Personal electric deterrents can reduce shark bites from the three species responsible for the most fatal interactions

Abstract

The frequency of unprovoked shark bites is increasing worldwide, leading to a growing pressure for mitigation measures to reduce shark-bite risk while maintaining conservation objectives. Personal shark deterrents are a promising and non-lethal strategy that can protect ocean users, but few have been independently and scientifically tested. In Australia, bull (Carcharhinus leucas), tiger (Galeocerdo cuvier), and white sharks (Carcharodon carcharias) are responsible for the highest number of bites and fatalities. We tested the effects of two electric deterrents (Ocean Guardian's Freedom+ Surf and Freedom7) on the behaviour of these three species. The surf product reduced the probability of bites by 54% across all three species. The diving product had a similar effect on tiger shark bites (69% reduction) but did not reduce the frequency of bites from white sharks (1% increase), likely because the electrodes were placed further away from the bait. Electric deterrents also increased the time for bites to occur, and frequency of reactions and passes for all species tested. Our findings reveal that both Freedom+ Surf and Freedom7 electric deterrents affect shark behaviour and can reduce shark-bite risk for water users, but neither product eliminated the risk of shark bites entirely. The increasing number of studies showing the ability of personal electric deterrents to reduce shark-bite risk highlights personal protection as an effective and important part of the toolbox of shark-bite mitigation measures.

Figure 1

Sub-surface views taken from 360-degree cameras during tiger shark trials of trial set-ups for a) Freedom+ Surf, and b) Freedom7, and c) location of trials. Map was created in R (version 3.3.0) with RStudio (version 2023.06.2), using the ggplot2 package (version 3.4.3).

Figure 2

Predicted likelihood (marginal means) of a bite from bull (red), tiger (orange), and white sharks (blue), showing effects of (a) Freedom+ Surf deterrent, and interactions between (b) species and trial set during Freedom+ Surf trials, and (c) species and Freedom7 deterrent. Black symbols indicate no difference between species. Circle symbols indicate Freedom+  Surf and triangles are Freedom7 products. Filled symbols represent active trials, empty symbols are control trials. Horizontal dashed lines indicate mean values during control trials.

Figure 3

Predicted time (marginal means) of bite on bait or board during (a–c) Freedom+ Surf and d–e) Freedom 7 trials. Orange symbols represent tiger sharks, blue is white sharks, and red is bull sharks. Black symbols indicate no difference between species. Horizontal dashed lines indicate mean values during control trials.

Figure 4

Predicted number of passes (marginal means) from individuals during (a) Freedom+ Surf and (b) Freedom 7 trials. Orange symbols represent tiger sharks, blue is white sharks, and red is bull sharks. Black symbols indicate no difference between species. Horizontal dashed lines indicate mean values during control trials.

Figure 5

Predicted probability of reactions (marginal means) during passes from tiger (orange), white (blue) and bull sharks during a) Freedom+ Surf, and b) Freedom7 trials. Circles indicate Freedom+ Surf and triangles are Freedom7 products. Filled symbols represent active trials, empty symbols are control trials. Horizontal dashed lines indicate mean values during control trials.

Figure 6

Predicted time (marginal means) that tiger sharks spent across behaviour states during (a) Freedom+ Surf trials and (b) Freedom7 trials for behaviours included in top-ranked models. Control trials are indicated as empty symbols/dashed lines, and active treatments are filled symbols/solid line.