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

Beach nets and drumlines are lethal devices that are used to minimize the interaction between potentially dangerous sharks and beachgoers. Mortality to these large shark species as a result of these lethal measures has led to the development of non‐invasive technologies that may minimize the risks of rare encounters with beachgoers while simultaneously protecting vulnerable sharks and other marine species. One such technology is the SharkSafe Barrier™, which uses visual and magnetic stimuli to non‐invasively deter sharks from a designated area. Previous experiments using this technology were performed on a small scale (e.g. 13 m × 13 m), with an attempt made to extrapolate the results to a larger scale application without actual large‐scale deployments and experimentation. The present study examined whether a large‐scale SharkSafe Barrier™ shoreline deployment could successfully exclude the bull shark (Carcharhinus leucas) from acoustic and olfactory cues and evaluated whether the technology could serve as a less invasive replacement to current culling practices. Generalized linear mixed‐model analyses based on 59 trials illustrate that C. leucas swimming behaviour (i.e. avoidances, entrances, and pass arounds) significantly differed between the control (i.e. unmanipulated area) and the experimental (i.e. SharkSafe Barrier™) regions. Unlike previous small‐scale experiments, 10 of 16 sharks repeatedly penetrated the barrier and swam in an accelerated manner once within the experimental barrier region. The present findings raise concerns that the size of the previous experimental areas may have been insufficient to provide a realistic representation of barrier efficacy for large‐scale deployments. With continued shark‐culling measures in various locations, a non‐invasive and eco‐friendly alternative is needed, but substantial modifications to the current Sharksafe barrier design or an entirely new eco‐friendly approach are needed as the barrier in its present state does not reliably deter large and potentially dangerous sharks from a large‐scale area.