apex predators such as sharks, is critical for a balanced understanding of ecosystem ecology and the physiology and behaviour of species. Innovative research approaches, such as those used in Dr Semmens' study, may help to answer key ecological questions for a species whose population status is poorly known. This information is key to understanding the role that top-order predators such as white sharks play in marine ecosystems. Dr Semmens would like to thank and acknowledge his co-authors Dr Nicholas Payne, Dr Charlie Huveneers, Professor David Sims and Mr Barry Bruce.
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Research article: Feeding requirements of white sharks may be higher than originally thought
Abstract
Quantifying the energy requirements of animals in nature is critical for understanding physiological, behavioural and ecosystem ecology; however, for difficult-to-study species such as large sharks, prey intake rates are largely unknown. Here, we use metabolic rates derived from swimming speed estimates to suggest that feeding requirements of the world's largest predatory fish, the white shark (Carcharodon carcharias), are several times higher than previously proposed. Further, our estimates of feeding frequency identify a clear benefit in seasonal selection of pinniped colonies - a white shark foraging strategy seen across much of their range.
Citation: Semmens, J. M., Payne, N. L., Huveneers, C., Sims, D. W., & Bruce, B. D. (2013). Feeding requirements of white sharks may be higher than originally thought. Scientific reports, 3(1), 1-4.
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Post by creature386 on Apr 26, 2013 13:29:07 GMT 5
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Post by Supercommunist on Apr 27, 2013 0:10:27 GMT 5
Teenage great white sharks are awkward bitersThe jaws of adolescent great white sharks may be too weak to capture and kill large marine mammals, according to a new study published in the Journal of Biomechanics by an international team of scientists.The researchers also found that, unlike mammals, sharks can maintain high bite forces no matter how widely their jaws are open, thanks to a unique jaw muscle arrangement that has helped them to be among the most successful predators of all time. The study is the first of its kind to use sophisticated three-dimensional computer models and advanced engineering techniques to examine how different sharks hunt and kill prey. Detailed computer simulations examined the feeding behaviour of two threatened shark species: the harmless grey nurse -- or sand tiger -- and the notorious great white. Digital models revealed that the jaws of grey nurse sharks are spring-loaded for a rapid strike on small, fast-moving fish, while those of great whites are better suited for a powerful bite on prey ranging in size from small fish to large marine mammals. "We were surprised that although the teeth and jaws of our sub-adult great white shark looked the part and the muscles were there to drive them, the jaws themselves just couldn't handle the stress associated with big bites on big prey," says study co-author Dr Stephen Wroe, who heads the Computational Biomechanics Research Group in the UNSW School of Biological, Earth and Environmental Sciences. The reason for this appears to be that until great whites reach a length of about 3 metres or more their jaws haven't developed enough stiff mineralised cartilage to resist the forces involved. The 2.5 metre great white shark used for the study was caught by the NSW Bather Protection Program. "It is hard to believe, but at this size great whites are basically just awkward teenagers that can't hunt large prey very effectively," says UNSW doctoral student Toni Ferrara, the lead author of the article. "It seems paradoxical that the iconic jaws of great white sharks -- made infamous by the classic Steven Spielberg movie Jaws -- are actually rather vulnerable when these sharks are young. Great white sharks are not born super-predators, they take years to become formidable hunters."Co-author Dr Vic Peddemors, of the NSW Cronulla Fisheries Research Centre of Excellence, says: "This study may also explain why many of the shark attacks off NSW are aborted after a single exploratory bite, as the great whites involved are usually juveniles that might sustain jaw injury if they persevered with the attack.
