Abstract
The number of shark-human interactions and shark bites per capita has been increasing since the 1980s, leading to a rise in measures developed to mitigate the risk of shark bites. Yet many of the products commercially available for personal protection have not been scientifically tested, potentially providing an exaggerated sense of security to the people using them. We tested five personal shark deterrents developed for surfers (Shark Shield Pty Ltd [Ocean Guardian] Freedom+ Surf, Rpela, SharkBanz bracelet, SharkBanz surf leash, and Chillax Wax) by comparing the percentage of baits taken, distance to the bait, number of passes, and whether a shark reaction could be observed. We did a total of 297 successful trials at the Neptune Islands Group Marine Park in South Australia, during which 44 different white sharks (Carcharodon carcharias) interacted with the bait, making a total of 1413 passes. The effectiveness of the deterrents was variable, with the Freedom+ Surf affecting shark behaviour the most and reducing the percentage of bait taken from 96% (relative to the control board) to 40%. The mean distance of sharks to the board increased from 1.6 ± 0.1 m (control board) to 2.6 ± 0.1 m when the Freedom Surf+ was active. The other deterrents had limited or no measureable effect on white shark behavour. Based on our power analyses, the smallest effect size that could be reliably detected was ∼15%, which for the first time provides information about the effect size that a deterrent study like ours can reliably detect. Our study shows that deterrents based on similar principles—overwhelming a shark’s electroreceptors (the ampullae of Lorenzini) with electrical pulses—differ in their efficacy, reinforcing the need to test each product independently. Our results will allow private and government agencies and the public to make informed decisions about the use and suitability of these five products.
Highlights
Shark-human interactions remain rare and unlikely events, their frequency has been increasing globally since the 1980s (Chapman & McPhee, 2016; McPhee, 2014)
We used the following terminology to describe and code shark behaviour following Huveneers et al (2013b): Pass: a directed swim towards the experimental set-up; Shark identity: We identified white sharks based on markings on five areas: caudal fin, pelvic fins, first dorsal fin, gills, and pectoral fins using standard methods (Nasby-Lucas & Domeier, 2012; Nazimi et al, 2018)
We investigated whether the effectiveness of the deterrents changed throughout the study by including ‘trial’ as a fixed integer covariate in the models and by plotting the mean distance between the shark and the board, and the number of passes across trials for sharks that interacted with the board for 15 trials or more
Summary
Shark-human interactions remain rare and unlikely events, their frequency has been increasing globally since the 1980s (Chapman & McPhee, 2016; McPhee, 2014). The frequent negative framing by the media and user-driven content sites (e.g., YouTube) might have contributed to exaggerating public anxiety about the pervasive presence of sharks and risk that they pose to humans (Muter et al, 2013; Sabatier & Huveneers, 2018). Such heightened public concern has pressured managers and governments to develop and implement new measures that reduce the risk of sharks bites, and provide information to the public to make more informed decisions about using specific areas at particular times
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