GREAT WHITE SHARKS
Carcharodon carcharias Immortalized in the 1974 film Jaws , great white sharks are the most dangerous of all sharks and the largest carnivorous fish in the sea. Despite their fearsome reputation and celebrity status very little is known about them. Even basic things like how they live, how they reproduce, how big they can get and how many there are, are still mysteries. Great white shark are also known as white sharks or white pointers. Its scientific name Carcharodon carcharias is derived from Greek for “jagged tooth.” [Sources: Paul Raffaele, Smithsonian magazine, June 2008; Peter Benchley, National Geographic, April 2000; Glen Martin, Discover, June 1999]
Fear of great white shark by humans has probably been around since the first time ancient man encountered one. According to the History of the Fishes of the British Isles , written in 1862, the great white “is the dread of sailors who are in constant fear of becoming its prey when they bathe or fall into the sea.” In 1812, British zoologist Thomas Pennant wrote that “in the belly of one was found a human corpse entire: which is far from incredible considering their vast greediness after human flesh.”
Great white sharks made their film debut in the 1971 documentary Blue Water, White Death , which consisted primarily of the filmmaker searching the globe for great whites and not finding any until he reached Australia, where a large beast was attracted to a shark cage with some fish heads and bloody chum. Jaws was the first film ever to earn $100 million at the box office, launching the era of the summer blockbuster. Leonard Compagno, a shark expert who helped design the mechanical shark used in the film told Smithsonian magazine, “The movie great white scared the hell out of people, and made the shark much feared,” and added that in reality they “rarely bother people and even more rarely attack them.”
Websites and Resources: National Oceanic and Atmospheric Administration noaa.gov/ocean ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Ocean World oceanworld.tamu.edu ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Montery Bay Aquarium montereybayaquarium.org
Websites and Resources on Fish and Marine Life: MarineBio marinebio.org/oceans/creatures ; Census of Marine Life coml.org/image-gallery ; Marine Life Images marinelifeimages.com/photostore/index ; Marine Species Gallery scuba-equipment-usa.com/marine Book: "The Devil's Teeth," by Susan Casey chronicles her sojourn among great white sharks and the scientists who study them off the Farallon Islands near San Francisco.
Great White Shark Range and Size
Great white sharks are found in tropical, subtropical and temperate, and occasionally in cold waters worldwide. They are generally found in somewhat cold temperate waters’such as off southern Australia, South Africa, Japan, New England, Peru, Chile, southern New Zealand and northern California. They only occasionally show themselves in warm shallow water such as in the Caribbean. Peter Benchley, the author Jaws , once encountered a great white shark in water around the Bahamas. They are seen from time to time in the Mediterranean. A dead 4.8 meter great white shark was found floating belly up in a canal of Kawasaki Port near Tokyo ones. Workers used a crane to remove it.
Female great white sharks are larger than males. They generally average 14 to 15 feet in length (4½ to 5 meters) and weigh between 1,150 and 1,700 pounds (500 to 800 kilograms). The largest great white ever caught and officially documented was 19½ feet long. It was caught with a lasso. It is believed that sharks great whites that weigh 4,500 pounds are not uncommon.
There have been claims of beasts up to 33 feet long, but none have been properly authenticated. In 1978, for example, a five-ton Great White Shark measuring 29 feet 6 inches was reportedly harpooned off the Azores. But there is no firm evidence of this feat. There was another unauthenticated reports of a 23-foot, 5,000-pound beast caught near Malta in 1987. A sea turtle, a blue shark, a dolphin and bag full of garbage were found in the fish’s digestive tract. A dead 4.8 meter great white shark was found floating belly up in a canal of Kawasaki Port near Tokyo. Workers used a crane to remove it. There was a report of 21-foot, 7,000 pounder captured off Cuba.
The largest fish ever caught with a rod and reel was a 2,664 pound, 16-foot, 10-inch great white shark caught near Ceduna, South Australia with 130-pound test line in April 1959. A 3,388 pound great white shark was caught off Albany West Australia in April 1976 but is not listed as a record because whale meat was used as bait.
Great White Characteristics
areas where Great Whites have been seen Great white sharks can be distinguished from other sharks by their unique caudal peduncles (rounded protrusions near the tail, resembling horizontal stabilizers). They have conical snouts and a grey to black upper body. Their name is derived from their white underbellies.
Great white sharks are powerful swimmers. They move through the sea with sideways thrusts from their crescent-shaped tail fin. Its fixed, sickle-shape pectoral fins keep it from nose-diving in the water. The triangular dorsal fin provide stability. They move through the water at or near the surface or just off the bottom and can cover long distances relatively quickly. It also good at short, fast chases and has the ability to leap far out of the water.