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Research article: Mechanics of biting in great white and sandtiger sharks
Abstract
Although a strong correlation between jaw mechanics and prey selection has been demonstrated in bony fishes (Osteichthyes), how jaw mechanics influence feeding performance in cartilaginous fishes (Chondrichthyes) remains unknown. Hence, tooth shape has been regarded as a primary predictor of feeding behavior in sharks. Here we apply Finite Element Analysis (FEA) to examine form and function in the jaws of two threatened shark species, the great white (Carcharodon carcharias) and the sandtiger (Carcharias taurus). These species possess characteristic tooth shapes believed to reflect dietary preferences. We show that the jaws of sandtigers and great whites are adapted for rapid closure and generation of maximum bite force, respectively, and that these functional differences are consistent with diet and dentition. Our results suggest that in both taxa, insertion of jaw adductor muscles on a central tendon functions to straighten and sustain muscle fibers to nearly orthogonal insertion angles as the mouth opens. We argue that this jaw muscle arrangement allows high bite forces to be maintained across a wider range of gape angles than observed in mammalian models. Finally, our data suggest that the jaws of sub-adult great whites are mechanically vulnerable when handling large prey. In addition to ontogenetic changes in dentition, further mineralization of the jaws may be required to effectively feed on marine mammals. Our study is the first comparative FEA of the jaws for any fish species. Results highlight the potential of FEA for testing previously intractable questions regarding feeding mechanisms in sharks and other vertebrates.
Citation: Ferrara, T. L., Clausen, P., Huber, D. R., McHenry, C. R., Peddemors, V., & Wroe, S. (2011). Mechanics of biting in great white and sandtiger sharks. Journal of biomechanics, 44(3), 430-435.
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Post by creature386 on May 17, 2013 23:05:26 GMT 5
Research article: Shark predation on North Atlantic right whales (Eubalaena glacialis) in the southeastern United States calving ground NOTESAggregations of North Atlantic right whales (Eubalaena glacialis) can be found seasonally in one of five known habitats in the western North Atlantic: Bay of Fundy, Roseway Basin, Cape Cod Bay, Great South Channel, and the southeastern United States. A portion of the population including pregnant females, migrates to thesoutheast calving ground during the winter months.
Leading contributions to mortality in right whales are entanglement in fishing gear and vessel collision (Knowlton and Kraus 2001, Moore et al. 2004). Determining the cause of death is more challenging for calves than for adults, and the majority of neonate necropsies are inconclusive (Moore et al. 2004). Undetected calf mortalitiesare likely far greater than documented cases, further under-representing mortalitysources in this demographic (Browninget al.2010). Predation pressure had notpreviously been considered a threat.
Sharks of both orders lamniformes and carcharhiniformes have been re-ported to attack odontocete cetaceans (Long 1991, Long and Jones 1996, Heithaus 2001, Heithaus and Dill 2002, Maldini 2003), but there is a paucity of literature describing predation on mysticetes. The majority of shark-mysticete interactions involve scavenging on carcasses rather than predatory attacks (Prattet al. 1982, Curtiset al.2006, Dicken 2008). Most documented cases of active predation on mysticetes involve debilitated animals, where predation is secondary to vessel collision, entanglement, perinatal defects, calf abandonment, illness, or unknown causes (Stroud and Roffe 1979, Mazzuca et al.1998). The few reported shark attacks on healthy mysticetes are limited to young whales (Mazzuca et al.1998).
Possible natural predators on the North Atlantic right whale include killer whales (Orcinus orca) and macropredatory sharks. Attacks evidenced in this population by scars on fluke tips of live individuals have been attributed to killer whale bites (Kraus 1990), but rarely to shark attacks. Based on known records of shark predation on comparably sized odontocetes, sharks that could potentially attack a right whale calf include the white (Carcharodon carcharias), tiger (Galeocerdo cuvier), shortfin mako (Isurus oxyrinchus), and possibly the bull shark (Carcharhinus leucas) (Lowe et al.1996, Heithaus 2001, Heithaus and Dill 2002).
