The ‘Mistaken Identity Hypothesis’ for shark bites on humans is an anthropomorphic fallacy

The Mistaken Identity Hypothesis (MIH) interprets shark bites on surfers, swimmers and snorkel-ers as ‘mistakes’ stemming primarily from similarities in the visual appearance of ocean users and the sharks typical prey. MIH is now widely accepted as fact by the general public and some sections of the scientiﬁc community despite remaining unproven. This hypothesis assumes that ‘mistaken’ shark bites on humans result primarily from confusing visual cues and ignores the important role of other senses (e


Introduction
The Mistaken Identity Hypothesis (MIH) interprets shark bites on surfers, swimmers and snorkelers as 'mistakes' stemming primarily from similarities in appearance of ocean users and the sharks typical prey. For example, Tricas & McCosker (1984) noted that "The shark attacks the surfer because it mistakes his silhouette for that of a seal". The MIH is appealing because: (i) it is simple to understand and therefore intellectually satisfying, especially for the general public, and (ii) it exonerates the shark from intentional responsibility for shark bites on humans by characterizing such bites as tragic 'accidents'. However, despite being widely accepted, the MIH remains at best an unproven hypothesis. Here we trace the origins of the MIH, critically evaluate the arguments for and against this hypothesis, and propose more plausible alternative natural explanations for shark bites on humans.

Origins and characteristics of the Mistaken Identity Hypothesis
The 'mistaken identity' concept was first mentioned by Baldridge (1974) who noted ". . . some shark attacks (may have) resulted from mistaken identity (black suited diver possibly appearing as a seal, etc.)" and "(it). . . is certainly not beyond reason that a person so clad might appear to a shark to resemble a seal or other marine animals upon which the shark might be feeding in a particular area, especially if the water were murky and the range of vision limited.". However, the term received relatively little attention (44 citations -source: google scholar) until it was again invoked by Tricas & McCosker (1984) (317 citations, source: Google Scholar) and began to enter the mainstream. The specific characterization of the mistaken identity concept as a hypothesis occurred relatively recently, appearing in two theses (Quester, 2013;Chapuis, 2017) and two recent peer-reviewed publications (Clua & Linnell, 2019b;Ryan et al., 2021). NB: Ritter & Quester (2016) mention the mistaken identity 'theory' as a synonym for 'hypothesis'. The MIH is now widely accepted by both the general public and many scientists as is demonstrated by the high percentage (30%) of articles mentioning the MIH as a given fact without providing any further description or proof of the hypothesis (see item 2 in Table 1). In a recent search we found the 'mistaken identity' concept mentioned in 50 scientific publications, including 46 peer-reviewed articles or book chapters and four popular articles (see Tables 1 and 2). Many scientific publications dealing with attacks on humans do not mention the MIH or propose alternative hypotheses. However, the grey scientific literature -including many popular books on sharks -and mass media articles are replete with mentions of the MIH. In this analysis we have voluntarily confined ourselves to publications that can be considered 'scientific' and that specifically mention the term 'mistaken identity'). Among these 50 publications, 72% (N = 36) accept the MIH (Table 1) while 38% (N = 14) are critical of it (Table 2). We have divided these publications into four categories which respectively mention: i) the hypothesis itself or an alternative hypothesis, ii) factors facilitating the probability or improbability of the hypothesis, iii) indirect evidence (for or against MIH) or iv) a factual demonstration (for or against MIH). Among publications in favour of MIH, approximatively 50% mention and describe the hypothesis (see Table 1). Proponents of MIH suggest 'mistaken identity' bites are attributable to combinations of four main factors including environmental conditions (such as turbidity or agitation in the water) (see item 3 in Table 1), the wearing of clothing reminiscent of shark prey (see item 4 in Table 1), a "state of petulance" in the sharks that would facilitate the strike (see item 5 in Table 1) and finally the proximity of the victims to an area inhabited by natural prey (see item 6 in Table 1). However, closer scrutiny suggests that these alleged causal factors may in fact be largely coincidental. For example, although turbid water is routinely invoked as a cause of mistaken identity bites and some shark bites do indeed occur in turbid waters, the majority of shark bites occur in clear water (see Collier, 1964;Baldridge, 1974;Taglioni at al., 2019). Until recently most neoprene wetsuits were black hence it has not been possible to compare shark bite frequency among subgroups of ocean users wearing wetsuits of different colours to demonstrate any statistically significant higher probability of being bitten by a shark while wearing a black wetsuit (item 4). The 'state of petulance' (item 5) results from a confluence of instinct, personality traits (such as boldness and risk taking) and hunger that increases the probability of shark bites but does not prove the validity of the MIH. For example, grey reef sharks (Carcharhinus amblyrhynchos) sometimes bite ocean users despite being predators of reef fishes that in no way resemble humans. The density of sharks may simply be higher in areas where their natural prey occur (item #6), hence the probability of a shark bite in such areas might be higher simply because there is a higher probability of encountering a shark in these areas.
The 'bite-spit-and wait' behaviour observed in white sharks (Tricas & McCosker, 1984) has been suggested by proponents of MIH as evidence of sharks first mistaking and then abandoning the 'mistaken' prey due to an unexpected or inappropriate taste (see item 7 in Table 1). However, this ignores the plausible alternative explanations that such bites may actually be intentional 'taste tests' to evaluate the palatability of potential prey (Curtiss et al., 2012, see some atypical events diagrammed in Fig. 10 in Klimley et al., 1996).

