Green turtle (Chelonia mydas) mixed stocks in the southwestern Atlantic, as revealed by mtDNA haplotypes and drifter trajectories

Abstract

Genetic analyses have the potential to elucidate many aspects of juvenile green turtle (Chelonia mydas) biology and ecology, such as foraging ground composition, hatchling dispersal and migrations. To evaluate genetic structure and assess natal origins of mixed stocks in Southern Brazil, we analyzed mitochondrial DNA control region sequences from Arvoredo Island (n = 115) and Cassino Beach (n = 101), comparing them to other mixed stocks and examining their composition in terms of Atlantic Ocean stocks (nesting areas). In order to compare natal origin estimates (obtained through Bayesian Mixed Stock Analysis) with oceanographic data and develop novel informative priors for this analysis, surface drifter trajectories in the Atlantic Ocean were analyzed. Each study area presented twelve haplotypes, of which ten were shared at extremely similar frequencies. Haplotypes CM-A8 and CM-A5 were most frequent, representing respectively around 60% and 20% of samples from both areas, and remaining haplotypes were present in less than 5% of samples. Genetic structuring was not observed between the study areas. Arvoredo Island and Cassino Beach also did not present structuring in relation to Ubatuba and Rocas/Noronha, in the southwestern Atlantic, but were structured when compared to farther feeding areas in Brazil, the Caribbean, and North America. Analysis of drifter trajectories revealed that drifters from Ascension and Trindade Islands are dominant at the eastern coast of Brazil. Informative priors developed for Mixed Stock Analysis did not greatly alter stock estimates; we do, however, consider them to be ecologically more realistic. According to the Bayesian mixed stock analyses applied here, Ascension, Aves and Trindade Islands, as well as Gulf of Guinea, were the main contributors to the Southern Brazil mixed stock. This analysis has important implications for the conservation of this species, since impacts on mixed stocks along the coast may affect some reproductive stocks which are frequently thousands of kilometers away.