Leatherback turtles in Sumatra: integrating regulatory, genetic, and ecological data for conservation

Leatherback turtles (Dermochelys coriacea) are among the most threatened marine megafauna, with steep population declines recorded across much of their global range. In the Northeast Indian Ocean, conservation efforts are hampered by limited ecological, genetic, and governance data, particularly in regions like Sumatra, Indonesia. This thesis aims to fill these knowledge gaps using an integrated, interdisciplinary approach that combines regulatory analysis, population genetics, and long-term ecological monitoring. By synthesising diverse datasets, the study provides novel insights into population status, conservation challenges, and management opportunities for leatherback turtles in this understudied region.

In Chapter 2, national and provincial regulations, alongside local customary law (Hukum Adat Laot), are assessed to evaluate the governance framework for sea turtle protection. Using text mining and policy evaluation, the chapter reveals extensive regulatory and institutional overlap, limited species-specific acknowledgement, and under-recognition of life-history traits in formal policies. In contrast, customary law demonstrates stronger habitat and species-specific protections, suggesting opportunities to formalise community-led governance through mechanisms like Other Effective Area-Based Conservation Measures (OECMs).

In Chapter 3, the study evaluates the potential of environmental DNA (eDNA) for detecting leatherback turtle haplotypes at nesting beaches. Water samples collected during the nesting season were analysed for mitochondrial haplotypes and compared with tissue-derived reference samples. The results show that eDNA can successfully detect leatherback presence and haplotype diversity, supporting its application as a complementary, non-invasive tool for population monitoring in remote and logistically challenging habitats.

In Chapter 4, mitochondrial DNA (mtDNA) sequences from leatherback turtles nesting in Sumatra are analysed to assess genetic diversity and population structure. The findings reveal the presence of multiple haplotypes, relatively high genetic diversity (h = 0.7538) and significant differentiation from other Indo-Pacific populations, indicating that the Sumatra rookeries may constitute a distinct Management Unit. These results support the need to reassess current Regional Management Unit (RMU) boundaries and highlight the conservation significance of these small, data-poor nesting populations.

In Chapter 5, a 12-year dataset (2012–2023) from Panga Beach, Sumatra, is analysed to examine trends in leatherback nesting activity. The results show a sharp decline between 2012 and 2014, followed by gradual increases until 2020, a marked drop in 2021, and a slight rebound in 2022. Nesting peaks consistently between November and February, with estimated annual nesting females ranging from 5 to 14 individuals per year. The maximum hatching success of relocated nests reached 76%. While overall nest counts remain low, signs of population persistence underscore the importance of sustained community-based monitoring and the conservation value of low-density rookeries.

In the final chapter, the thesis synthesises the findings from each component and emphasises the importance of integrated conservation approaches. By combining regulatory review, genetic data, and ecological monitoring, this work demonstrates that interdisciplinary methods can bridge key knowledge gaps and improve conservation strategies for wide-ranging and vulnerable species like the leatherback turtle. The findings contribute not only to regional management planning in Indonesia but also to broader efforts aimed at conserving important populations in the Northeast Indian Ocean.