First Satellite Tracks of Neonate Sea Turtles in the South Atlantic Ocean

The PIFSC International Fisheries Program is working to understand the migratory behavior and dispersal patterns of oceanic stage loggerhead sea turtles (Caretta caretta) in the South Atlantic Ocean. This study complements our ongoing research to identify means of reducing incidental capture of sea turtles in pelagic longline fisheries. Working with collaborators from the University of Central Florida (UCF) and Projecto Tamar in Bahia, Brazil, PIFSC scientist Yonat Swimmer tagged and released nineteen neonate loggerhead turtles using modified small-scale solar-powered satellite tags (Fig. 1) developed by Dr. Kate Mansfield of UCF.

Figure 1. A solar-powered satellite transmitter enables tracking of neonate loggerhead turtles (photo credit: TAMAR).
Figure 1. A solar-powered satellite transmitter enables tracking of neonate loggerhead turtles (photo credit: TAMAR).

The turtles had been reared in a laboratory to an age of 4-13 months, growing to a straight carapace length (SCL) of 10.8-26.8 cm and a weight of 235-2800 grams. They were released at 4 times spanning the loggerhead nesting season (November and December 2012, and March and May 2013) to coincide with changes in the ocean current pattern along the coast of Bahia, Brazil where the turtles were born. Current direction is southerly during early/mid season, and northerly later in the nesting season (Fig. 2). Oceanographic drifters were released along with the turtles to collect concurrent information on current patterns, and to examine the probability that turtles were passively drifting with the prevailing ocean currents.

Except for two turtles whose tags transmitted for less than 5 days, the transmission duration of the tags varied from 26 and 120 days (mean =65 days, SD=24 days, n=17). Over the tracking period the turtles traveled between 575 and 4758 km (Fig 3). While some of the turtles traveled along the continental slope (north or south depending on the prevailing current pattern), others also moved to oceanic waters. Initially, all turtles followed a general circulation pattern observed with initial drifter trajectories. Unlike loggerhead turtles in the North Atlantic, they drifted off the continental shelf with trajectories parallel to the coast. The preliminary tracking data suggest that the distribution and movement of young loggerhead turtles in the South Atlantic are influenced by seasonal changes in current regimes. This information is helpful for identifying loggerhead turtles' vulnerability to fishing activity in the region in relation to season and changes in current regimes.

Figure 2. Sea surface currents in the South Atlantic Ocean, where tagged neonate loggerhead turtles were released, vary by season.
Figure 2. Sea surface currents in the South Atlantic Ocean, where tagged neonate loggerhead turtles were released, vary by season.
Figure 3. Tracks of 17 satellite-tagged neonate loggerhead turtles after their release (in 4 batches) from Bahia, Brazil during in 
        2012-2013.
Figure 3. Tracks of 17 satellite-tagged neonate loggerhead turtles after their release (in 4 batches) from Bahia, Brazil during in 2012-2013.