Great white sharks have about 240 serrated teeth in up to five rows. The teeth are about as long as a finger and sharper than daggers. A great white bite is extremely powerful. It can exert pressure of 2,000 pounds per square inch. Their pectoral fins can reach a length of four feet.
Great whites have huge livers that can weight to 500 pounds. The sharks use their livers to store energy and can go months without eating.
Great whites, salmon shark and makos are warm blooded. This gives them the ability to maintain body heat in a wide range of temperatures but requires a lot of energy and food to maintain. Great whites maintains it muscles at very high temperatures and recycle heat from its warming muscles to the rest of its body, helping it swim more efficiently.
The white shark prefers cool and temperate seas worldwide. According to Natural History magazine Its brain, swimming muscles, and gut maintain a temperature as much as twenty-five Fahrenheit degrees warmer than the water. That enables white sharks to exploit cold, prey-rich waters, but it also exacts a price: they must eat a great deal to fuel their high metabolism. Great whites burn a lot of calories and keep their blood warmer than the surrounding water. Their body temperatures are usually around 75̊F and they tend to hang out in water that is between 5̊F and 20̊F colder than their bodies. Staying warmer than the surrounding water alone requires a large amount of energy.
Great White Brain and Sensory Organs
Based on the examination of a head supplied to researchers at the University of South Florida by a fishermen, the great white shark’s brain weighs only an ounce and a half. The scientists determined that 18 percent of the brain was devoted to smell, the highest percentage among sharks.
Great white sharks possess acute color vision, the largest scent-detecting organs of any shark, and sensitive electroreceptors that give it access to environmental cues beyond human experience. They have sensitive eyes with rods and cone receptors like human that pick up color and heighten the contrast between dark and light, which is useful for making out prey at long distances away under water. They also have a reflective layer behind their retina---the same thing that makes cat’s eyes glow---and that helps bounce extra light to the retinal cells to enhance vision in murky water.
Great white sharks have a number of other features that help them detect prey. They have unusually large olfactory bulbs in their nostrils that give them a more acute sense of smell than nearly any other fish. They also have tiny electrical sensors in their pores, connected to nerves via jelly-fill canals, that detect the heartbeats and movements of prey and electrical fields.
Their mouths are also sensory organs with pressure sensitive jaws and teeth that may be able to determine whether potential prey is worth eating or not. Shark expert Ron Taylor told the International Herald Tribune, "Great white sharks are made to hunt marine mammals. The only way they can really investigate something is by feeling it with its teeth.”
Peter Klimly of the University of California are Davis, who has studied sharks for almost 40 years, told Smithsonian magazine that great white sharks operate from a “hierarchy of senses.” depending on it distance from potential prey. “At the greatest distance, it can only smell something, and as it draws close it can hear, and then see it, When the shark gets really close, it can’t actually see the prey right under its snout because of its eye position, so it uses electroreception.”
Great White Shark Behavior
Leonard Compagno, a shark expert who has worked with great white sharks for more than 20 years in South Africa, says great white sharks are surprisingly intelligent creatures. He told Smithsonian magazine, “When I’m on the boat, they’ll pop their heads out of the water and look me directly in the eye. Once when there were several people on the boat, a great white looked each person in the eye, one by one, checking us out. They feed on large brained social animals such as seals and dolphins and to do this you have to operate on a level higher than the simple machine mentality of an ordinary fish.”
Alison Kock, another shark researcher, regards great whites as “are intelligent, highly inquisitive creatures.” She told Smithsonian magazine that she once saw a great white shark come up from below a sea bird floating in the surface of the water and “gently” grab the bird and swim around a boat---in what almost seemed like an act of play--- and release the bird which flew away, apparently unharmed. Researchers also found living seals and penguins with “curiosity bites.” Compagna says many so-called “attacks” on human are equally playful. He said, “I interviewed two divers here who were grabbed lightly by the hand by a white shark, towed a short distance and then released with minimal injury.”