The presence of white sharks in the southeast U.S. right whale calving habitat has been documented through opportunistic sightings (Casey and Pratt 1985), conventional tagging and fisheries-dependent observer data (NMFS 2009), and scavenging events (Table 1). Satellite-based tagging data provide evidence of overlap in the migration routes of these species from Massachusetts to Florida.1 Four different right whale carcasses were documented being scavenged by white sharks off the southeastern U.S. by research teams between 1994 and 2011 (Table 1). However, interactions are not limited to scavenging events. Necropsies and wound analyses provide supporting evidence for the occurrence of fatal and nonfatal predatory shark attacks on right whales. Citation: Taylor, J. K., Mandelman, J. W., McLellan, W. A., Moore, M. J., Skomal, G. B., Rotstein, D. S., & Kraus, S. D. (2013). Shark predation on North Atlantic right whales (Eubalaena glacialis) in the southeastern United States calving ground. Marine Mammal Science, 29(1), 204-212.LINK: onlinelibrary.wiley.com/doi/full/10.1111/j.1748-7692.2011.00542.x----- Here some accounts of great whites preying on right whales (calves):
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Post by Grey on Jun 4, 2013 5:38:07 GMT 5
The main up-to-date information to be known about the great white shark from the Western Australian Museum. The White Shark
The White Shark (Carcharodon carcharias)
Large sharksThe White Shark, otherwise known as the Great White or White Pointer, is one of the largest sharks. There are only two species of sharks known to exceed the White Shark in size and both are plankton feeders; the Whale Shark ( Rhincodon typus) and the Basking Shark ( Cetorhinus maximus). Close relativesThe White Shark belongs to the order Lamniformes which also includes the Basking Shark, the Megamouth Shark, Mako Sharks, Porbeagles, Thresher Sharks, the Crocodile Shark, the Goblin Shark, and Sand Tiger Sharks.
How big do they get?Females mature between 4 and 5 metres in total length and can reach 6 metres weighing as much as 2 tonnes. Males mature between 3.5 to 4 metres long and do not grow as large as mature females. How long do they live?In most lamniform sharks, annual growth bands are deposited within their back bones and these can be used to determine the age of the shark. Females mature between the ages of 12-17 and males between the ages of 7-9. White sharks are believed to live for almost 30 years. BabiesFemales gestate around 10 embryos. The mother produces additional unfertilised eggs that the newly-hatched sharks feed on in the uterus. Newborn free-swimming pups are estimated to be 1.2-1.4 metres long. With an estimated 18 months gestation period and a 3-year reproductive cycle, white shark populations are highly vulnerable to over fishing/culling.
Teeth!White Sharks have huge serrated teeth, much bigger than those of other sharks of comparable size. They continually replace teeth with slightly larger ones as their jaws grow. As White Sharks increase in size their teeth become broader, and at a body length around 3 metres they begin to predate on marine mammals like seals and dolphins, in addition to fishes. White Sharks are commonly observed feasting on whale carcasses and preferentially feed on the blubber.
When are they most active?Like other sharks feeding on large, highly mobile prey, White Sharks become more active during overcast days, or when water visibility is otherwise poor. Sharks do not depend solely on their sight to hunt prey, but more on smell and hearing, plus electroreception at close range, so reduced visibility enables them to get closer before they are detected. White Sharks maintain a variable body temperature 3-14?C higher than the surrounding water by a heat-exchanging circulatory system. This enables them to hunt in waters too cold for other large sharks, such as Tiger Sharks. White Sharks are powerful swimmers and are known to jump out of the water as they attack seals at the surface. Where do they live?The distribution of white sharks is mainly in temperate, coastal waters, but they may also frequent waters around oceanic islands, especially near seal colonies, and sometimes occur in tropical waters. Tagging programs have revealed that large individuals undertake major migrations across the ocean basins and may dive down to 1,000 metres or more. Who eats them?Orcas, (killer whales) are the only animals in the oceans known to kill White Sharks. In 1997, an adult female orca, accompanied by a second adult female, was observed attacking and killing a 3-4 metre White Shark at Southeast Farallon Island, California. Following the attack the other White Sharks in the area disappeared and did not return until the following season.
White Sharks as top predatorsWherever they occur, adult White Sharks are typically at the top of the food chain. By preying on juveniles and reproducing adults that take unnecessary risks (for example seals swimming at the surface rather than along the bottom whenever possible), White Sharks play an important role in maintaining or even improving the fitness of prey species.
ConservationIronically, the enormous jaws and large teeth that enable the White Shark to be such a formidable predator might eventually lead to its extinction. As rare top predators, White Sharks are usually not specifically targeted for their meat by shark fisheries. Their jaws and teeth however fetch very high prices on the black market. Even though they are protected by law in some areas, like Australia, they may be killed elsewhere as a result of their migratory lifestyle.
