[Image: Wikimedia Commons]
It wasn’t so long ago that Gansbaai was home to nearly 1,000 apex predators.
Google the Western Cape bay and images of great whites pop up, as the area is meant to be well-known for the mighty species.
However, Gansbaai has recently become a mere shadow of its former self, thanks to the relentless onslaught of orcas.
The fishy business began in February 2017, when the first carcass of a great white washed up in South Africa. Nobody could blame the usual suspects as the 2.6-metre-long body of the female shark had no hook or net marks, ruling out human involvement.
Soon after, all the great white sharks had vanished from Gansbaai and the mystery of whatever killed the poor animals remained unsolved.
Sightings of sharks didn’t return to their peak until May, but then, over five days, three more carcasses turned up, followed by a fifth in June. For a haunting eight weeks, not a single great white was spotted, raising serious concern among ocean scientists.
Per The Guardian, Dr Alison Towner, a Rhodes University marine biologist, was doing her doctorate on the white shark movement, which had to be curtailed as the creatures have become more elusive than ever.
What was supposed to be an area with a teeming population of 800-1,000 great white sharks (especially in the 2010s), has turned into an eery sharkless void over time. With each killing the bay’s sharks fled for longer and returned in smaller numbers. When a sixth carcass appeared in June 2021, they did not return for another year.
“Witnessing the very predator I’d dedicated my life to studying wash up dead on the beaches was surreal, and something I will never forget,” Dr Towner recalled after finding the first washed up shark in 2017.
“We had several sharks acoustically tagged, and later realised three had moved as far as Plettenberg Bay and Algoa Bay, more than 500km [300 miles] east,” she added.
Throwing themselves into trying to solve the mystery, Dr Towner and her colleagues quickly realised that all the shark deaths were connected as their injuries and cause of death were chillingly similar: a liver removal with surgical precision by none other than the ruthless, and probably hungry as heck, orcas.
Actually, the culprits turned out to be two very specific orcas who had made Gansbaai their home since 2015. Maybe you know them already- Port and Starboard, named by local zoologists who could identify them with their distinctive dorsal fins, collapsed to the left and right respectively.
The notorious shark-eating orcas, Port & Starboard, found the sevengill shark aggregation at Seal Island today @SANParks #orcas #sharks #liveyourwild To learn more about these orcas https://t.co/k3YQ6E6VF0 pic.twitter.com/nK8JMiqYAs
— Dr. Alison Kock (@UrbanEdgeSharks) May 26, 2019
The pair had been seen off Gansbaai’s coast just hours after each dead shark was found. They were also spotted in nearby False Bay, hunting sevengill sharks and feasting on their livers.
If it wasn’t obvious enough that Port and Starboard were dominating the great whites, Christiaan Stopforth managed to capture a live attack on 16 May 2022 with his drone. He managed to record five orcas in the middle of attacking a three-metre-long white shark just east of Gansbaai, biting between its pectoral fins and ripping out its liver. One of the orcas was Starboard.
As Esther Jacobs, founder of the marine conservation charity Keep Fin Alive, said: “To witness one of the ocean’s top predators defeated so easily was heartbreaking.”
More killings were witnessed and reported, and the remaining sharks left Mossel Bay for 45 days, at which time – da-da-dum – Port and Starboard also returned. More great white shark liver devouring occurred, which was “both awe-inspiring and harrowing” per Jacobs, and now, Mossel Bay’s great white sharks have all but disappeared.
“Since the 2023 incident, they haven’t returned in any meaningful way,” says Jacobs. “As far as I know, there have been fewer than 10 confirmed observations in 2024.”
Shame.
New paper lead by Alison Towner documents how killer whales likely caused white sharks to leave a South African aggregation site, and some of the subsequent impacts.https://t.co/0HC8dfGxHN pic.twitter.com/Dv6OBepWby
— Yannis Papastamatiou (@Dr_Yannis) June 30, 2022
While the orcas are happy with their fatty liver meals, the great white shark disappearances are a major problem for the balance of the ecosystem. Noted as “doctors of the ocean”, great whites are critical for keeping the populations of other animals at a reasonable level, like the cape fur seal and the bronze whaler shark, which have only surged in Gansbaai lately.
Not only does the explosion of prey species cause a ‘trophic cascade’, where the loss of a predator reverberates down the food chain, unbalancing the entire ecosystem, but Towner reckons it is also why our Cape seals have become more aggressive and more diseased.
Towner notes that the seals, no longer under threat, “became bolder, some even predating on the critically endangered African penguins”.
There is also the outbreak of rabies in the seal population, which in Towner’s opinion, “if white shark populations were at their previous peak, they might have helped mitigate the rabies situation, as rabid seals would likely be easier targets.”
It is everyone’s concern that these damaged ecosystems could be a gruelling reflection of our oceans’ future; something that goes beyond just two orcas.
[Source: The Guardian]
