Exploring Oceanographic Frontiers: Insights from Animal Telemetry Data of four Captive-Born Loggerhead Sea Turtles released in the Macaronesia

A pioneering exploration into oceanographic phenomena in Macaronesia and the west North Atlantic Ocean is presented utilizing animal telemetry data collected from four captive-born Loggerhead sea turtles. Noting the cosmopolitan nature and migratory behaviors of sea turtles, this analysis assesses the potential of sea turtles to offer valuable insights into oceanic environmental variables. 

 

The turtles' interactions with upwelling sites, eddies, and ocean currents are revealed through the integration of georeferenced data (location and time) and oceanographic products from the Marine Copernicus Service. The oceanographic data were interpolated to the turtles’ location in time to obtain remotely-sensed Sea Surface Temperature (SST), chlorophyll-a (chl-a) concentrations and altimeter-derived ocean currents along the routes they performed. 

 

The results showcase the versatility of these animals as ocean gliders if they were instrumented with temperature and chl-a sensors, providing valuable measurements mostly about the atmosphere-ocean interaction, given their known diving behavior usually ranges from the surface down to 200 m. One of the turtles stayed for over two years near Banc d’Arguin. The simulation of its performance (if it were instrumented with oceanographic sensors) resembled that of a mooring in a key region of high productivity, capturing the seasonal cycle of SST and the chl-a bloom. A second turtle crossed the North Atlantic Subtropical Gyre as if it were an ocean glider leaving the Canary Islands and reaching the Gulf Stream in about 4 months. The path followed by this turtle reveals likely corridors used by sea turtles in cross-basin migrations which would be of high interest to be used for long-term and recurrent monitoring of the upper open ocean interior. Lastly, the third and fourth turtle navigated along the shelf of the Northwest African upwelling area, demonstrating their capability to sample not only open ocean but also coastal areas; the latter being particularly important given the relevance of counting with in situ SST measurements for validation of satellite data. 

 

Jointly, the four turtles of study and their associated navigational routes encourage further study of the potential of instrumenting Loggerhead sea turtles in Macaronesia as a complementary tool to more traditional approaches for measuring environmental variables.