Abstract
Many large coastal sharks are vulnerable to population declines, however, conflict with human activities often results in unselective culls. Successfully and non-destructively, addressing human-wildlife conflicts requires understanding of animal behaviour. However, knowledge about white shark (Carcharodon carcharias) behaviour near surf zones, where shark bites usually occur, is still limited. We used drones to obtain high-resolution tracks of 108 white sharks directly off coastal beaches on the east coast of Australia. White sharks ranged from 1.9 to 4.0 m (total length) and typically swam parallel to the beach line at an average speed of 0.82 m s-1 (~ 3.0 km h-1), with behaviour being characteristic of energy conserving motion and foraging. Notably the presence of schools of fish increased mean swim speeds of sharks by 0.33 m s-1 and caused tracks to be more convoluted. White sharks were also observed to swim straighter and faster with time either side of midday, increasing predicted mean swim speeds by 0.11 m s-1 and net travel velocities by 0.25 m s-1. White sharks also displayed inquisitive behaviour towards various potential food and non-food items. We demonstrate that white sharks display largely predictable track trajectories and slow movement speeds along coastal beaches, which has utility in further developing non-destructive shark mitigation strategies. Whilst some of the behaviour observed might support the exploratory bite hypothesis, there is likely an increased risk of a shark bite to bathers during situations where there are large shark-attracting food sources present.
Highlights
The importance of large sharks for exerting predation influence across marine ecosystems is increasingly recognized (Ferretti et al, 2010; Hussey et al, 2014)
We demonstrate for the first time the localized movement behavior of white sharks along coastal beaches using drones
From the white sharks sampled, which were not influenced by the presence of whale carcasses or seal colonies, movements observed were typically behind the surf break, relatively parallel to the shoreline at around 0.61 m s−1 (∼2.2 km h−1) for potentially long stretches of beach
Summary
The importance of large sharks for exerting predation influence across marine ecosystems is increasingly recognized (Ferretti et al, 2010; Hussey et al, 2014). Many are undergoing severe population declines from direct and indirect human exploitation (Dulvy et al, 2014; Roff et al, 2018). Amongst the most vulnerable are large coastal sharks, with many being protected or assigned a conservation status with the International Union for the Conservation of Nature (IUCN; Dulvy et al, 2014; Davidson et al, 2016). White Shark Behavior Along Beaches potential for unprovoked shark bites, or “shark attacks,” presents a human-wildlife conflict dilemma that often jeopardizes conservation efforts (Reid et al, 2011; Roff et al, 2018). Common forms of cull-based mitigation can often cause negative consequences for other threatened marine wildlife caught as bycatch (Sumpton et al, 2011)
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