Effects of an electric field on white sharks: in situ testing of an electric deterrent

PLoS One. 2013 May 2;8(5):e62730. doi: 10.1371/journal.pone.0062730. Print 2013.

Abstract

Elasmobranchs can detect minute electromagnetic fields, <1 nV cm(-1), using their ampullae of Lorenzini. Behavioural responses to electric fields have been investigated in various species, sometimes with the aim to develop shark deterrents to improve human safety. The present study tested the effects of the Shark Shield Freedom7™ electric deterrent on (1) the behaviour of 18 white sharks (Carcharodon carcharias) near a static bait, and (2) the rates of attacks on a towed seal decoy. In the first experiment, 116 trials using a static bait were performed at the Neptune Islands, South Australia. The proportion of baits taken during static bait trials was not affected by the electric field. The electric field, however, increased the time it took them to consume the bait, the number of interactions per approach, and decreased the proportion of interactions within two metres of the field source. The effect of the electric field was not uniform across all sharks. In the second experiment, 189 tows using a seal decoy were conducted near Seal Island, South Africa. No breaches and only two surface interactions were observed during the tows when the electric field was activated, compared with 16 breaches and 27 surface interactions without the electric field. The present study suggests that the behavioural response of white sharks and the level of risk reduction resulting from the electric field is contextually specific, and depends on the motivational state of sharks.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Electricity*
  • Islands
  • Predatory Behavior*
  • Safety
  • Sharks*
  • Time Factors

Grants and funding

This project was funded by SafeWork SA, Winifred Violet Scott Charitable Trust, Neiser Foundation, University of Adelaide, Flinders University, Wildlife Conservation Fund, Nature Foundation of South Australia, and Solar Online. This research was also partly supported under Australian Research Council’s Discovery Projects funding scheme (project number DP0988554; www.arc.gov.au). Fieldwork in South Africa was funded under the umbrella of a Save Our Seas Foundation grant provided to AAK as part of a white shark monitoring project. The authors thank Andrew Fox, Jennifer Taylor, and Rachel Robbins from the Rodney Fox Shark Expeditions for the logistic support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.