South Africa's great white shark mystery: The full story

2017-05-12 06:30 - Paul Steyn
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Cape Town - An orca whale killing spree of great white sharks has gripped the coast of South Africa this month, resulting in the first ever dissection of a white shark following an attack of this nature.

In the past two weeks, three dead white sharks washed up on the shores near Cape Town; and like all good serial killer mysteries, this killer left a common clue at the scene of each crime.

With almost surgical precision, the livers of the sharks in all three cases were neatly removed, but little else was eaten.

Even the hearts of the two of the sharks were left intact.

Following the unprecedented dissections, the Department of Environmental Affairs (DEA), confirmed this week that orca whales were responsible for all three killings, and that they were targeting the large nutrient-rich livers of the sharks. Various small pods of orcas have been spotted around Gansbaai in recent weeks.

"We have never seen anything like this," said Alison Towner, a biologist from the Dyer Island Conservation Trust, who contributed to the dissection of the sharks. In all three cases, "there was a large gaping hole between her pectoral fins where they were torn apart to reveal her body cavity … and that their large livers were completely missing. This information, combined with the recent sightings of orca and disappearance of white sharks in the area, provides convincing evidence that the orcas are responsible for the shark's death."

“This is an extremely rare occurrence,” she said in an email with Traveller24, “This is also the first time worldwide the carcass of a white shark was recovered post orca predation, let alone three carcasses within one week!”

The Timeline of Events

The first dead shark—a massive one-ton great white—washed up on the shore in Gansbaai on 3 May. The first people at the scene were initially perplexed as to how such a large shark could have died, and it wasn't until a dissection, authorised by the Department of Environmental Affairs (DEA) in conjunction with the White Shark Research Group, Marine Dynamics and the Dyer Island Conservation Trust, revealed that the shark’s liver was missing.

The next day, another 3,5 meter shark washed up on the shore at Franskraal beach, and a later dissection revealed that this one’s liver was also missing.  “This is a difficult yet fascinating time,” said Towner on the Marine Dynamics blog. “It is something rarely documented in marine top predator behaviour in South Africa,”

On 7 May, a third dead shark washed up, this time in Struisbaai, matching the injuries of the previous two specimens, and cementing the suspicion that these were not just random isolated incidents. “Obviously this is a very sad time for us all,” said Towner, who was on hand to assist again. “Nature can be so cruel and the dexterity these enormous animals are capable of is mind blowing, almost surgical precision as they remove the liver of the white sharks and dump their carcass."


How and Why are Orcas targeting Great White Sharks?

Known as the “Wolves of the Sea”, orcas are the true apex predators of the ocean, and the only known predator of the great white shark. 

They are extremely intelligent, specialised hunters, feeding above sharks on the overall oceanic food chain. They hunt in organised social groups, using echo-location, strategy, and teamwork to kill their prey, which can be anything in the ocean, from seals, to dolphins, dugongs, otters, turtles, birds, squid, and sometimes even land mammals.

According to the DEA statement, the orcas were targeting the squalene rich livers that assists sharks with their buoyancy. This substance is also highly nutritious pound for pound, compared with the muscle tissue. Although this type of selective feeding on livers is extremely rare in orca whales, seals have been known to predate sea birds where they often remove and consume only the stomach/abdominal content and not the rest of the carcass.   

Orcas are also suspected to be responsible for a decline in Cape Town’s cow shark population, and have been known to predate these sharks. Alison Kock, a Marine Scientist for Shark Spotters, reported recovering several cow shark carcasses in a similar condition with their livers removed, in False Bay subsequent to a series of orca sightings.

How the orcas are able to extract the livers so neatly from the sharks is a bit of a mystery. But footage off the coast of California showed team-work between the orcas pushing a white shark to the surface, belly up, biting into its flesh, before letting buoyant, oil-rich liver as it float out of the cavity. 


What does this mean for Great White Sharks in South Africa?

Orca whales are widely distributed in the ocean, extending from the Arctic to the Antarctic, into the tropics, and are present in both coastal and oceanic waters.

According to figures from the DEA, orca whales are fairly common along the coast of South Africa, and some 785 sightings have been recorded ranging from the Western Cape all the way to Northern KwaZulu-Natal. “The sightings of Orca pods appears to be increasing in South Africa,” they said in a recent statement, but these sightings could also be attributed to more people on the ocean with eyes on the water.

The incidents have already affected the number of great white sightings, as the sharks leave the bay to avoid the orcas. The killings are a blow to the already struggling population of great white sharks in South Africa, a local population which some scientists say is facing extinction.

The DEA, along with various shark scientists and marine mammalogists, is currently collating all the scientific information about the incidents, and they are urging the public to be aware that this is a natural phenomenon, and might have to do with changes in seasons or temperatures and prey regimes of the orcas.

Time will tell whether these massive apex predators continue with their unprecedented great white shark killing spree.

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