Great white compared to Megalodon
Great White Shark Intelligence, Curiosity and Learning
R. Aidan Martin and Anne Martin wrote in Natural History magazine, “ Complex social behaviors and predatory strategies imply intelligence. White sharks can certainly learn. The average shark at Seal Island catches its seal on 47 percent of its attempts. Older white sharks, however, hunt farther from the Launch Pad and enjoy much higher success rates than youngsters do. Certain white sharks at Seal Island that employ predatory tactics all their own catch their seals nearly 80 percent of the time. For example, most white sharks give up ira seal escapes, but a large female we call Rasta (for her extremely mellow disposition toward people and boats) is a relentless pursuer, and she can precisely anticipate a seal's movements. She almost always claims her mark, and seems to have honed her hunting skills to a sharp edge through trial-and-error learning. [Source: R. Aidan Martin, Anne Martin, Natural History magazine, October 2006]
We are also learning that white sharks are highly curious creatures that systematically escalate their explorations from the visual to the tactile. Typically, they nip and nibble to investigate with their teeth and gums, which are remarkably dexterous and much more sensitive than their skin. Intriguingly, highly scarred individuals are always fearless when they make "tactile explorations" of our vessel, lines, and cages. By contrast, unscarred sharks are uniformly timid in their investigations. Some white sharks are so skittish that they flinch and veer away when they notice the smallest change in their environment. When such sharks resume their investigations, they do so from a greater distance. In fact, over the years we have observed remarkable consistency in the personalities of individual sharks. In addition to hunting style and degree of timidity, sharks are also consistent in such traits as their angle and direction of approach to an object of interest.
There is a guy in South Africa that attracts great white’s to his boat, rubs their nose, which causes the fish to flop back and beg like a dog that wants its stomach scratched.
AC/DC Can Calm Great White Sharks
According to NME, Australian boat operator Matt Waller has been conducting experiments to determine how certain music affects the behavior of great white sharks. After pawing through his music library and playing tons of different songs to no avail, he hit the jackpot. He noticed that when he played AC/DC tracks, the ordinarily frenzied sharks became much more calm. [Source: NME, Andrea Kszystyniak, pastemagazine.com]
“Their behavior was more investigative, more inquisitive and a lot less aggressive,” Waller said to Australian news outlet ABC news. “They actually came past in a couple of occasions when we had the speaker in the water and rubbed their face along the speaker which was really bizarre.”
These sharks are responding to the music without even being able to hear it. Waller says that they are simply reacting to the frequencies and vibrations of the Aussie rock band. “Sharks don’t have ears, they don’t have long hair, and they don’t head bang past the cage doing the air guitar,” Waller said to Australian Geographic. So which album do they like best? Is it AC/DC’s 1979 record, Highway to Hell? Or a piece off of 1981 hit, For Those About to Rock, We Salute You? Nope. Apparently the shark’s top track is “You Shook Me All Night Long.”
Great White Shark Social Behavior
Great whites mostly hunt alone but that doesn't mean they are they are the loan wolves they are often made out to be. They are sometimes seen in pairs or small groups feeding on a carcass with the largest individuals feeding first. Individuals can swim in a variety of patterns in order to establish their hierarchy.
Compagno told Smithsonian great white shark can be very social animals. When great white sharks congregate, he said, “some are assertive, others relatively timid. They body slam, nudge or carefully bite each other in dominance displays.” Fishermen have told him they have seen great white’s hunt cooperatively. “One great white will draw the attention of a seal, allowing another to come from behind and ambush it.”
Explaining what he had learned by tracking great whites implanted with electronic devices, Burney Le Boeuf, marine biologist at the University of California at Santa Clara, told Discover, "Specific sharks spent significantly more time with some sharks than other sharks. It was clear some kind of bonding had occurred.”
The bodies of great whites are often covered in scares. It is not known whether these scares are caused by resisting prey, whales, sex partners or other great white rivalry or even playfulness. Le Boeuf tracked one shark that had captured a seal and then engaged -n aggressive tail-slapping behavior, which seemed to indicate that there was only enough food for one shark and others should stay away.
Great White Shark Social Life
Around Seal island in South Africa when a seal is killed by one great white shark other great whites appear on the scene in minutes or in seconds. Usually they swim around one another, sizing each other up, with the lower-ranking sharks hunching their backs, and lowering their pectoral fins and then veering away while the higher ranking sharks’sometimes the one that made the kill, sometimes not---claim what remains of the carcass.
