Pair of orcas targeting great white sharks off South Africa’s coast

According to a new study a pair orcas drove great black sharks from a section of South African coast. They had killed five sharks in a matter of months in 2017 and drove them away.

The Gansbaai coast was dominated by great whites for approximately 100 kilometres (62 mi). east of Cape Town but have been avoiding them for the past few years, according to A paper was published in the African Journal of Marine Science Wednesday.

Gansbaai’s coast was once a popular spot to spot great white sharks. However, sightings have dropped significantly in recent years. The study used long-term data and tagging data in order to prove that great whites were being driven away by the orcas.

Researchers also analysed five carcasses of great white sharks found washed up on shore, four of which had their nutrient rich livers removed by researchers One with its heart removed as well. Researchers believe that the same pair of orcas inflicted similar wounds on all three.

Over five and a quarter years, 14 great whites were tracked and found to have fled the area when orcas were present. Researchers believe that sharks sense fear triggers a long-term mass migration if they are aware of the predator.

“Initially, after an attack by Gansbaai orca, great white sharks did no appear for weeks or months.” saidAlison Towner, Dyer Island Conservation Trust’s senior white shark biologist, is the study lead author. News release

Towner believes that this is “large-scale avoidance,” much like how wild dogs in Serengeti avoid certain areas if lions are present.

She added that “the more orcas visit these sites, the more great white sharks stay away.”

A CHANGING ECOSYSTEM

The sharks were absent from Gansbaai only for a week in 2007 and three weeks 2016 before the orcas began attacking great whites.

This means that the long absences observed by researchers are unprecedented and is changing the ecosystem in the region.

As mid-ranking predators, bronze whaler sharks have been introduced to the area. said Towner.

“These bronze whalers also get attacked by the orcas, who are also indicating a high level of skill and experience in hunting large sharks.” saidTowner added that cape-fur seals are now preying upon African penguins, which are already endangered.

“That’s top-down, but we also have trophic pressures from the extensive removal abalone, who graze kelp forests these species were all connected through,” she said.

“To simplify, although this is a hypothesis at the moment, there is only so much pressure that an ecosystem can handle, and the effects of orcas removing sharks are likely to have far greater-reaching consequences.”

AN ABRUPT DECLINE

Towner believes that orcas are becoming more common off the coast South Africa’s coast, and that this particular pair may be part of a unique group of shark-eaters.

She stated that “this change in the behavior of both top predators could be linked to a decline on prey populations, including sharks and fishes, causing changes to their distribution pattern.” said.

She is the younger sharks that the orcas are focusing on. saidThis could have a greater impact on the great white population, as the sharks mature late and grow slowly.

Researchers acknowledge that sea temperature may also have an impact on sightings. However, “the abrupt decline in sightings at 2017. and the extended and growing periods of absence cannot both be explained.”

They add that there are other possible explanations, such as direct fishing of greatwhites or decreased numbers prey due to fish fishing. However, although this may “potentially lead to an overall decrease in South Africa’s great white population”, it is unlikely to explain the sudden localized drop.

Another 2016 study showed that there were only a few hundred great-white sharks left in South Africa compared to earlier estimates which had been closer to a few thousand.

Additionally, DNA analysis of shark tissue has shown that South Africa white sharks are extremely susceptible to environmental shocks like disease and climate change.