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Diet of the great white shark.

Today we have solid evidence that great white sharks (Carcharodon carcharias) attain 6.6 meters, and probably even over 8 meters. Great white sharks are apex predators, and play an important ecological role in marine communities. As predators, they are fundamental instruments of natural selection. As scavengers they process organic material so that it can then be used by other creatures.

The great white shark is one of the more omnivorous sharks, and, in fact, they eat almost anything, though they are primarily carnivorous, or flesh-eating animals. Great white shark teeth are adapted for sawing or shearing pieces from large animals. The teeth are large, triangular in shape, sharp, and with serrate edges. The mouth, pharynx, esophagus and stomach are sufficiently wide to enable the great white shark to ingest whole animals, large chunks of prey or a large amount of smaller prey. Ingesting large amounts of food at a time means that they do not need to feed often.

Great white shark stomachs are "U" shaped, consisting of two portions: the cardiac stomach and the pyloric stomach. Food can be stored in the cardiac stomach undigested for long periods of time. Often, when a great white shark is eviscerated, prey is found in a near perfect state of preservation, intact or marked by only a few superficial teeth marks.

While most sharks have body temperatures equal to that of the surrounding seawater, great white sharks exhibit regional endothermy, enabling them to maintain a higher body temperature than that of the seawater because of a heat-retaining system. A peculiar structure of the circulatory system allows the great white shark to maintain a body temperature between 4[degrees]C and 14[degrees]C higher than the ambient water temperature. Heat is a form of energy, so great white sharks have more energy at their disposal than most sharks that are cold-blooded. Therefore great white sharks are very powerful, fast, capable of fast acceleration and able to leap high above the sea surface.

The very active warm-blooded great white sharks have a higher metabolism rate than many other sharks that are cold-blooded animals. So, species phyletically far from the great white shark, such as the blue shark (Prionace glauca) and the sandbar shark (Carcharhinus plumbeus), are cold-blooded and eat 0.2 percent to 0.6 percent of their body weight per day. A 1.5 m great white shark in captivity ate 1.6 percent of its body weight per day.

It has been estimated that a 4.6 m great white shark could survive 1.5 months between meals. It has also been estimated that about 30 kilograms of fatty tissue taken from a whale or a pinniped would provide enough energy to sustain a great white shark for this period. Sharks expend considerable time and energy looking for prey and in hunting activity, so it is beneficial for a large shark to consume one large food item rather than to capture numerous small items. This notion is supported by the preference for large prey, such as tuna, other sharks, pinnipeds, dolphins, and marine turtles, which are dominant parts of the white shark diet.

It has been suggested that the great white shark favors an energy-rich fatty diet. In fact, these sharks show preference for northern elephant seals (Mirounga angustirostris) and harbor seals (Phoca vitulina) over sea lions (family Otariidae) and sea otters (Enhydra lutris), for pinniped pups over adults, and for baleen whale blubber over muscle.

Great white sharks are opportunistic feeders, meaning they are versatile and able to utilize diverse food sources depending on the availability of each food type. This species obtains most of its prey by killing it, but readily scavenges available carrion. Feeding on dead animals is very advantageous because it often provides enough energy to sustain a shark for long periods, with minimal energy expenditure. Its diet in different areas may vary according to the availability and vulnerability of suitable prey.

Great white sharks usually prey on animals of smaller size. Live prey of great white sharks range in size from small schooling fishes to grey whale calves (Eschrichtius robustus). The diet of a great white shark is closely related to its size and age. As the size of the great white shark increases, the prey spectrum also increases as the larger shark can feed on larger prey. Larger white sharks (above 3 m in length) tend to prey more readily on marine mammals, and in general will feed on any large size prey. Sharks below 3 m in length feed more readily on small and medium-sized bony fishes and other sharks. The great white shark's tooth shape is related to its age. Tooth shape changes as the great white shark grows larger and feeds on different animals. As the shark grows, the teeth become thick and strong to accommodate larger prey.

