South Africa has long been a Mecca for shark scientists, SCUBA divers, adrenaline junkies and shark lovers alike. For decades the area has been a hotspot of white shark (Carcharodon carcharias) activity; with a permanent population of sharks being boosted by seasonal migrants during the winter. There was a time when you could see dozens of sharks from your boat every day. However, in recent years, there has been a marked decline in the number of great whites in the area. Whatsmore, sometimes the sharks are entirely absent from the area for extended periods of time. So why is this!? Have their numbers seriously declined? Or have the sharks left? And if so, where have they gone?
White Out
South Africa is famous for its great white sharks (Carcharodon carcharias). In the past, there were certain locations where you could see these magnificent animals year-round. It is thought that great whites are born somewhere in the east, near Algoa Bay, and they move along the coastline as they increase in size and are able to target larger, more challenging prey. In the east at ZwaZulu-Natal, juvenile sharks (between from 1.5 to 2.5 metres in total length (aka TL)) feast on the abundant fish, crustaceans, dolphins and other, smaller shark species which are common in the area. In the Western Cape larger sharks (above 3 metres TL) target cape fur seals which live on island colonies along the coast (Hussey et al, 2012).
Great white sharks have been considered threatened with extinction for several decades and they are currently listed as Vulnerable by the IUCN. In response to these global declines, South Africa became the first country in the world to implement legislation to preserve great whites in 1991. Henceforth, it became illegal to purposefully fish white sharks in South African waters and sales of their body parts have been strictly controlled, both within the country and across international borders (Fisher, 2021; Bowlby et al, 2023).
Going Down
However, local researchers began to notice their white shark populations were seriously dwindling since the beginning of the new millennium. For example, in False Bay, in the Western Cape, scientists recorded a steady, long-term decline from 2007 onwards. In the neighbouring town of Gansbaai, the number of sharks sighted from research and tourism vessels has dropped significantly since 2011 (Fisher, 2021; Bowlby et al, 2023).
When I first visited the white sharks in Gansbaai in 2008, it was not uncommon for us to see 5 to 10 different sharks in one trip, but this has dropped to an average of only 0.81 sharks per trip in 2018. That is a seriously alarming fall (Hewitt et al, 2018; Fisher, 2021).
What is also of concern is that scientists have also noticed startling absences of white sharks at their usual hotspots, with zero sightings for days, or even weeks at a time (Engelbrecht et al, 2009). This was unheard of before a few years ago. So, where are all the white sharks going?
Global Declines
The most obvious concern is that white shark disappearances in South Africa are representative of their general declines around the world. Whilst great whites are protected in South Africa (and several other countries), their global population has been markedly reduced from its natural level and is still decreasing (Fisher, 2021; Bowlby et al, 2023).
"White sharks continue to be killed at unsustainable levels in the sharks board lethal control program and as bycatch in longline fisheries [in South Africa]"
Dr Neil Hammerschlag, personal communication
Scientists have also wondered if the declines were caused by local mortalities. White sharks are killed by humans every year in South Africa, both legally and illegally! For example, it is perfectly legal for sharks to be killed when they are caught in nets which are implemented to protect ocean users at bather beaches. The KwaZula-Natal Sharks Board, reports that an average of 16.8 white sharks are killed every year in their beach nets. Great whites also commonly wander into South African fishing grounds and are caught as bycatch. Whilst the law states that these sharks must be safely released if possible, there are also a small number of incidental mortalities (Fisher, 2021).
On the Move
There is a possibility that great white sharks populations in South Africa are actually not declining, but the sharks may have redistributed themselves to different locations. For example, one study indicated that where there have been localised shark declines in Gansbaai and False Bay in recent years, there have been corresponding increases in white shark numbers in neighbouring Algoa Bay and Mossel Bay (Bowlby et al, 2023).
However, other experts doubt the reliability of this study and question the validity of the findings. They continue to express concern that there is still uncertainty about the stability of great white shark populations in South Africa and they may even still be declining in the region (Gennari et al, 2024).
Some scientists wonder if reduced prey availability might be driving declines or localised shifts in white shark distributions. In South Africa, other species of shark (such as the dusky shark (Carcharhinus obscurus), smoothhound (Mustelus mustelus) and tope (Galeorhinus galeus) are critical prey items for great whites. As extensive fisheries have driven many of these sharks to decline significantly in the region in recent years, it may be possible that the great white sharks have gone elsewhere in order to find food (Fisher, 2021; Bowlby et al, 2023).
Or is it possible that the great whites themselves are becoming the meal!? Two orca - called Port and Starboard - have been implicated in the deaths of several large sharks in South Africa in recent years. One of the pair was even recorded assaulting a juvenile white shark in 2024; remarkably removing it's nutritious liver in just two minutes. Scientists suspect that, as these orca are now such a threat to the white sharks, they may have run away from their old stomping grounds in Gansbaai and Mossel Bay to avoid them (Engelbrecht et al 2009; Fisher, 2021; Bowlby et al, 2023), but as the orca arrived after white sharks had already started disappearing, this cannot be the only factor (Gennari et al, 2024). To learn more, check out Clash of the Marine Titans.
White Knights
Whether white shark populations are genuinely declining or they have shifted their habitats, it is still alarming that their populations have not even started recovering since they were protected back in 1991 (Fisher, 2021; Bowlby et al, 2023). We would have hoped to have noted some signs of improvement by now. Therefore, it is very important that we take a cautious approach and continue to protect white sharks in South Africa (and everywhere else in the world!), to ensure that their populations don't decline any further.
References
Bowlby HD, Dicken ML, Towner AV, Waries S, Rogers T & Kock A (2023). Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa. Ecological Indicators, 154, 110720. Access online.
Engelbrecht TM, Kock AA, O’Riain MJ (2009). Running scared: When predators become prey. Ecosphere, 10:1, e02531. Access online.
Fisher R (2021). Possible causes of a substantial decline in sightings in South Africa of an ecologically important apex predator, the white shark. South African Journal of Science, 117:8101. Access online.
Gennari E, Hammerschlag N, Andreotti S, Fallows C, Fallows M & Braccini M (2024). Uncertainty remains for white sharks in South Africa, as population stability and redistribution cannot be concluded by Bowlby et al.(2023):“Decline or shifting distribution? a first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa. Ecological Indicators, 160:111810. Access online.
Hewitt AM, Kock AA, Booth AJ & Griffiths CL (2018). Trends in sightings and population structure of white sharks, Carcharodon carcharias, at Seal Island, South Africa, and the emigration of subadult female sharks approaching maturity. Environmental Biology of Fishes, 1:101, 39-54.
Hussey NE, McCann HM, Cliff G, Dudley SFJ, Wintner SP & Fisk AT (2012). Size-based analysis of diet and trophic position of the white shark, Carcharodon carcharias, in South African waters. In : Domeier, M. (Ed.). Global Perspectives on the Biology and Life History of the Great White Shark, Taylor & Francis, New York, p. 27-49.
By Sophie A. Maycock for SharkSpeak