Evolution of white sharks
The origin of the White Shark and its relationship to the extinct shark megalodon (meaning mega-tooth) are controversial subjects in palaeontology. Megalodon, at an estimated adult length of almost 20 metres and a mouth big enough to swallow a small car, is justifiably regarded as the mother of all predators. One theory is that megalodon is closely related to the modern White Shark (and was therefore named Carcharodon megalodon). Another theory regards the two as only distantly related, belonging to separate families within the order Lamniformes. In recent years, the latter theory has gained ground and most palaeontologists working on fossil sharks recognise Carcharocles as the valid genus name for the extinct megalodon.
The beginnings of the White SharkThe origin of the White Shark can be traced back to the Paleocene or earliest Eocene geological periods, about 55 million years ago. Molecular and palaeontological evidence indicate that White Sharks are a sister group of Mako Sharks and that the two groups separated from a common ancestor approximately 50-60 million years ago.
More about teethSediments laid down in the ocean 2-7 million years ago but now exposed in the Peruvian desert preserve the transition from unserrated to serrated teeth in the White Shark lineage. The transformation took several million years as sharks evolve slowly compared to most other vertebrate groups. ResearchIn 2012, palaeontologists at the Western Australian Museum plan to explore 15-20 million-year-old rocks in the Southern Carnarvon Basin in search of fossil remains of Carcharocles megalodon and its favourite prey, baleen whales. Video clips and photographs will be uploaded on the MuseumÂ’s web site so you can follow the search for the ultimate super predator. Western Australia is already well known for its rich record of fossil sharks from the Cretaceous period (140-65 million years ago).
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Post by elosha11 on Jun 4, 2013 23:29:53 GMT 5
Good resource. I do think the "up to two tons" is a very conservative maximum weight. There have been numerous documented cases of great whites (mostly females but also some males) well exceeding two tons. For instance, the male shark Apache caught and release a couple years ago off Guadalupe was almost 18 feet and weighed 4225 pounds. newsfeed.time.com/2011/05/09/spontaneous-shark-week-18-foot-great-white-breaks-record/. And there are quite a few reports of great whites of around 6 meters or more exceeding 5000 pounds and even up to 6000. I think the maximum weight of a modern great white is around 3 tons, although it would be extremely rare. A 5000 pound shark today would be an uncommon giant. Prehistoric great whites (and probably even ones that existed a few centuries ago) could probably get significantly larger, maybe closer to 7 meters and 3-4 tons. As with many iconic animals such as polar bears, elephants, and big cats, mankind's encroachment and culling of the great white has diminished its overall size. |
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Post by elosha11 on Jun 17, 2013 21:11:11 GMT 5
Research article: An analysis of photographic evidences of the largest great white sharks (Carcharodon carcharias), Linnaeus 1758, captures in the Mediterranean sea with considerations about the maximum size of the species.Abstract We analysed photographic evidences of the largest white sharks Carcharodon carcharias caught in the Mediterranean Sea, reported in literature as measuring near to 6 metres or even more in length. We studied 7 specimens and estimated their lengths as TOT (total length with the caudal fin in the depressed position), TLn (total length with the caudal fin in the natural position) and PRC (Precaudal length) on the basis of the measurements of a 583 cm TOT specimen preserved in the Museum of Zoology in Lausanne. The following TOT were obtained: 507 cm (Procida, Italy, June 1924), 597 cm (Enfola, Isola d'Elba, Italy, 12 August 1938), 666 cm (Ganzirri, Sicily, Italy, June 1961), 492 - 547 cm (Piran, Slovenia, 22 October 1963), 594 cm (Favignana, Isole, Egadi, Italy, May 1974), 668 - 681 cm (Filfa, Malta, 17 April 1987), 591 cm (Sète, France, 9 January 1991). Five specimens therefore measured over 590 cm and at least two of these, Ganzirri 1961 and Malta 1987, grossly exceeded the 6 m mark both as TOT and TLn. Also, these two specimens could be the largest ever recorded world-wide. We discuss the more solid cases of other white sharks in the same size range (Kangroo Island, Australia, 1987; Castillo de Cojimar, Cuba, 1945; Dakar, Senegal, 1982). We conclude that C. carcharias can reach at least 640-660 cm TOT and very probably even more.
