Gillnet illumination as an effective measure to reduce sea turtle bycatch.

The growing demand for fish around the world is an immediate threat to marine megafauna that are unintentionally captured in commercial and artisanal fishery operations. Bycatch mitigation strategies such as turtle excluder devices, circle hooks, and net illumination have successfully reduced this risk in some fisheries. This study explored the effectiveness of gillnet illumination to reduce sea turtle captures in two artisanal fisheries (Mankoadze and Winneba, Ghana) under normal fishing conditions. We first quantified sea turtle bycatch in Ghana's artisanal gillnet fishery from 15 boats for 12 months. We then quantified target catch and sea turtle bycatch from 20 boats for 15 months (7,427 net sets); ten of the boats were equipped with Centro Economy green LED lights (1 LED) at 10-meter intervals on the nets. We also quantified target catch and sea turtle bycatch from 30 boats for 8 months (2,250 net sets) with 15 boats equipped with Centro Deluxe green lights (3 LEDs) at 15-meter intervals. Boats with Economy lights and those with Deluxe lights both exhibited an 81% decrease in sea turtle captures (W = 1, p<0.001, n = 20; W = 215, p<0.001, n = 30) compared to control boats without lights. Illuminated nets reduced turtle catch for each species: the leatherback, olive ridley, and green sea turtle (p<0.05 for all species). Target catch (mass) (W = 53, p = 0.853 n = 20; W = 76, p = 0.449, n = 23) and value (W = 50, p = 1, n = 20; W = 69, p = 0.728, n = 23) were not different across treatments. Our study affirms net illumination can reduce the capture rates of three species of sea turtles, including the imperiled leatherback. Gear modification methods can be successful at reducing bycatch if they are affordable and have broad applicability across threatened species in different fisheries. Article Impact Statement: Net illumination reduces capture rates of 3 species of sea turtles, including the imperiled leatherback. This article is protected by copyright. All rights reserved.