Population viability analysis (PVA) for olive ridley turtles (Lepidochelys olivacea) nesting in Alas Purwo National Park, Indonesia

Population Viability Analysis (PVA) is a common tool used to quantitatively assess the risks of extinction and time to extinction in a population and it provides justification for management responses to conserve threatened species. PVA was performed on the olive ridley turtle population nesting in Alas Purwo National Park (APNP) using a computer simulation program i.e. VORTEX, to predict population changes of the olive ridley turtles nesting at APNP in relation to the direct management established by the national park through hatchery. Forty scenarios using different emergence success and sex ratios potentially generated from the hatchery were simulated. The models revealed the importance of high emergence success from the hatchery for the long-term viability of the olive ridley turtle population nesting in the park which would not be possible under natural conditions with an extremely high predation rate on natural nests. A skewed sex ratio to a male sex bias over time, combined with low emergence success could negatively affect the population. Early stage mortalities of the hatchlings also influenced the population growth rate (t=-89.500, P<0.001 for hatchling mortality). This exercise clearly highlighted the importance of the hatchery in maintaining and/or increasing the emergence success of hatchlings, and that management practices should be monitored to ensure a healthier balance between male and female hatchling's sex ratio.