Effect of visual and electrosensory deterrents on captive elasmobranchs

Commercial gillnet fisheries interact with a wide range of elasmobranch species, many of which are incidentally captured as bycatch. Deterrent technologies have emerged as a potential approach for reducing interactions with threatened elasmobranchs. In this exploratory study, captive Giant Shovelnose Rays (Glaucostegus typus) and Brownbanded Bamboo Sharks (Chiloscyllium punctatum) were exposed to a static green LED light and a pulsed electrosensory deterrent attached to an experimental gillnet. The light deterrent initially reduced interactions by Giant Shovelnose Rays; however, this response diminished over time. Over a 10-min period, deterred Giant Shovelnose Rays showed a significantly greater distance of deterrence in both treatments compared to the control. There was also a significant difference in mean eye distance between the control and light treatments, but not in nose distance. In contrast, Brownbanded Bamboo Sharks exhibited no significant response to either deterrent. These contrasting responses may reflect differences in the sensory ecology of the two species, underscoring the importance of species-specific considerations in developing elasmobranch bycatch mitigation technologies. Given the promising outcomes reported for these deterrents in other studies, and the apparent variability in responses among elasmobranch taxa, further evaluation across a broader range of bycatch species is warranted.