In 2015, great white sharks vanished from Australia's Neptune Islands. Experts still aren't sure exactly why
In 2015, great white sharks vanished from Australia's Neptune Islands. Experts are still trying to work out why
White sharks – also known as white pointers – have one known natural predator: the orca, or killer whale. When killer whales are in town, white sharks flee. This might not be surprising, given that some types of killer whale know exactly how to overcome a white shark and bite out its liver.
After six killer whales attacked and killed a white shark in South Australia in February 2015, no great whites were seen in the area for around two months. Similar disappearances have been seen in South Africa after a predation.
The long absence of white sharks from the region was widely put down to this attack by killer whales, but a new study questions this theory.
Researchers analysed 12 years’ of sightings data at the Neptune Islands, South Australia, from 2013 to 2024. They also looked at acoustic tracking data to find patterns in the sharks’ distributions.
The findings revealed that white sharks can flee after a killer whale attack – the dying animal releases chemicals called necromones into the water that warn other sharks of the danger – but this is not the only reason they might vanish.
"Our results show that killer whales can absolutely trigger an immediate response from white sharks, but they are not always the whole story when it comes to long-term shark disappearances,” says Dr Isabella Reeves from Flinders University’s Southern Shark Ecology Group and the Western Australian Cetacean Research Centre (CETREC).
"Across the 12-year study, we recorded six prolonged absences of more than 42 days, and only one of them coincided with the presence of killer whales,” she says. “The longest absence we recorded was even longer than the 2015 event and occurred when no killer whales were detected at all.”
In some instances, the sharks only departed for a short time after an incident. For example, after the death of a white shark in October 2023, sharks were absent from the area for just four days.
The predation event at the Neptune Islands took place at a time when white shark sightings tend to be low – there were few or no sharks for the majority of February and March 2016, 2017, 2018 and 2024. "While this could be a learnt response to avoid the area at this time of the year because of the 2015 events, low presence or abundance during these months were also observed before 2015,” write the authors in the study which was published in Wildlife Research.
There were other long periods without white sharks that weren’t related to killer whale sightings or attacks on white sharks. "Given the timing of the absence in 2015 and other prolonged absences, it is unclear whether the predation event directly caused the prolonged disappearance of white sharks,” write the study’s authors.
The timing also didn’t align with things that might draw the sharks away from the area, such as the annual harvesting of bluefin tuna nearly 40 miles further north.
The research shows that more studies are needed to better understand what is influencing the sharks’ distribution in the area, says co-author Dr Lauren Meyer, a researcher at Flinders University: "This study highlights the importance of long-term monitoring to understand white shark movements and site fidelity, while challenging the idea that killer whales are always or solely responsible for prolonged shark absences.”
Top image: Great white shark. Credit: Julian Cohen/Getty Images
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