Abstract
A better understanding of the characteristics and motivation of shark bites on humans should lead to improved anticipation and management of this threat. Anti-predatory motivation (APM), first described in the 1960s-70s, refers to a defensive response in which sharks bite when they perceive humans as potential threats. In such situations, sharks typically display agonistic warning behaviour prior to biting. Among modern human practices at sea, high-speed pursuit of sharks using jet skis can satisfy the behavioural triggers associated with APM. Greater awareness and/or adapted legal regulation of this risk are needed to reduce harassment-induced shark bites and improve the public image of sharks, potentially facilitating their conservation.
Introduction
Worldwide, there are around a hundred shark bites on humans every year, with an annual average of less than ten fatalities in recent decades (GSAF, 2025). By comparison, dog bites affect around 4.5 million humans every year, with over 30,000 deaths (WHO, 2025). Nevertheless, many people continue to view themselves as potential prey for sharks, or assume that sharks may mistake them for natural prey, a belief commonly referred to as the “mistaken identity” hypothesis (Clua and Meyer, 2023). Indeed, as early as the late 60s, Baldridge and Williams (1969) in their paper entitled “Shark Attack; Feeding or Fighting?” presented a case for multiple attacks on humans motivated by factors other than the desire to feeding (p.76). As stated by Johnson and Nelson (1973), this work represented one of the first serious challenges to the assumption that most shark attacks were predatory, pointing instead to social or defensive motivations in certain cases.
While predation remains a possible motivation for shark bites on humans, these cases - often the most lethal - remain very rare (Clua and Linnell, 2019) compared with other motivations such as competition, reflex, territoriality, self-defense and exploration (see Klimley et al., 2023 for a review). A further category that deserves consideration is the “anti-predatory” motivation (hereafter ‘APM’) described in early observational studies of shark behaviour (see p. 72 in Klimley et al., 2023). Fellows and Murchison (1967) initially characterized this behaviour as a defensive response provoked when a shark is pursued in a confined area. In such situations, the shark perceives the human as a potential threat, and the distance between the shark and the human becomes a critical factor determining whether a bite occurs - particularly if the human approaches rapidly or restricts the shark’s escape route (Johnson and Nelson, 1973).
To investigate these interactions, early researchers relied primarily on scuba diving to approach sharks and, in some cases, on small submersibles (Nelson, 1977; Nelson et al., 1986). At the time, such technologies were relatively sophisticated and largely inaccessible to the general public. Since then, underwater scooter technology has become much more widely available, with hundreds of thousands of users worldwide. Similarly, the production and recreational use of surface scooters (jet skis), devices that did not exist in the 1970s, has expanded rapidly. The global market for ‘aqua scooters’ (surface and underwater devices combined) approached USD 2 billion in 2025 and is projected to exceed USD 3 billion by 2030 (CMR, 2025). Their increasing use may alter the frequency and nature of human-shark interactions, making it timely to reassess APM in sharks within this modern context.
Here we do not describe a new shark behaviour. Rather, we revisit the characterization of APM in the context of contemporary human–shark interactions, particularly those involving motorized pursuit of sharks by ocean users. Our objective is to evaluate whether recent documented cases meet the established behavioural criteria for APM and to clarify how this motivation can be distinguished from other proposed causes of shark bites. In doing so, we also highlight recent examples involving large shark species capable of causing severe trauma to humans. A better understanding of these behavioural mechanisms may help inform public awareness and improve shark-risk management strategies as well as shark conservation.
Methods
Our study combined a bibliographical approach with an analysis of videos publicly available online depicting human–shark interactions in marine environments (including underwater, surface and shallow coastal waters). We proceeded in three stages: First, we synthesized scientific knowledge on shark bites attributed to APM in order to identify the behavioural criteria commonly associated with this type of interaction. For this step, our approach followed the standards of the 2020 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards (Page et al., 2021). Relevant publications were identified in the shark behaviour literature using the scientific search engine Google scholar based on targeted keyword searches combining the words “shark+attack+bite” with “anti-predatory”, “anti-predation”, and “agonistic display”. This step provided a framework through (n=21) studies (Figure ESM1) for identifying modern cases consistent with APM.
We also compiled shark species for which APM or agonistic threat displays have been described in the literature. With regard to identifying the species involved in APM type interactions, we limited ourselves to a more qualitative than quantitative approach by selecting only a single study (the first of its kind) that clearly identified a specific species.
Second, we searched for recent video footage depicting potential APM interactions, particularly those involving technologies or practices that were uncommon or unavailable during the 1960s–1970s. The search was not intended to be exhaustive but aimed to identify representative examples consistent with the behavioural criteria established in the first stage and to potentially identify additional shark species that could be involved in such agonistic interactions. For this purpose, key-word combinations such as “shark+attack+scooter+jetski” were used. Videos were retained when the behavioural sequence (human pursuit followed by shark defensive response) could be clearly interpreted.
