THE HUNTER BECOMES THE HUNTED: Orcas preying on Great Whites' livers in horrifying apex battle
Great white sharks used to dominate the Gansbaai coast -- around 62 miles east of Cape Town -- at one point
A pair of orcas have reportedly driven great white sharks off a stretch of the South African coast after five sharks were found dead over just a few months in 2017, a new study has revealed.
According to a paper published in the African Journal of Marine Science on Wednesday, June 29, great whites used to dominate the Gansbaai coast -- around 62 miles east of Cape Town -- at one point. However, they have reportedly been avoiding the coast in recent years. The area was once a popular hotspot for spotting great whites, but sightings have considerably decreased in recent years. The study is said to have used long-term sightings and tagging data to demonstrate that the sharks have been driven away by the Orcas, sometimes referred to as killer whales.
Researchers analyzed five great white carcasses that were washed up on the shore and found that four of them had their nutrient-rich livers removed, while one had its heart taken out. Experts concluded the wounds were made by the same pair of orcas, which have possibly claimed the lives of several great whites. The aforementioned study tracked the movements of 14 great whites over five and a half years and found they fled the area when the orcas were there. Researchers believe that the phenomenon has sparked an exodus where sharks know the predators are present.
"Initially, following an orca attack in Gansbaai, individual great white sharks did not appear for weeks or months," Alison Towner, a senior white shark biologist at the Dyer Island Conservation Trust who led the study, said in a news release. According to Towner, this is "large-scale avoidance" similar to how wild dogs in the Serengeti avoid areas where lions are present. "The more the orcas frequent these sites, the longer the great white sharks stay away," she added.
Orcas that have developed a taste for the organs of great white sharks have transformed the entire ocean ecosystem in South Africa. @MichConstant speaks to Alison Towner - Senior White Shark Biologist @MarineDynamics #SAfmJetSetBreakfast pic.twitter.com/TsVnqrs7lC— SAfmRadio 📻 (@SAfmRadio) July 3, 2022
The sharks had reportedly only been absent from Gansbaai for one week in 2007 and three weeks in 2016 before the orcas started attacking them, which means the extended absences observed are unprecedented in nature and are permanently changing the ecosystem in the region. Towner said bronze whaler sharks had emerged as new mid-ranking predators in the area.
"These bronze whalers are also being attacked by the orcas too, who are indicating a level of experience and skill in hunting large sharks," said Towner, who revealed that cape fur seals were now preying on African penguins, which are themselves endangered. "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," she continued. "To put it simply, although this is a hypothesis, for now, there is only so much pressure an ecosystem can take, and the impacts of orcas removing sharks, are likely far wider-reaching." Towner also said that orcas are increasing in numbers off the coast of South Africa and that the pair in question could be part of a rare group of shark eaters. "This change in both top predators' behavior could be related to a decline in prey populations, including fishes and sharks, causing changes in their distribution pattern," she added.
New paper on the orcas Port & Starboard killing white sharks in 🇿🇦. Was lucky enough to be loosely part of the 5th necropsy described here as an intern in Gansbaai 2017 (see pics). Big congrats to Alison Towner et al. Very nice to see this published: https://t.co/DfSA8UtGnd pic.twitter.com/HRV2AgzIrr— Jack Cooper 🦈 (@CooperPalaeo) June 30, 2022
The orcas primarily focus on younger sharks, Towner said, which could eventually threaten the vulnerable great white populations as the sharks grow slowly and mature late in life. While sea surface temperatures could also impact great white sightings, researchers say "the immediate and abrupt decline in sightings at the beginning of 2017 and the extended and increasing periods of absence cannot be explained." There could be other reasons for the decline in numbers, such as unregulated fishing, but while that would "potentially contribute to an overall decline in numbers of great whites in South Africa, they are unlikely to explain the sudden localized decline," researchers explained in the release.