The shark that fatally mauled a man off a Sydney beach this week in what was a "rare and uncommon" tragedy" might never be tracked down, experts say.
Authorities are still searching for what is believed to be a great white shark which killed 35-year-old Wolli Creek man Simon Nellist off rocks near Buchan Point at Little Bay on Wednesday afternoon.
Mr Nellist, a certified diving instructor, was attacked just after 4:30pm on Wednesday.
It was the first fatal shark attack in Sydney since 1963, when actress Marcia Hathaway died from bite wounds while standing in Middle Harbour.
Yesterday, smart drum lines were deployed from Little Bay to Long Bay as police, life savers and the Department of Primary Industries (DPI) worked to locate the shark.
Police and the DPI have the power to destroy the animal if it is deemed an extreme risk to public safety, but it is understood the preference would be to tag and track the shark.
Marine scientist Vanessa Pirotta, however, told the ABC it was likely the shark, estimated to be 3 metres long, had already left the area and "we will never see it again".
Dr Pirotta said great whites were able to travel great distances and their presence in waters off Sydney was not a daily occurrence.
"Shark incidences like this are rare and uncommon," the Macquarie University expert said.
"Now, it's not every day that we see an animal of this size off our beaches, but it is possible.
"These animals are capable of large geographical movements and we will see them from time to time."
The shark could have been drawn to the area by currents, or because it was chasing prey or seeking warmer water, Dr Pirotta speculated.
"Or simply this animal may have just been passing through the area and unfortunately, in this case, has had a negative interaction with a human," she said.
Tributes have been posted on social media for British native and ex-serviceman Mr Nellist, with many coming from those he grew up with in Penzance, Cornwall.
"The ocean and our world are now one incredible human short. You will forever be our ocean protector, Simon," one friend wrote.
A former military colleague described Mr Nellist as "a gentle giant, lovely bloke and always would do anything for you".
Another shared a photograph of the 35-year-old riding in an army vehicle, saying he had "not one bad bone in his body".
One person published a screen shot of a post Mr Nellist made on Facebook last year, in which he reminisced on his time deployed in Afghanistan.
The post from August 21 included a picture of Mr Nellist in his military uniform with two young Afghan children.
"I've been thinking a lot about the children of Afghanistan recently," he wrote.
"They were so nice. Just good hearted kids who had nothing.
"I hope they're OK, if they manage to escape I hope we can look after as many of them as possible."
His friend wrote: "He was rare, salt of the earth, lived life to the max, an incredible diver and photographer, a brave soldier, a fine looking man, his heart was wholesome ... Simon was far too young to leave this planet and under no circumstances did he ever deserve to go the way he did."
A study by the CSIRO, released in 2018, estimated 750 adult great whites occupied the waters off eastern Australia.
When juveniles are counted, there was said to be 5,500 great white sharks in the seas stretching from Victoria's southern coast to central Queensland and across to New Zealand.
Randwick mayor Dylan Parker said Mr Nellist was a familiar face at Little Bay, and the community was "chilled to the bone" at the fatal attack.
"What we do know is that the deceased swam regularly across Little Bay, was well known to people who regularly frequent this beach, and unfortunately came to their end," he said.
"If you came on any given Saturday or Sunday [Little Bay) would be packed with families, beach umbrellas and young children.
"To hear that there was a death like this ... is really quite shocking to everyone."
Despite 13 beaches from Bondi to Cronulla being closed yesterday as authorities searched for the shark, swimmers were seen venturing into the water along the city's coast.
One man was turned away by surf life savers on jet skis as he walked into the waves at Little Bay yesterday.
Randwick council on Thursday afternoon confirmed that all beaches would re-open on Friday after there were no further sighting of the shark.
The attack took place at a popular fishing spot located up the headland from Little Bay Beach.
Its deep water location meant it would not have been protected using shark nets even if they had been deployed in the area.
Shane Daw, from Surf Life Saving NSW Australia, said he believed little could have been done to prevent the attack.
"A shark attack can happen, fatalities are rare and uncommon," he said.
"It's one of those things where we hope it never happens, but there's always that chance."
Mr Daw said people needed to be aware of where they were swimming and be mindful of behaviour that might attract the attention of patrolling sharks.
He put the risk of shark attacks in context, saying out of the 241 fatalities at NSW beaches last year only one was caused by a shark.
Minister for Agriculture Dugald Saunders said the government was providing technical advice and resources to police and Surf Life Saving NSW as the search continued.
"The shark attack that happened at Little Bay Beach late Wednesday afternoon was nothing short of a tragedy and a huge shock for the people of Sydney, especially since the last incident of similar nature was almost 60 years ago," he said.
