RPELA v2 Scientific Report
Globally, the occurrence of unprovoked shark bite has been increasing due to various natural and anthropogenic factors and many of the bites, including some that were fatal, have been to surfers. White sharks (Carcharodon carcharias), tiger sharks (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas) have accounted for most of the bites.
Various personal shark deterrents are commercially available to surfers. The Rpela is a battery-powered, water-activated electric personal deterrent fitted to a surfboard that produces an electric field around the surfer. It is designed specifically to deter sharks from approaching or biting surfers by disrupting a sharks’ sensitive electro-reception organs. It has been recently reconfigured from previous models to increase the strength of its electric field with a view to increasing its effectiveness.
The reconfigured Rpela (version 2) was tested on white sharks at Salisbury Island, Western Australia, in March and April 2018 using a custom-built floating board with fish bait attached (to tempt a bite). Testing involved attracting white sharks to the stern of an anchored vessel by hanging bait (tuna) in the water and tapping the hull of the vessel with a metal pole then removing and replacing it with the test board mounted with the Rpela v2. The test board also had fish bait hanging 45 cm below it in a canister. In total, 46 trials were done with the Rpela v2 either active or inactive (a control) to determine the device’s effect on (1) the probability of a shark biting or touching (interacting) with the bait, (2) the number of passes a shark took prior to biting or interacting with the bait and when it did not, (3) the mean distance between a shark and the bait. The presence of any habituation in shark behaviour was also explored by examining the number of passes and mean distance for sharks through time. Each trial was recorded by independent scientific observers and statistical analyses were done to determine the significance of differences in shark response when Rpela v2 was active and inactive.
Key findings include the following:
· When active, Rpela v2 significantly reduced the probability of a bite and interaction (i.e. bite or touch) occurring compared with when it was inactive. The probability of a bite reduced from 0.75 to 0.25 (a 66% reduction) and an interaction from 0.80 down to 0.50 (a 38% reduction);
· The number of passes taken by a shark regardless of whether a bite or interaction took place and when a bite or an interaction did take place also reduced when Rpela v2 was active; and
· The mean distance between the shark and the bait increased when Repla v2 was active.
When active, Rpela v2 did not completely remove the risk of shark bite, but there was strong evidence that it did deter sharks from doing so. The magnitude of the reduction in risk is of a level that consumers are likely to consider meaningful. It is noted that the nature of the trials, using fish bait to attract sharks, does not make it directly comparable with the type of encounter for which the device is designed (i.e. whilst surfing). However, it is reasonable to assume that if the device is effective at deterring sharks from biting fish baited surfboards, it would also be so during chance encounters with surfers where fish bait was absent.
Based on these results, it could be expected Rpela v2 would benefit surfers by significantly reducing the risk of shark bite and providing more time to leave the water (i.e. as inferred from the number of passes) when a potentially dangerous shark is present. It is noted that the small sample size (seven sharks), limited size range of sharks in the trials (i.e. 2.4 – 3.6 m) and single location of the study limits generalisations regarding Rpela v2’s effectiveness. These limitations could be overcome with further trialling at other locations, in other seasons at the same locations, with larger sharks and on other potentially dangerous species, particularly bull sharks or tiger sharks. It is also recommended that further studies are done if any further substantial modifications to the Rpela v2 are made that may influence its effectiveness. Finally, although the results of the Salisbury Island trials infer that the configuration of Rpela v2 has improved its effectiveness from a previous version, this can only be proven unequivocally if Rpela v2 is tested against the previous version in a further trial.