Sea turtle population structure and connections between oceanic and neritic foraging areas in the Atlantic revealed through trace elements

Assessing population structure and connectivity of species that have cryptic life stages, such as sea turtles, is a challenge in conservation biology. The early oceanic stage of sea turtles, also known as the 'lost years', is poorly known. Green turtle Chelonia mydas hatchlings emerge from their nests, enter the sea, and inhabit oceanic (open ocean) habitats where they are rarely seen until they recruit to coastal (neritic) foraging grounds several years later. Therefore, the location of and population structure in oceanic foraging grounds, as well as the connections between oceanic and neritic foraging grounds, are difficult to determine. Given that long-term tracking devices are not available for sea turtle hatchlings, the use of other markers, such as trace elements and stable isotopes, is necessary to study the oceanic stages of sea turtles. We analyzed the elemental composition and ratios of stable isotopes of carbon and nitrogen of scute tissue that was deposited when turtles were in the oceanic habitat to characterize 6 oceanic foraging areas used by green turtles in the Atlantic Ocean. We determined that there is significant structuring among oceanic green turtle aggregations and multiple links between oceanic and neritic foraging areas. We discuss the conservation implications of structured oceanic aggregations with multiple links, as well as the use of trace elements (particularly titanium, chromium, zirconium and barium) in the characterization of oceanic regions.