Australian biologists said Sunday a great white shark measuring up to 12 feet likely killed a 57-year-old surfer off Sydney this weekend, as harrowing details of the attack emerged and authorities stepped up surveillance for the predators.

The experienced surfer, identified by Australian media as Mercury Psillakis , was mauled to death by a shark on Saturday off a popular beach in northern Sydney, police and rescuers say, leading to a string of beach closures.

The man, who had a wife and young daughter, lost "a number of limbs" and his surfboard was broken in two, police said.

The victim's friend, Toby Martin, talked to surfers who were with Psillakis and a lifeguard who helped render treatment, the Australian Broadcasting Corporation reported .

"Really dramatic and quite gra

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