Shark attack victim Nico Antic, 12, dies in hospital

Shark attack victim Nico Antic has died in a Sydney hospital.

The 12-year-old was attacked by a suspected bull shark as he was jumping off a rock face at Neilson Park, near Shark Beach in Vaucluse, on Sunday.

The boy's friends jumped into the water to pull him to safety, but Nico suffered serious leg wounds and was taken to hospital in a critical condition.

READ MORE: Shark sighting at Manly forces closure of beach

Nico's parents, Lorena and Juan, said in a statement they were "heartbroken" to deliver the news of his death.

"Nico was a happy, friendly, and sporty young boy with the most kind and generous spirit," they said.

"He was always full of life and that's how we'll remember him.

"We would like to sincerely thank the first responders and the teams at Sydney Children's Hospital, Randwick for everything they did to care for Nico.

"We would also like to thank everyone in the community for their support and kind messages.

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"We ask you please respect our privacy during this exceptionally difficult time."

The 12-year-old's friends have also posted tributes to Nico online, with one posting a bouquet of flowers with the message "long live Nico".

String of shark attacks

Nico, a junior lifesaver, was the first of four shark attack victims in 48 hours on NSW beaches this week after last weekend's wild weather.

A surfer, 27-year-old musician Andre De Ruyter, was attacked in the water at a Manly beach on Monday.

He was pulled to shore by fellow surfers and was taken to hospital in a critical condition, with part of his lower right leg amputated.

He is now in a stable condition.

Hours early at nearby Dee Why Beach, also on the northern beaches, an 11-year-old surfer had his board bitten by a shark.

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The whole stretch of beaches were closed on Monday.

The next day Paul Zvirzdinas was surfing at Point Plomer, north of Port Macquarie on the NSW Mid North Coast, when a shark took a bite out of his board and wetsuit at about 10am.

The 39-year-old said he saw his board shake then paddled to shore.

"Just paddle as hard as you can," he said he recalled thinking.

He only suffered minor injuries and has since been discharged from hospital.

This morning a shark sighting at Manly forced the closure of the beach just hours after flags were set up for the day.

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The state's recent wet weather, considered a once-in-a-500 year event, has been a perfect storm for bull sharks to lurk in coastal waters around Sydney and the rest of NSW.

Heavy rain means more fresh water than usual is running through rivers and estuaries into saltwater systems and beaches, creating brackish water.

This is a phenomenon where fresh and saltwater mix, being saltier than normal freshwater, but less salty than typical seawater.

"Bull sharks are also one of the few species of sharks and rays that can tolerate brackish and even freshwater for extended periods," Professor Jodie Rummer from James Cook University said.

"Which means they are especially comfortable moving in and out of river mouths and turbid coastal waters after heavy rain."

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