Determining critical inter-nesting, migratory, and foraging habitats for the conservation of East Atlantic green turtles (Chelonia mydas)

Abstract

Satellite telemetry was used to track inter-nesting, post-nesting, and foraging movements of six green turtles that nested on Bioko Island, Equatorial Guinea at the end of the 2019 nesting season, as well as foraging movements of five green turtles after the 2018 nesting season (n = 11 across two seasons), from the same nesting population. These tracks were fit with a switching state-space model to characterize movements and then analyzed in relation to environmental and anthropogenic factors. Inter-nesting movements of two turtles included separate oceanic loops, in which turtles traveled > 40 km away from nesting beaches. Four complete migrations were observed to two distinct foraging grounds, with two turtles migrating west for an average of 1064 km to the coastal waters of Ghana, and two migrating south for an average of 1563 km to a newly discovered foraging ground in the coastal waters of Angola. All migrations included intermittent foraging at stopover sites, including one period of possible oceanic foraging. Turtles at both foraging grounds maintained distinct core use areas in shallow, near-shore (< 20 km from coast) waters. Spatial and depth data reveal critical habitats for this population throughout inter-nesting, post-nesting, and foraging behaviors. Tracks spanned nine countries, highlighting the need for multi-national cooperation in the development of marine conservation management plans in the area. The long distances covered by these turtles suggests that fisheries bycatch and direct harvest throughout the East Atlantic may impact this population. Additionally, spatial and dive depth data can inform zonal fishing regulations and provide the information needed to modify fishing practices and gear in ways likely to reduce sea turtle bycatch.