By Victoria Gill

Science and nature reporter, BBC News

Until they are mature, great white sharks are not such formidable predators

At up to 3m in length, adolescent great white sharks certainly look like formidable predators. But until they reach maturity, the sharks have surprisingly weak jaws, according to researchers. A team of scientists in Australia used 3-D digital models of the sharks' heads to reveal the mechanics behind their infamous mouths. This showed that tough skin and bone of large prey could actually damage their relatively delicate young jaws. Great white sharks are not born super-predators, they take years to become formidable hunters

Toni Ferrara

University of New South Wales The scientists say that this could explain why many shark attacks on humans off the Australian coast are aborted after a single "exploratory" bite. To study the shark's bite in detail, the researchers took images of the creatures, using computerised tomography (CT) scans. With these scans, they were able to create digital three-dimensional models of the sharks' heads. The models revealed that the great white's jaws are reinforced by layers of tough "mineralised cartilage", which take years form. So until the sharks grow to approximately 3m long, they are unable to gouge chunks out of larger, tougher prey, such as sea mammals. Great whites reach maturity at around 10 years of age and can grow up to 5m in length. In the digital models, white-hot areas showed weak spots in the shark's jaws However, the exact age at which they reach this critical size is one of the many mysteries surrounding these threatened creatures. Dr Stephen Wroe, from the University of New South Wales (UNSW), in Australia, was one of the co-authors of the study published in the Journal of Biomechanics. The researchers studied a great white shark caught as part of the New South Wales Bather Protection Programme. "The teeth and jaws of our sub-adult great white shark looked the part, and the muscles were there to drive them," Dr Wroe explained. "[But] the jaws themselves just couldn't handle the stress associated with big bites on big prey." Biting force Models showed how muscle fibres in a great white's jaw are pulled straight The study also showed that sharks have a unique jaw muscle arrangement, allowing them to maintain very high bite forces no matter how wide their jaws are open. Toni Ferrara, also of UNSW, who led the study, explained that sharks' upper and lower jaw muscles are divided by a tendon. "As the mouth opens, this tendon pulls the muscle fibres straight and perpendicular," she said. "Imagine if you were moving something heavy; you wouldn't push it at an angle, you'd keep your arms straight. "It's the same with how the muscle fibres move a shark's jaws." Ms Ferrara and her colleagues also examined the jaws of the far more docile sand tiger shark. This species is slow-moving and prefers to hunt small fish, rather than attack the much larger prey that great whites tackle. "They look fierce because their teeth stick out, but they're really the couch potatoes of the sea," said Ms Ferrara. "They use their jaws like traps for the small, fast moving fish they feed on. Please turn on JavaScript. Media requires JavaScript to play. "The jaws are spring-loaded, so they move in towards a fish with their jaws at a really wide gape and snap them shut around it." Awkward teenagers Mr Ferrara says the experiment reveals a fragile and vulnerable side to white sharks. Previous studies have shown that juvenile great whites feed preferentially on "softer flesh", rather than tougher but very energy-rich fatty tissues of seals and whale carcasses. This study could help explain this dietary choice. "It is hard to believe, but at this size great white sharks are basically just awkward teenagers that can't hunt large prey very effectively" said Ms Ferrara. The researchers used CT scans to peer inside the sharks' heads

"Great white sharks are not born super-predators, they take years to become formidable hunters." The team also suggest that the great whites involved in attacks on humans off the New South Wales coast are usually juveniles. They often give up after one bite, because they could sustain jaw injury if they persevered with the attack. Ms Ferrara told BBC News: "They're not the omnipotent killing machines that people seem to think."



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