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Where Are South Africa's Great White Sharks?
Written by <a href="index.php?option=com_comprofiler&task=userProfile&user=54688"><span class="small">Heather Richardson, Mongabay</span></a>   
Sunday, 14 June 2020 13:14

Richardson writes: "South Africa's great white shark population has been the subject of international scrutiny since 2017, when cage-diving operators reported a sudden, sharp decline in sightings around False Bay and Gansbaai."

White shark, Gansbaai: Ten years ago, there were an estimated 300 breeders in the white shark the population. The minimum to avoid inbreeding is thought to be around 500. (photo: Olga Ernst via Wikimedia)
White shark, Gansbaai: Ten years ago, there were an estimated 300 breeders in the white shark the population. The minimum to avoid inbreeding is thought to be around 500. (photo: Olga Ernst via Wikimedia)

Where Are South Africa's Great White Sharks?

By Heather Richardson, Mongabay

14 June 20


APE TOWN — South Africa’s great white shark population has been the subject of international scrutiny since 2017, when cage-diving operators reported a sudden, sharp decline in sightings around False Bay and Gansbaai.

From 2010 to 2016, white sharks (Carcharodon carcharias) were sighted in False Bay an average of 205 times each year, according to conservation and research organization Shark Spotters. In 2018, the sharks were spotted just 50 times; and in 2019, nothing. In January 2020, the first white shark in 20 months was seen in False Bay.

“The reality is that we have way more theories than we have facts to support them at the moment,” says marine biologist Alison Kock, who currently works for South African National Parks. She has been researching white sharks in South Africa since 1998. “There are three or four possible reasons. Each one may be contributing in its own way.”

It’s unclear how many white sharks there are around South Africa — estimates have ranged from around 500 to 900. Sara Andreotti of Stellenbosch University studies the genetics of white sharks around the South African coast. Her research found the sharks to be a single population, moving from site to site and breeding with each other. In a study from 2009 to 2011, she estimated there were around 300 breeders in the population­ — but the minimum to avoid inbreeding, she says, is thought to be around 500. “So our population was in real trouble already,” she says.

But what explains the sudden disappearance of white sharks from False Bay and Gansbaai in 2017?


The answer most white shark scientists point to is the presence of orcas in the area — two in particular. Port and Starboard, as they have been named, were first spotted in False Bay in 2015 (though orcas had become increasingly present since 2009). At this time, several carcasses of broadnose sevengill sharks (Notorynchus cepedianus) were found in the bay — and the predator appeared to be the orcas. These were the first records of orcas predating on sharks in South Africa.

Kock published a paper on “the first documentation of a novel feeding technique”: The killer whales were using force to break the shark’s pectoral girdle to enable them to bite out the liver, discarding the rest of the carcass.

Following the attacks, sevengill sharks vanished from the bay — one of the largest known aggregation sites for this species anywhere in the world — for up to a month.

Then, in 2017, five white shark carcasses washed up on the shores around Gansbaai. Like the sevengill sharks, only their livers had been removed. Teeth marks clearly pointed to orcas as the predators. Sharks’ livers are rich in fat and make up a third of their total weight, so it’s no surprise these incredibly intelligent predators target this nutritious organ.

Kock theorized that the disappearance of white sharks from False Bay and Gansbaai could be due to the presence of the orcas. In 2017, there was an increase of white shark sightings further along the coast, in Mossel Bay, where they may have relocated to evade the orcas.

Orca predation on white sharks has also been documented in California. Salvador Jorgensen showed that white sharks disappeared from an area when orcas were present; in 2009, 17 tagged white sharks suddenly vanished from the area around the Farallon Islands, which he linked to the presence of orcas in a 2019 paper. Jorgensen found that white sharks might disappear for up to year when orcas passed through their hunting grounds.

A common theme in the study of white sharks is uncertainty. Orcas have been observed with white sharks in the past; Andreotti says she recalls sampling white sharks in Gansbaai in 2012, while orcas were also in the bay. “I had almost 20 sharks around,” she says.

Kock says while there is evidence that the overnight disappearance of white sharks is related to orcas, it’s not clear-cut. “It doesn’t seem to be all orca pods that have the effect at this stage. So, sometimes we’ve got orca pods that come into an aggregation site, and there’s no change in white shark sightings.”

Until last year, Port and Starboard were the only orcas thought to be having an impact on the shark population off South Africa, says Kock. “Then at the end of last year, a totally different pod that didn’t have Port and Starboard in it came into Mossel Bay. There’s a video of one of the orcas [showing] an interest in one of the white sharks around a cage diving boat. And overnight, they went from having seven to 10 different white sharks to having nothing.”

Kock has been working on a paper led by marine biologist Alison Towner, which she hopes will be published later this year, revealing the extent of the orcas’ impact on the white shark population.

