As teenagers, he said, great whites primarily feast on fish and go through an awkward hunter stage when they cannot hunt large prey very effectively.
"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," Wroe's colleague Toni Ferrara said. "Great white sharks are not born super-predators; they take years to become formidable hunters."
It might seem that, as adults, great whites would dine often and well during their ocean migrations. Prior research, however, has found that the sharks fuel up -- especially with elephant seal flesh -- before moving offshore.
Great white sharks store energy in the form of oil in their massive livers. The oil also helps with buoyancy, Barbara Block and her team from Stanford University found. Too much girth would weigh the sharks down, so there is not much incentive for an adult great white to overeat, or to practice cannibalism, if it is not starving to death and if other desirable prey is available.
In fact, when great whites scavenge on whale carcasses, they are rather picky. Researchers from Apex Expeditions, in collaboration with University of Miami Scientists, determined that adult great whites preferentially feed on the whale's fluke, leaving the lower quality parts for smaller, younger sharks.
McCosker indicated that adult great whites are capable of eating each other, and mentioned that other shark species, such as sevengill cow sharks, regularly feed on other sharks.
"However, I don't know if they are cannibalistic," he said. "I am not aware of adult white sharks cannibalizing other adults."
If the "colossal cannibal great white shark" theory does prove true over time, it's likely to have been similar to the Donner Party tragedy: rare and out of desperation.