Green Turtles Highlight Connectivity Across a Regional Marine Protected Area Network in West Africa

Abstract

Networks of marine protected areas (MPAs) are invaluable for the protection of species with high dispersal capacity, yet connectivity within networks is poorly understood. We demonstrate the connectivity within the regional MPA network in West Africa (RAMPAO), mediated by the largest green turtle population in the eastern Atlantic Ocean. We equipped with satellite tags 45 female green turtles nesting in the Bijagós Archipelago, Guinea-Bissau, and tracked them during internesting, migration, and foraging to quantify the degree of coverage the RAMPAO network provides during each of these critical periods. During the internesting period, turtles were largely concentrated around the nesting islands, with a mean of 94.8% (SD 0.1%, range: 46% - 100%, n = 40 turtles) of tracking positions falling within MPA limits. Among the 35 turtles successfully tracked into the foraging period, we identified variable migratory strategies, with 12 turtles remaining near-resident at distances of 40-90 km from breeding sites, 10 turtles migrating 300-400 km to The Gambia and Senegal, and 13 turtles traveling >1000 km to northern Mauritania. Of the 35 foraging turtles, 26 used MPAs, with a mean of 78.0% (SD 34.8%, range: 3.7% - 100%) of their tracking positions falling within the limits of RAMPAO MPAs, across Guinea-Bissau, Senegal and Mauritania. Migration corridors with high concentrations of passing turtles were mostly located nearshore, and 21% of these high passage areas fell within the MPA network. Overall, we found that this population connects five RAMPAO MPAs, yet some foraging sites (e.g., in the Bijagós) and important migration areas (e.g., Cap-Vert peninsula) described here are currently unprotected. These results are relevant to any considerations of MPA extension or establishment within the regional network, which would contribute towards meeting the Convention on Biological Diversity targets for national marine protected area estate coverage. By documenting biological connectivity across RAMPAO, this study represents an important example of the relevance of international protected area networks for green turtle conservation and for wider conservation action at a regional scale.

Satellite tracking reveals sex-specific migration distance in green turtles ( Chelonia mydas )

“…Understanding whether sex ratios are biased at foraging grounds is relevant to understanding wider population dynamics, as mortality rates can differ across sites due to varying exposure to threats [32]. Females previously tracked from Poilão indicate that the foraging destinations used can vary among annual breeding cohorts, with four of four turtles migrating to Mauritania in 2001, seven of 15 in 2018, none of eight in 2019 and six of 12 in 2020 [19,33]. However, without contemporaneous data on male movements, it remains unclear whether sex-specific migration distances remain consistent despite annual variation in foraging destinations.…”

“…To assess whether the sexes use different foraging habitats, potentially explaining differences in migration distance, we overlapped the tracks of males during foraging on areas identified in a previous study from the tracks of 35 foraging females [19]. We calculated the number of males which used known female foraging areas and the percentage of points falling within those areas, and for males not using female foraging areas, we calculated the distance to the closest known area.…”

“…From a boat, mating pairs were spotted near Poilão, a fishing net was cast to catch the male which was equipped with a transmitter either onboard or on the nearby beach. Transmitters were deployed on females in November of the same year, either during nesting or when found stranded in intertidal rock pools after nesting (see [19] for details).…”

“…Mauritania). To do so, we analysed 26 migrations performed in two earlier years (2018 and 2020), reported in a previous study [19]. We then fitted a logistic regression with migration destination as a binary variable (short/long) and departure date and deployment year as explanatory variables.…”

Fine-scale foraging segregation in a green turtle (Chelonia mydas) feeding ground in the Bijagós archipelago, Guinea Bissau

“…Previous surveys identified a green turtle foraging aggregation around the islands of Unhocomo and Unhocomozinho, Guinea Bissau (Catry et al, 2009;Patrıćio et al, 2022), but their foraging habits remain for the most part unknown. We conducted in-water surveys in four foraging sites around these islands aiming to (1) characterize available foraging habitats (2) describe the size structure of foraging green turtles and (3) use SIA to assess the isotopic niches, potential diet of turtles, and potential ontogenetic and habitatrelated differences.…”