Genetic assessment of confiscated hawksbill turtles (Eretmochelys imbricata) in China reveals transboundary poaching hotspots and cryptic diversity

The critically endangered hawksbill turtle (Eretmochelys imbricata) faces severe pressure from the illegal tortoiseshell trade, with Hainan Island, China, emerging as a major regional confiscation hub. However, the geographic origins of trafficked individuals and the genetic structure of local populations remain poorly understood. To elucidate these patterns, we analyzed 720-bp mitochondrial control region sequences from 107 hawksbills sampled between 2015 and 2020, comprising 102 individuals from the illegal trade and five rescued from the Xisha Islands. In total, 25 haplotypes were identified, of which nine were novel, and all clustering within Indo-Pacific clades I and III. Phylogeographic network analyses, integrated with a comprehensive Indo-Pacific reference dataset, revealed extensive haplotype connectivity across Southeast Asia and the Ryukyu Archipelago, Japan. Mixed-stock analysis (MSA) identified the Philippines (58.5%; 95% CI: 46.2%–70.4%) and East Malaysia (25.8%; 95% CI: 15.6%–37.2%) as the primary sources, pinpointing the geographic interface between the South China Sea and the Sulu Sea as the principal extraction zone for the Hainan trade. Although contributions from local Hainan foraging aggregations, represented by the five Xisha samples, appeared negligible, this inference requires verification using more comprehensive regional baseline data in future research. Significantly, the identification of nine novel haplotypes within the trade cohort points to the existence of cryptic or unsurveyed nesting populations in the South China Sea and adjacent regions. As the first large-scale genetic assessment integrating both traded individuals and native hawksbill turtles around Hainan Island, this study demonstrates that the illegal trade is sustained predominantly by transboundary trafficking from Southeast Asia. Collectively, these findings underscore the urgent need to strengthen international enforcement and to expand genetic research to elucidate the population structure of this critical region.