'Don't swim in Sydney Harbour': Former police diver's warning after recent shark attacks

As a former police diver of 20 years, Glenn Johns has recovered murder, drowning and shark attack victims from Sydney Harbour and the New South Wales coastline.

Now Mr Johns is using his experience — both as an ex-police diver and former surf lifesaver on the northern beaches — to warn people not to swim in Sydney Harbour's open waters.

His message comes following the death of 12-year-old Nico Antic, who authorities believe was bitten by a bull shark while jumping off a rock ledge along Hermitage Foreshore Walk near Shark Beach at Vaucluse.

While Mr Johns is not alone in his view, many other stakeholders feel differently and call for swimmers to instead be aware and 'shark smart'.

Experiences with sharks in Sydney Harbour

Sydney Harbour has always had a population of bull sharks, although there is no formal estimate of how many.

Mr Johns said while he was working as a police diver in the 70s and 80s, he was sometimes bumped by sharks under the Sydney Harbour Bridge.

"In the murk, it's all stirred up, and it's black water," he said.

"No matter what you're looking for, whether it's a knife, a gun, or a victim, it's a matter of running into them [bull sharks] and finding them."

While in the water testing a search and rescue strobe light for divers and boats at Clifton Gardens, a chunk was taken out of Mr Johns's diving fin.

"It was a small juvenile; I assume a bull shark. It grabbed my fin, and it was a tug of war," he said.

These days, he gets updates on shark activity from local professional fishermen.

All of this has led Mr Johns to advocate for no swimming or jumping off the back of boats in the harbour's unprotected areas.

Surf Life Saving NSW chief executive Steven Pearce encouraged swimmers to stay in netted areas.

"That will provide the best form of protection from any encounters with sharks," he said.

'Not like jaws', charter boat operator notes

Charter boat business owner, Dean Cropp, has spent 11 years boating in the Sydney Harbour area.

Two of his three boats commercially host parties of 10 to 400 people.

"A large part of what we do is encouraging people to enjoy the beautiful water of Sydney Harbour, get them swimming, get them enjoying themselves in the water, splashing around," Mr Cropp said.

He disagrees with Mr Johns.

"I understand the concern, especially from someone who has seen the worst of things that can happen to a person," Mr Cropp said.

He said swimming should not be banned, but people should know the risks.

"Plenty of guests, especially over the last few weeks, have been asking, 'What about the sharks?'" he said.

"And I jokingly make the comment, 'Don't worry, the sharks aren't going to be anywhere near us'. We have loud music, we have people stomping around, jumping in the water, moving about, yelling and screaming. The sharks do not like that."

NSW Department of Primary Industries and Regional Development (DPIRD) senior fisheries scientist, Amy Smoothey, has been researching bull sharks in the state and along the east coast for 15 years.

She said there was so far "no scientific study" to determine whether loud noises repel sharks.

"What we do know is low frequency pulses studies have been done and have resembled struggling fish and led sharks to investigate those areas," Dr Smoothey said.

Mr Cropp said he had never seen a shark near his charter boats, and he, along with his crew, got into the water with customers on every trip.

Lifeguards, medical equipment and staff who can treat traumatic injuries are also always onboard, he said.

Mr Cropp said his boats used tagging information to try and anchor in areas where sharks do not frequent.

He also believes having boat nets would be more dangerous than the sharks themselves, as people could get tangled in them.

Swimmers encouraged to be 'aware, but not alarmed'

Dr Smoothey said climate change had altered when bull sharks visited Sydney Harbour and nearby waterways.

She is part of the NSW shark management program that tags and tracks bull sharks in Sydney Harbour, which received a $4.2 million funding boost after four shark attacks last month.

That research found bull sharks were now arriving a month earlier, in October, and staying longer until May, when temperatures cool.

While there is no total safeguard, Dr Smoothey said people could be 'shark smart' by avoiding swimming in murky water and after heavy rain, and not swimming in open water at dawn, dusk and night-time.

"It's really important for people to be aware, but not alarmed."