LED light specifications to reduce marine pollution, mitigate bycatch and increase target catch in pelagic longline fisheries

Eric Gilman , Cheng Zhou, Milani Chaloupka, Eric Kingma, Brendan Godley, Francois Poisson, Daisuke Ochi

Pelagic longline fisheries use millions of single-use chemical lightsticks each year. These contribute to plastic and toxic pollution and increase at-risk bycatch. We explored reusable light-emitting diode and phosphorescent lights as potential replacements. We evaluated candidate lights’ potential effects on economic viability, practicality, crew safety and at-risk bycatch rates. We measured light properties that are potentially informative predictors of catch rates of target and at-risk bycatch species, including peak wavelengths (λmax), wavelength range, flicker rate, flicker duration, light level (total radiant power and at λmax), diminution and directionality. We compiled and synthesized the sensitivities of species captured in longline fisheries to light spectral, temporal and intensity characteristics, which informed defining criteria predicted to increase commercial species’ and reduce at-risk bycatch species’ catch rates. For example, to include peak spectral sensitivities of pelagic longline target species while avoiding longer wavelength peak spectral sensitivities of marine turtles, pelagic sharks and possibly other marine megafauna visual predators, we shortlisted lights with λmax between 400-480 nm (violet to blue to humans) and with low or no radiant power at longer wavelengths. We assessed apparent (submerged) weight and activation mechanism, which are attributes that might affect seabird bycatch. Following demonstrations of short-listed lights in three longline fisheries, overall, captains preferred smaller and dimmer LED models, preferred water- or pressure-activation over manual activation, and were ambivalent on preferences for flickering versus constant lights. The study identified characteristics of lights that hold high promise for meeting objectives for commercial viability, bycatch mitigation, and reducing marine pollution.