Warmer Sydney waters mean longer shark season

Sydney needs to prepare for more sharks in popular swimming areas as climate change raises sea temperatures and makes conditions more hospitable to bull sharks and tiger sharks.

Professor Culum Brown, a shark expert at Macquarie University, said bull sharks spend summer in embayments and estuaries such as Sydney Harbour because the warm water was good for the development of their young.

January and February is the peak time for spotting bull sharks in the harbour, with Sydneysiders sharing footage on social media. The SharkSmart app reveals several previously tagged bull sharks have been swimming near Sydney beaches in the past week.

They remain until the water temperature drops below 22 degrees, usually about April, when they migrate up to northern NSW or Queensland. Brown said it was possible in the future they could remain until winter or even stay all-year-round.

“The bad news, or the good news, depending on whether you like sharks or not, is that as climate change comes it’ll be warmer for longer, so it’s likely that we’ll see more bull sharks in Sydney Harbour and in and around Sydney estuaries ... because of that change in temperature,” Brown said.

“We’ve had some pretty warm winter bay temperatures over recent years, so there’s a potential for them to stay year-round.”

Dr Amandine Schaeffer, a physical oceanographer at the University of NSW, said the surface water temperature in Sydney was above 22 degrees from January to April, for the 1991-2020 average.

“However, in the last few years, it has been [22 degrees] from mid-December to May,” she said.

The 2023-24 and 2021-22 summers were records around Sydney for marine heatwaves, she said. Although milder by comparison, this year was still hotter than the 20-year average.

Brown said warming waters would also extend the natural range of tiger sharks further south to visit Sydney’s ocean beaches more frequently.

The habitat of white sharks would also shift further south, but Sydney was already well within range.

Nearly all shark encounters with humans in Sydney Harbour are with bull sharks, according to the Australian Shark Incident Database maintained by Taronga Conservation Society Australia, which goes back to the 19th century.

A year ago, kayaker Lauren O’Neill was seriously injured by a bull shark in Elizabeth Bay after jumping in for a quick dip after her evening paddle.

The only fatalities in NSW in the past five years have all involved white sharks.

Brown said people were more afraid of bull sharks than they should be, given there had been only two incidents in the past five years. “You’re far more likely to drown or have a boating accident or get swept off rocks or something like that,” he said.

Shark mesh nets are installed at 51 beaches on the NSW coast every summer, but they do not block sharks from swimming to shore and they kill most marine animals that swim into them, including turtles and dolphins.

The NSW government is reviewing its shark mitigation program for the 2025-26 summer and beyond. Most coastal councils have voted in favour of their removal because of the high bycatch and evidence that other methods such as drone surveillance and SMART drumlines are more effective.

Nets at harbour beaches are permanent rigid structures that provide a complete barrier for sharks. Unlike the ocean nets, Brown said these were not a problem environmentally because marine animals, including sharks, could avoid them.

“If anything, they probably provide habitat for things like seahorses, so they’re probably not such a bad thing,” he said.

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