South Africa's great white sharks face the threat of extinction after a rapid decline in numbers caused by trophy hunting, shark nets and pollution, according to a study released Wednesday.
The six-year research project along the country's coastline revealed that only between 353 and 522 of the sharks are still alive, half the level previously thought.
"The numbers in South Africa are extremely low. If the situation stays the same, South Africa's great white sharks are heading for possible extinction," said study author and Stellenbosch University researcher Sara Andreotti.
Scientists conducted the census by collecting biopsy samples and photographs of dorsal fins of the great predators, including in the Gansbaai area, near Cape Town, a hotspot for shark cage diving.
"We have come to the conclusion that South Africa's white sharks faced a rapid decline in the last generation and that their numbers might already be too low to ensure their survival," said Andreotti.
The study published in the journal Marine Ecology Progress Series also blamed shark nets, ocean pollution and baited hooks on the eastern seaboard of South Africa for the dwindling numbers.
"The chances for their survival are even worse than what we previously thought," said Andreotti.
About 333 of the sharks are thought to be capable of breeding.
Although the great whites population has dropped off South Africa, the report said the sharks were still found in large numbers off the coast of Canada, Australia and the United States.
The South African coast is notorious for shark attacks, with regular cases of deadly mauling of surfers and swimmers.
New study illustrates the physics behind great white shark attacks on seals
A new study examining the complex and dynamic interactions between white sharks and Cape fur seals in False Bay, South Africa, offers new insights on the physical conditions and biological factors underlying predator-prey interactions in the marine environment.
University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science assistant professor Dr. Neil Hammerschlag, and a colleague from the University of British Columbia, describe how sharks are camouflaged as they stalk their prey from below. Low-light conditions, from the optical scattering of light through water, along with a shark's dark grey back and the dimly light rocky reef habitat allow sharks to remain undetected by seals swimming at the water's surface.
"Animal hunting in the ocean is rarely observed by humans," said Hammerschalg, director of the RJ Dunlap Marine Conservation Program at UM. "The high frequency of attacks by white sharks on seals at our study site in South Africa provides a very unique opportunity to uncover new insights about predator-prey relationships."
Sharks typically search, stalk and strike their prey from below. The vast majority of predatory strikes by sharks and Cape fur seals occur against small groups of young-of-the-year seals. Predatory activity by sharks is most intense within two hours of sunrise and quickly decreases as light penetration in the water column increases.
"Stealth and ambush are key elements in the white shark's predatory strategy," said Hammerschlag.
Cape fur seals also have unique techniques to detect, avoid, outmaneuver and in some cases injure the white sharkin order to avoid predation by sharks.
According to the authors, if a seal is not disabled during the shark's initial shark, the small seal can use its highly maneuverable body to leap away from the shark's jaws to evade a second strike.
Great white sharks hunt just like Hannibal Lecter
In this undated photo released by The University of Miami, a white shark is seen successfully lunging for and capturing a juvenile fur seal at the surface in False Bay, South Africa in 2004.
Great white sharks have some things in common with human serial killers, a new study says: They don't attack at random, but stalk specific victims, lurking out of sight.
The sharks hang back and observe from a not-too-close, not-too-far base, hunt strategically, and learn from previous attempts, according to a study being published online Monday in the Journal of Zoology. Researchers used a serial killer profiling method to figure out just how the fearsome ocean predator hunts, something that's been hard to observe beneath the surface.
"There's some strategy going on," said study co-author Neil Hammerschlag, a shark researcher at the University of Miami who observed 340 great white shark attacks on seals off an island in South Africa. "It's more than sharks lurking at the water waiting to go after them."
The sharks feeding at Seal Island could have just hovered right where the seals congregated if they were random killers-of-opportunity, Hammerschlag said. But they weren't.
The sharks had a distinct M.O.
They were focused. They stalked from a usual base of operations, 100 yards from their victims. It was close enough to see their prey, but not close enough to be seen and scare off their victims. They attacked when the lights were low. They liked their victims young and alone. They tried to attack when no other sharks were around to compete. They learned from previous kills.
And they attacked from below, unseen.
There's a big difference between great white sharks and serial killers and it comes down to that old gumshoe standard: motive. The great whites attack to eat and survive, not for thrills. And great whites are majestic creatures that should be saved, Hammerschlag said.
"They both have the same objective, which is to find a target or prey or victim," said study co-author D. Kim Rossmo, a professor of criminal justice at Texas State University-San Marcos. "They have to lurk. They want to be efficient in their search."
The human criminal has to worry about being caught by police and thus is even more careful, said Rossmo, who was a police officer for more than 21 years in Vancouver, British Columbia.
The entire shark-serial killer connection is something right out of a crime novel.
R. Aidan Martin, a Canadian shark researcher who has since died, was reading a whodunit that detailed the relatively new field of geographic profiling, which tries to find criminals by looking for patterns in where they strike. He connected with Rossmo, a pioneer in that criminal field, and they applied the work of tracking down criminals to sleuthing shark strategy.
Martin and Hammerschlag watched sharks from sunrise to sunset, applied the "fancy math" of geographic profiling and came out with plots that showed there was some real stalking going on, Hammerschlag said. Older sharks did better and were more stealthy than younger, smaller sharks, demonstrating that learning was occurring, he said.
The study focused on just one location, but the same principles are likely to be applied to other shark hunting grounds. They can't really apply to shark attacks on people because those are so infrequent, Hammerschlag said. But if you could figure out the base of operations for the great whites, it would give you a good idea of places to avoid if you were worried about shark attacks, he said.
Other animals, such as lions, also reveal strategies in their hunting, Hammerschlag said. Land animals have been observed more easily from the air or elsewhere on the ground.
University of Florida shark attack researcher George Burgess, who had no role in the study, said the researchers simply used a new tool to show what scientists pretty much knew all ready: "Sharks are like many other predators that have developed patterns to their attacking that are obviously beneficial as a species."