Third, we compared these modern observations with descriptions of APM in the literature in order to refine the behavioural characterization of this motivation in sharks. This comparison allowed us to assess how contemporary human practices may trigger APM behaviours, and to clarify how APM may be distinguished from other possible motivations for shark bites, particularly ‘self-defence/retaliatory’ responses and ‘territoriality/dominance’ behaviours (see Klimley et al., 2023). Based on these comparisons, we propose a simple behavioural framework that considers both human actions and shark responses to help discriminate among these motivations.
Results
Features of an APM
One of the earliest descriptions of APM motivation was reported in a diving incident described by Church (1961), in which“a shark passed from a confined location against a reef between the two divers toward open water. The divers made moves toward the shark as it passed, apparently initiating the display quoted above. Immediately upon termination of the display the shark rapidly dashed at one of the divers, Jim Stewart, who received two severe bites just above the elbow”.
This observation was later analysed by Johnson and Nelson (1973), who described the agonistic display of the grey reef shark Carcharhinus menisorrah (now C. amblyrhynchos). The display includes two locomotor components: [1] laterally exaggerated swimming and [2] rolling and/or spiral looping, and four postural components: [1] lifting of the snout, [2] lowering of the pectoral fins, [3] arching of the back, and [4] lateral bending of the body. These authors concluded that this display occurs under approach-withdrawal conflict situations, and that rapid approach by a diver may act as a releasing stimulus.
Similar behaviour was later described as a “hunching posture” by Myrberg and Gruber (1974) in the Bonnethead shark Sphyrna tiburo. Johnson and Nelson (1973) further proposed that agonistic displays are triggered by two primary factors: (1) decreasing distance between the shark and a potential aggressor, and (2) restriction of the shark’s escape route depending on the angle of approach (Figures 1A, B). Nelson et al. (1986) also describe a form of collective defensive behaviour termed “mobbing”, in which sharks attempt to drive away a potential predator. Although not necessarily leading to a bite, this behaviour reinforces the concept that sharks may respond defensively to perceived threats.
Figure 1
“a threat or as competition in the form of an unfamiliar presence,… to which the shark responds with a preemptive strike”.
Based on this literature review, we compiled a list of shark species for which APM behavior has been specifically documented (Table 1). These include seven species from two families. Among the Carcharhinids, five are small to medium-sized reef sharks (average total length < 3.5m) and one is a pelagic species of similar size. The sphyrnid species is the bonnethead shark Sphyrna tiburo (average total length < 1.5.m). Notably, none of the three large shark species most commonly associated with severe or fatal human injuries, namely the white shark Carcharodon carcharias, the tiger shark Galeocerdo cuvier, and the bull shark Carcharhinus leucas, are included in this list.
Table 1
| Shark Species | Reference (documenting threat display) |
|---|---|
| Grey Reef Shark (Carcharhinus amblyrhynchos) | Fellows and Murchison (1967) and Johnson and Nelson (1973). Agonistic display in the grey reef shark. Pectoral fins down; back arched; erratic swimming. Also mentioned in Klimley et al. (2023). |
| Galapagos Shark (Carcharhinus galapagensis) and Silvertip Shark (Carcharhinus albimarginatus) | Martin (2007). Agonistic behaviours elicited in these species (including Silvertip shark) through sustained, oriented pursuit using a diver propulsion vehicle (DPV). |
| Blacktip Reef Shark (Carcharhinus melanopterus) | Klimley et al. (2023). Context-dependent agonistic displays. Lateral swings; rapid speed/direction change. |
| Oceanic Whitetip Shark (Carcharhinus longimanus) | Bass et al. (1973). Sharks of the east coast of southern Africa. Pacing behavior; circling with rigid posture. |
| Lemon Shark (Negaprion brevirostris) | Nelson (1983). Agonistic behavior of the lemon shark. Head tilts; rapid turns. |
| Bonnethead hammerhead shark (Sphyrna tiburo) | Myrberg and Gruber (1974). Early account of a “defensive behaviour” (hunched posture). Also mentioned in Klimley et al. (2023) |
| Sandtiger Shark (Carcharias taurus) | Martin (2007). Agonistic displays were elicited in sandtiger sharks by oriented diver pursuit at the wrecks of the Aeolis and Carib Sea, off Moorehead City, North Carolina. |
Compilation of shark species for which the anti-predatory display has been specifically documented in scientific literature.