R. Aidan Martin and Anne Martin wrote in Natural History magazine, “After the morning flush of predatory activity at Seal Island, white sharks turn to socializing. For white sharks socializing trumps dining. Sneaky turns his attention to Couz. Is he friend or foe? Of higher or lower rank? For half a minute, Sneaky and Couz swim side by side, warily sizing each other up as white sharks do when they meet. All of a sudden, Sneaky hunches his back and lowers his pectoral fins in response to the threat posed by the larger shark, whereupon he and Couz veer apart. As we record their interactions, a female sweeps in and usurps the remains of Sneaky's abandoned meal. Then calm returns to the sea. Just six minutes have passed since the seal pup was innocently making its way to shore. [Source: R. Aidan Martin, Anne Martin, Natural History magazine, October 2006]
White sharks have a number of markings that may serve a social purpose. The pectoral fins, for instance, feature black tips on the undersurface and white patches on the trailing edge. Both markings are all but concealed when the sharks swim normally, but are flashed during certain social interactions. And a white patch that covers the base of the lower lobe of the shark's two-pronged tail may be important when one shark follows another. But if those markings help white sharks signal to one another, they may also make the sharks more visible to their prey. And if so, the trade-off between camouflage and social signaling demonstrates the importance of social interactions among white sharks.
Rank appears to be based mainly on size, though squatter's rights and sex also play a role. Large sharks dominate over smaller ones, established residents over newer arrivals, and females over males. Why such a focus on rank? The main reason is to avoid combat. As many as twenty-eight white sharks gather at Seal Island each day during the winter seal-hunting season, and competition among them for hunting sites and prey is intense. But since white sharks are such powerful, heavily armed predators, physical combat is a risky prospect. Indeed, unrestrained combat is extremely rare. Instead, the white sharks at Seal Island reduce competition by spacing themselves while hunting, and they resolve or avert conflicts through ritual and display.
At Seal Island, white sharks arrive and depart year after year in stable "clans" of two to six individuals. Whether clan members are related is unknown, but they get along peacefully enough. In fact, the social structure era clan is probably most aptly compared to that of a wolf pack: 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 era fascinating variety of interactions.
Types of Great White Shark Social Behaviors
R. Aidan Martin and Anne Martin wrote in Natural History magazine, “White sharks engage in at least twenty distinct social behaviors; eight are shown below. The significance of the behaviors remains largely unknown, but many help the sharks establish social rank and avoid physical conflict. They include: 1) Parallel Swim. Two white sharks swim slowly, side by side, several feet apart, perhaps to compare size and establish rank, or to determine ownership of a disputed kill. The submissive shark flinches and swims away. 2) Lateral Display. A white shark stretches out perpendicular to another shark for a few seconds, perhaps to show off its size and establish dominance. 3) Swim By. Two white sharks glide slowly past each other in opposite directions, several feet apart. They may be comparing sizes to determine which is dominant, or simply identifying each other. [Source: R. Aidan Martin, Anne Martin, Natural History magazine, October 2006]
4) Hunch Display. White shark arches its back and lowers its pectoral fins for several seconds in response to a threat, often from a dominant shark, before fleeing or attacking. 5) Circling Two or three white sharks follow one another in a circle, perhaps to identify one another or to determine rank. 6) Give Way. Two white sharks swim toward one another. The first to swerve cedes dominance--a white-shark version of "chicken." 7) Splash Fight. Two sharks splash each other with their tails, a rare behavior, apparently to contest the ownership of a kill. The shark that makes the most or biggest splashes wins, and the other accepts a submissive rank. A single shark may also splash another to establish dominance or contest a kill. 8) Repetitive Aerial Gaping. White shark holds its head above the surface, repeatedly gaping its jaws, often after failing to capture a decoy. The behavior may be a socially nonprovocative way to vent frustration.
Two white sharks often swim side by side, possibly to compare their relative sizes; they may also parade past each other in opposite directions or follow each other in a circle. One shark may direct splashes at another by thrashing its tail, or it may leap out of the water in the other's presence and crash to the surface. Once rank is established, the subordinate shark acts submissively toward the dominant shark--giving way if they meet, or avoiding a meeting altogether. And rank has its perks, which can include rights to a lower-ranking shark's kill.
Another form of nonviolent, tension-diffusing behavior often takes place after a shark repeatedly fails to catch bait (typically a tuna head) or a rubber seal decoy: the shark holds its head above the surface while rhythmically opening and closing its jaws. In 1996 Wesley R. Strong, a shark investigator then affiliated with the Cousteau Society in Hampton, Virginia, suggested the behavior might be a socially nonprovocative way to vent frustration--the equivalent era person punching a wall.
Great White Shark Migrations
It was once though that great white sharks remained near the surface in relatively small areas, where they could hunt seals and other prey. But studies have shown they move considerable distances and sometimes dive great depths. One study found that a single shark moved 1,800 miles along the Australian coast in three months. Another study found that great white shark swim to great depths, routinely reaching depths of between 900 and 1,500 feet and occasionally exceeding depths of 2,000 feet. DNA studies of great white sharks indicates that males tend to roam the seas while females stay closer to one place.
