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// On :Friday, 28 February 2014
WHITE SHARK
Order - LamniformesFamily - Lamnidae
Genus - Carcharodon
Species - carcharias
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.
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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.
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.
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Habitat
The 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 Features
- · Coloration
- Dorsal 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.
Juvenile male white shark showing coloration
© George Burgess - · Dentition
- Teeth 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 - · Dermal Denticles
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.A Top view of white shark denticles (magnified) and B Side view of a single denticle
ex RadCliffe (1916) Bull. Bur. Fish. Circ. 822
- · 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 Behavior
- Although 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 even launching itself clear from the surface. 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 Habits
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 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.In most areas where white sharks occur, pinnipeds such as these California sea lions (Zalophus californianus), make up the bulk of the white shark's diet
© D. A. Sutton, Amer. Soc. Mammalogists Library
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.White shark scavenging a dead humpback whale
©Tobey Curtis
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 Behavior
- Some 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.
- · Reproduction
- White 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. Click here for more information on the reproductive strategy of white sharks.
Killer whales: mother and calf
courtesy National Marine Mammal Laboratory - · Predators
- The 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. Click here for a first hand account of a killer whale/white shark encounter and here for an interpretation of the encounter.
- · Parasites
- Parasites of the white shark include thePandarus sinuatus and Pandarus smithii. These copepods parasitize the body surface of this shark.
Importance to Humans
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Despite 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 Humans
The 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
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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.
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.
Prepared by:
Carol Martins & Craig Knickle
