Two 'serial killer' orcas are terrorising great white sharks off South Africa
A pair of orcas killed five great white sharks over a few months in 2017 causing the remaining population to flee the waters in South Africa they once dominated, a new study suggests.
The paper, published in African Journal of Marine Science, examines why the sharks have abandoned parts of the Gansbaai coast, east of Cape Town.
In total, eight dead great whites have washed ashore since 2017, all were the victims of orca attacks.
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Since 2017 eight dead great whites have washed up on the Gansbaai coast. Dyer Island Conservation Trust
Seven of them had their livers removed, while some had their hearts removed too.
Researchers concluded the wounds are the signatures of the same two orcas, which may be members of a rare shark-eating morphotype.
Lead author Alison Towner, a senior white shark biologist at the Dyer Island Conservation Trust, said the "more orcas frequent the site, the longer they stay away".
During the study, which was carried out over five-and-a-half years, 14 sharks have been tracked fleeing the areas when the orcas are present and visual sightings have dropped dramatically in certain Western Cape Bays.
"Initially, following an orca attack in Gansbaai, individual great white sharks did not appear for weeks or months," Towner said.
"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."
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Prior to the study great whites were only absent from Gansbaii for a week or more twice; one week in 2007, and 3 weeks in 2016. AP
The removal of great white sharks will likely cause pressure on the food chain.
It has already triggered the emergence of a new predator, bronze whalers, a shark known to be eaten by great whites.
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Orcas are the apex predator of the ocean and the ones responsible for the shark attacks may be members of a rare shark-eating morphotype. Getty Images/iStockphoto
"These bronze whalers are also being attacked by the orcas too, who are indicating a level of experience and skill in hunting large sharks," Towner said.
"Balance is crucial in marine ecosystems, for example, with no great white sharks restricting Cape Fur seal behaviour, the seals can predate on critically endangered African penguins, or compete for the small pelagic fish they eat.
"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."
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