Response of white sharks exposed to newly developed personal shark deterrentsUpdated 6 months ago
- In Australia, the number of shark-human interactions and shark bites per capita has increased, leading to a rise in shark-bite mitigation measures being developed. Yet, many of the products commercially available have not been scientifically tested, potentially providing an exaggerated sense of security to members of the public using them.
- We tested five shark deterrents developed for surfers (Shark Shield Pty Ltd [Ocean Guardian] Freedom+ Surf, Rpela, SharkBanz bracelet, SharkBanz surf leash [Modom], and Chillax Wax) by comparing the percentage of baits taken, time to take the bait, number of passes, distance to the bait, and whether a shark reaction could be observed.
- A total of 297 successful trials were done at the Neptune Islands Group Marine Park. During these trials, 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 (increased number of reactions) and reducing the percentage of bait taken from 96% (relative to the control board) to 40%. This led to an increase in the number of passes because exposed sharks continued to attempt taking the bait. Shark's mean distance to the board increased from 1.6 ± 0.1 m (control board) to 2.6 ± 0.1 m when the Freedom Surf+ was active, but the time it took to interact with the bait remained indistinguishable. The other deterrents had limited or no measureable effect on white sharks.
- Based on our power analyses, the smallest effect size that could be reliably detected was ~ 15%. Although we did not find evidence that the magnet band and leash, Chillax Wax, and Rpela affected White sharks during the trials, it is possible that these deterrents have small effects that could not be detected by the 50 trials per deterrent we imposed. This does not infer that additional trials would have necessarily resulted in our models detecting an effects from these deterrents; rather it means that more than 50 trials would be required to detect changes of a magnitude < 15% greater than we observed if there were any effects.
- Manufacturers should consider these findings to assess the suitability of their product and gauge whether changes are required to ensure that their product performs as intended. Our results will allow private and government agencies to make informed decisions about the use of these devices for occupational activities and enable the public to make appropriate decisions about the use and suitability of these five products.
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