82 We also attempted to further our understanding of nesting females’ site fidelity at an intergenerational scale through the investigation of a maternally inherited genetic marker. Almost no diversity was detected in the mtDNA control region (63 out of 64 individuals shared the same haplotype) leaving insufficient signal to conclusively investigate any level of population differentiation. Therefore, we cannot assess the level of female mediated gene flow based on this marker. However, this result is not surprising since previous studies have shown very low levels of mtDNA diversity within and between nesting areas in eastern Australia and RP, New Caledonia (Limpus et al. 2005b; Boyle et al. 2009; Fitzsimmons and Limpus 2014). Investigation of the whole mitogenome might provide further insight on population structure patterns. Identification of a unique genetic stock and evidence for a male-mediated gene flow Contrary to mtDNA, the analysis of the nuclear genome has revealed high levels of diversity among the nine microsatellite loci genotyped. Yet, no genetic differentiation was detected between nesting individuals from the RP and the GLS areas. These results indicate that, despite evidence of restricted female movements from one nesting area to another based on telemetry and CMR data interpretation, sufficient gene flow occurred between the two areas to prevent genetic differentiation. We suggest that gene flow between the RP and GLS areas is mainly induced by males. This hypothesis is supported by the available literature. Indeed, opportunistic mating behaviors of males in multiple courtship areas have been reported from the foraging grounds, through migration routes to targeted breeding rookeries, and extending to nearby nesting areas (Fitzsimmons et al. 1997b; Stiebens et al. 2013; Fitzsimmons and Limpus 2014; Beal et al. 2022). A single MU but breeding grounds facing threats of various nature and intensity: implications for conservation Based on the gene flow recorded between the two distinct nesting areas, and despite the strong fidelity displayed by females to their breeding grounds, we now consider that the populations breeding at the RP and the GLS areas are part of the same genetic stock. This information leads us to conclude for a unique Management Unit, encompassing both nesting areas and aggregating 10-25% of all the reproductive females of the South Pacific critically endangered subpopulation (Limpus and Casale 2015; Bourgogne et al. 2024c), hence highlighting its major importance in terms of conservation issues. However, significant differences in nesting habitats geomorphology are reported between the RP and the GLS areas, leading to a context where different threats nature and intensity are affecting these two distinct breeding grounds. On one hand, the RP area is a coastal, publicaccess beach, facing anthropogenic pressures with the annual presence of visitors and
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