First satellite tracks of South Atlantic sea turtle ‘lost years’: seasonal variation in trans-equatorial movement

Abstract

In the South Atlantic Ocean, few data exist regarding the dispersal of young oceanic sea turtles. We characterized the movements of laboratory-reared yearling loggerhead turtles from Brazilian rookeries using novel telemetry techniques, testing for differences in dispersal during different periods of the sea turtle hatching season that correspond to seasonal changes in ocean currents. Oceanographic drifters deployed alongside satellite-tagged turtles allowed us to explore the mechanisms of dispersal (passive drift or active swimming). Early in the hatching season turtles transited south with strong southward currents. Late in the hatching season, when currents flowed in the opposite direction, turtles uniformly moved northwards across the Equator. However, the movement of individuals differed from what was predicted by surface currents alone. Swimming velocity inferred from track data and an ocean circulation model strongly suggest that turtles' swimming plays a role in maintaining their position within frontal zones seaward of the continental shelf. The long nesting season of adults and behaviour of post-hatchlings exposes young turtles to seasonally varying ocean conditions that lead some individuals further into the South Atlantic and others into the Northern Hemisphere. Such migratory route diversity may ultimately buffer the population against environmental changes or anthropologic threats, fostering population resiliency.

Olive ridley inter-nesting and post-nesting movements along the Brazilian coast and Atlantic Ocean

“…The importance of currents for sea turtle dispersal and migratory routes was proposed by Hays et al (2010) and Scott et al (2014), and for early stages of sea turtle life by Putman & Mansfield (2015). Variations in the bifurcation of the South Equatorial Current (biSEC), and in the origin of the Western Boundary Brazil and North Brazil currents (Stramma & England 1999, Silveira et al 2000, Amorim et al 2011, Pereira et al 2014) ap pear to be related to the north and south dispersion patterns recorded for loggerhead turtles in Brazil (Mansfield et al 2017). As the biSEC generally oc curs between 10°a nd 14°S (Rodrigues et al 2007), olive ridley hatchlings leaving Sergipe nesting beaches are exposed to seasonally varying ocean current conditions.…”

Predicted distributions and abundances of the sea turtle ‘lost years’ in the western North Atlantic Ocean

“…As this approach to predicting animal distributions is more widely applied, further development of these movement models would benefit from continued basic research in marine animal behavior and physical oceanography. Incorporating species-specific (Putman and Mansfield 2015) and population-specific (Christiansen et al 2016, Mansfield et al 2017) swimming behavior, with explicit consideration for the sensory-basis of movement decisions in animals (Putman et al 2012), is likely to improve the model's skill (Putman 2018a). Likewise, efforts to refine the representation of physical ocean circulation processes will yield better insight into the mechanisms shaping organismal distributions (Putman 2018b).…”

Global Perspectives on Observing Ocean Boundary Current Systems

“…These systems are home to intense and highly variable oceanic currents that redistribute mass, heat, salt, biogeochemical constituents, plankton, and pollution. Circulation patterns also influence the life history, foraging behavior, and abundance of many marine species (e.g., Mansfield et al, 2017). The coastal and open oceans are linked through boundary current systems where events such as coastal upwelling, sea level anomalies, primary productivity, fisheries, and weather are propagated between domains by various processes (e.g., eddies, Rossby waves, and advection).…”