Post-release movements of leatherback turtles captured by the Peruvian small-scale driftnet fishery: insights from satellite telemetry

The subpopulation of leatherback turtles Dermochelys coriacea in the eastern Pacific Ocean is classified as Critically Endangered due to multiple anthropogenic threats, the most urgent of which remains mortality at sea from fisheries interactions. Here we used satellite telemetry to assess the post-capture movements of leatherbacks in foraging grounds off Peru and attempt to evaluate post-release mortality. The 16 turtles tracked were bycatch from small-scale driftnet fishing vessels from the Peruvian ports of San Jose, Salaverry, and Parachique between 2014 and 2018. Sampled individuals included juveniles, subadults, and adults (curved carapace length range: 100.0 to 150.0 cm). Post-release overlap with driftnet fishing grounds was low and, upon release, all but one leatherback tracked for >30 d (n = 10) moved offshore beyond the continental shelf. From the subset of 6 tags with dive data, turtles spent 39.1 ± 11.8% of their time (range: 27.5 to 55.9%) within 10 m of the surface. Turtles spent significantly more time conducting shallow dives compared to deep dives during the day and night, carried out significantly more shallow dives compared to deep dives during the day and night, and carried out significantly more shallow dives during the day compared to night. Of the 16 tracks, biofouling (n = 3) and turtle injury or death (n = 3) were identified as the possible cause of tag cessation. Study results can inform ongoing population modeling and bycatch mitigation initiatives and efforts to predict and prevent bycatch interactions and mortality of this population.