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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

Bar graphs show the proportion of sharks that interacted (grey bar) during each encounter with a control (A) or active (B) Shark Shield™ treatment.Overlaid is the average proximity of sharks to the Shark Shield™ during each encounter (± Std. Error). Proximity trend line (Control): y = -20.876x + 323.56; Proximity trend line (Active): y = -116.37x + 1283.
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pone.0157717.g006: Bar graphs show the proportion of sharks that interacted (grey bar) during each encounter with a control (A) or active (B) Shark Shield™ treatment.Overlaid is the average proximity of sharks to the Shark Shield™ during each encounter (± Std. Error). Proximity trend line (Control): y = -20.876x + 323.56; Proximity trend line (Active): y = -116.37x + 1283.

Mentions: Based on an individual shark’s first 7 encounters with a ReMoRA (as this is the maximum number of encounters for which there are data available in both control and active trials), when only considering interactions (not proximity), there was no evidence of habituation between encounters during control (p ≥ 0.05; Table 2: #1; Fig 6A) or active trials (p ≥ 0.05; Table 3: #1; Fig 6B). There was also no relationship observed between the proportion of sharks interacting per encounter and the total number of sharks (all p ≥ 0.05; Control: Table 2: #2; Active: Table 3: #2), or between the proportion of sharks interacting per encounter and the number of encounters (all p ≥ 0.05; Control: Table 2: #3; Active: Table 3: #3).


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)

Bar graphs show the proportion of sharks that interacted (grey bar) during each encounter with a control (A) or active (B) Shark Shield™ treatment.Overlaid is the average proximity of sharks to the Shark Shield™ during each encounter (± Std. Error). Proximity trend line (Control): y = -20.876x + 323.56; Proximity trend line (Active): y = -116.37x + 1283.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0157717.g006: Bar graphs show the proportion of sharks that interacted (grey bar) during each encounter with a control (A) or active (B) Shark Shield™ treatment.Overlaid is the average proximity of sharks to the Shark Shield™ during each encounter (± Std. Error). Proximity trend line (Control): y = -20.876x + 323.56; Proximity trend line (Active): y = -116.37x + 1283.
Mentions: Based on an individual shark’s first 7 encounters with a ReMoRA (as this is the maximum number of encounters for which there are data available in both control and active trials), when only considering interactions (not proximity), there was no evidence of habituation between encounters during control (p ≥ 0.05; Table 2: #1; Fig 6A) or active trials (p ≥ 0.05; Table 3: #1; Fig 6B). There was also no relationship observed between the proportion of sharks interacting per encounter and the total number of sharks (all p ≥ 0.05; Control: Table 2: #2; Active: Table 3: #2), or between the proportion of sharks interacting per encounter and the number of encounters (all p ≥ 0.05; Control: Table 2: #3; Active: Table 3: #3).

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