Killer whales could be responsible for the disappearance of great white sharks from South African waters, according to a new government report.
Great whites are a big draw in Cape Town as visitors view them from excursion boats or protective shark cages.
However, their number has fallen sharply since at least 2017.
Experts have suspected everything from illegal hunting and overfishing to pollution and even climate change.
A team of government experts reported that there may be a "causal link" between the absence of the sharks and the appearance of a pod from orcas that specialize in hunting great white sharks.
Scroll down for video
At least seven great white shark carcasses have washed ashore in False Bay since 2017. Telltale tooth marks indicate that orcas have struck them. Researchers say great whites who encounter killer whales will immediately leave their usual hunting grounds for a year
According to the conservation organization Shark Spotters, great whites were sighted in False Bay more than 200 times a year from 2010 to 2016.
There were only 50 sightings by 2018 – and none during all of 2019.
The first great white in 20 months was seen in False Bay in January, according to Mongo Bay, the only sighting that year.
A pair of killer whales, nicknamed Port and Starboard, were first seen in the area in 2015.
Great white sharks are a major tourist attraction in South Africa, and brave visitors are lowered into shark cages for an up-close visit. But the number of shark sightings near Cape Town has plummeted since 2017, threatening ecotourism in the area
The absence of the sharks has been blamed for everything from climate change to illegal hunting. A group of government experts said Tuesday they believe they are being deterred by another apex predator, the killer whale
Between 2010 and 2016, shark spotters in False Bay, near Seal Island (pictured), had more than 200 great white sightings a year. No sharks were sighted in 2019 and only one was seen in 2020 so far.
Two years later, the remains of five great whites were discovered nearby on a beach in Gansbaai, widely recognized as one of the best regions in the world for shark diving.
Their livers had been ripped out, and tooth marks pointed to orcas as their killers.
Another shark, killed in a similar way, was found on a beach earlier this year, reports the France-Presse agency.
Experts suggest that Port and Starboard developed a taste for squalene, an organic chemical compound that is abundant in shark liver oil.
WHY DO ORCAS HUNT GREAT WHITE SHARKS?
Orcas are the great white's only natural predator.
Scientists have found evidence that the sharks crack open and eat their fatty liver.
Scientists speculate that this behavior may be due to the disappearance of large whites from the waters of False Bay off the coast of Cape Town.
Great whites visited the area between June and October each year as part of their annual winter hunting season.
They were drawn to the region by the presence of what is known as Seal Island, a rock that contains a huge seal colony.
However, they themselves have fallen to pray to orcas – and are on the retreat.
Orcas have been seen hunting great white sharks around the world.
According to a 2019 study published in Scientific Reports, the sharks will leave their hunting grounds immediately and will stay away for up to a year if confronted with them.
A panel of experts gathered by Environment Minister Barbara Creecy reported that the disappearance of the sharks near Capte Town was more a shift in distribution … as a result of the recent emergence and predation of orcas rather than being related to fishing activity. & # 39;
Speaking at a conference Tuesday, Creecy said the lack of the great white had "had a devastating impact on the shark diving industry and immensely disappointed the hundreds of tourists who visit our shores to see this great predator."
A wide variety of Chondrichthyes are found in South Africa, including some of the largest populations of more than 180 different species of sharks, rays and chimeras.
30 percent of these fish are only found in the country's waters.
However, 14 species of shark native to South Africa are considered endangered or critically endangered.
The carpenter shark, also known as the sawfish, has not been sighted since 1999.
While Cape Town's great whites may be deterred by another apex predator, most of that loss is due to habitat degradation and illegal fishing practices.
"Their disappearance can be traced back to a combination of illegal gillnets and habitat degradation in the estuary," Creecy said. "Unfortunately protection for this species came into effect after the last one was caught."
Creecy allowed shark fishing to have a long tradition in South Africa that predates the arrival of Westerners.
The disappearance of the great white "has had a devastating effect on the shark diving industry, immensely disappointing the hundreds of tourists who visit our shores to see this great predator," said Environment Minister Barbara Creecy
However, she called for a compromise between fishermen and tour operators on the "consuming and non-consuming use of sharks".
"The impact of fishing on ocean biodiversity is undeniable and sharks are no exception," Creecy said. "Many shark species produce only a few, live young and cannot withstand the unregulated fishing pressure."
(tagsToTranslate) Dailymail (t) sciencetech (t) South Africa (t) Climate change and global warming