Variable response to electric shark deterrents in bull sharks, Carcharhinus leucas

Abstract

Although relatively rare, human-shark interactions and sharks bites are increasing globally, which has led to the development of various mitigation measures. Electric shark deterrents (ESDs) have, so far, been the most effective personal deterrents, but have only been scientifically tested on one of the species most frequently responsible for shark bites, i.e. white shark (Carcharodon carcharias). We tested the effectiveness of five ESDs (E-Shark Force, NoShark, Rpela v2, Freedom + Surf, Freedom + Surf—Shortboard) on bull sharks, Carcharhinus leucas, over a period of 21 days in September 2019, in New Caledonia. Standardised bait was attached 30 cm below an experimental board that had an active ESD for up to 15 min, or until a bull shark touched the bait or the board. We compared the numbers of baits taken, numbers of passes and reactions around the board, as well as the distance between the sharks and the board among ESDs and against a control board with bait and no active ESD. The Freedom + Surf was the most effective ESD, reducing the amounts of baits taken by 42.3%, while the Rpela v2 and Freedom + Surf—Shortboard also significantly reduced the number of baits taken by 16.5% and 16.2% respectively. Mean distance between sharks and the bait was not affected by the ESDs, but the number of approaches and the proportion of reactions were both significantly higher when the Freedom + Surf was active compared to other ESDs. The effectiveness of all ESDs decreased over time, with the likelihood of the bait being taken increasing and the number of approaches and distance between sharks and the bait decreasing. Our findings show that the ability of ESDs to deter bull shark varies between products, with the Freedom + Surf resulting in the most behavioural changes, followed by the Rpela v2 and Freedom + Surf—Shortboard. However, none of the products tested completely stopped sharks from taking the bait.

Evaluating the effects of a SharkSafe Barrier™ shoreline deployment on bull shark (Carcharhinus leucas) behaviour

“…As previous elasmobranch‐related studies demonstrate that repeated exposure to an unchanging auditory (Myrberg, Banner & Richard, 1969; Myrberg, Gordon & Klimley, 1978) or electro‐sensory (e.g. Gauthier et al, 2020) stimulus could lead to shark habituation, future studies should either: (i) implement a more comprehensive technique to identify each individual shark’s initial and subsequent interactions to assess whether shark habituation occurs; and/or (ii) deploy a barrier system for multiple months or year(s) so that the potential effects of long‐term repeated exposure to a consistent visual and electro‐sensory stimulus can be assessed. As multiple entrances were observed during this experiment, and should this technology be implemented as an eco‐friendly alternative to beach nets and drumlines, assessing whether shark habituation occurs must be a precursor to ensure such a system is a practical and safe alternative.…”

“…As previous elasmobranch-related studies demonstrate that repeated exposure to an unchanging auditory (Myrberg, Banner & Richard, 1969;Myrberg, Gordon & Klimley, 1978) or electro-sensory (e.g. Gauthier et al, 2020) stimulus could lead to shark habituation, future studies should either: (i) implement a more comprehensive technique to identify each individual shark's initial and subsequent interactions to assess whether shark habituation occurs;…”

Short-term response of research activities on white shark behaviour

“…These animals are considerably resilient to anthropogenic-induced stressors; for example, capture of up to 75 min on SMART drumlines, followed by acoustic tagging and muscle biopsies and blood draws does not lead to physiological impairment or mortality (Gallagher et al 2019;Tate et al 2019). With regards to the deterrent trials, the devices tested have either had no effects (Huveneers et al 2018b) or have a very small range of less than 2 m (Gauthier et al 2020;Thiele et al 2020). Therefore, we would not have expected sampling or deterrent testing to lead white sharks to leave the Neptune Islands.…”

Synopsis of global fresh and brackish water occurrences of the bull shark Carcharhinus leucas Valenciennes, 1839 (Pisces: Carcharhinidae), with comments on distribution and habitat use

“…Carcharhinus leucas also occurs in Papua New Guinea (fricke et al 2014; white et al 2018, 2019). Furthermore, C. leucas is distributed around the oceanic islands of Melanesia's New Caledonia (fourmanoir & laBoute 1976;fricke & kulBicki 2006fricke & kulBicki , 2007lanGlois et al 2006;maillaud et al 2009;fricke et al 2011;Gauthier et al 2020), Vanuatu (Brunnschweiler 2018a(Brunnschweiler , 2018b, the Solomon Islands (hylton et al 2017), Fiji (e.g. Brunnschweiler 2005Brunnschweiler , 2010Brunnschweiler et al 2014Brunnschweiler et al , 2017Brunnschweiler et al , 2018Brunnschweiler & marosi 2019;Glaus 2019;Glaus et al 2015Glaus et al , 2019aGlaus et al , 2019bGlaus et al , 2020drew & mckeon 2019;ward-PaiGe et al 2020;BouverouX et al 2021), Samoa and American Samoa (wass 1984).…”