Wroe added that "intrauterine (pre-birth) cannibalism is practiced by white shark pups, and it is likely that any white shark that makes it into the big wide world has already eaten one or more of its siblings. It's a hard life!"
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.