Great white sharks, one of the ocean’s top predators, have been found to be scared from their habitat by just 2 predators: orcas. Since 2017, scientists have documented that the sharks have made themselves extremely scarce off the coast of South Africa, where they usually congregate. Initially, the strange disappearance was blamed on human activity, such as overfishing. However, research has confirmed that the true culprit is a pair of orcas, hunting the sharks and slurping out their delicious, nutritious, vitamin-rich livers.
The fishing town of Gansbaai on the South African coast was once a mecca for shark-spotters, heavily populated with great whites, but over the last few years, the sharks’ presence has been diminishing. In addition, since 2017, at least eight great white sharks have washed ashore at Gansbaai, several of them missing livers (and some without their hearts) – the hallmark of an orca attack.
Scientists believe that the pair of orcas are responsible for many more great white deaths that haven’t washed ashore. We know from other studies that the presence of orcas can drive great white sharks away pretty adroitly. One study in 2020 found that great whites will scarper away, without fail, from preferred hunting waters off the coast of San Francisco if an orca makes an appearance in the region.
In a study from 2022, using long-term sighting and tracking data from tagged sharks, a team of scientists led by marine biologist Alison Towner of the Dyer Island Conservation Trust found that orcas are the reason sharks are starting to avoid what used to be some of their favorite spots.
“What we seem to be witnessing though is a large-scale avoidance (rather than a fine-scale) strategy, mirroring what we see used by wild dogs in the Serengeti in Tanzania, in response to increased lion presence. The more the orcas frequent these sites, the longer the great white sharks stay away,” Towner explained.
This is a huge deal as it is altering the ecosystem. In the absence of great white sharks, copper sharks are moving in to fill the vacant ecological niche. These sharks are preyed upon by great whites; with no great whites around, the orcas are hunting the coppers instead. And, notably, they’re doing so with the skill of predators who have had experience in hunting large sharks, the researchers said.
“However, balance is crucial in marine ecosystems, for example, with no great white sharks restricting Cape fur seal behavior, the seals can predate on critically endangered African penguins, or compete for the small pelagic fish they eat. That’s a top-down impact, we also have ‘bottom up’ trophic pressures from extensive removal of abalone, which graze the kelp forests these species are all connected through,” Towner said.