The idea that sharks attack surfers and swimmers because they mistake them for a seal, is so pervasive and commonly parroted that it is routinely taken as fact. But is this accurate? Actually, not only has there been no scientific testing to prove if this theory is right, but there have also been many scientific discoveries that have actually indicated it is probably wrong. So where did The Mistaken Identity Hypothesis come from? How do we know it is inaccurate? And if it is not right, then what is the reason for sharks biting people?
Off the Menu
To get off on the right foot, we first need to start by debunking a different myth - sharks DO NOT eat people. If you want more detail about this, you can check out the full article Myth Busted: Sharks DO NOT See Humans as Prey, but to summarise for you, there is no species of shark that targets humans for food and no sharks regularly incorporate human beings into their diet.
Sharks attacks are incredibly rare (you are more likely to be killed by your dog or injured by an air freshener than by a shark!) and for a victim to actually be consumed by a shark is even rarer still. They simply don't see us as food because we do not have enough fat and protein to be worth their effort.
So if sharks do not want to eat people, why do they occasionally bite?
Who Are You?
One idea that has became very popular is known as The Mistaken Identity Hypothesis. This theory was first described by Baldridge in 1974, who suggested that sharks may attack people, because surfers or swimmers in the water - especially those wearing dark wetsuits - resemble a seal. The idea gained traction as it was mentioned in few scientific papers and in the mainstream media (Tricas & McCosker, 1984).
Bizarrely, the phrase started to be thrown around more regularly and so everyone just took it as gospel (Ryan et al, 2021; Clua & Meyer, 2023).
The good news is that this theory helped to exonerate sharks to some degree - it encouraged the public to consider that sharks were not attacking people maliciously, and helped people to start to see sharks as something other than blood thirsty killing machines. However, the problem is that there was never actually any scientific work conducted to directly test whether The Mistaken Identity Hypothesis was right or not (Clua & Meyer, 2023).
"The theory of mistaken identity, where white sharks erroneously mistake surfers for [seals], does not hold true".
- Ritter & Quester, 2016
On the Wrong Scent
As our knowledge of shark anatomy, cognition and behaviour has advanced, we now actually have a wealth of evidence that indicates that The Mistaken Identity Hypothesis is wrong (Ritter & Quester, 2016; Clua & Meyer, 2023).
It is now clear to us that this idea is actually very anthropocentric. Because we rely so heavily on our vision to navigate our world, we assume all other animals must do too. But that is not the case for sharks (and many other creatures!). It seems very unlikely that sharks would misidentify something based on their vision alone, when they utilise a diverse array of spectacularly well-developed senses - lateral line, smell, hearing, electroreception - to identify and hone in on their prey (Compagno, 1993; Clua & Meyer, 2023).
Going hand in hand with this is the fact that (contrary to popular belief) sharks actually have very good eyesight. So it doesn't seem likely that they would not be able to tell the difference between a human and a seal (Ryan et al, 2021; Clua & Meyer, 2023).
Additionally, if sharks are simply not able to discriminate based on vision, we would expect more attacks to happen in murky waters. However, the majority of incidents actually occur when waters are very clear (despite what you may have heard to the contrary!), when a shark's vision would be at its most reliable. So mistaken identity seems unlikely (Clua & Meyer, 2023).
Bad Behaviour
Scientists have also begun to doubt The Mistaken Identity Hypothesis based on how the sharks are behaving during an attack upon a person. Every species of shark has a specific suite of behaviours that they use when they are hunting, so if you know what to look for, it becomes very clear when a shark is (and is not) in predator mode (Clua & Meyer, 2023).
For example, great white sharks (Carcharodon carcharias) use an ambush hunting strategy during predatory attacks. They surprise their prey sneaking up at depth and then rushing vertically upwards to take them at the surface - disabling their prey in one blow / bite. This often results in a spectacular "breach", where the white shark shoots out of the water (Anderson et al, 1996; Strong, 1996; Martin et al, 2005; Semmens et al, 2019).
However, when we look at incidents involving and humans, we do not see any of these characteristic behaviours we would associate with a white shark that is hunting (Ritter & Quester, 2016; Clua & Meyer, 2023).
