Share and Follow
Recent findings from a 12-year study in Australia challenge previous beliefs about shark behavior.
Dr. Isabella Reeves, a postdoctoral researcher at Flinders University, spearheaded the research. Her team discovered six occasions when sharks vacated the Neptune Islands for extended periods.
“These absences lasted over 42 days, and just one coincided with the killer whale incident we observed in 2015,” Dr. Reeves explained.
On February 2, 2015, a cage diving company from Port Lincoln led a group to the Neptune Islands to observe sharks up close.
However, only 20 meters from their boat, they witnessed a dramatic scene as six orcas launched an attack.
But just 20 metres from their vessel, they witnessed six orcas going in for the kill.
Three orcas appeared to fence in a shark, while the others rammed it with their heads.
They pushed the shark underwater and an oil slick appeared on the surface, indicating the liver had been consumed.
The footage of the encounter went viral and gained national interest.
Reeves said it was considered very rare at the time but has been recorded more over the years, particularly in Australia, South Africa, California and Mexico.
“The fact that killer whales had rocked up to the Neptunes, which is a really small island group that’s offshore, and someone was there to actually document it, it was a really rare opportunity to try to dissect the situation more once we had gotten more data over the years,” she said.
Sharks disappear from Neptune Islands
Sharks disappeared from the waters in the Neptune Islands for the next 69 days after the orca attack.
Andrew Fox from Rodney Fox Shark Expeditions said he saw an increase in sharks at the Neptunes from the early 2000s, but that changed in 2015.
“It’s been very much more patchy since then, and in the last two years, it’s been really slow,” he said.
“It seems like there’s a lot more than there is, but I’m worried that there has been a bit of a slow decline, and we’re certainly seeing a lot less in the last two years than we’ve ever seen.”
There have also been environmental changes in recent years, including record oceanic upwellings and a toxic algal bloom.
Fox has only seen orcas at the Neptune Islands a handful of times in his 50 years in the business.
“We had a really big Orca, a big male with an extremely tall dorsal fin, come up to the back of our vessel and smash its tail up and down repetitively and scare away a big white shark we knew, a formidable, five-metre male we know as Dragon,” he said.
“We haven’t seen Dragon since, so I’m a bit worried about what happened to him. But other white sharks did come back a week and a half or 10 days later.”
Twelve years of research
The research team used acoustic telemetry data, based on listening stations that ping once a tagged shark is near, and sightings from tourism companies to track sharks over 12 years to understand whether the 2015 absence was exceptional or behavioural.
They identified six instances of prolonged absences, including a brief five-day departure during an orca sighting in October 2024 and a four-day absence during the death of a tagged whale.
But they found that not every orca encounter or shark death led to these absences.
Reeves said movement patterns of great white sharks in the Neptune Islands were highly variable.
”There’s definitely long gaps in their presence, which can happen with or without killer whale activity,” she said.
“It’s really hard to say. There’s so much going on in our oceans right now, which could be contributing to this.
“But I think the main takeaway is that it’s not the killer whales at the Neptunes that are causing the prolonged absences.”
Another study is currently under way to understand what causes prolonged shark absences.
NEVER MISS A STORY: Get your breaking news and exclusive stories first by following us across all platforms.