A great white shark captured in the wake of an attack on a surfer south of Perth has died and been disposed of at sea, Western Australia's Department of Fisheries has confirmed.

The 4.2-metre shark was caught on a drum line close to where 29-year-old Ben Gerring was attacked at Falcon Bay beach in Mandurah on Tuesday afternoon.

Mr Gerring lost a leg above the knee in the attack and he remains in a critical condition in Royal Perth Hospital.

Fisheries officers set the drum lines early yesterday and the shark was hooked several hours later.

The Department said the shark died on the drum line, and was dragged out to sea and dumped after samples and measurements were taken.

Mr Gerring, a fly-in fly-out heavy machinery operator, has lived and surfed in the area his whole life.

Surfer Ben Gerring remains in a critical condition. ( Supplied: Facebook )

Mandurah Boardriders Club president Brian Williams who arrived at the scene after fellow surfers dragged Mr Gerring onto the beach said it was a traumatic experience.

"It's pretty harrowing seeing somebody you know lying there motionless, hoping that everything's going to be OK," he said.

Mr Gerring's family yesterday issued a statement thanking those involved in the rescue effort.

"We would like to say a heartfelt thank you to everyone involved in Ben's rescue and his treatment," the statement said.

"The bravery and efforts of his rescuers and the care provided by the doctors and nurses has been amazing."

Beaches in the vicinity of the attack will remain closed today.