New insights on sea turtle behaviour during the 'lost years'.

Several marine turtle species spend their first years of life in oceanic habitats. This early life stage is referred to as the 'lost years' due to the difficulty of accessing individuals for study offshore. We satellite tracked 114 wild-caught juvenile turtles (straight carapace lengths 12.3-29.9 cm) from the Gulf of Mexico between 2011 and 2022 to investigate 'lost years' movements with respect to traditional definitions assigned to the life stage. Satellite-tracked turtles included 79 green turtles (Chelonia mydas), 26 Kemp's ridleys (Lepidochelys kempii), 5 loggerheads (Caretta caretta) and 4 hawksbills (Eretmochelys imbricata). Many tracked turtles transited between oceanic (>200 m depth) and neritic waters (<200 m depth), challenging the assumption that this life stage is exclusively found in oceanic habitats. Turtle movements differed from oceanographic surface drifters, providing further evidence that sea turtles of this life stage do not exclusively drift with currents. We recommend redefining the 'oceanic stage' as a 'dispersal stage' to better reflect their behaviour and habitat plasticity. Our findings establish the West Florida Shelf as a high-use area, particularly among green turtles and Kemp's ridleys. The northeastern Gulf of Mexico is an important region for these species of conservation concern.