When the man jumped off the board, he was attacked by a shark.
A paramedic was on the scene to assess and treat the man, before he was airlifted to Mackay Base Hospital on Queensland's east coast at about 8.30pm (11.30pm NZT).
"CPR was ongoing for a very long time and every solid effort was made to save that man's life", Mr O'Connell said.
Insp O'Connell said Dr Christidis' friends were "extremely distraught".
He said: "We see this pattern time and time again - all around the world - and we don't really understand why it is".
RACQ CQ Rescue in Australia assisted with the rescue of a man who had been mauled by a shark in Cid Bay - the third person to be attacked in the area in two months.
Australia has averaged fewer than two deadly shark attacks per year in recent decades.
Dr Christidis had just completed a PhD in the area of prostate cancer at Austin Health and started working as a surgical registrar in urology at Western Health in February.
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The Queensland government yesterday ruled out shark control measures - including drumlines and shark nets which are already in place at 86 Queensland beaches.
Steve O'Connell, Whitsundays patrol inspector, told reporters that the man had lost a substantive amount of blood, and had began to go into cardiac arrest.
"Definitely one of the more hard ones for everyone involved", McCauley said.
"This is a bad tragedy".
He said without knowing the type of shark that killed a tourist on Monday, he had assumed it was a tiger shark because of the number that were caught following an attack seven weeks ago.
In the same harbour, Justine Barwick, a 46-year-old tourist, was attacked on September 19 while swimming from a yacht; she survived and is now recovering.
"We can't be clearer - don't swim in Cid Harbour", he said, according to the news outlet.
"If I were the Premier, I would issue the command: Put the drum lines back in Cid Harbour immediately until further notice".
A male patient is now being airlifted to Mackay Hospital with significant leg and wrist injuries following a shark attack in waters near #CidHarbour which occurred at 5.37pm.