Sharks regularly interact with fishing vessels at Cocos Keeling Islands (CKI), leading to high rates of depredation. This human-wildlife conflict results in costly loss of target catch and gear for artisanal fishers, extra mortality for target species, and increasing negative actions taken against sharks. Initial community consultation surveys and engagement activities highlighted the need for testing a selected range of suitable mitigation methods to reduce depredation levels at CKI. As such, for the deepwater line fishing, we co-designed a study to test the effectiveness and practicality of a shark deterrent device, currently available on the market and specifically designed to mitigate fisher-shark interactions (RPELX), in deepwater demersal line fishing. A randomised experimental design was used to test the RPELX against a control treatment during 11 days of fishing. In total, 262 fish were caught across 51 fishing sessions. Grey reef sharks (Carcharhinus amblyrhynchos) were the main species responsible for depredation. Results of a Generalised Linear Model indicated that treatment and skipper had a significant effect on the number of fish depredated, with the RPELX reducing the probability of depredation events by 63%. Using the RPELX device also substantially reduced shark bycatch and loss of fishing gear. Further community consultation suggested improvements to the device’s design to promote better uptake and recommended a new prototype for pelagic fishing. Overall, the RPELX device can provide environmental and socio-economic benefits to the marine ecosystem, the local artisanal fishery and the community at CKI, by enabling improved human-shark coexistence. Further testing is recommended in other line fisheries around the world.