Effectiveness of five personal shark-bite deterrents for surfers


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.Wetested 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�0.1m(control board) to 2.6�0.1mwhen 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.