How close is too close? The effect of a non-lethal electric shark deterrent on white shark behaviour
Ryan Kempster, Jessica Meeuwig | Jul 01, 2016
Scientists use sea kayaks to track the movements of great white sharks in South Africa and better understand the drivers of their presence inshore during the summer months.
Photo: Thomas Paschal
Kempster R, Hart N, Chapuis L, Ryan L, Kerr C, Huveneers C, Yopak K, Meeuwig J, Collin S. How close is too close? The effect of a non-lethal electric shark deterrent on white shark behaviour. PloS ONE, 11(7): e0157717.
Sharks play a vital role in the health of marine ecosystems, but the potential threat that sharks pose to humans is a reminder of our vulnerability when entering the ocean. Personal shark deterrents are being marketed as the solution to mitigate the threat that sharks pose. However, the effectiveness claims of many personal deterrents are based on our knowledge of shark sensory biology rather than robust testing of the devices themselves, as most have not been subjected to independent scientific studies. Therefore, there is a clear need for thorough testing of commercially available shark deterrents to provide the public with recommendations of their effectiveness. Using a modified stereo-camera system, we quantified behavioural interactions between white sharks (Carcharodon carcharias) and a baited target in the presence of a commercially available, personal electric shark deterrent (Shark Shield Freedom7™).The stereo-camera system enabled an accurate assessment of the behavioural responses of C. carcharias when encountering a non-lethal electric field many times stronger than what they would naturally experience. Upon their first observed encounter, all C. carchariaswere repelled at a mean (± std. error) proximity of 131 (± 10.3) cm, which corresponded to a mean voltage gradient of 9.7 (± 0.9) V/m. With each subsequent encounter, their proximity decreased by an average of 11.6 cm, which corresponded to an increase in tolerance to the electric field by an average of 2.6 (± 0.5) V/m per encounter. Despite the increase in tolerance, sharks continued to be deterred from interacting for the duration of each trial when in the presence of an active Shark Shield™. Furthermore, the findings provide no support to the theory that electric deterrents attract sharks. The results of this study provide quantitative evidence of the effectiveness of a non-lethal electric shark deterrent, its influence on the behaviour of C. carcharias, and an accurate method for testing other shark deterrent technologies.
FUNDING & ACKNOWLEDGEMENTS
This study was funded by The University of Western Australia and the West Australian State Government Shark Hazard Mitigation Applied Research Program. The UWA Neuroecology Group would also like to express sincere gratitude and appreciation for the continued support and generous financial assistance provided by Craig and Katrina Burton. Without which, completion of this research would not have been possible. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors wish to thank the South African Department of Environmental Affairs: Biodiversity and Coastal Research, Oceans and Coasts Branch for their support and help in conducting this research. The authors also wish to thank all of the interns at the Oceans Research campus in Mossel Bay for all of their help and hard work during this investigation. Finally, the authors would like to thank the anonymous reviewers for their thorough and critical feedback of this research, which ultimately resulted in a much improved final manuscript.
Diagram of a Remote Monitoring Research Apparatus (ReMoRA). (A) Shows the ReMoRA in its deployed configuration with downward facing cameras. (B) Shows the measurements recorded to calculate proximity of C. carcharias to the visible Shark Shield™ electrode. Figure: Yates et al. 2016.
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