The emerging field of electrosensory and semiochemical shark repellents: Mechanisms of detection, overview of past studies, and future directions

Since the sinking of the USS Indianapolis (CA-35) and associated shark attacks in 1945, the quest to find an effective shark repellent has been endless. Early efforts were focused on finding a shark repellent which would minimize the probability of a shark attack. However, studies illustrate that shark populations are drastically declining which has led to calls for effective management policies and practices to reduce both directed catch and bycatch of various shark species. With increased need for shark conservation, the focus has shifted to protecting sharks from harmful anthropogenic pressures, such as fishing gear and beach nets. Current shark repellent technologies which aim to minimize elasmobranch mortality in fishing gears include: permanent magnets, electropositive metal (EPM) alloys, and semiochemicals. This paper will review present electrosensory and semiochemical shark repellents, the mechanisms of elasmobranch (e.g. shark, skate and ray) detection and repellency, species-specificity in elasmobranch response to the stimuli, and environmental and biological conditions which may influence repellent success. Future research to enhance our knowledge on electrosensory repellents and to improve the success of repellent implementation and application will be discussed.