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Hatching success of sea turtle eggs can be reduced by a variety of biotic and abiotic factors. This study of the nesting ecology of leatherback (Dermochelys coriacea) and green (Chelonia mydas) sea turtles, investigated how several environmental factors and beach characteristics on Bioko Island, Equatorial Guinea influence sea turtle reproductive success. Average hatching success was 40.4% for green turtles and 41.73% for leatherback turtles. For leatherback turtles, clutch elevation relative to the high tide line (HTL) was found to be the most influential factor in determining hatching success, highlighting the sensitivity of this species to sea-level rise (SLR). Multiple linear regression analysis demonstrated that nest distance to vegetation, temperature, sand grain size, location on the beach, and sand conductivity also played significant roles in leatherback clutch hatching success. For leatherback clutches, 33% percent of nests were affected by inundation and 17% by predation. An optimum clutch elevation range for leatherback turtles was identified, where a distinct increase in hatching success was observed between − 0.286 and − 0.0528 m above the HTL. For green sea turtles, 64% of experimental nests were affected by predation, confounding conclusions about the roles of environmental characteristics in green turtle hatching success. We propose further investigation into influential characteristics in green turtle nests and confirmation of the observed optimum elevation range on Bioko Island and other nesting grounds. Identified sensitivities of each species to SLR and beach characteristics will be used to encourage the government of Equatorial Guinea to consider the vulnerability of their resident turtle populations when planning for future coastal development. [ABSTRACT FROM AUTHOR]

Sea level is expected to rise 44 to 74 cm by the year 2100, which may have critical, previously un-investigated implications for sea turtle nesting habitat on Bioko Island, Equatorial Guinea. This study investigates how nesting habitat will likely be lost and altered with various increases in sea level, using global sea level rise (SLR) predictions from the Intergovernmental Panel on Climate Change. Beach profiling datasets from Bioko's five southern nesting beaches were used in GIS to create models to estimate habitat loss with predicted increases in sea level by years 2046–2065 and 2081–2100. The models indicate that an average of 62% of Bioko's current nesting habitat could be lost by 2046–2065 and 87% by the years 2081–2100. Our results show that different study beaches showed different levels of vulnerability to increases in SLR. In addition, on two beaches erosion and tall vegetation berms have been documented, causing green turtles to nest uncharacteristically in front of the vegetation line. We also report that development plans are currently underway on the beach least susceptible to future increases in sea level, highlighting how anthropogenic encroachment combined with SLR can be particularly detrimental to nesting turtle populations. Identified habitat sensitivities to SLR will be used to inform the government of Equatorial Guinea to consider the vulnerability of their resident turtle populations and projected climate change implications when planning for future development. To our knowledge this is the first study to predict the impacts of SLR on a sea turtle nesting habitat in Africa. [ABSTRACT FROM AUTHOR]

This study uses satellite telemetry to track post-nesting movements of endangered green turtles (Chelonia mydas) (n = 6) in the Gulf of Guinea. It identifies a migratory corridor linking breeding grounds of Atlantic green turtles nesting on Bioko Island, Equatorial Guinea, to foraging grounds in the coastal waters of Accra, Ghana. Track lengths of 20–198 days were analyzed, for a total of 536 movement days for the six turtles. Migratory pathways and foraging grounds were identified by applying a switching state space model to locational data, which provides daily position estimates to identify shifts between migrating and foraging behavior. Turtles exhibited a combination of coastal and oceanic migrations pathways that ranged from 957 km to 1,131 km. Of the six turtles, five completed their migration and maintained residency at the same foraging ground near the coastal waters of Accra, Ghana until transmission was lost. These five resident turtles inhabit heavily fished waters and are vulnerable to a variety of anthropogenic threats. The identification of these foraging grounds highlights the importance of these coastal waters for the protection of the endangered Atlantic green turtle. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]