Few marine inhabitants elicit such profound apprehension, whether justified or not, as the white shark.
Possessing an elegant physique finely tuned for predation, formidable dentition, and a reputation—arguably somewhat unfairly earned—for a predilection for consuming human flesh, the great white shark (Carcharodon carcharias) is universally recognized as one of the ocean’s apex predators.
While this designation is accurate, an even more formidable entity commands the fear of this formidable predator.
The video presented below offers a distillation of scientific investigations that have illuminated the existence of a creature that even formidable predators regard with trepidation.
Since 2017, marine researchers have observed a marked decline in the presence of great white sharks along the South African coastline, a region typically frequented by these apex predators. Initially, this puzzling scarcity was attributed to anthropogenic influences, such as the impacts of unsustainable fishing practices.
However, a comprehensive study conducted in 2022 definitively identified the true instigator: a pair of orcas (Orcinus orca), distinguished by the distinctive notches in their dorsal fins and affectionately nicknamed Port and Starboard. These marine mammals engage in the hunting of great white sharks, extracting and consuming their nutrient-dense, vitamin-rich livers.
In bygone eras, the coastal fishing community of Gansbaai in South Africa served as a veritable hub for shark enthusiasts, so abundant were the great white sharks that the adjacent Dyer Island was lauded as the global epicentre for great white shark populations.
Nevertheless, in recent years, a discernible reduction in the sharks’ prevalence has become apparent.
Furthermore, commencing in 2017, no fewer than nine great white sharks have been discovered ashore in Gansbaai, many of them exhibiting missing livers (and some even lacking their hearts)—a definitive characteristic indicative of orca predation.
And the predation extends beyond great white sharks. Port and Starboard have been implicated in the decimation of a broadnose sevengill shark population, accounting for the demise of at least 17 individuals within a single day.
The distinctive trauma inflicted upon these sharks has been unequivocally linked to this specific pair of orcas. Scientific consensus suggests that these two individuals are likely responsible for a considerably greater number of great white mortalities that have not been recovered on shore.
Existing research substantiates that the mere presence of orcas can effectively displace great white sharks with remarkable efficiency.
A study conducted in 2020 revealed that great white sharks exhibit an unwavering tendency to retreat from their preferred feeding grounds off the coast of San Francisco upon the appearance of an orca in the vicinity.
In a 2022 investigation, utilizing extensive observational data and tracking information from tagged sharks, a cadre of scientists, spearheaded by marine biologist Alison Towner from the Dyer Island Conservation Trust, concluded that orcas are the primary impetus behind the sharks’ increasing avoidance of previously favored locales.
“Initially, following an orca attack in Gansbaai, individual great white sharks would vanish from the area for weeks or even months,” Towner elucidated.
“What we appear to be observing, however, is a widespread avoidance strategy rather than a localized one, mirroring the adaptive behaviors observed in wild canids in the Serengeti, Tanzania, in response to heightened lion activity. The more frequently the orcas patrol these territories, the longer the great white sharks maintain their distance.”
Over a five-year period, the research team meticulously tracked 14 sharks equipped with GPS tags as they departed the area whenever orcas were detected. Concurrently, observations of great white shark presence have experienced a precipitous decline in several coastal bays.
This phenomenon represents a development of significant magnitude. Prior to these recent occurrences, great white shark absences of a week or more in Gansbaai had been documented only twice since record-keeping commenced: a solitary week in 2007, and a three-week period in 2017.
At least 17 sevengill #sharks have been killed by infamous #killerwhale pair Port & Starboard this week in South Africa. Only the livers were eaten with the leftover carcasses washing ashore [1/3] 📸 @MarineDynamics Christine Wessels pic.twitter.com/PQVk1KI9mF
— Dr. Alison Kock (@UrbanEdgeSharks) February 24, 2023
These contemporary disappearances, as noted by the researchers, are unprecedented and ongoing. In a publication from 2024, Towner and her co-authors documented two separate instances of Port and Starboard engaging in shark predation and selectively consuming their livers.
Alarmingly, these predatory activities are initiating shifts within the marine ecosystem.
In the absence of great white sharks, bronze whaler sharks (Carcharhinus brachyurus) are migrating to occupy the ecological void. These sharks themselves fall prey to great white sharks; consequently, with the apex predators absent, the orcas are now targeting the bronze whalers.
Furthermore, it is noteworthy that these orcas are exhibiting a proficiency in hunting large sharks that signifies considerable experience, according to the researchers.
“However, ecological equilibrium is paramount in marine environments. For instance, without the regulatory presence of great white sharks influencing the behavior of Cape fur seals, these seals may prey upon critically endangered African penguins or compete for the limited pelagic fish resources they consume,” Towner commented.
“This represents a ‘top-down’ ecological influence. We also observe ‘bottom-up’ trophic pressures stemming from substantial depletion of abalone, which are grazers within the kelp forests to which these species are intricately linked.
“To put it plainly, while this remains a hypothesis for the time being, ecosystems possess a finite capacity to withstand stress, and the ramifications of orcas preying on sharks are likely to extend far beyond immediate impacts.”
It is also pertinent to investigate the motivations behind the orcas’ choice to hunt sharks. Their livers are recognized as exceptionally rich sources of nourishment, substantial in size, and packed with the fats and oils that sharks utilize to power their extensive oceanic migrations.
Nevertheless, the precise mechanisms by which the orcas acquired this knowledge, or their rationale for prioritizing shark livers as a dietary staple, remain obscure.
It is conceivable that certain orca populations are adapting their hunting strategies to preferentially target sharks, perhaps in response to a decline in their preferred prey species. Independently, a pod in the Gulf of California has developed distinct methodologies for hunting whale sharks.
However, given that great white shark populations are facing a global decline worldwide, the additional pressure exerted by an adept predator represents a legitimate cause for concern.
“The orcas are specifically targeting subadult great white sharks, which can further exacerbate the precarious status of an already vulnerable shark population due to their slow maturation rates and late-maturing life-history characteristics,” Towner stated.
“Enhanced monitoring through citizen science initiatives (e.g., reports from fishermen, observations from tourism vessels), alongside continued tracking studies, will be instrumental in accumulating further insights into how these predatory events might influence the long-term ecological equilibrium within these intricate coastal marine landscapes.”
The findings from the research team have been disseminated within the African Journal of Marine Science, accessible here and here.
