Father of killed Aussie surfer says sea is 'shark's domain'

The father of a surfer killed by a great white shark off an Adelaide beach does not want it destroyed, saying the ocean is the animal's domain.

As authorities ordered the 5m long shark to be found and destroyed, Philip Peterson, the father of 18-year-old victim Nick Peterson, said his son admired and respected sharks.

Nick Peterson was killed instantly when he was attacked by the shark as he was towed behind a boat on a surfboard just 300 metres off Adelaide's popular metropolitan West Beach yesterday.

"It came up from nowhere -- he didn't see it for a second before it happened," Adam Floreani, one of three 16-year-old friends in the boat who watched the horrific attack, told Channel Seven.

The friends said Mr Peterson had fought for his life, hitting the shark as it took him away.

"He went down fighting -- he didn't give up," said Mr Floreani.

Police initially believed they had found some of Mr Peterson's remains today but tests later showed they were not human tissue.

Philip Peterson today visited West Beach with his wife Leonie to see where their son died.

He said the decision to destroy the shark was "out of my hands".

"We acknowledge that the sea is, in fact, the shark's domain.

"We don't, and I certainly personally don't, advocate the indiscriminate killing of any shark. They are to be admired, appreciated and respected, and Nick knew that."

Great whites are a protected species, but a meeting today of government, police, fisheries and coast guard officials ordered the killer shark be found and destroyed.

"Any shark posing a threat or risk to human life ... should be destroyed, that is unequivocal," acting SA Premier Kevin Foley said.

He defended inaction over a sighting last week of a shark, believed to be the one involved in yesterday's killing, at an adjoining beach to West Beach.

"Should action have been taken earlier? Every summer we are confronted with that dilemma," Mr Foley said.

"We don't know at all whether the shark that took this poor victim was the shark that was sighted last week.

"What we don't want is a standard culling approach to great white sharks at the beginning of every summer."

Several sightings of the killer shark were made near West Beach today as about 50 emergency service boats, supported by helicopters, searched for the animal and any remains of Nick Peterson.

Mr Peterson said the death of his son, an experienced ocean-goer, should prompt more funding to make beaches safer from shark attack.

"I am concerned, as are the family, that there will be a number of (ocean) activities in a very warm period in the ensuing days," he said.

Uncertainty arose today whether one or two sharks were involved in the attack, in which a shark grabbed the surfer by an arm and pulled him from the board.

Nick Peterson's three friends, Mr Floreani, Ty Wheeler and Andrew Tomlin, told authorities two sharks were involved in the attack.

However SA Sea Rescue Squadron spokesman Fraser Bell said today authorities were searching for one shark.

West suburban beaches remained open today as temperatures reached 35 degrees celsius amid police warnings to the public.

"People who use our waters need to consider the risk of shark attacks," SA Police Commissioner Mal Hyde said.

"But unfortunately it's the case that people forget very quickly.

"Within about 20 minutes of people being alerted to get out of the water yesterday at West Beach, some people were going back in again."

But Surf Lifesaving South Australia chief Shane Daw said it was inevitable the numbers of beachgoers would now fall.

"We have got to be realistic - there are going to be fears," Mr Daw said.

- AAP