Preliminary assessment of sensory deterrents for reducing threatened elasmobranch bycatch in northern Australian gillnet fisheries

Bycatch of threatened, endangered, and protected species (TEPS) in gillnet fisheries represents a critical conservation challenge globally. In northern Australia, gillnet fisheries interact with multiple TEPS, with threatened elasmobranchs (sawfishes, river sharks, and devil rays) facing the highest interaction risks. This study provides the first assessment of two commercially available sensory deterrent technologies for reducing elasmobranch bycatch in gillnets in the turbid, highly tidal environments of northern Australia: static green LED lights and a pulsed electric deterrent. Fishery independent trials (paired 60-m gillnet deployments), consisting of a treatment and control, were conducted and catch composition was quantified. Both devices showed non-significant trends for reduced sawfish interactions, though interaction rates were low and insufficient to draw firm conclusions. Green LEDs significantly reduced aggregated elasmobranch catch by 35% and significantly increased bony fish catch by 76%. Electric deterrents showed no significant effects on the overall catches of either bony fish or elasmobranchs. Limited replication constrained statistical power to detect species-specific effects, particularly for threatened species encountered at low frequencies. These findings provide preliminary data suggesting both technologies warrant continued investigation with optimised configurations, increased replication, and trials targeting threatened species across more diverse environmental conditions before commercial fishery implementation is feasible. This study establishes baseline bycatch deterrent performance data for elasmobranchs in turbid tropical waters and identifies critical research priorities for these conservation-priority species.