GWN7 News has published photos of Mr Longgrass and his board with visible teeth marks.
Channel Nine reporter Michael Stamp said the man did not realise the beach was closed. The man said he saw a four-metre shark coming towards him.
It comes as the first attack victim, Alejandro Travaglini, 37, was rushed to Royal Perth Hospital for emergency surgery. He is in a stable condition after being bitten on the lower leg.
A St John Ambulance spokesman told AAP that man managed to bodysurf back to shore before friends used rope from his board as a tourniquet.
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. Channel Nine reports the man was conscious and breathing when he was pulled from the water.
Surf photographer Peter Jovic saw the first attack from the beach and said there were only about five people in the water at the time.
"If anyone is familiar with the Mick Fanning moment at Jeffreys Bay a couple of years ago, it was very similar to that, where a shark pretty much popped up and ended up knocking a surfer off his board," Mr Jovic told ABC radio.
"There was a lot more thrashing around after that, it was pretty hard to see what was going on.
"The surfer who was being attacked ended up miraculously body surfing into a little wave and getting pushed in by a local at the same time, who was out there with him, and making it to shore before everyone came to his aid."
Mr Jovic said everyone was "walking around like stunned mullets" after the attack.
AAP understands the man has lived in Gracetown for some time, with one friend describing him as "an awesome guy".
Surf Life Saving WA said a four-metre shark and whale carcass were spotted at 10am at nearby Lefthanders surf break.
Beach closures are in place for the Gracetown area, including North Point, Big Rock and Lefthanders.
The Margaret River Pro international surfing competition, which is about 15km away from the attack, was suspended for about one hour, but then resumed at Main Break.
"Surfer and staff safety are top priorities for the World Surf League," a spokeswoman said.
"Further enhanced safety measures, including ski and drone presence, will be added to the event's mitigation protocols."
Opposition Leader Mike Nahan said the attack would make international news given the Margaret River Pro event was on nearby.
He said the incident emphasised the need to do more, including using SMART drumlines, rather than the Labor government's subsidised shark deterrent devices.
"Sharks are still a threat to surfers and people in the ocean here," he told reporters.
"The current policies are simply not adequate."
AAP is seeking comment from Fisheries Minister Dave Kelly.