Animals that undergo long distance migrations face high energy costs and navigational challenges influenced by multiple environmental factors. By integrating data on environmental variables, animal movements, known physiological data, and predictive migration models, we investigated the effects of these factors on highly migratory green sea turtles (Chelonia mydas). This study uses ocean current data to better understand observed migration routes and strategies of green turtles nesting on Bioko Island, Equatorial Guinea. We used satellite data from completed post-nesting migrations of green turtles (n=9) that traveled in two separate directions (west and south) and used two distinct migration strategies (coastal and pelagic). Ocean current data was used to compare estimated energy costs between migration strategies. Simulated pre-breeding migrations, from known foraging grounds to Bioko, were used to test whether vector navigation (maintaining a constant heading for a given amount of time) could account for the migration routes of individual turtles.
Results/Conclusions
Our results indicate that ocean surface currents did impact energy cost, with coastal migrations being less impacted by currents in both directions, and southern migrations having a greater difference in estimated energy cost between strategies. Results also suggest that vector navigation may be feasible for western but not southern post-nesting migrations. Pre-breeding migrations from both known foraging grounds could not be explained by vector navigation and most likely require more complex navigational strategies. Understanding the costs and vulnerabilities for sea turtles associated with different migratory routes can better inform regulations on fishing, resource extraction, and other human impacts to more effectively protect this species.