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How Close is too Close? The Effect of a Non-Lethal Electric Shark Deterrent on White Shark Behaviour.

Kempster RM, Egeberg CA, Hart NS, Ryan L, Chapuis L, Kerr CC, Schmidt C, Huveneers C, Gennari E, Yopak KE, Meeuwig JJ, Collin SP - PLoS ONE (2016)

Bottom Line: Therefore, there is a clear need for thorough testing of commercially available shark deterrents to provide the public with recommendations of their effectiveness.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.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.

View Article: PubMed Central - PubMed

Affiliation: The Oceans Institute and the School of Animal Biology, The University of Western Australia, Crawley, Western Australia, Australia.

ABSTRACT
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. carcharias were 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.

No MeSH data available.


Related in: MedlinePlus

Plot to show the Shark Shield™ voltage gradient decline with increasing distance.The dashed arrows indicate the average proximity/encounter (82 cm) of C. carcharias and the corresponding voltage gradient (15.7 V/m); Red dots depict actual measurements recorded using the voltage gradient probe (see Fig 4). Voltage gradient curve plotted using Harris model: y = 1/(0.0101 + 0.0003x^1.1706).
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pone.0157717.g007: Plot to show the Shark Shield™ voltage gradient decline with increasing distance.The dashed arrows indicate the average proximity/encounter (82 cm) of C. carcharias and the corresponding voltage gradient (15.7 V/m); Red dots depict actual measurements recorded using the voltage gradient probe (see Fig 4). Voltage gradient curve plotted using Harris model: y = 1/(0.0101 + 0.0003x^1.1706).

Mentions: Measurements of the electric field generated by the Shark Shield™ showed that the voltage gradient was greatest in close proximity to the electrodes of the Shark Shield™ and decreased rapidly with distance (Fig 7). The Shark Shield™ measured in this study discharged at a frequency of 1.67 Hz, with a peak voltage gradient of ≥100 V/m within 5 cm of the electrode surface (Fig 7). The gradient of the electric field at equal distances around the Shark Shield™ varied slightly (± 2.7%) depending on the angle of the recording probe relative to the Shark Shield’s electrodes. For consistent measurements, the gradient was plotted along the same axis, parallel to the end of the electrode. Based on the average proximity to an active Shark Shield™, when controlling for the effect of encounter number (82 ± 12 cm; Table 1: #14), the estimated average voltage gradient necessary to elicit a deterrent response equated to approximately 15.7 (± 2.1) V/m (Fig 7). However, as proximity has been shown to decline over subsequent encounters (Table 3: #6 and #7), the estimated voltage gradient to elicit a deterrent response during the first encounter (131 ± 10 cm) is much lower than the average and equates to approximately 9.7 (± 0.9) V/m. Therefore, based on an average decrease in proximity by 11.6 cm per encounter, the voltage tolerance of individual sharks would be expected to increase by approximately 2.6 (± 0.5) V/m per encounter.


How Close is too Close? The Effect of a Non-Lethal Electric Shark Deterrent on White Shark Behaviour.

Kempster RM, Egeberg CA, Hart NS, Ryan L, Chapuis L, Kerr CC, Schmidt C, Huveneers C, Gennari E, Yopak KE, Meeuwig JJ, Collin SP - PLoS ONE (2016)

Plot to show the Shark Shield™ voltage gradient decline with increasing distance.The dashed arrows indicate the average proximity/encounter (82 cm) of C. carcharias and the corresponding voltage gradient (15.7 V/m); Red dots depict actual measurements recorded using the voltage gradient probe (see Fig 4). Voltage gradient curve plotted using Harris model: y = 1/(0.0101 + 0.0003x^1.1706).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4930202&req=5

pone.0157717.g007: Plot to show the Shark Shield™ voltage gradient decline with increasing distance.The dashed arrows indicate the average proximity/encounter (82 cm) of C. carcharias and the corresponding voltage gradient (15.7 V/m); Red dots depict actual measurements recorded using the voltage gradient probe (see Fig 4). Voltage gradient curve plotted using Harris model: y = 1/(0.0101 + 0.0003x^1.1706).
Mentions: Measurements of the electric field generated by the Shark Shield™ showed that the voltage gradient was greatest in close proximity to the electrodes of the Shark Shield™ and decreased rapidly with distance (Fig 7). The Shark Shield™ measured in this study discharged at a frequency of 1.67 Hz, with a peak voltage gradient of ≥100 V/m within 5 cm of the electrode surface (Fig 7). The gradient of the electric field at equal distances around the Shark Shield™ varied slightly (± 2.7%) depending on the angle of the recording probe relative to the Shark Shield’s electrodes. For consistent measurements, the gradient was plotted along the same axis, parallel to the end of the electrode. Based on the average proximity to an active Shark Shield™, when controlling for the effect of encounter number (82 ± 12 cm; Table 1: #14), the estimated average voltage gradient necessary to elicit a deterrent response equated to approximately 15.7 (± 2.1) V/m (Fig 7). However, as proximity has been shown to decline over subsequent encounters (Table 3: #6 and #7), the estimated voltage gradient to elicit a deterrent response during the first encounter (131 ± 10 cm) is much lower than the average and equates to approximately 9.7 (± 0.9) V/m. Therefore, based on an average decrease in proximity by 11.6 cm per encounter, the voltage tolerance of individual sharks would be expected to increase by approximately 2.6 (± 0.5) V/m per encounter.

Bottom Line: Therefore, there is a clear need for thorough testing of commercially available shark deterrents to provide the public with recommendations of their effectiveness.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.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.

View Article: PubMed Central - PubMed

Affiliation: The Oceans Institute and the School of Animal Biology, The University of Western Australia, Crawley, Western Australia, Australia.

ABSTRACT
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. carcharias were 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.

No MeSH data available.


Related in: MedlinePlus