According to a new study, orcas are tearing up great white sharks off South Africa

Great whites used to dominate areas of the Gansbaai coast, about 100 kilometers (62 miles) east of Cape Town, but have avoided them accordingly in recent years to an article published in the African Journal of Marine Science on Wednesday.

The Gansbaai coast was once a popular spot for great white shark viewing, but sightings have decreased significantly in recent years. The study used long-term sighting and tagging data to show that great whites were chased away by the orcas, sometimes called killer whales.

Researchers also analyzed five great white shark carcasses that washed up on shore, four with nutrient-rich livers removed and one with the heart taken out. They all had wounds from the same pair of orcas that likely killed more great whites, researchers say.

The study followed 14 great whites over five and a half years and found that they fled the area when the orcas were there. Researchers believe the sharks’ fear triggers rapid, long-term mass migration when they know the predator is present.

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“Initially, after an orca attack in Gansbaai, individual great white sharks would not show up for weeks or months,” said the study’s lead author Alison Towner, a senior great white shark biologist at the Dyer Island Conservation Trust, in a press release.

Towner believes this is “large-scale avoidance,” similar to how wild dogs in the Serengeti avoid certain areas when lions are present.

“The more often the orcas visit these sites, the longer the great whites stay away,” she added.

An ecosystem in transition

Before the orcas began attacking the great whites, the sharks were absent from Gansbaai for just a week in 2007 and three weeks in 2016.

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This means the prolonged absences observed by research are unprecedented and are changing the ecosystem in the region.

Bronze whalers have emerged as a new medium-sized predator in the region, Towner said.

“These bronze whalers are also attacked by killer whales, which indicates a high level of experience and skill in hunting large sharks,” said Towner, adding that Cape fur seals are now preying on critically endangered African penguins .

“That’s a top-down influence, we also have bottom-up trophic pressures from the extensive removal of abalone grazing the kelp forests that these species are all linked by,” she added.

“To put it simply, while this is a hypothesis for now, there are limited pressures that an ecosystem can withstand, and the impact of orcas removing sharks is likely more far-reaching.”

An “abrupt decline”

Towner also thinks orcas are becoming increasingly common off the coast of South Africa, and this particular pair could be part of a rare group of shark eaters.

“This change in behavior of the two top predators could be related to a decline in prey populations, including fish and sharks, leading to changes in their distribution pattern,” she said.

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The orcas are concentrating on younger sharks, she said, which could have a bigger impact on vulnerable large white populations because the sharks are slow growers and mature late in life.

Researchers concede that sea surface temperatures could also be affecting great white shark sightings, but “the immediate and abrupt decline in sightings in early 2017 and the prolonged and increasing periods of absence cannot be explained.”

Other explanations could be direct fishing for whites or reduced numbers of prey due to fishing, they add, but while this “may possibly contribute to an overall decline in the number of whites in South Africa, it is unlikely to account for the.” explain sudden local decline.”

Another 2016 study found that there are only a few hundred great white sharks left in South Africa, compared to previous estimates of a few thousand.

In addition, DNA analysis of shark tissue showed that the genetic diversity of South African whites is exceptionally low, making them more vulnerable to external shocks such as disease or environmental changes.