Drones spot sharks 73 times in two days off Sydney beaches

New dawn-to-dusk drone patrols of Sydney's beaches spotted sharks 73 times in the first two days, forcing multiple closures, data obtained by AFP showed on Friday.

Authorities launched the expanded drone programme on Wednesday to protect beachgoers after a spate of shark attacks in Sydney and further across New South Wales.

Data from Surf Life Saving NSW, which runs the programme, showed 73 shark sightings in greater Sydney by drone pilots on Wednesday and Thursday, with the greatest concentration at beaches north of the city, where 67 reports were made.

The drones only report bull, tiger and white sharks, species considered most likely to attack humans.

Lifesavers say it is likely some sharks are being spotted multiple times as they move through the ocean. But one group of 13 sharks swimming together was reported at a single beach at northern Sydney's South Narrabeen on Wednesday.

"Having so many drones out all day, they are picking up everything," said Surf Life Saving New South Wales spokeswoman Donna Wishart.

At northern Sydney's Dee Why Salty Surf School, owner Dan O'Connell was 15 minutes into a surf lesson on Friday when a drone spotted a shark near the beach and lifesavers evacuated the water for the second time that day.

O'Connell had just succeeded in coaxing his students into the ocean by telling them a shark was unlikely to venture near the knee-high water where they were practising board moves.

"They were already scared and paranoid because the beach had been closed," he told AFP.

Drones made three shark sightings on Thursday at Dee Why Beach, with another sighting on Friday morning closing the beach for an hour before it reopened, only to close again.

Expecting beach closures will increase, O'Connell is diversifying his business to offer skateboarding lessons at the nearby carpark.

School groups had cancelled surf lessons after a child was killed by a shark in Sydney Harbour in January, and a woman was mauled at popular Coogee Beach last month.

"It has been really hard," he said.

"We will lose a percentage of fairweather surfers because they will feel paranoia more than the enjoyment they get from the ocean."

Northern Beaches Mayor Sue Heins told AFP millions of visitors are attracted to Sydney's coast each year, and the drones support safety.

"Naturally, increased surveillance will mean increased sightings," she said.

A surfer was killed by a shark on a northern Sydney beach in September.

New South Wales Premier Chris Minns said on Sunday that swimmers and surfers "will have to get used to" leaving the water as the world's biggest drone surveillance program ramps up.

"It is almost certain that sharks have always been present," said shark expert Daryl McPhee, an associate professor of environmental science at Bond University, who expects the high number of beach closures to continue for several weeks.

White sharks roam large distances but may "take up residence" where prey is abundant, he said, noting an increase in humpback whale populations and salmon.

"The sightings over the last couple of days have increased due to the increased drone spotting effort which is occurring at a time when conditions are right for coastal food resources of white sharks to be abundant."

There have been nearly 1,300 shark incidents around Australia since 1791, of which more than 260 resulted in death, according to a database of shark encounters with humans.