Another study recorded a male shark in northern California traveling 3,800 kilometers to Hawaii. It traveled at a rate of 71 kilometers a day, remained there during the winter months and returned to California. It is not clear why it traveled since there seemed to be plenty of food in California. Three other California great white shark swam hundreds of kilometers southward into the open sea of Baja California for several months and returned. A number of tagged California have lingered at a spot about halfway to Hawaii. What they do there---eat or mate perhaps---is still unknown.
It is believed that great whites follow regular migration patterns They feed on seals and elephant seals when the sharks are hanging out in sea mammals breeding areas. When the seals leaves to hunt in the open sea, the great whites also leave. It is not known where they go. Most likely the don’t hunt seals, who are widely dispersed. It believed that the sharks pursue other prey, possibly whales, but nobody knows.
Great White Shark regularly swim between Australia and South Africa, presumably to seek food. On great white shark tagged off of South Africa showed up about three months later 10,500 kilometers away off the western coast of Australia and then was seen back in South African waters. Research seem to indicate that the populations in North Pacific and those that migrate between South Africa and Australia are two separate populations that do not mingle.
R. Aidan Martin and Anne Martin wrote in Natural History magazine, “ In recent studies, electronic tags attached to individual white sharks and monitored by satellites have shown that the animals can swim thousands of miles a year. One individual swam from Mossel Bay, South Africa, to Ex-mouth, Western Australia, and back--a round trip of 12,420 miles--in just nine months. Such long-distance swimming may take white sharks through the territorial waters of several nations, making the sharks hard to protect (not to mention hard to study). Yet a better understanding of their habitat needs, their movement patterns, their role in the marine ecosystem, and their social lives is critical to the species' survival. [Source: R. Aidan Martin, Anne Martin, Natural History magazine, October 2006]
As September approaches, the white sharks' hunting season at Seal Island draws to a close. Soon most of them will depart, remaining abroad until their return next May. The Cape fur seal pups that have survived this long have become experienced in the deadly dance between predator and prey. They are bigger, stronger, wiser--and thus much harder to catch. The handful of white sharks that remain in False Bay year-round probably shift to feeding on fishes such as yellowtail tuna, bull rays, and smaller sharks. In effect, they seasonally switch feeding strategies from energy maximization to numbers maximization.
Tags placed on tuna, sharks and seabirds record levels of ambient lights that can be translated into longitude and latitude. See Tracking Great White Sharks.
Great White Shark Mating Behavior
Great white sharks seldom breed. They take about 15 years to reach reproducible age and breed only once in two years. Where and the details of how great white sharks mate is unknown. No one has ever seen great whites mate, scientist speculate the mate in the ocean depths after fattening themselves up near the coasts.
Like other sharks and cartilaginous fish, males possess a pair of sperm-delivering organs called claspers that extend from the pelvic fins. After mating eggs hatch inside the female’s uterus. The gestation period is about 11 to 14 months. It is not whether strong shark fetuses eat weaker one in the womb as is the case with other sharks.
Great white pups are born live. Females generally give birth to four to 14 pups that emerge from their mothers at about 1.5 meters (four or five-and-half feet) in length and weigh 25 kilograms (60 pounds) and appear ready to hunt. Even so may pups don’t survive their first year and are believed to be consumed by other sharks, including great whites.
Feeding Great White Sharks
Great white sharks feed primarily on seals, sea lions, dolphins, elephant seals, turtles, sea birds and large fish, including salmon and other sharks. They have been seen feasting on dead whales and and will feed on creature they can catch, including crabs, snails, squid, small fish and occasionally humans. Their preferred prey are young seals or elephant seals, which have a high-calorie layer of thick blubber, don't put much of fight and weigh about 200 pounds. They and can be killed and consumed by a single shark in less than a half hour. The large mouth, powerful jaws and large, triangular, serrated teeth of the great white shark are designed for ripping into the flesh of its prey.
