A Gilded Cage?
Updated: Aug 18
The cage-diving industry, whilst becoming increasingly popular over recent decades, still remains controversial. People are often concerned that cage diving activities may affect the behaviour of great white sharks (Carcharodon carcharias), which may lead to an increase in the number of shark attacks amongst other ocean users. But does cage diving teach sharks to associate humans with food and is this likely to cause a rise in shark attacks?
It is possible to cage dive with white sharks at several locations along the South African coastline and the industry has expanded significantly since 1991, when legislation was enforced to protect the dwindling great white population from fishing. Cage diving operators attract sharks to their vessel for easier viewing presenting bait at the end of a bait line (as a short-range visual attractant) and by dispersing liquidated fish tissues and oils into the water (creating a long-range olfactory attractant). It is illegal to feed great white sharks in South Africa (Johnson & Kock, 2006).
As there are many neighbouring areas along the coastline which are used by other ocean users, such as swimmers, surfers, kayakers, recreational fishers etc., there is concern that sharks will learn to associate humans with food, which could cause a rise in unprovoked shark attacks in other contexts.
To assess whether this is true, we need some basic knowledge about how sharks learn. In order to learn to associate humans or boats with food, sharks must be "conditioned". This means that they encounter cage diving activities repeatedly and receive "positive reinforcement" (being fed) that encourages them to continue to approach these vessels on subsequent occasions. In order for sharks to be a heightened threat in other contexts, the association between humans and reward must continue even if baiting and chumming attractants are not being used. So is there any evidence that sharks might become conditioned to cage diving?
Positive Conditioning Does Not Occur
Long-term exposure to stimulus and reward is required for sharks to become conditioned; they must learn to associate humans with food rewards through repeated experiences with the boats. Great white sharks move westwards along the South African coastline as they grow towards maturity, at which point they migrate seasonally over long-distances. Migrations are interspersed with periods of "residency" (sharks stay in one particular area) at particular locations. In South Africa's cage diving locations, white shark residency periods range between 4 - 30 days before an individual shark moves on. Therefore, sharks with longer residency periods could potentially experience cage diving activities repeatedly...
In order for a shark to be a heightened threat to ocean users in other contexts outside of the cage diving locations, great white sharks must be able to associate all human beings in the water with food rewards. Scientists assessed the threat white sharks may pose to ocean users by comparing what response occurred around various human activities (including kayaking, board riding, swimming, scuba diving, spear fishing, recreational non fishing vessels, and commercial and recreational fishing vessels) after exposure to cage diving. They found that situations which were more visually similar to cage diving vessels were more likely to elicit a conditioned response. Therefore, they concluded that white sharks might mistake a commercial or recreational fishing vessel for a cage diving vessel, but that it is 'highly improbable' that sharks will associate swimmers, surfers, kayakers, scuba divers or spear fishermen to food rewards in South Africa because they are so dissimilar to a cage diving vessel (Johnson & Kock, 2006).
"[The] assumption that 'cage diving' is causing an increase in attacks due to conditioning is an unfounded claim"
- Johnson & Kock, 2006
White sharks ignore chumming and baiting
If sharks were being conditioned to associate cage diving with food, we would expect sharks to stay around boats for longer periods over time. However, the opposite pattern is true. Sharks which are identified and known to operators, spend progressively less time around a boat with increasing experience. This actually provides evidence that sharks are being "negatively conditioned" to cage diving in South Africa; they learn they are not rewarded by responding to chumming and baiting and so do not approach boats at all.
In order to asses whether white sharks were being conditioned by cage diving, scientists tagged sharks to use "acoustic telemetry" to track their movements around cage diving vessels during tours. This method involves the tag on a shark can be detected by an array of acoustic receivers in the study site, so when a shark swims past a particular receiver it 'pings' at that location and its movements can be tracked continuously. Researchers found that very often, white sharks did not respond to chumming attractants at all; ignoring the cage diving activities completely and going on with their usual activities.
Another study analysed how many sharks were sighted from cage diving boats, compared to how many were actually patrolling the area, to assess whether all sharks respond to cage diving attractants. They found that less than 30% of sharks came close enough to be sighted from the boat. This provides us with further evidence that cage diving activities cause 'negative' conditioning"; sharks learn that they are not rewarded with food at the cage diving boats, so their energy is better spent elsewhere (Johnson & Kock, 2006).
"It is highly unlikely that cage diving is related to attacks on humans."
- Johnson & Kock, 2006
Cage Diving Does Not Increase Shark Attacks
Scientists who have been commissioned by the South African government to assess whether cage diving tourism poses a risk have concluded that shark attacks are not increasing as a result of cage diving activities.
Instead, scientists believe that rising incidents of unprovoked shark attacks are caused by increasing human populations in coastal areas and rising recreational ocean use. Sharks are commonly sighted in waters around surfers and swimmers in South Africa and have no negative interactions with people sharing the water. In fact, sharks are sighted so commonly behaving peacefully that South Africa's 'Shark Spotters' do not necessarily clear the water when the observe a white shark near a beach. Rather, they assess how much of a risk the shark might pose and only alert ocean users when it approaches too close (Kock et al, 2012).
It is still incredibly rare for a human being to be attacked by a white shark... you are statistically more likely to be killed by a coconut or a lightening strike than by a shark. Therefore, in my opinion, the threat posed by cage diving is minimal, and the educational and conservation benefits it provides for white sharks far outweigh the risks.
If you would like to learn more about how cage diving affects the behaviour of great white sharks, you can check out: How Does Cage Diving Affect Great Whites?
Johnson R & Kock A (2006). South Africa’s white shark cage-diving industry- is there cause for concern? In: Nel DC & Paschal TP (Eds.). Finding a Balance: White Shark Conservation and Recreational Safety in the Inshore Waters of Cape Town, South Africa; Proceedings of a Specialist Workshop. WWF South Africa Report Series- 2006/Marine001. Access online.
Kock A, Titley S, Petersen W, Sirweyiya M, Tsotsobe S, Colenbrander D, Gold H & Oelofse G (2012). Shark spotters: A pioneering shark safety program in Cape Town, South Africa. (Ed.). Global Perspectives on the Biology and Life History of the Great White Shark, Taylor & Francis, New York, p. 447-465.