In early 2018, Divernet / Diver magazine ran an exclusive story by shark expert Richard Peirce. It carried a stark warning: tourism based on cage-diving with great whites in South Africa was in jeopardy, because orcas with a taste for shark liver were killing or scaring away the sharks.
Two particular orcas, named Port and Starboard, had launched a reign of terror on what had always been considered the ultimate apex predator. For some involved in the lucrative shark-diving industry, the suggestion was painful to accept.
Now, seven years on and with great whites still scarce off South Africa, DNA evidence has for the first time confirmed that an orca was responsible for hunting down and killing a white shark for its liver.
This time the incident happened in Australia. Witnesses saw several killer whales (Orcinus orca), including two locally recognised individuals named Bent Tip and Ripple, catch a large prey in Bridgewater Bay near Portland in Victoria in 2023.
Two days later the carcass of a 4.7m white shark (Carcharodon carcharias) was washed ashore and collected by state fisheries officers for investigation.
Four bite-wounds
The just-published study of the shark was led by a Flinders University scientific team, who analysed swabs taken from four distinctive bite-wounds on the carcass.
The proof was there in the DNA when the swabs were sequenced for genetic material left by the predator. An orca had eaten the shark’s mid-section, where the nutritionally rich liver had once been, and the other three wounds revealed the DNA from scavenging broadnose seven-gill sharks. The great white’s digestive and reproductive organs were also missing.
The analysis builds on anecdotal evidence of predation by orcas on great whites and other species of sharks in South Africa and also California.
“These findings provide compelling evidence of killer whale predation on white sharks in Australian waters, with a strong indication of selective liver consumption,” says the study’s lead author Isabella Reeves, a PhD candidate with the university’s Southern Shark Ecology Group and the West Australian Cetacean Research Centre (CETREC).
“This suggests that such predation events may be more widespread and prevalent across the globe than previously believed.”
Other sharks
Orcas had occasionally been recorded preying on blue, porbeagle, shortfin mako, ground and tiger sharks in Australia, but no proven killings of great whites had occurred before.
“Evidence suggests that the white sharks being displaced or directly killed as a result of the killer whale predation in South Africa has led to cascading shifts in the wider marine ecosystem,” commented co-lead author Adam Miller, an associate professor at Flinders.
“We know that white sharks are key regulators of ecosystem structure and functions, so it’s very important we preserve these top predators. Therefore it is important that we keep a tab on these types of interactions in Australian waters where possible.”
The new study is published in Ecology and Evolution.
Also on Divernet: Great white shark tourism in South Africa in jeopardy as orcas attack sharks, Lone orca killed great white shark in 2 minutes, Female killers v blue whale –a world-first, Old Tom, killers of Eden and their DNA secrets