Case studies: harassments with jet skis
Key-word searches identified several videos depicting humans with surface scooters harassing sharks. Three cases were selected as particular illustrative. These included incidents involving bull sharks recorded in Florida in 2024 (CS1/ESM1) and Australia in 2021 (CS2/ESM2), as well as an interaction involving a white shark recorded in Australia in 2016 (CS3/ESM3). The 2024 Florida case study is particularly informative because it includes both aerial and underwater footage (ESM1). The video shows a surface scooter repeatedly pursuing a bull shark estimated to exceed 2 m in length at depths of approximately 3 m. The shark initially flees but subsequently turns towards the scooter several times, attempting to bite it. A short underwater sequence shows a clear “finnage” display, defined as the lowering of both pectoral fins (sensuJohnson and Nelson, 1973), corresponding to the agonistic component described above. This behaviour signals an escalating defensive response by the shark toward the scooter and rider (sensu Martin, 2007). Shortly thereafter, the shark breaches between the two scooters in an apparent biting attempt, although no human injury occurred.
The two additional cases similarly show surface scooters approaching sharks until a pre-emptive bite attempt is triggered. Underwater footage is not available for these events, preventing direct confirmation of pectoral-fin posture. However, both sharks exhibited rapid directional changes and sudden acceleration immediately prior to the bite attempt, behaviours consistent with agonistic responses described previously.
In addition to these cases, a video attached to the definition of APM in the Chondrichthyan Ethogram (Klimley et al., 2023; video #15), provides a fourth case study (CS4). In this sequence, a grey reef shark displays the complete agonistic posture described above before biting a scuba diver who was pursuing the shark using an underwater scooter (ESM4). Across all four case studies, the human does not necessarily restrict the shark’s escape route (as described in Figure 1). However, the rapid approach speed combined with decreasing distance between human and shark appears sufficient to trigger agonistic defensive behaviour, consistent with the framework proposed by Gruber (1988).
Characterization of shark bites induced by human-space triggers
All four case studies met the criteria for APM. In each case, a motorized human repeatedly approached a shark at high speed and close range prior to the onset of a bite attempt directed at the scooter or associated equipment. In all cases (CS1 to CS4), sharks exhibited partial or complete agonistic displays, suggesting a warning signal prior to the bite. Such warning behavior has been previously described in both territorial/dominance interactions (Clua et al., 2024) and APM contexts, but appears largely absent during self-defence or retaliatory bites (Clua et al., 2025). In territorial/dominance situations, the mere presence of a human within the shark’s idiosphere (sensuMartin, 2007 - a three-dimensional space defined primarily by distance from the animal) may be sufficient to trigger a bite without explicit aggression from the human. Conversely, self-defence bites are typically triggered by direct human aggression that instantly triggers the bite, such as physical contact or injury inflicted on the shark (e.g., spearing). In such cases, the bite occurs immediately and without prior agonistic display. These observations suggest the existence of a behavioural continuum linking three distinct motivations: territoriality/dominance, anti-predation, self-defense (Figure 2). Along this continuum, both the degree of human aggression and the presence of shark warning behaviour vary.
Figure 2
Within this framework, the presence of an agonistic display may serve as a useful diagnostic indicator. Such displays are typically present during territoriality/dominance interactions (Clua et al., 2024) and APM bites (this study), but are absent in self-defence bites (Clua et al., 2025) (Table 2).
Table 2
| Factors/motivations | Territoriality/dominance | APM | Defence/retaliatory |
|---|---|---|---|
| No human threat nor aggression | + | 0 | 0 |
| Perceived human threat | 0 | + | 0 |
| Materialized human aggression | 0 | 0 | + |
| Agonistic behavior display (before bite) | + | + | 0 |
Discriminating factors between ‘territoriality/dominance’, APM and ‘self-defence/retaliatory’ motivations in the context of a shark bite to a human.
The information provided in this table is gathered from descriptions of shark behaviours in Martin (2007); Klimley et al. (2023) and Clua et al., (2024, Clua et al., 2025). (+) means a positive match whereas (0) means no match.
Discussion
A review of studies carried out in the 1960s and 1980s on agonistic behavior in sharks towards humans enabled us to synthesize the behavioural characteristics of APM, which were originally described from interactions involving scuba diving, and in some cases, human-operated submersibles. At the time, these technologies were relatively specialized and accessible only to a small number of researchers and experienced divers. Thanks to several videos available online, we identified recent cases that meet the behavioural criteria associated with APM, mostly involving the harassment of sharks by jet skis, i.e. devices that were largely absent from earlier observations of human–shark interactions but have since become widely used in recreational marine activities. In these interactions, sharks typically responded to persistent pursuit by displaying agonistic warning signals including the characteristic “hunching” posture or abrupt changes in trajectory and swimming speed. Such manoeuvres may also reflect an acoustic startle response, as sharks are known to react strongly to high-amplitude sounds generated by motorized devices (Myrberg et al., 1978; Klimley and Myrberg, 1979). Whatever the trigger, when these signals were ignored by the approaching human, the shark sometimes responded with a preemptive defensive bite directed toward the source of disturbance. The presence of such warning behavior leads to two important considerations.