Scientists who have assessed great whites attacks on surfers along the Pacific coastline of the USA, have found that - thankfully - in 72% of the incidents assessed, the victim suffered only superficial cuts, small bruises and minimal scratches to their board, where we would expect to see much, much more damage if a shark had struck at full force (Ritter & Quester, 2016; Clua & Meyer, 2023).
Curious as a Catshark
So... why are sharks biting people then? Scientists now think that many shark attacks are actually the result of the shark investigating an unfamiliar object in their environment. It is an inquisitive behaviour, not aggression (Ritter & Quester, 2016; Clua & Meyer, 2023).
When sharks encounter something they don't recognise in the water, they will investigate by "mouthing" it. Loaded with sensory receptors, the mouth and face of a shark is a focal point of sensory information gathering in the absence of hands or a similar appendage. So sharks mouth things to gather information about it (and see if it's something they might like to eat). It's similar to the drive we all have as small children to put things into our mouths. This is why, for the vast majority of incidents, a shark bites a person once, maybe twice, and then discards them and leaves - because they have investigated and decided that we are not palatable (Ritter & Quester, 2016).
"Sharks don’t make ‘mistakes’ but instead continually explore their environments and routinely investigate novel objects as potential prey by biting them."
This makes sense when you consider that sharks have no parental care at all, so they have to learn to hunt and navigate their habitat without learning anything from their parents (Clua & Meyer, 2023).
Supporting this idea is the fact that the majority of white shark bites are perpetuated by young, immature individuals that are still learning how to hunt. They are either unfamiliar with humans - so take a bite to investigate - or they are practicing their hunting skills - so that they will be ready when they start targeting seals for food (Ritter & Quester, 2016).
So all in all, it seems very likely that The Mistaken Identity Hypothesis is likely not correct. BUT this does not mean that sharks seeking revenge or mindlessly eating anything that comes in their way. They are just using the tools they have at hand (or maybe more accurately "at mouth") to assess their environment, in order to survive.
References
Anderson S, Henderson R, Pyle P & Ainley D (1996). White shark reactions to unbaited decoys. In: Klimley AP & Ainley DG (Eds.). Great White Sharks The Biology of Carcharodon carcharias. Academic Press, San Diego, p. 223–228.
Baldridge HD (1974). Shark attack: a program of data reduction and analysis. — Mote Marine Laboratory, Sarasota, FL.
Clua EEG & Meyer CG (2023). The 'Mistaken Identity Hypothesis' for shark bites on humans is an anthropomorphic fallacy. Behaviour, Special Issue on Elasmobranch cognition, 1-13. Access online.
Compagno LJV (1993). Great white shark. Fish Biology. Fish. 3: 188-191
Martin RA, Hammerschlag N, Collier RS & Fallows C (2005). Predatory behaviour of white sharks (Carcharodon carcharias) at Seal Island, South Africa. Journal of the Marine Biological Association UK, 85, 1121-1135. Access online.
Micarelli P, Chieppa F, Pacifico A, Rabboni E & Reinero FR (2021). Passive Prey Discrimination in Surface Predatory Behaviour of Bait-Attracted White Sharks from Gansbaai, South Africa. Animals, 11:9, 2583. Access online.
Ritter E & Quester A (2016). Do white shark bites on surfers reflect their attack strategies on pinnipeds? Journal of Marine Biology, 9539010. Access online.
Ryan LA, Slip DJ, Chapuis L, Collin SP, Gennari E, Hemmi JM, How MJ , Huveneers C, Peddemors VM, Tosetto L & Hart NS (2021). A shark's eye view: testing the ‘mistaken identity theory’behind shark bites on humans. Journal of the Royal Society Interface, 18:183, 20210533. Access online.
Semmens JM, Kock AA, Watanabe YY, Shepard CM, Berkenpas E, Stehfest KM, Barnett A & Payne NL (2019). Preparing to launch: biologging reveals the dynamics of white shark breaching behaviour. Marine Biology, 166:95. Access online.
Strong WR (1996). Shape discrimination and visual predatory tactics in white sharks. In: Klimley AP & Ainley DG (Eds.). Great White Sharks The Biology of Carcharodon carcharias. Academic Press, San Diego, p. 229-240.
Tricas TC & McCosker JE (1984). Predatory behavior of the white shark (Carcharodon carcharias), with notes on its biology. Proceedings of the California Academy of Science, 43:14. Access online.
By Sophie Adele Maycock for SharkSpeak
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