Sea turtles are globally threatened, following the decline and extirpation of many local populations. Though > 100,000 olive ridley turtles (Lepidochelys olivacea) have been reported to nest during mass nesting events at Gahirmatha in Orissa on the east coast of India, this population currently suffers severe fishery related mortality. In general, the globally distributed olive ridley turtle has received significantly less conservation attention than its congener, the Kemp’s ridley turtle (L. kempi), because the latter is recognized as a distinct species consisting of a single endangered population.  

In this study attempts to understand the genetic structure of olive ridley turtle populations along the east coast of India. For the purpose, olive ridley sea turtles sampled from four major nesting sites, three in Orissa and one in Tamil Nadu, were analyzed using cross-species microsatellite markers and also nucleotide diversity in the mitochondrial control region. The microsatellite analysis revealed moderate to high level of polymorphism among the 80+ individuals from four sites. Interestingly, all the samples exhibited heterozygosity for at least one microsatellite loci analyzed in the study. The observations thus  suggest that olive ridley turtles in Indian waters have reasonably wide genetic base and represent a genetically vibrant population. Further, allelic diversity at microsatellite loci as well as the mitochondrial haplotypes were found randomly distributed across the samples, suggesting that there is no genetic differentiation between the populations from different nesting sites and that these probably represent the continuum of the same one large interbreeding population all along the East coast of India. This observation provides support to the field data that olive ridley sea turtles routinely use more than one nesting beach in Orissa.  

Further, our study of mitochondrial DNA haplotypes suggests that this large and distinct Indian population is likely to be the ancestral source for contemporary global populations of olive ridley turtles as a result of recent (re)colonization events from the Indian Ocean. Nested clade analysis and conventional analysis both support range expansions from the Indian ocean clades to other oceanic basins. Moreover, the occurrence of a signature 7 bp indel in the Indian haplotypes, which is shared with Kemp’s ridleys and other marine turtles, supports their ancestry to other olive ridley turtles. The data supports the distinctiveness of the Kemp’s as well as Indian ocean ridleys whereby both populations need to be prioritized, suggesting that conservation decisions should be based on appropriate data and not solely on designations of certain populations or groups of populations as species.