Virtual tests of the Mistaken Identity Hypothesis (Ryan et al., 2021)
In a recent study, Ryan et al. (2021) used computer simulations to demonstrate that the visual acuity of young white sharks is so low that they may mistake a surfer's silhouette for that of a pinniped, thus validating the MIH promoted by Tricas & McCosker (1984). However impeccable it may be from a technical point of view, this study is a simplified computer simulation of predator behaviour and does not capture the complex reality of this process in the natural environment. As the authors themselves admit in the discussion, their hypothesis, which is based entirely on low visual resolution, completely ignores the other six senses that a top marine predator -which has evolved for more than 5 million years in this environment -can use to apprehend its prey. For example, sound likely plays an important role in shark predation (Gardiner et al., 2014) and a recent study showed that pinnipeds porpoising strokes are spectrally and temporally different from the sounds made by paddling surfers (Chapuis, 2017). Therefore, given the array of sensory cues that sharks simultaneously process (Gardiner et al., 2014) it is hard to understand and accept how sharks would mistake a human for a prey such as a pinniped (Chapuis, 2017). Thus, although vision plays an essential role in the surface predation process as demonstrated in some studies Strong et al., 1996), there is no reason to seriously hypothesize, as Ryan et al. (2021) do, that the shark's other senses will be unable to compensate for a potential impairment of sight.
In addition to basing their simulation on vision as the essential sense in the pinniped predation process, Ryan et al. (2021) use the fact that the attack rate of surfers is inversely correlated with the age of white sharks to reinforce their hypothesis. Ryan et al. (2021) postulate without reason or evidence that young sharks have less effective vision than adults and are hence more likely to mistakenly bite surfers. However, they ignore the plausible alternative link between behaviour and ontogenetic development. At around 3 m total length young sharks undergo a dietary shift toward larger prey (Estrada et al., 2006;Hussey et al., 2012) that may make them more likely to explore potential large prey in their environment. Such exploratory/learning behaviour could lead young white sharks to target surfers more often than larger individuals without "making a mistake".