One theory is that the shark-eating orcas are part of a different ecotype, drawn to coastal waters from deeper, pelagic waters for a variety of reasons, including changing water temperatures due to climate change and overfishing.


In media coverage of South Africa’s white sharks, demersal shark longline fisheries have been portrayed as a central culprit for their disappearance — but many white shark scientists are quick to point out the lack of data.

The longline fisheries target small sharks that are important prey for juvenile white sharks (mature sharks tend to eat marine mammals, such as seals). Scientists from South Africa’s Department of Environment, Forestry and Fisheries recommend catch control based on their data, but there are currently no limits in place and there are concerns about the impact on the ecosystem of overfishing sharks such as soupfins and common smooth-hounds. Additionally, the monitoring of South Africa’s coastlines is notoriously weak and some boats still fish in the no-take zones of marine protected areas.

One interesting finding by Ph.D. student Dylan Irion, supported by observations of some fishermen in and around Algoa Bay, is that as white shark sightings in the Western Cape have dropped off, sightings in the Eastern Cape have spiked — suggesting the sharks have relocated eastward, even though there is more demersal longline fishing of sharks there.

This weakens the argument that fishing of smaller sharks is denying juvenile sharks their prey — though overfishing in the open ocean could be a reason some orcas have moved from deeper waters to the coast.

Kock cautions against speculating before there is data to confirm these theories. “You have to be careful, because you can have unintended consequences … for people’s livelihoods. It’s really important, particularly for people in the decision-making sphere, to have evidence-based information, so that they can make the right decision. And at the moment, in terms of the white sharks disappearing, that needs a lot more work.”

Andreotti says she believes the fisheries should be more strictly regulated in any case, as sustainable fishing will have positive effects for people, sharks and the whole ecosystem in the long run. “They’re dealing with the livelihood of people,” she says. “I respect that. But I would appreciate it if they could try and see … the long-term goal.”

Shark nets and drumlines (baited hooks specifically targeting sharks) pose additional risks to white sharks along the South African coastline. Although the species has been protected in South Africa since 1991, the province of KwaZulu-Natal (KZN) uses baited hooks to cull white sharks as a method of preventing them swimming close to the shore. Between 2013 and 2017, an average of nearly 17 white sharks died on KZN’s drumlines each year, as well as scores of other marine animals: turtles, dolphins, and other shark species.

Uncertainties and COVID-19

Kock emphasizes the importance of taking a wider view. “If you talk to people in the Western Cape … the shark spotters aren’t seeing [the white sharks], the surfers aren’t seeing them, the fishermen aren’t seeing them, the cage diving operators aren’t seeing them, our science shows that we’re not seeing them. But if you talk to fishermen in Algoa Bay and the Eastern Cape, they’ll tell you the opposite — [they’ve] never seen so many white sharks,” she says. “When people focus on just one aggregation area, they’re missing the bigger picture.”

Irion is currently using available data sets to look at the whole South African coastline. The information is relatively new; white sharks live an estimated 70 years, but the earliest data only starts from the early 1990s, recorded by Gansbaai cage-diving operators; in False Bay, recorded observations began in 1996. In addition, white sharks, especially the larger individuals, spend so much time far offshore — and satellite tags are extremely expensive — that there is a great deal of movement and behavior that scientists never see.

“We always concentrate on the things that we do know because obviously, they’re the facts that we have at hand,” Kock says, “but I think it’s equally important to realise [what we don’t know] … so much could be happening that we’re just not aware of.”

COVID-19 means there will be a gap in the data. Towner, who works for Dyer Island Conservation Trust in Gansbaai and alongside a local cage-diving operator, says the blue NGOs engaged in white shark research in South Africa are “heavily reliant” on international tourism, partly for the funding, but also with the cage-diving boats affording continuous monitoring of the sharks. Towner says the emergence of bronze whaler sharks in Gansbaai saved the industry when the white sharks dropped off in 2017.

“We’ve got the largest database,” Towner says. “It’s been 15 years and still going, with no seasonal interruptions in the data. So, we notice if something’s wrong very quickly.”

But with South Africa on a strict lockdown, tourism — even domestic — has ground to a standstill and, at the time of writing, researchers aren’t allowed out to sea.

Perhaps what has captivated people so much about the white shark population in South Africa is all these unknowns and how an array of possible factors — the orcas, a decline of prey species, climate change, culling — may be impacting these elusive apex predators. What is clear is that without data, we cannot draw any firm conclusions.

Kock laughs when asked about the expected publication date of the paper on the orca impacts she’s been working on with Towner, which is in the process of being submitted, after which it will undergo peer review.

“The slowness of science is frustrating for everyone — but it is slow for a reason,” she says. “It has to be verified.”

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Last Updated on Sunday, 14 June 2020 14:15