Great whites often return year after year to the same hunting grounds. It is believed that they have a feast or famine diet. They may gobble up an entire seal one day and then go a month or more without eating anything. R. Aidan Martin and Anne Martin wrote in Natural History magazine, “ The white shark's diet includes bony fish, crabs, rays, sea birds, other sharks, snails, squid, and turtles, but marine mammals may be its favorite meal. Many of them are big, powerful animals in their own right, but predators with the means to catch them hit caloric pay dirt when they sink their teeth into the mammals' thick layer of blubber. Pound for pound, fat has more than twice as many calories as protein. By one estimate, a fifteen-foot white shark that consumes sixty-five pounds of whale blubber can go a month and a half without feeding again. In fact, a white shark can store as much as 10 percent of its body mass in a lobe of its stomach, enabling it to gorge when the opportunity arises (such as when it encounters a whale carcass) and live off its hoard for extended periods. Usually, though, white sharks eat more moderately. [Source: R. Aidan Martin, Anne Martin, Natural History magazine, October 2006]
Great whites like to stalk their prey from behind and below, and then attack, taking a massive bite and then waiting for their victim to bleed to death. They often sneak up on sea lions, seals and elephant seals from below and attack from behind. They usually take a powerful first bite underwater and the first indication on the surface is a large slick of blood. Minutes later, the victim appears on the surface with a large chunk missing. The shark thne appears and finishes it off.
Great whites have been observed shooting vertically upwards from a depth of 10 meters and knocking their prey right out of the water to stun it. Off South Africa great whites have been seen leaping five meters out of the water with a seal in their mouth. The impact stuns the prey and often leaves it with a chunk taken out it. The sharks then attack again or wait for their victims to bleed to death.
Great white sharks hunting for seals in waters off South Africa swim around three meters off the bottom in water that is 10 to 35 meters feet deep and wait up to three weeks before making a lightning quick strike from below on a seal at the surface. They sometimes swim with their teeth bared, apparently to warn off competitors for food or let other great whites know they are approaching too close to shark’s personal space. Tagged sharks in False Bay in South Africa, hunt seals when they are present at Seal Island but abandon the island when summer approaches---and the seals leave the island---and patrol close to shore, just beyond the breakers.
Great White Shark Hunting and Foraging Theory
Megalodon tooth with great white sharks teeth R. Aidan Martin and Anne Martin wrote in Natural History magazine, “ How does a white shark decide what to eat? A model known as optimal foraging theory offers a mathematical explanation of how predators weigh the calorie content of food against the energetic cost of searching for it and handling it. According to the theory, predators employ one of two basic strategies: they seek to maximize either energy or numbers. Energy maximizers selectively eat only high-calorie prey. Their search costs are high, but so is the energy payoff per meal. Numbers maximizers, by contrast, eat whatever kind of prey is most abundant, regardless of its energy content, thereby keeping per-meal search costs low. [Source: R. Aidan Martin, Anne Martin, Natural History magazine, October 2006]
Based on optimal foraging theory, A. Peter Klimley, a marine biologist at the University of California, Davis, has proposed an intriguing theory about the feeding behavior of the white shark. According to Klimley's theory, white sharks are energy maximizers, so they reject low-fat foods. That neatly explains why they often feed on seals and sea lions but rarely on penguins and sea otters, which are notably less fatty. As we mentioned earlier, however, white sharks eat maW other kinds of prey. Although those prey may be low-cal, compared with sea mammals, they may also be easier to find and catch, and thus sometimes energetically more attractive. It seems likely that white sharks follow both strategies, depending on which is the more profitable in a given circumstance.
Of all marine mammals, newly weaned seals and sea lions may offer the best energy bargain for white sharks. They have a thick layer of blubber, limited diving and fighting skills, and a naivete about the dangers lurking below. Furthermore, they weigh in at about sixty pounds, a good meal by anyone's standards. Their seasonal presence at certain offshore islands--Seal Island, the Farallon Islands off San Francisco, and the Neptune Islands off South Australia--draws white sharks from far and wide. Each winter, white sharks drop by Seal Island for between a few hours and a few weeks, to feast on young-of-the-year Cape fur seals. White sharks that visit either Seal Island or the Farallon Islands come back year after year, making those islands the marine equivalent of truck stops.
Great White Sharks: Picky Eaters?
R. Aidan Martin and Anne Martin wrote in Natural History magazine, “ Far from being the indiscriminate killers the movies have portrayed, white sharks are quite selective in targeting their prey. But on what basis does a shark select one individual from a group of superficially similar animals? No one knows for sure. Many investigators think predators that rely on single-species prey groups, such as schools of fish or pods of dolphins, have developed a keen sense for subtle individual differences that indicate vulnerability. An individual that lags behind, turns a little slower, or ventures just a bit farther from the group may catch the predator's eye. Such cues may be at work when a white shark picks a young, vulnerable Cape fur seal out of the larger seal population at Seal Island. [Source: R. Aidan Martin, Anne Martin, Natural History magazine, October 2006]
The location and timing of predatory attacks are also far from indiscriminate. At high tide on the Farallon Islands, for instance, there is heavy competition for space where northern elephant seals can haul themselves onto the rocks, and the competition forces many low-ranking juvenile seals into the water. Klimley--along with Peter Pyle and Scot D. Anderson, both wildlife biologists then at the Point Reyes Bird Observatory in California--has shown that at the Farallons, most white-shark attacks take place during high tide, near where the mammals enter and exit the water.