Further criticisms of the MIH
We found 16 publications containing criticisms of the MIH (Table 2). In the earliest example Compagno (1993) notes that "Attacks on surfers are attributed to mistaken identity, because the boards and riders look like seals to us. However, little is known of the white shark's discriminatory powers, and arbitrarily assuming that such attacks are triggered by resemblance to a seal may be misinterpreting the white shark's senses.". Subsequent authors also criticize the MIH with half of them postulating alternative explanations (Collier at al., 1996;Clua & Séret, 2010;Clua & Reid, 2013;Tinker et al., 2015;Ritter & Amin, 2017;Roy et al., 2018;Clua & Linnell, 2019b) (see item 1 in Table 2). A recurrent (see Anderson et al., 1996;Strong et al., 1996; Downloaded from Brill.com06/29/2023 12:28:59PM via communal account Ritter & Levine, 2004) counter-argument to the MIH is that shark vision is not as bad as advocates of the MIH suggest and this fact is supported by several studies of shark visual systems (Lisney et al., 2007;Collin, 2018). Several authors cite circumstantial evidence that directly contradicts the MIH, such as the fact that; (i) pinnipeds are not yet prey for the sub-adult white sharks that bite surfers (Clua & Séret, 2010;Curtis et al., 2012;Clua & Reid, 2013;Ritter & Quester, 2016) (see item 3 in Table 2), (ii) if a white shark attacked a pinniped with the same low intensity as it bites a surfer or a board, the prey would be barely stunned and definitely not incapacitated, hence would likely get away (Quester, 2013), (iii) if white sharks were mistaking surfers for seals, we would likely see energetically expensive breaching behaviour associated with these interactions (Martin et al., 2005;Semmens et al., 2019) whereas the 'low-energy' interactions with surfers are more consistent with energy-saving hunting strategies than typical seal predation behaviour , (iv) white sharks in South Africa frequently bite but rarely consume penguins (Randall et al., 1988;Hammerschlag et al., 2012) despite millions of years of co-evolution of these species suggesting that these interactions are not simply mistakes, (v) other species of sharks that bite surfers do not consume pinnipeds (Ritter & Amin, 2018;Clua & Haguenauer, 2018) (see item 6 in Table 2), vi) shark bites often happen in clear water (Clua & Haguenauer, 2018) (see item 7 in Table 2), (vii) sharks use other senses than vision to identify and locate prey during the predation process reducing their probability of making 'mistakes' (Compagno, 1993;Gardiner et al., 2014;Chapuis, 2017) (see item 5 in Table 2), and (viii) sharks also bite inanimate objects of various shapes, colours and sizes with no similarities to pinnipeds (Compagno, 1993;Collier et al., 1996;Hammerschlag et al., 2012) (see item 4 in Table 2). Collectively, these arguments make a compelling logical case against the veracity of the MIH without directly disproving it. However, there is a simple alternative hypothesis that not only explains the shark bites attributed to MIH but also those that cannot be reasonably explained by this hypothesis.

Natural investigative/exploratory behaviour is a simple, logical explanation for many shark bites
Sharks are opportunistic predators whose survival and lifetime fitness depends on their ability to optimize their environment and available resources.
Sharks have personalities (Jacoby et al., 2014) with traits such as Shyness/ Boldness or Taking/Avoidance of risk that influence their behaviour (Careau et al., 2008) and all share a propensity to explore their environment. This exploratory behaviour is particularly crucial for sharks which lack parental care and thus any vertical transmission of knowledge about prey or hunting -individual sharks must use innate senses and exploration to learn predatory skills by themselves. Despite this natural reliance on exploration and investigation, sharks have a limited capacity to touch and examine objects and thus have little choice but to bite these unfamiliar substrates/objects in order to determine whether they are viable prey.
Although exploration/investigation is clearly crucial behaviour for sharks, most individuals will remain naturally cautious in novel situations with only a few bolder risk-taking individuals likely to bite novel prey (Clua & Linnell, 2019a). This would explain why despite a growing population of surfers and despite drones revealing frequent interactions between sharks and surfers (Butcher et al., 2021), shark bites remain rare events (Ferretti et al., 2015). If sharks were simply mistaking surfers for seals because of turbid water, then attacks on surfers should be far more common than they actually are. The prey exploration hypothesis neatly explains superficial shark bites on humans regardless of the turbidity of the water, the proximity to natural prey colonies or the colour of the victim's attire. The fact that sharks often abandon human victims with superficial wounds after an initial bite suggests is better explained by sharks rejecting novel prey because of low palatability rather than by sharks mistaking humans for another more typical prey (Klimley, 1994;. Thus, in our opinion, sharks are very well adapted to exploring an environment where they sometimes encounter, and depending on the animal's personality and hunger levels, investigate novel objects such as humans by biting them. External environmental factors (such as water turbidity) or internal factors (other than satiety, such as 'petulance') can certainly have an influence, but only to a limited and marginal extent. Sharks don't make 'mistakes' but instead explore novel objects as potential prey, which may be either abandoned or consumed.