Effectiveness of five personal shark-bite deterrents for surfers

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.

Response of blacktip reef sharks Carcharhinus melanopterus to shark bite mitigation products

“…Instead, we recorded the maximum number of sharks during each trial within 30 m of the Scuba7. We used the following terminology to describe shark behaviour and code the videos, modified from previous studies 12,15 :…”

“…We investigated the effect of the Scuba7 on the following response variables: whether the bait was taken, time taken to take the bait, distance to electrode, number of approaches, and whether a reaction was observed. Following the method in Huveneers et al 15 , we minimised potential temporal correlation by testing the effects of the Scuba7 on all response variables using a generalised linear mixed-effects model (GLMM) with Day coded as a random effect, the natural logarithm of the maximum number of sharks as offset, and the status of the Scuba7 (on or off) and the approach direction as fixed effects. Current direction was initially included as a fixed factor but was later removed from the model due to strong correlation with approach direction.…”

“…The increasing demand for personal shark deterrents has led to the development of several new products, but few have been scientifically tested. Out of those tested, fewer have shown to significantly affect shark behaviour and reduce probability of shark bites (but see 12,15,16 ). Most studies have also focused on white sharks, Carcharodon carcharias, because it is the species responsible for the most fatal shark bites 5 .…”

“…The Scuba7 differs from other products in the size and configuration of electrodes which are placed on the ankle and tank of the diver (vs the Freedom7 where one of the electrode streams ~1.5 m behind the diver or snorkeler). Previous studies assessing the ability of electric deterrents to reduce the probability of shark bites have focused on white sharks, with testing predominantly occurring when the number of sharks present was relatively small, e.g., 1-4 12,15,16 . The response to an electric deterrent can, however, vary between species.…”

Future Research Directions on the “Elusive” White Shark

“…The quick succession of shark bites occurring in multiple locations has led to the development and use of various shark bite mitigation measures (e.g., personal deterrents; surveillance/realtime monitoring), many of which still need to be assessed. Although a few devices have recently been tested (e.g., Huveneers et al, 2013bHuveneers et al, , 2018bKempster et al, 2016;O'Connell et al, 2018), there is a need for transparency and standardization of protocols and variables used to test the effectiveness of personal and arearelated deterrents. Ensuring such consistency will enable direct comparisons of products and mitigation measures.…”