Similarly, at Seal Island, Cape fur seals leave for their foraging expeditions from a small rocky outcrop nicknamed the Launch Pad. Coordinated groups of between five and fifteen seals usually leave together, but they scatter while at sea and return alone or in small groups of two or three. White sharks attack almost any seal at Seal Island--juvenile or adult, male or female--but they particularly target lone, incoming, young-of-the-year seals close to the Launch Pad. The incoming seal pups have fewer compatriots with which to share predator-spotting duties than they do in the larger outgoing groups. Furthermore, they're full and tired from foraging at sea, making them less likely to detect a stalking white shark.
Great White Sharks Attack of Seals
Peter Klimey of the University of California has videotaped more than 100 attacks by great white sharks of elephant seals, sea lions and harbor seals at the Farallon Island, a group of rock islets west of San Francisco. Recalling an attack of an 400 pound elephant seal, Klimley told Time magazine, "It was stunning. The shark ambushed the seal, then came back several times to take three or four bites out of it. I had never seen anything like it...The white shark is a skillful and stealthy predator that eats with both ritual and purpose." Klimley told Discover, "The sharks appear to attack from ambush. From a seal's perspective, the dark grey of the sharks' backs could blend almost perfectly with a rocky bottom, and heavy surf could further serve to obscure them. The area of the best attacks...is one that provides them with the best camouflage."
One of the best places to see great white sharks is offshore from Seal Island in False Bay, near Cape Town in South Africa. Large sharks are routinely seen here leaping from the water with seals in their mouths. The waters around Seal Island are a favorite feeding area for great white sharks. On the flat, rocky island, a third of a kilometer long, 60,000 Cape fur seals gather. The seals are often attacked in the morning as they leave the island for their feeding ground 60 kilometers out in the bay. The attacks generally occur in the hour after dawn, because, scientists think, after that time, the seals can see the sharks approaching them from underwater and can escape. In the morning the seals are often jittery. Shark expert Alison Kick told Smithsonian magazine, “They want to go to sea to feed but they’re afraid of the white sharks.”
Great white sharks begin attacking the seals minutes after the first ones leave Seal Island to go out to sea. Paul Raffaele wrote in Smithsonian magazine, “The attacks begin...A 3,000-pound great white explodes out of the water. In mid air the shark lunges at a seal and flips back into the water with a mighty splash, Moments later another shark breaches and bites a seal, We speed to the spot, in time to see a pool of blood. Scores of gulls hover above, screeching in excitement, they swoop down to gobble up any leftovers...During an hour and a half, we witness ten great white sharks hurtling out of the water to grab seals. As the rising sun brightens the sky, the attacks stop.”
Joe Mozingo of Los Angeles Times wrote: "Even the great white's dynamic with seals is not what you might suspect in the open water, Winram said. Sharks attack injured seals or sneak up on them as they enter the water from the beach. But once the seals can see them in the open water, they are too agile for the sharks to catch. "I've seen them swim all around them and nip the shark in the tail." [Source: Joe Mozingo, Los Angeles Times, August 22, 2011]
Great White Shark Hunting Seals at Seal Island, South Africa
Describing an attack on a seal pup, Adrian and Anne Martin wrote in Natural History magazine, “Suddenly a a ton of white shark launched from the water like a Polaris missile, the little seal clamped between his teeth...the shark clears the surface by an astonishing six feet. It hangs, silhouetted in the chill air for what seems like an impossibly long time before it falls back into the sea, splashing thunderous spray...Now mortally wounded and lying on its side at the surface, the seal raises its head and weakly wags its left foreflipper...The shark, an eleven-and-a-half-foot male. Circles back unhurriedly and seizes the hapless seal pup. He carries it underwater, shaking his head violently from side to side, an action that maximizes the cutting efficiency of his saw-edged teeth. An enormous blush stains the water and an oily, coppery smell of the wounded seal pricks our nostrils. The seal carcass float to the surface while gull gulls and other seabirds compete for its entrails.”