First, it highlights the importance of informing the public about the behavioural signals displayed by sharks prior to defensive interactions. Recognition of these signals could allow ocean users to interpret escalating risk and withdraw from the interaction before a bite occurs.
Second, the presence of agonistic behaviour provides a potentially useful criterion for distinguishing anti-predatory responses from other bite motivations, particularly self-defense/retaliatory bites. In the latter case, the bite is triggered not by the perception of a threat but by direct human aggression toward the shark, and therefore typically occurs without prior warning behaviour (Clua et al., 2025). The absence of agonistic display in self-defence interactions can be explained in two non-exclusive ways. First, the shark may already be under acute stress, for example when captured on a fishing line or stranded on a beach, leaving little opportunity to perform warning displays. Second, the aggression may occur too suddenly, such as when a shark is struck or speared at close range preventing the shark from displaying threat signals prior to biting (see the case studies described in Clua et al., 2025). Although a shark might occasionally display agonistic behaviour before being attacked and then respond with a retaliatory bite, such situations are likely to be very rare. Conversely, when no human aggression is directed towards the shark, the most plausible explanation for a bite is territoriality/dominance (Klimley et al., 2023; Clua et al., 2024).
According to the International Shark Attack File classification system (ISAF, 2025), APM falls within the category of “Provoked bites” defined as incidents in which humans initiate interaction with a shark. These include cases where divers attempt to touch or harass sharks. Our observations indicate that modern ocean users riding jet skis may also provoke APM-type bites. The ISAF classification also includes bites involving spearfishing, shark feeding, or attempts to remove sharks from fishing gear. Among these categories, bites occurring while removing sharks from fishing gear correspond most closely to self-defence or retaliatory motivation (Clua et al., 2025).
Bites involving spearfishers often arise from competition for a food resource (Nelson et al., 1986; Klimley et al., 2023), whereas bites occurring during shark feeding interactions may reflect clumsy or exploratory responses toward a perceived food stimulus (see Clua and Torrente, 2015, Clua, 2018; Klimley et al., 2023). However, territorial or dominance-motivated bites (Clua et al., 2024) are not explicitly recognized in the current ISAF classification, suggesting that this framework may not fully encompass the diversity of behavioural motivations underlying shark bites.
Johnson and Nelson (1973) noted that because agonistic displays had been documented in multiple shark species, agonistic motivation could represent a widespread cause of shark attacks on humans. Our study was not designed to quantify the global prevalence of APM-related shark bites. However, our present observations suggest that two large shark species capable of causing severe trauma, the white shark and the bull shark, may also exhibit defensive responses consistent with APM. The potential involvement of these species broadens the range of sharks capable of displaying such behaviour and reinforces the need for caution during close encounters. Approaches toward sharks, whether intentional or accidental, may be perceived as threatening and can trigger defensive responses. Consequently, interactions involving pursuit or harassment of sharks, particularly using motorized devices, may increase the likelihood of defensive bites.
Recognizing and respecting the behavioural warning signals displayed by sharks may therefore represent an important component of shark-risk mitigation strategies. By the meanwhile and anticipating users who may be reluctant to acknowledge that their behaviour is inappropriate, the authorities should probably consider introducing legislation tailored to the challenges of curbing this type of behaviour in relation to the use of jet skis.
Statements
Author contributions
EC: Writing – original draft, Writing – review & editing. CM: Writing – review & editing.
Funding
The author(s) declared that financial support was not received for this work and/or its publication.
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Supplementary material
The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fcosc.2026.1861931/full#supplementary-material
Supplementary Figure 1Preferred reporting items for systematic reviews and meta-analysis (PRISMA) flow diagram, detailing the process of record collection and study for this mini-review.
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Summary
Keywords
dangerous marine predator, human-wildlife conflicts, jet ski, provoked bite, risk management, shark conservation
Citation
Clua EEG and Meyer CG (2026) Harassment has a cost: anti-predatory behaviour as a motivation for sharks to bite humans. Front. Conserv. Sci. 7:1861931. doi: 10.3389/fcosc.2026.1861931
Received
21 April 2026
Revised
18 June 2026
Accepted
18 June 2026
Published
22 September 2026
Volume
7 - 2026
Edited by
Christian Kiffner, Leibniz Center for Agricultural Landscape Research (ZALF), Germany
Reviewed by
Jacopo Gobbato, University of Milano-Bicocca, Italy
Updates
Copyright
© 2026 Clua and Meyer.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Eric E. G. Clua, eric.clua@univ-perp.fr
†ORCID: Eric E. G. Clua, orcid.org/0000-0001-7629-2685; Carl G. Meyer, orcid.org/0000-0002-0350-3784
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.