70 1. Abstract The loggerhead turtle (Caretta caretta) South Pacific subpopulation is classified as 'Critically Endangered’ in the International Union for Conservation of Nature’s Red List, based on its estimated demographic decline. The Southern Province of New Caledonia shelters two distinct major nesting areas for this subpopulation, aggregating approximately 10-25% of all reported nesting activities at the ocean basin scale. A prejudicial knowledge gap subsisted in whether the nesting population of these two breeding grounds are part of a single or two distinct Management Unit(s), which could have significant implications for conservation strategies to be implemented. Based on a dataset collected from November 2016 to March 2023, we evaluated the sex-specific connectivity of loggerhead turtles over various temporal scales using three complementary methodologies: satellite telemetry (intra-annual), Capture-MarkRecapture surveys (inter-annual) and molecular analysis (inter-generations). Our results suggest that reproductive populations from both nesting areas form a unique genetic stock, and that the gene flow is presumably ensured by males, contrasting with the high fidelity to nesting areas shown by females. Considering that both nesting areas show heterogeneous habitat conformations and substantial differences in the associated threat levels, this study highlights the importance to consider both the site-specific aspects and the more global Management Unit scale to ensure a prioritized and coherent conservation strategy. Not considering those aspects could result in management failure and loss of local population segments. Key words Marine turtles. Caretta caretta. Endangered species. Connectivity. Satellite tracking. Capture-mark-recapture. Gene flow. Management Units. Science-based conservation. South Pacific. New Caledonia. 2. Introduction Marine turtles form a long-lived taxonomic group with complex life cycles, including expansive hatchling dispersals and adult ocean-scale distributions (Musick and Limpus 1997; Casale et al. 2007, 2013; Arendt et al. 2012; Read et al. 2015). Reproductive individuals undertake important philopatric-induced migrations as they return to their natal beaches to breed and nest (Meylan et al. 1990; Bowen and Karl 2007). This ecological trait enhances the formation of population structures by reducing gene flow among groups of individuals mating at geographically separated locations (Bakker et al. 2010). Ultimately, it can lead to a loss of genetic diversity and adaptive potential (Stiebens et al. 2013). Defining both the geographic distribution of population units and their level of connectivity is therefore required to set up efficient conservation actions (Wallace et al. 2010; Fitzsimmons and Limpus 2014; Wallace et
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