The Martins wrote: “The white shark relies on stealth and ambush when hunting seals. It stalks its prey from the obscurity of the depths, then attacks in a rush from below. Most attacks at Seal Island take place within two hours of sunrise, when the light is low. Then, the silhouette of a seal against the water's surface is much easier to see from below than is the dark back of the shark against the watery gloom from above. The shark thus maximizes its visual advantage over its prey. The numbers confirm it: at dawn, white sharks at Seal Island enjoy a 55 percent predatory success rate. As the sun rises higher in the sky, light penetrates farther down into the water, and by late morning their success rate falls to about 40 percent. After that the sharks cease hunting actively, though some of them return to the hunt near sunset. [Source: R. Aidan Martin, Anne Martin, Natural History magazine, October 2006]
But Cape fur seals are hardly helpless victims. They are big, powerful predators in their own right, and take defensive advantage of their large canine teeth and strong claws. They also exhibit a remarkable range of antipredator tactics. Swimming quickly in small groups to or from the Launch Pad minimizes their time in that high-risk zone, and they remain in the relative safety of the open sea for extended periods. When they detect a white shark, seals often do a headstand, vigilantly scanning underwater with their rear flippers in the air. They also watch one another closely for signs of alarm. Alone, in pairs, or in threes, Cape fur seals occasionally even follow a white shark, swirling around it as if to let the would-be predator know its cover has been blown.
To avoid a shark attack, seals may leap in a zigzag pattern or even ride the pressure wave along a shark's flank, safely away from its lethal jaws. If an attacking shark does not kill or incapacitate a seal in the initial strike, superior agility now favors the seal. The longer an attack continues, the less likely it will end in the shark's favor. Cape fur seals never give up without a fight. Even when grasped between a white shark's teeth, a Cape fur seal bites and claws its attacker. One has to admire their pluck against such a formidable predator.
Great White Sharks Strategy Killing Seals
A study by Neil Hammerschlag of the University of Miami published in the Zoology Society of London’s Journal of Zoology found that great white sharks at Seal Island don’t just go after their victims randomly but rather use methods similar to those used by serial killers. “There’s some strategy going on,” Hammerschlag, told AP. “It’s more than sharks lurking at the water waiting to eat them.” [Source: Seth Borenstein. AP, June 2009]
Hammerschalg observed 340 great white shark attacks of seals at Seal Island. He observed that the sharks had a clear mode of operation. They tended to stalk their victims from a distance of 90 meters, close enough to see their prey and far enough away so their prey couldn’t see them. They attacked when the light was low and sought victims that were young and alone. They liked to attack when no other sharks were present. Most of all the liked to surprise their victims, sneaking up from below, unseen.
Hammerschalg’s team analyzed the great white’s action using “geographic profiling,” a method used in criminology that looks for patterns in where criminals strike. They surmised that the sharks learned from previous kills by the fact that larger, older sharks had more success making kills than younger, inexperienced ones.
Great White Shark Bites and Eating Methods
Describing the results of experiments with great white sharks and fake plywood seal, Burney L. Beoeuf of the University of California at Santa Cruz told Discover, "More often than not, they tended to initially mouth prey candidates delicately rather than just munch down. They're very particular about what they bite into. I have an intuitive sense that they have a soft mouth, like bird dogs. They get a tremendous amount of information from their mouths."
Klimey theorizes that great whites can tell the consistency and fat content of objects when they bite into them. If it is a seal they clamp on and go for the kill. If it is not they back off and save their energy for a more productive attack.
Because seals have sharp claws and can badly injure a shark during an attack, a great white usually bites once and then waits for their prey to die. The last thing a shark wants to do is eat or fight with an animal that is still struggling wildley.
Once their prey is dead, great whites go about eating it in a leisurely way, not a frenzy. Tom Cunneff wrote in Sports Illustrated, "Every minute or so the surface ripples. The shark takes a bite of the elephant seal, dives and circles back. Bite by bite over the next half hour the predator eats the 200-pound pinniped. The scene is peaceful and rhythmic."
Great whites often release animals after biting into them and more like to do this if they bite into a relatively low fat creature like a sea otter or human than a high-fat seal or sea lion. Klimley told Smithsonian magazine, “It may be a textural discrimination [of fat], more than what we could call taste...We once took a seal and stripped the fat off it and put it all the water. The shark ate the fat but not the rest of the body. They are actually very discriminating predators.”
Image Source: National Oceanic and Atmospheric Administration (NOAA) noaa.gov/ocean ; Wikimedia Commons
Text Sources: Mostly National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
Last updated March 2011