Pre and post-settlement movements of juvenile green turtles in the Southwestern Atlantic Ocean

Abstract

Detailed knowledge on migratory routes connecting distant breeding, developmental and foraging areas is a key prerequisite for the successful management of marine vertebrates. The present study combines stable isotopes analysis of carapace scutes and satellite tracking of juvenile green turtles as an experimental approach to understand the pre and post settlement (recruit to neritic habitats) movements in the Southwestern Atlantic Ocean. To this end, carapace scute biopsies were collected from 20 turtles foraging on coastal rocky outcrops in East Uruguay and sliced in successive 30-μm layers using a cryostat. The δ15N and δ13C values of the newest layer increased significantly with turtle size and they also increased from the oldest to the newest layer in most of the individuals. According to the regional isoscape, such a pattern was consisted with the shift from tropical, oceanic habitats to neritic habitats in northern Brazil and the subsequent southward movement along the coast. Using the δ15N values of the scute layers, seven turtles were considered new-settlers and 13 residents, as only the latter had δ15N and δ13C values consistent with those of local potential prey. According to satellite tracking, some resident turtles perform short seasonal migrations to northern Brazilian waters during the austral winter. This behaviour is also recorded in scute layers as a small drop of δ15N values. The present study thus provides empirical evidence supporting the hypothesis that turtles reaching 40–45 cm of curved carapace length arrive to Uruguayan waters following a coastal migratory route along the Brazilian coast and confirms the existence of seasonal movements between Uruguayan and South-Brazilian waters and a high fidelity for feeding grounds in the Southwestern Atlantic Ocean.