According to a new study, two killer whales have killed at least 8 great white sharks in recent years by eating their livers in waters off the coast of South Africa.
Image courtesy of Save Our Seas Magazine
The two "serial killers" are killer whales called Port and Starboard, which have been regularly seen in the waters around Gansbaai since 2015 and appear to have scared away all the great white sharks in the waters.
Image from: cnet.com
Great white sharks usually congregate off the coast of South Africa and prey on the seal colonies there. Located about 120 kilometres east of Cape Town, South Africa, Gansby is a year-round haven for sharks, making it an excellent location for cage diving with the ocean's top predators. Years of eyewitness data show that Gansbay was a hotbed of great white shark activity, with an average of at least nine sharks found every day between 2008 and 2011 — until killer whales entered the waters.
Image courtesy of MailOnline / Debasish Sarmah
In a new study published June 29 in the African Journal of Marine Science, researchers examined years of tracking and sensor data to show how great white shark populations changed near the Gansbay Sea — and the results and preliminary indications: The presence of a killer duo "frightened" sharks in the area.
Dead great white sharks began to wash away off the South African coastline, and their livers were pulled out. Between 2017 and 2020, a total of 8 sharks were washed ashore. The number of sights of live sharks has also plummeted.
Image credit: Hennie Otto / Dyer Island Conservation Trust
Alison Towner, shark biologist and lead author of the paper at the Dyer Island Conservation Trust, said in a statement: "The more frequently killer whales are present at these locations, the longer the great white shark will be away. ”
Image credit: Hennie Otto / Dyer Island Conservation Trust
Towner has long studied sharks near Gansbay and, along with her colleagues, noticed this unusual change in shark populations. The team performed an autopsy on the bodies, which revealed they had been attacked by killer whales, which tore off the shark's energy-rich liver. "The liver of the great white shark makes up about a third of its body weight and is rich in lipids. It's very nutritious," Towner said.
Although the team did not directly witness predation, they often saw a pair of "serial killer" combinations in the area: Port and Starboard. The fleeing great white sharks often do not return to the area for weeks or months.
One interesting phenomenon in the study was that the short-tailed true shark (Carcharhinus brachyurus), another shark that often appears off the coast of South Africa, began to migrate in as the great white shark moved out. Great white sharks sometimes feed on short-tailed true sharks, but short-tailed true sharks are not as afraid of killer whales as great white sharks, so they feel safe enough to enter Gansbay and feed on seals. However, Towner notes that even short-tailed sharks are now attacked by killer whales. No shark seems safe.
Short-tailed shark, image from Andy Murch
One question the study sought to answer was why killer whales like Port and Starboard suddenly started preying on great white sharks. The team suggested a number of reasons, including that the reduction in prey may have readjusted the range of motion of killer whales and sharks to bring them closer together.
However, the researchers believe that the loss of prey caused by fishing and fishing may also be responsible for the overall decline in the population of the great white shark in Gansby.
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