Whether people are seeking the adreneline, or looking to experience being so close to such enormous sharks in their natural environment, cage-diving with great white sharks is certainly an unforgettable experience! Yet, whilst the cage-diving has become increasingly popular over recent decades, the activity still remains extremely controversial. Some argue that cage diving exploits sharks and they should be left alone. Others are concerned that cage diving may affect the behaviour of great white sharks (Carcharodon carcharias), and lead to an increase in the number of shark attacks. But does cage diving teach sharks to associate humans with food? Is this likely that cage diving increases the risk of shark attacks? In short... Is cage diving bad?
Where to Go Cage Diving with Great White Sharks
There are five regions around the world where it is possible to cage-dive with great white sharks (Carcharodon carcharias): Australia, Mexico, New Zealand, South Africa and the USA (specifically off the California coast). Each place has different rules and regulations about how cage-diving mud be conducted. As an example, we will look at South Africa...
In South Africa the cage-diving industry expanded significantly since 1991, when legislation was enforced to protect the dwindling great white population from overfishing. Cage diving operators attract sharks to their vessel for easier viewing by 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; Kock et al, 2012).
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 (Johnson & Kock, 2006; Kock et al, 2012).
Do Sharks Learn to Associate Cage-Diving with Food?
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. 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 (Johnson & Kock, 2006; Kock et al, 2012).
In order for sharks to be a heightened threat in other contexts, the association between humans and the reward must continue even if baiting and chumming attractants are not being used. Also, to be a threat to people in the water, great white sharks must associate human beings (rather than the boat and cage) with these food rewards (Johnson & Kock, 2006; Kock et al, 2012).
So is there any evidence that sharks might become conditioned to cage diving?
Cage Diving Does NOT Cause Positive Conditioning in South Africa
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" 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 and become conditioned...
To determine whether this is something to be concerned about, scientists assessed the threat white sharks may pose by assessing the response of the sharks around various human activities. They considered kayaking, board riding, swimming, scuba diving, spear fishing, recreational non-fishing vessels, and commercial and recreational fishing vessels (Johnson & Kock, 2006).
The scientists found that situations which were more visually similar to cage diving vessels were more likely to elicit a conditioned response - white sharks might mistake a commercial or recreational fishing vessel for a cage diving vessel, but it is 'highly improbable' that sharks will associate swimmers, surfers, kayakers, divers or spear fishermen with food rewards in South Africa because they are so dissimilar to a cage diving vessel. For example, they predicted that a scuba diver would only be 8% similar to the cage-diving vessel that the white shark is conditioned to associate with a food reward (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
Whatsmore, there is actually evidence that white sharks learn to ignore cage-diving boats! If sharks were being conditioned to associate cage diving with food, we would expect the 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 (Johnson & Kock, 2006).
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 tagging, so that the tag can be detected by an array of acoustic receivers throughout the study site - when a shark swims past a particular receiver it 'pings' at that location and its movements can be tracked continuously (Johnson & Kock, 2006).
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 (Johnson & Kock, 2006).
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 the cage diving attractants. These scientists 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 & Kok, 2006
Cage Diving Does NOT Cause Shark Attacks
Scientists who have been commissioned by the South African government to assess whether cage diving tourism poses a risk to human beings have concluded that shark attacks are not increasing as a result of cage diving activities in South Africa (Kock et al, 2012).
Instead, scientists believe that rising incidents of unprovoked shark attacks are caused by increasing human populations in coastal areas and rising recreational ocean use. with more people in the water, the number of incidents with sharks naturally rises. This does not mean that cage diving is causing this increase (Kock et al, 2012).
Sharks are commonly sighted in waters around surfers and swimmers in South Africa, with no negative interactions. In fact, sharks are sighted so commonly 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. Very often the sharks just peacfully pass by, completely ignoring the people in the water (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 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 endangered white sharks far outweighs the risks.
If you would like to learn more about how cage diving affects the behaviour of great white sharks, you can check out: Rattling the Cage.
References
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. Access online.
By Sophie A. Maycock for SharkSpeak
