Great white sharks: top predators or unlikely prey?

Written by Eve Dean

The great white shark (Carcharodon carcharias) has been portrayed as a ferocious ‘mindless eating machine’ for generations. Fears, fuelled by the media and movies, lurk in the back of people’s minds every time they step into the ocean. However, there is a creature who has, in recent years, gone head to head with the great white shark for the title of ‘top predator’.

Orca’s (Orcinus orca) are certainly deserving of the name of ‘killer’ whales, but it is only in the past few years that we have begun to discovered just how deadly these predators really are. In 2017, two orca’s, which became known as Port and Starboard, hunted great whites along the south-west coast of South Africa. I was told this story, first-hand, in 2018, when I was in the small town of Gansbaai, situated in the Western Cape. In this article, I hope to share the story of Port and Starboard, including data I was given by the cage dive company, White Shark Projects.

Google maps image with a photo taken from the White Shark Projects boat in Van Dyks Bay (photo by Eve Dean)

Orca sightings have been recorded in Gansbaai long before this story takes place. In April 2011, a male and a female made an appearance. Then in 2012, six adult orcas were observed chasing common dolphins. However, it was only in 2015, Port and Starboard made their first noted appearance. At the time, this was no major concern. But when they returned to the area in February 2017, things took a dark turn.

Port and Starboard were seen increasingly around Gansbaai. The two males had a very distinct appearance, due to their collapsed dorsal fins. One was collapsed to the right and the other to the left, hence the names Port and Starboard. The collapsed dorsal fin is a stress response sometimes seen in captive orcas. However, only 1% of wild orcas suffer from this stress response, leading many to suspect that the Port and Starboard had been rejected from their pod. Orcas are social animals and rely on their social structure to hunt, breed and ultimately survive. Without a pod Port and Starboard became highly stressed, which would explain their infamous dorsal fins. It would also explain their drastic change of behaviour and their motive for desperately hunting great whites.

Graphic showing Port and Starboard hunting a Great White Shark. The orcas were named in correspondence with the direction of their collapsed dorsal fins. Port to the left, Starboard to the right, (Artwork by Marc Dando).

On the 8th of February 2017, a 2.7 metre female shark washed up fully intact except from one large gaping hole where her liver once was. With her liver missing, the otherwise healthy shark intrigued scientists. At this point, there was still little evidence to make a connection between the orcas’ presence and the shark’s death. However, on the 1st of April, a tagged female shark, known as ‘Khaleesi ’, was found in the same condition. But Khaleesi was not a small shark, she was an impressive 4.9 meters.

The next three wash ups were found in quick succession to one another, all discovered in May 2017. The first of which was a 3.6m male, which had evidently been floating in the water for a while, as the body had started to break down. The next wash up was a 4.5m male, followed by a 4.1m male. Between each attack, virtually no great whites were sighted, it seems the sharks had fled from Gansbaai. After the last body was found, not a single great white was seen in the area for 45 days.

The sharks eventually began to return with caution. However, Port and Starboard were still present and shark number six soon washed up on the 8th of November 2017. Unfortunately, there is no data for this shark regarding sex or size. This may be because the shark was too badly mutilated or because the attack was long before it was found.

Every shark that washed up was autopsied by local researchers and experts. The standard autopsy included taking skin and blood samples, checking for parasites, measuring the jaw and checking the infamous content of the Great White Sharks stomach. One thing was evident in all sharks; every single shark had their liver removed.

Over 2017, theories as to the cause of the shark deaths and disappearances became increasingly connected to Port and Starboard. Their collapsed dorsal fins and their appearance corresponding with shark wash ups began to make sense. The only thing up for debate was the theory of attack.

A female great white shark with mating scars and mouth open. Seal in the background.

A commonly agreed upon theory is that the shark is stalked their unlikely from below. The orca ambushes the shark, ramming it from underneath and flipping the shark over. The shark is vulnerable belly up because it can enter a state of tonic immobility — a trance-like-state that can be triggered in lots of sharks — and will start to drown. Due to the shark’s inverted body, the liver floats up towards the exposed torso and one bite then removes and consumes the entire organ. Because the liver is so rich is nutritional oils, this is all the Orcas require. Presumably, the Orcas take it in turns to perform each role; one to bump and ram the shark, one to rip open the shark and feed.

The great white killing spree carried out by Port and Starboard was also notable for another reason. It allowed another shark species to take the place of the dispersed great whites. That species was the bronze whaler shark (Carcharhinus brachyurus), also known as copper sharks. They are high speed, group hunters that can grow to over 2 metres long. Previously, Bronze Whaler sharks were a rare sighting around Gansbaai, with white sharks dominating. However, as the great whites disappeared during 2017, more and more bronze whaler sharks were seen in locations they were rarely seen before. It seems the relocation of the great whites opened up an ecological niche that the Bronze Whalers could exploit. This made it harder for the great whites to return, and they didn’t fully establish their presence in Gansbaai until June 2018.

It turns out that Port and Starboard had caused quite a bit of trouble using their risky new solution to their rogue lifestyle. The future relationship between the two orcas and the Gansbaai sharks is uncertain, but seemingly, 2017 was the worst of it. There has not been events as severe as 2017 since and the great white sharks are recovering steadily. Although, everyone in Gansbaai will always have their eyes open for the two Orcas and their collapsed dorsal fins.

A

Eve is currently studying Marine Biology at the University of Plymouth and was appointed the 2020/2021 Secretary of the Marine Biology Society at Plymouth. Eve aspires to gain her PhD and contribute to the research and protection of sharks. You can get in contact with Eve via her LinkedIn profile here.


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