Long-range electric deterrents not as effective as personal deterrents for reducing risk of shark bite

Abstract

While personal electric deterrents can reduce the risk of shark bites, evidence for the efficacy of other products is limited. We assessed two versions of a novel electric deterrent - 80 and 150 volts (V) - designed to protect a large area (8 m deep × 6 m wide) or to be linked together for greater spatial coverage. We did 116 experimental trials on 43 white sharks (Carcharodon carcharias) to assess: (a) percentage of baits taken; (b) distance between bait and shark; (c) number of passes; and (d) whether sharks reacted to the deterrent. The proportion of baits taken was reduced by 24% (80 V) and 48% (150 V), although the high variance of the effect coefficient precluded statistical differentiation. Only the 150-V deterrent increased the distance between bait and shark (control: 1.59 ± 0.28 m versus active deterrent: 3.33 ± 0.33 m), but both versions increased the likelihood of a reaction (average reaction distance: 1.88 ± 0.14 m). Results were similar whether we measured distances using stereo-cameras or estimated them in situ, suggesting that stereo-cameras might not be necessary to quantify distances between sharks and baits. Our findings provide more evidence that electric deterrents can reduce the risk of shark bite, but the restricted efficacy limits the suitability of this device.