Citation: De Maddalena, A., Zuffa, M., Lipej, L., & Celona, A. (2001). An analysis of the photographic evidences of the largest great white sharks, Carcharodon carcharias (Linnaeus, 1758), captured in the Mediterranean Sea with considerations about the maximum size of the species. In Annales, Series historia naturalis (Vol. 11, No. 2, pp. 193-206). ----- ----- -----
Very good research paper published in 2001 on the length/weight estimates of the some of the giant great whites found in in the Mediterranean, including the Malta specimen.
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Post by elosha11 on Jun 17, 2013 21:16:27 GMT 5
Research article: Tracing the Ancestry of the Great White Shark, Carcharodon carcharias, Using Morphometric Analyses of Fossil TeethAbstractThe evolutionary origin of the great white shark (Carcharodon carcharias) is unclear, with debate centering around two principal hypotheses. The first, based on similarity in tooth shape, claims that C. carcharias originated from a group of extinct mako sharks that includes Isurus hastalis. The second hypothesis, based mostly on cladistic evidence, claims that C. carcharias originated from the same lineage as the giant megatoothed sharks, sharing a close evolutionary ancestor with the extinct Carcharodon megalodon. To distinguish between the two hypotheses we performed several morphometric analyses. In the first analysis, we used Procrustes method and principal components analysis to quantify variation between C. carcharias, I. hastalis, and C. megalodon in four different positions within the dentition. The results indicate no significant difference in tooth shape between C. carcharias and I. hastalis. In the second analysis, correlating tooth size with age, we analyzed teeth from upper anterior and lower anterior positions. For both tooth positions, we show that the growth rate of C. carcharias is more congruent with the growth rate of I. hastalis than that of C. megalodon. Finally, we used scanning electron microscopy to show that the tooth serrations of C. carcharias are distinct from those of the megatooths and more similar in size to those of slightly serrated mako teeth. Taken together, these results indicate that C. carcharias originated from an extinct group of mako sharks and not from the megatoothed sharks.
Citation: Nyberg, K. G., Ciampaglio, C. N., & Wray, G. A. (2006). Tracing the ancestry of the great white shark, Carcharodon carcharias, using morphometric analyses of fossil teeth. Journal of Vertebrate Paleontology, 26(4), 806-814.
----- Excellent Duke University research paper from 2006 tracing the ancestral origins of the great white. The papers strongly correlates and agrees with the latest findings from the Peruvian fossil, Carcharodon hubbelli, which indicate that the GWS traces its ancestory to the prehistoric mako Isurus hastalis, rather than the mega-toothed line.
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Post by elosha11 on Jun 17, 2013 21:19:56 GMT 5
Research article: Predation by White Sharks Carcharodon carcharias (Chondrichthyes: Lamnidae) Upon Chelonians, with New Records from the Mediterranean Sea and a First Record of the Ocean Sunfish Mola mola (Osteichthyes: Molidae) as Stomach ContentsAbstractThe occurrence of marine turtles in the diet of white sharks, Carcharodon carcharias, is reviewed worldwide. Four records of chelonians eaten by white sharks in the Mediterranean Sea are described, which on the basis of carapace remnants confirmed both the loggerhead Caretta caretta and green turtle Chelonia mydas to be preyed upon in those waters. The condition of these remains indicates that large white sharks can ingest turtles essentially intact. As well as falling prey to white sharks, we suspect that some interactions involve turtles being ‘grab-released’ in a non-predatory mannner and their survivability from such low-intensity bites or other mouthings may be quite high. The white shark may be the chief marine predator of adult chelonians in the Mediterranean Sea, albeit the impact of this predation upon turtle populations is nominal compared to other sources of mortality. Further, we give an account describing an adult ocean sunfish, Mola mola, in the stomach of a white shark taken in Italian waters. Citation: Fergusson, I. K., Compagno, L. J., & Marks, M. A. (2000). Predation by white sharks Carcharodon carcharias (Chondrichthyes: Lamnidae) upon chelonians, with new records from the Mediterranean Sea and a first record of the ocean sunfish Mola mola (Osteichthyes: Molidae) as stomach contents. Environmental Biology of Fishes, 58(4), 447-453.
Full read: citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.1057.5693&rep=rep1&type=pdfInteresting accounts of great white predations on sea turtles and ocean sunfish in the Mediterranean.
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