Not all electric shark deterrents are made equal: Effects of a commercial electric anklet deterrent on white shark behaviour

PLoS One. 2019 Mar 11;14(3):e0212851. doi: 10.1371/journal.pone.0212851. eCollection 2019.

Abstract

Personal shark deterrents offer the potential of a non-lethal solution to protect individuals from negative interactions with sharks, but the claims of effectiveness of most deterrents are based on theory rather than robust testing of the devices themselves. Therefore, there is a clear need for thorough testing of commercially available shark deterrents to provide the public with information on their effectiveness. Using a modified stereo-camera system, we quantified behavioural interactions between Carcharodon carcharias (white sharks) and a baited target in the presence of a commercially available electric anklet shark deterrent, the Electronic Shark Defense System (ESDS). The stereo-camera system enabled accurate assessment of the behavioural responses of C. carcharias when approaching an ESDS. We found that the ESDS had limited meaningful effect on the behaviour of C. carcharias, with no significant reduction in the proportion of sharks interacting with the bait in the presence of the active device. At close proximity (< 15.5 cm), the active ESDS did show a significant reduction in the number of sharks biting the bait, but this was countered by an increase in other, less aggressive, interactions. The ESDS discharged at a frequency of 7.8 Hz every 5.1 s for 2.5 s, followed by an inactive interval of 2.6 s. As a result, many sharks may have encountered the device in its inactive state, resulting in a reduced behavioural response. Consequently, decreasing the inactive interval between pulses may improve the overall effectiveness of the device, but this would not improve the effective deterrent range of the device, which is primarily a factor of the voltage gradient rather than the stimulus frequency. In conclusion, given the very short effective range of the ESDS and its unreliable deterrent effect, combined with the fact that shark-bite incidents are very rare, it is unlikely that the current device would significantly reduce the risk of a negative interaction with C. carcharias.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Behavior Observation Techniques / methods
  • Bites and Stings / prevention & control*
  • Female
  • Humans
  • Indian Ocean
  • Motor Activity / physiology
  • Predatory Behavior*
  • Remote Sensing Technology / methods
  • Sharks / physiology*
  • South Africa
  • Video Recording / methods
  • Wearable Electronic Devices*

Grants and funding

This study was funded by The University of Western Australia, the West Australian State Government Shark Hazard Mitigation Applied Research Program, and through the very generous support of Mr Craig Burton and Mrs Katrina Burton. The funders listed above provided support in the form of research costs and salaries for the following authors: RMK, SPC, and NSH. Author EG is the director of Oceans Research. Oceans Research provided support in the form of salary for author EG, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this author is articulated in the ‘author contributions’ section.