A man in his 30s was attacked by a shark shortly before 8am.
Friends used the rope from the victim's board as a tourniquet and gave him first aid until emergency crews arrived from Margaret River within six minutes, according to a St John Ambulance spokesman.
Surf photographer Peter Jovic witnessed the attack from the beach.
"A shark popped up and pretty much ended up knocking a surfer from his board", Jovic said.
'There was a lot more thrashing around. "After that it was hard to see what was going on".
'They got him to shore and started working on him to stem the bleeding'.
Surf Life Saving WA said a four-metre shark and whale carcass were spotted at 10am at nearby Lefthanders surf break.
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Another radio caller said other surfers had been spooked by the shark and had started leaving the water just before the attack happened. Nick Edwards, 31, also died after a shark attack while surfing at nearby South Point in 2010.
"All the other surfers swam to him, helped him get away from his board and leg rope and helped him get on a wave, and luckily [he] caught a wave onto the reef".
"He had cuts to both legs".
"After discussing with local authorities, the water safety team and surfers, the WSL commissioner's office has chose to resume competition for the Margaret River Pro at Main Break at 10.40am, following a one-hour hold prompted by reports of a shark incident at Gracetown - approximately 15km away from the event site", a spokeswoman said.
A spokeswoman for the event said the surf contest was under way at Margaret River's main break at the time of the attack.
The WSL later said the competition, which forms part of the WSL's World Championship Tour and features top ranked surfers, was back up and running.
In a statement posted to its Facebook page following the incident, the WSL said it had made a decision to suspend the competition for an hour after "discussions with local authorities".