Orca predators overthrow great white sharks

ScienceAlert reveals in its article that for years, the great white shark has been considered one of the ocean's top predators, but new research has uncovered an unexpected challenge to its dominance—killer orcas. 

Few sea creatures evoke as much fear, whether justified or not, as the great white shark. Known for its streamlined body built for hunting, razor-sharp teeth, and its (often unfair) reputation for preying on humans, the great white (Carcharodon carcharias) is widely considered one of the ocean's most formidable predators.

While the great white shark is often seen as the apex predator of the ocean, there is something that even it fears.

Since 2017, scientists have observed a significant decline in the number of great white sharks off the coast of South Africa, a region where they are typically abundant. Initially, human activities such as overfishing were blamed for the sharks' sudden disappearance. However, in 2022, research revealed the true cause: a pair of orcas, known as Port and Starboard due to the distinctive bends in their dorsal fins, were hunting and consuming the sharks' livers, which are rich in nutrients and vitamins.

Gansbaai, a fishing town on the South African coast, was once a popular destination for shark enthusiasts, with nearby Dyer Island earning the title of the great white shark capital of the world due to the area's high shark population.

In recent years, the presence of great white sharks in the area has noticeably declined. Since 2017, at least nine great white sharks have washed ashore in Gansbaai, with several of them missing their livers and, in some cases, their hearts—clear signs of an orca attack. It's not just white sharks that are being targeted; Port and Starboard have also been linked to a killing spree of broadnose sevengill sharks, taking down at least 17 in one day.

The injuries on these sharks are unmistakable, and scientists believe the same pair of orcas is behind numerous great white shark deaths that have not washed ashore. Research has shown that orcas can effectively drive great white sharks away. For example, a 2020 study revealed that when orcas appear off the coast of San Francisco, great whites flee their favored hunting grounds. A 2022 study led by marine biologist Alison Towner, using long-term sighting and tracking data from tagged sharks, confirmed that orcas are causing sharks to abandon what were once their prime feeding areas.

"Initially, following an orca attack in Gansbaai, individual great white sharks did not appear for weeks or months," Towner explained.

"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."

Over the span of five years, the research team tracked 14 GPS-tagged sharks, who fled the area whenever orcas were present. In addition, sightings of great white sharks have significantly decreased in several bays.

This is a significant development. In fact, since record-keeping began, great white sharks had only been noted as absent for a week or more in Gansbaai on two previous occasions: one week in 2007 and three weeks in 2017.

The researchers stated that the recent absences of great white sharks are unprecedented and continue to persist. In a paper published earlier this year, Towner and her team recorded two incidents of Port and Starboard attacking sharks and consuming their livers.

Alarmingly, these attacks are causing disruptions to the ecosystem.

With the great white sharks gone, copper sharks (Carcharhinus brachyurus) are now moving into the vacant ecological role. Normally preyed upon by great whites, the copper sharks are now being hunted by the orcas instead.

By Naila Huseynova