Two of the few methods available to describe the migratory routes of turtles are flipper tag recovery, and satellite transmitters. Sea turtles travel the longest distances ever recorded for reptiles.
The historical, opportunistic recoveries of flipper tags from leatherback turtles nesting in Costa Rica and French Guiana, for example, indicate a wide dispersion throughout the northern Atlantic Ocean, with individuals routinely sighted from the western to the eastern Atlantic, and from boreal to tropical latitudes.
Tags tell of distance travelled
Tag recoveries along the western coast of Africa of turtles from nesting beaches in South America include: 2 females tagged in French Guiana which were found along the Moroccan coast; and a female tagged in Surinam which was recaptured one year later in Ghana. The latter represents the longest known movement of a leatherback turtle, which travelled 5,900 km after nesting in Suriname, proving that transatlantic movements may lead turtles that nest in South America as far as the interior of the Gulf of Guinea. One female tagged in French Guiana was also recaptured near the Azores.
Recapture sites along the north-western Atlantic Ocean, of leatherbacks turtles previously tagged in the Guianas include: USA (South Carolina, Texas, New Jersey), Campeche (Mexico), and the Gulf of Venezuela.
Filling the information gaps
Tag recoveries, however, only provide information of the start and end points of movement. No information is disclosed on the whereabouts of turtles between these points. Now, new technologies make it possible to learn much more about what happens to turtles at sea:
- the exact routes that are used
- their movements
- the dispersion cues
- the potential interactions with human activities and environmental changes
Turtle on the radar
Satellite telemetry is such a technology, allowing the precise monitoring of post nesting movements of sea turtles and their behaviour at sea. The advantages of satellite telemetry over other tracking techniques is that it provides information over extended periods of time and does away with the need for a vessel.
What past turtle tracking experiments tell us
A pioneering study tracked for 24 days a female that had nested in French Guiana, during which the turtle travelled north for 820 km before transmission stopped.
Ever since, surprisingly little has been published on the biology of leatherback turtles at sea in the Atlantic Ocean. There are presently less than 10 scientific publications presenting the movements or behaviour of Atlantic leatherback turtles at sea using electronic technologies. However, most of these studies focused on the nesting season, when turtles remain close to the shore between two nesting events.
Going the distance
Movements of female leatherbacks after nesting in Puerto Rico, and the southern end of the Caribbean (Trinidad) have been successfully monitored, indicating that some of those nesting assemblage disperse to widely separated Atlantic regions. For example one turtle travelled over 4,500 km from Puerto Rico (Culebra and Fajardo Islands) to the Azores front; while turtles that left from Trinidad crossed the Atlantic and approached African waters (off the coast of Mauritania).
Similarly, female leatherbacks tracked after nesting in Grenada and in French Guiana dispersed widely in the North Atlantic. Some of their movements are associated with ocean fronts where the abundance of jelly fish is probably high. Most of their diving happens within 250 m of the surface, making the interaction with fisheries quite likely. However, leatherbacks are known to dive deeper than 1,200 m, as recorded in recent years by satellite telemetry.
Adult males are rarely captured for tracking purposes, and juveniles have never been tracked to date.