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

Abstract

Globally, the frequency of shark bites is rising, resulting in an increasing demand for shark deterrents and measures to lessen the impact of shark bites on humans. Most existing shark protection measures are designed to reduce the probability of a bite, but fabrics that minimise injuries when a shark bite occurs can also be used as mitigation devices. Here, we assessed the ability of the ocean Guardian Scuba7 and Kevlar material to reduce the likelihood of blacktip reef sharks, Carcharhinus melanopterus, from feeding, and to minimise injuries from shark bites. Sharks were enticed to consume a small piece of local reef fish (bait) placed between the two Scuba7 electrodes with the deterrents randomly being turned on or kept off. In the second experiment, the bait was attached to a small pouch made of either standard neoprene or neoprene with a protective layer of Kevlar around it. The Scuba7 reduced the proportion of baits being taken by 67%, (from 100% during control trials to 33%). Sharks also took more time to take the bait when the device was active (165 ± 20.40 s vs. 38.9 ± 3.35 s), approached at a greater distance (80.98 ± 1.72 cm vs. 38.88 ± 3.20 cm) and made a greater number of approaches per trial (19.38 ± 2.29 vs. 3.62 ± 0.53) than when the Scuba7 was inactive. The sizes of punctures from shark bites were significantly smaller on neoprene with Kevlar compared to standard neoprene (3.64 ± 0.26 mm vs. 5.88 ± 0.29 mm). The number of punctures was also fewer when Kevlar was used (14.92 ± 3.16 vs. 74.1 ± 12.44). Overall, the Ocean Guardian Scuba7 and Kevlar reduced the impact of blacktip reef shark bites. These findings may help consumers make informed decisions when purchasing shark deterring and protective products.

Variable response to electric shark deterrents in bull sharks, Carcharhinus leucas

“…However, the peculiar quasi-hemispherical shapes of each field around the electrodes, for an isosurface of 3 V/m, do not overlap between the electrodes where the bait was, likely contributing to a lower efficacy when compared to the Freedom + Surf. The Rpela v2 has smaller electrodes and fewer discharges per second (14.5 Hz vs. 9.5 Hz) than its predecessor, allowing the deterrent to better recharge between pulses and emit a stronger electric field 14 . The intensity of the electric field 1 m away from the electrode were previously measured as being over 1 V/m 15 , which would be comparable to the Freedom + Surf, but our in situ measurements revealed a lower intensity of 0.38 V/m.…”

“…The Rpela v2 has smaller electrodes and fewer discharges per second (14.5 Hz vs . 9.5 Hz) than its predecessor, allowing the deterrent to better recharge between pulses and emit a stronger electric field 14 . The intensity of the electric field 1 m away from the electrode were previously measured as being over 1 V/m 15 , which would be comparable to the Freedom + Surf, but our in situ measurements revealed a lower intensity of 0.38 V/m.…”

“…All our trials were realised in 18 days, over a 21-day period, and with fewer than 40 individual sharks. Trials in other studies were either done over 18 days spread between five trips over 5 months 12 , or during a short one-week trip on a large number of sharks 14 . During these studies, the same individual sharks were not as frequently exposed to electric fields as our study, reducing the ability to detect habituation or temporal changes in response to electric fields.…”

“…The effect of the water surface on the field was taken into account using the method of image charges 14 . This method states that, for a given distribution of charges, the solution of the Poisson equation is unique.…”

“…The Shark Shield technology that powers Ocean Guardian products has been tested several times, purportedly repelling sharks in 60% 12 and 89% 13 of trials for their Freedom + Surf and Freedom7 products respectively ( https://ocean-guardian.com/ ). A more recent study showed that the Scuba7 reduced the risk of bites from Carcharhinus melanopterus by 67% 14 . The Rpela, an ESD for surfers requiring some experience in shaping boards or using fibreglass, did not reduce the probability of a bait being taken 12 .…”