Where Have All the White Sharks Gone!?
Updated: Apr 14, 2022
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!? Where are the sharks going? And does it warn us that something is seriously amiss with the ecosystem in South Africa?
South Africa enjoys a resident population of white sharks, which can been seen 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 in length) also 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).
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.
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?
The answer is... we just don't know. Their numbers certainly seem lower in general and it seems the the sharks might have changed their residency patterns in the area; moving away from their usual home ranges for a period of time and then returning. Exactly where they go or why, we are not sure. Many scientists have worked tirelessly and speculated endlessly to find an answer. There are currently several hypothesises:
White sharks are declining globally
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. As these sharks have a global distribution and are capable of transoceanic migrations, it is possible that declines elsewhere in the world have reduced the numbers of sharks in South Africa. As of it is thought that the current population of white sharks numbers around (Fisher, 2021).
South African white sharks are still being fished
It also possible that these sharks die within South African waters. Despite being protected, white sharks are killed 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. That is 85 sharks over the last 5 years! 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).
Overfishing has depleted the white sharks' prey in South Africa
It is also very possible that South African fisheries have depleted prey species to such a degree hat the area if no longer favourable to white sharks. 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. There are extensive fisheries targeting these sharks in South Africa and subsequently there have been significant declines in both the tope and smoothhound. If there is not enough prey for the white sharks, it is likely they would look elsewhere to find food (Fisher, 2021).
White sharks have been usurped by orca
Or is it possible that the great whites themselves are being the meal!?
Shark fisheries have also been responsible for seriously depleting the numbers of shortfin makos (Isurus oxyrinchus) and blue sharks (Prionace glauca) throughout several of our worlds oceans. These sharks are common prey items for the magnificent orca (Orcinus orca) and concurrently, the declines have forced orca to look further afield for their food. It has been suggested that this may be why orca began attacking and eating great whites in South Africa in recent years. Two orca especially, which have been called Port and Starboard, have been implicated in the deaths of several large sharks in South Africa recently. If orca are now targeting white sharks for food, this would contribute to their decline would explain their extended absences; as the white sharks vacate the area to avoid predation (Fisher, 2021). (To learn more, check out Clash of the Marine Titans).
We do not yet know for certain why white sharks are dwindling in South Africa, but it is, in fact, quite likely that the declines are actually caused by a combination of all these factors to some degree. What we do know is that these declines are serious and unsustainable. If we do not take action to save white sharks it is very possible that they could be "extirpated" in South Africa. This means they become locally extinct and no longer live in the region at all. As South African waters have been a critical feeding habitat for white sharks and are also a potential breeding area, if great whites discontinue their use of the area it would have serious implications for their conservation.
As if that wasn't be enough, the decline in white sharks also points towards a serious imbalance in the South African marine ecosystem, driven largely by human activity. We are not living in harmony with our natural world and our activities have serious, international consequences, not just for great whites, but type of animal alive. if we want to keep our white sharks flourishing, very serious action has to be taken right now to improve their conservation, not only in South Arica, but throughout every country in the world that they call home.
"[There has been] a potentially serious decline to the South African white shark population, characterised by a substantial decline in white shark sightings. This decline correlates with the overfishing of prey species, bycatch, the use of lethal gill nets and ecological changes such as the novel presence of orca. Better marine management is required if South Africa wishes to keep a healthy white shark population".
- Dr R. Fisher, 2021
If you would like to become involved in great white shark conservation in South Africa, you can support the Shark Life and the White Shark Trust charities, and follow the White Shark Conservancy. There are also many opportunities to volunteer in scientific research and conservation initiatives in South Africa, such as with Marine Dynamics or White Shark Projects. To contribute to global white shark conservation, you can support the Shark Angels and Shark Trust.
References
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.
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.