Whole mitochondrial DNA sequencing improves resolution of population structure for Pacific green turtles (Chelonia mydas)

Amy Frey ^1* Erin LaCasella ¹ Michael P Jensen ^2,3 Peter H. Dutton ¹

• ¹ Southwest Fisheries Science Center, National Oceanic and Atmospheric Administration, La Jolla, United States
• ² Department of Chemistry and Bioscience, Aalborg University, Aalborg, Denmark
• ³ World Wide Fund for Nature, Healthy Land and Seascapes, Brisbane, QLD, Australia, Brisbane, Australia

Mitochondrial DNA (mtDNA) analysis is a key tool for defining population structure in marine turtles, due to their strong natal homing behavior, which leads to genetic differentiation among rookeries. However, the widespread occurrence of common haplotypes across large geographic areas, has limited the ability to resolve fine-scale population structure, particularly in the western Pacific. Understanding these population dynamics is crucial for effective conservation and management, as distinct nesting populations may face different threats. This study evaluates the use of whole mitochondrial genome sequencing to improve genetic resolution of population structure and enhance the accuracy of mixed stock analysis (MSA). We analyzed 197 nesting green turtles from six Pacific rookeries, representing two common mtDNA haplotypes (CmP20.1 and CmP22.1). Using mitochondrial capture enrichment and MSA simulations, we detected significant genetic differentiation between the rookeries in Guam and the Commonwealth of the Northern Mariana Islands (CNMI), which were previously considered a single genetic stock based on traditional control region sequencing. Our findings demonstrate that whole mitochondrial genome sequencing enhances stock resolution, improves the accuracy of MSA, and strengthens the ability to determine connectivity between nesting and foraging populations throughout the region. Refining genetics baselines using whole mitogenome sequencing will support more precise conservation strategies, allowing for targeted protection of genetically distinct populations, improved assessments of bycatch impacts, and better-informed management of critical foraging and nesting habitats.