David Quinlivan was paddling a surf ski near the New South Wales state town of Forster, 300km north of Sydney, when he was attacked, police said.
He fell into the water, and bystanders on-shore helped him from the water.
One of those bystanders, Warren Thompson, said he and others ran into the surf to help Quinlivan.
“He had lost his paddle, but was able to climb back onto the ski and caught a wave to the shore,” Thompson said.
Thompson added: “It looked to us like he was having a heart attack. When we reached him, he told us to stay out of the water.”
Quinlivan was flown by helicopter for emergency surgery to a leg injury.
Two weeks ago, a 38-year-old surfer suffered life-threatening injuries when he was attacked by a shark at Port Macquarie, 100km (60 miles) north of Forster.
Three weeks earlier, a 52-year-old surfer was seriously injured as he repeatedly punched a shark that mauled him off Evans Head, 230km (140m) north of Port Macquarie, in the eleventh attack — including one fatality — in five months along a 20-kilometre (12-mile) stretch of northern New South Wales coast.