Tracking the movement of leatherbacks in the Atlantic: How it works
Fitting turtles with a useful dress
... the turtle is not captured, but rather the radio-transmitter is fitted during egg-laying, without restraining the animal in any way.
...the turtles are typically caught in the fishing gear of fishing vessels during routine activities.
Leatherbacks in the South-western Atlantic will be captured by the Uruguayan trawl and/or artisanal fishery fleet as bycatch. Researchers on board of these vessels will coordinate the handling of the turtle with the captain.
In the trawl fishery, the animal is first freed from the fishing gear once it has been hauled on board, in order to fit the radio-transmitter to the turtle. Any medical intervention required to assist the animal in recovering will be provided on board.
The harness and transmitter unit are then fitted and the turtle is released into the sea. Depending on the vessel, the release might involve lifting the turtle with a crane in an additional harness, before it is carefully lowered in the water.
In the artisanal fishery, due to the fact that the boats are small and fish near the coast, the fishermen usually take the leatherback turtle to the beach in order to disentangle it. There, the turtle would be fitted with the transmitter and released.
Although the sample size is small, turtles fitted with transmitters in Uruguay will shed information, as individual case studies, on the post-release fate of leatherbacks victim of by-catch. All turtles caught during this project will be tagged, sexed and measured.
Fitting the turtle with its new dress
Radio-transmitters for leatherback turtles are fitted to the soft carapace with a specifically designed harness. Parts of the harness are designed to disintegrate in time, and release the turtle from the harness should the opportunity for removal not arise. The equipment does not harm the turtles.
Breaking new ground in migratory data collection
The radio-transmitters are expendable equipment. The main limitation for the duration of the tracking is battery life, which is currently in the order of seven months to a year. This project, however, hopes to obtain up to three years worth of information from each turtle by resorting to state-of-the-art transmitter technology.
We may even record the return of a leatherback to the beach where it was fitted with the transmitter in the first place, and hence complete the tracking of a complete migration cycle for the first time. This would happen, of course, only if the turtle does not fall victim to fisheries gear during migration.
A simple transmitter, such as the KiwiSat 101 PTT, will provide basic information such as location of the animal and water temperature. More sophisticated transmitters include time-depth recorders to monitor diving behaviour, among other features. Transmitters need to be compatible with satellite-tracking services.
Radio-transmitters will be fitted to at least two leatherback turtles per site at nesting beaches in Panama (Playa Chiriqui), French Guiana (Awala-Yalimapo Beach) and Gabon (Gamba Protected Area Complex), and off the coast of Uruguay.
Aware that the sample size is small for a comprehensive characterization of movements of leatherbacks in this region, the authors believe that the project will help trigger additional sponsorships to track a larger number of turtles. We are aiming to secure funds to fit about 25 turtles with transmitters.