These three genetic stocks each include several rookeries, and are situated in the South (Europa and Juan de Nova), Central (Tromelin, islands in the north Mozambique Channel, and rookeries along the coast of Kenya and Mozambique) and North (rookeries in the Seychelles granitics and Amirantes) of the SWIO. Using mtDNA control region sequences from 15 rookeries, at least three separate genetic stocks (or management units) were identified spanning the entire SWIO. Previous work has characterized the genetic population structure of breeding populations throughout the SWIO region. Some smaller, nesting populations are also found along the African mainland (Kenya, Tanzania and Mozambique) and the coastline of Madagascar. Of these, the green turtle is the most abundant and widespread, and nests primarily on isolated islands, namely: the French Eparses Islands (Europa, Tromelin, Glorieuses, Juan de Nova), Mayotte, Comoros, Seychelles (granitics, Amirantes, southern islands, including Aldabra) and the Chagos archipelago. It is considered a biodiversity hotspot, and hosts five species of sea turtles, which are found throughout the region. The Southwest Indian Ocean (SWIO) is home to some of the world’s most unique terrestrial and marine biodiversity and ecosystems. Results of these models show that, while ocean currents broadly shape dispersal pathways, habitat-driven movements strongly modulate the spatial and temporal distribution of juveniles along these pathways. More elaborate models have recently been developed that simulate dispersal under the combined effect of ocean currents and active swimming movements motivated by the need to find suitable habitats (i.e., adequate water temperatures and food). This simple approach has been, and is still widely used, to obtain a first-order estimate of the pelagic juveniles’ spatial and temporal distributions (e.g., ). Dispersal patterns can be inferred by analyzing large numbers of simulated trajectories with computed trajectories, based on the assumption that hatchlings (and then juveniles) released from natal beaches drift passively with ocean currents. However, numerical simulations can provide a better understanding of the dispersal of juvenile sea turtles and the connectivity between nesting and foraging habitats. The migratory pathways used by adult turtles are becoming well understood from satellite telemetry studies. Adult foraging aggregations often comprise turtles from multiple genetic stocks, with some turtles migrating to local rookeries less than 100 km away, and others traveling several thousand kilometers to more remote breeding grounds. Upon reaching adulthood, female green turtles usually demonstrate strong philopatry, as they migrate back to their natal region to breed. They typically show strong fidelity to a feeding area before reaching adulthood, or may move through a succession of developmental foraging sites. The young turtles mature and grow in size, and upon reaching a curved carapace length (CCL) of about 35 cm, they settle into neritic feeding areas. Integrating genetic and oceanographic data helps researchers to better understand how marine species interact with ocean currents at different stages of their lifecycle, and provides the scientific basis for effective conservation management.Īfter emerging from their nests onto tropical and subtropical beaches around the world, green turtle hatchlings ( Chelonia mydas) enter the sea and are dispersed by ocean currents during the first several years of their lives, while drifting in pelagic habitats. The results from the genetic analysis could largely be explained by regional current patterns, as shown by the results of passive numerical drift simulations linking breeding sites to developmental areas utilized by juvenile green turtles. The MSA showed that the juvenile turtles at all sites originated almost exclusively from the three known SWIO stocks, with a clear shift in stock contributions between sites in the South and Central Areas. A mixed stock analysis (MSA) was applied to estimate the level of connectivity between developmental sites and published genetic data from 38 known genetic stocks. We analyzed mitochondrial (mt)DNA sequenced from 358 juvenile green turtles, and from eight developmental areas located throughout the Southwest Indian Ocean (SWIO). Here, we used a combination of molecular genetics and ocean drift simulations to investigate the spatial ecology of juvenile green turtle ( Chelonia mydas) developmental habitats, and assess the role of ocean currents in driving the dispersal of green turtle hatchlings. Understanding how ocean currents impact the distribution and connectivity of marine species, provides vital information for the effective conservation management of migratory marine animals.
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