FOUR shark attacks in just two days have sparked panic along the New South Wales coast as swimmers are being urged to stay out of the water.
It comes as scientists are scrambling to explain what triggered the sudden surge in incidents.
The spate has left two people fighting for their lives, shut down beaches and triggered urgent warnings for Australians to stay out of the water.
The latest attack struck off the state’s mid-north coast near Port Macquarie, where a 39-year-old surfer was injured after a shark clamped down on his board near Limeburners Creek National Park.
He was taken to hospital with minor injuries and later released.
It followed three attacks around Sydney in just 24 hours.
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On Sunday afternoon, 12-year-old Nico Antic was mauled while jumping off rocks at Nielsen Park in Vaucluse, suffering catastrophic injuries to both legs as friends watched in horror before dragging him from the water.
Paramedics applied tourniquets and performed CPR before rushing him to hospital, where he remains in critical condition.
On Monday morning, an 11-year-old boy was knocked into the water at Dee Why after a shark tore chunks from his surfboard, leaving a large section missing.
And that evening, 27-year-old musician Andre de Ruyter was savaged at North Steyne Beach in Manly, suffering life-changing leg injuries.
Surf Life Saving NSW chief executive Steven Pearce issued a stark warning as Sydney’s northern beaches were closed.
“If anyone’s thinking of heading into the surf this morning, anywhere along the northern beaches, think again,” he said.
“We have such poor water quality that’s conducive to bull shark activity.
“We have two people critically injured in hospital this morning. Just go to a local pool, because at this stage, we’re advising that the beaches are unsafe.”
Experts analysing the attacks say bull sharks were almost certainly responsible for all four incidents.
Dr Amy Smoothey examined images of the bites and said bull sharks were behind them, pointing to their distinctive broad, overlapping triangular teeth.
Bull sharks are known to operate close to shore, particularly in murky water after heavy rainfall.
Professor Rob Harcourt, a shark expert from Macquarie University, said the timing of the attacks created what he described as a “perfect storm”.
He told The Guardian: “For bull sharks, the likelihood of a bite is tightly linked to freshwater inflows, and that is no surprise if we understand their ecology.”
Bull sharks are unusually tolerant of low-salinity water and actively move toward runoff-filled areas where fish gather.
Tracking data shows they head quickly into turbid water after heavy rain.
But low visibility doesn’t deter them.
Dr Daryl McPhee, a shark bite expert at Bond University, said bull sharks rely on pressure changes and electrical signals rather than eyesight when hunting.
He explained to The Guardian: “They are well adapted to feeding in those murky waters.”
Scientists say the sharks were almost certainly not hunting humans.
“Some people will definitely be taken [by sharks] as prey,” Harcourt said.
“Others are probably investigatory bites, such as the surfboard that was bitten.”
Professor Shokoofeh Shamsi said the increased danger should have been predictable.
Some people will definitely be taken [by sharks] as prey
Professor Rob Harcourt,
The attacks followed a period of intense rainfall, which flushed dirty runoff into the sea, attracting bait fish and drawing freshwater-tolerant bull sharks closer to shore while drastically reducing visibility.
She said rainstorms do more than muddy the water as they dramatically change the chemical makeup of the ocean.
She told the Daily Mail: “Just imagine it: You’re walking down the street, and the clean air suddenly changes to become very smoky.
“It smells different, you don’t have the visibility, you cannot do your daily activities, you get restricted in the places you can go, and the food you can eat.
“That happens in the ocean when all this fresh water enters, and just like we would get stressed and become a bit jumpy, why shouldn’t the same thing happen to sharks?”
Professor Shamsi said runoff can carry sewage, pesticides, pharmaceutical products and industrial chemicals into the ocean, which can disrupt the nervous systems of marine animals.
She also warned that parasites and infections washed into the water after heavy rain may further alter animal behaviour.
“These parasites have evolved over millions of years to manipulate the host’s behaviour to get what they want,” she said.
“When they are stressed, they do things that distressed animals do; and that includes biting.”
Additional stress may also come from underwater noise.
Professor Shamsi said sharks are extremely sensitive to sound, and research has shown that noise from shipping, construction and sonar can disrupt hunting behaviour and trigger stress responses.
Vincent Raoult said it can take days after heavy rain for water conditions to improve.
“In the conditions where bull sharks do encounter people, it’s in those really brackish, murky waters, so they’re not relying on their eyesight,” he said.
“Like most shark species, the way that they can really sense their surroundings is by biting things. And unfortunately, if you’re talking about a larger shark on a person, a nibble can be lethal.”
Authorities say the danger may persist until the water clears, with drones, helicopters and jet skis continuing to scan the coastline.
What makes bull sharks so deadly?
Bull sharks are aggressive, medium sized sharks that weigh between 200 and 500 pounds.
They get their name from a short, blunt spout and a tendency to head-butt prey before attacking.
They are third most likely to attack humans behind tiger sharks and great whites and can swim in salt AND fresh water.
They are often found lurking in shallow, warm and turbid waters.