Great white sharks feed on a wide variety of prey, including bony fishes, elasmobranchs, marine mammals, molluscs, crustaceans, sea turtles and birds. The bony fish and cartilaginous fish prey of the white shark includes a variety of sizes from small to large, and includes pelagic, demersal and benthic species, such as anchovies (family Engraulidae), hakes (genus Merluccius), barracudas (family Sphyraenidae), tuna (genus Thunnus), scorpionfish (genua Scorpaena), swordfish (Xiphias gladius), stingrays (genus Dasyatis), and many others.

Great white sharks are known to congregate near concentrations of schooling bony fishes such as tuna, pilchards and bluefish. The great white shark's diet even includes a number of other shark species such as the sandbar shark (Carcharhinus plumbeus) and the blue shark (Prionace glauca). Many sharks can eat conspecifics. While large white sharks can attack hooked or injured conspecifics, and can deliver severe bites to other healthy white sharks, no white shark has been found in another white shark's stomach.

It has been suggested that white sharks have behavioral inhibitions on cannibalization under ordinary circumstances, as reflected from social interactions of white sharks within aggregations. Marine mammals, both pinnipeds and cetaceans, are an important food source for white sharks. Pinnipeds tend to congregate in colonies where they are highly vulnerable. Live small and medium-sized cetaceans, as well as dead large cetaceans, contribute a significant amount to the white shark diet. Sea turtles are occasionally eaten by the great white shark. Marine birds are commonly grabbed, killed and often eaten. Terrestrial mammalian carrion from slaughterhouses and other sources has also been found in the stomachs of white sharks.

Invertebrate prey, including squids, abalone and other gastropods, bivalves, and crabs are also eaten. The occurrence of algae and seaweed in shark stomachs is usually associated with benthic animal remains. Sometimes the prey grasps the substratum when trying to escape, and the predator ingests both prey and algae. In other circumstances, the prey may be hiding in the canopy of large algae, such as kelp (Macrocystissp.), and the algae is ingested with the hiding animal. Otters, sea lions and harbor seals are commonly found in the canopies of kelp forests.

The stomachs of some great white sharks contain inedible items and other oddities. These materials are rarely found in the stomachs of most shark species. However, the great white shark, tiger shark (Galeocerdo cuvier) and the bull shark (Carcharhinus leucas), swallow inedible items more frequently than others.

The list of oddities found in the stomachs of great white sharks from various locations (including the Mediterranean Sea, South Africa, Australia and other locations) includes stones of up to 7 kg, a 2.74 m long wire, a buoy chain, thirty-one hooks that were 15 cm long, pants, boots, shoes, baskets, a small board of cork, a raincoat, two or three coats, other clothes, a wig, a broom handle, an automobile license plate, a plastic bin, plastic bags, garbage, a sheet of cardboard, a duster, a ship scraper, a wicker-covered scent bottle, plastic bottles and two pumpkins. Some researchers have hypothesized that stones, pebbles and other dense inedible items may be useful as ballast. Some of these materials are also thought to have been ingested as part of the stomach contents of the prey.

Additional Reading

To learn more about sharks, visit The World & I Online archives:

Article #25301: "Shark Teeth: Form and Function," Alessandro De Maddalena, December 2006.

Article # 25044: "The Social Lives of Hammerheads," Alessandro De Maddalena and Alex Buttigieg, June 2006.

Article # 24744: "The Mako: Most Picturesque of All the Sharks," Alessandro De Maddalena, December 2005.

Article #23648: "Sharks: Dangerous or Endangered?" by Alessandro De Maddalena, January 2004.

Alessandro De Maddalena is president of the Italian Ichthyological Society, curator of the Italian Great White Shark Data Bank, and a founding member of the Mediterranean Shark Research Group.
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Title Annotation:NATURAL SCIENCE
Author:De Maddalena, Alessandro
Publication:World and I
Geographic Code:4EUIT
Date:Nov 1, 2009
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