Abstract
In Aotearoa New Zealand, 86% of indigenous reptile species are at risk or threatened with extinction, highlighting the urgent need for baseline data to inform conservation management. Reptiles in Aotearoa are most threatened by invasive mammalian predators and sweeping habitat loss. Conservation methods aimed at mitigating these threats have included translocations, mammalian predator control, and protecting and restoring essential habitats. Understanding a species’ ecology and responses to conservation management is essential to improving outcomes and mitigating declines.
The Otago green skink (Oligosoma aff. chloronoton “eastern Otago”), a taxon considered ‘At Risk-Declining’, fits many of the criteria for a species that needs conservation attention. They are understudied, taxonomically cryptic, highly vulnerable to invasive mammal predation, and have slow life histories, making conservation management and monitoring challenging. My research focused on two populations: one in the mountains of Oteake Conservation Park, a location where Otago green skinks are reasonably numerous, and one translocated to the fenced Orokonui Ecosanctuary in 2016. I aimed to build a foundation of knowledge about Otago green skink ecology to develop and implement post-translocation success indicators for the evaluation of the long-term success of the translocated population. My project addresses two main questions for Otago green skinks: 1. How does habitat use compare with availability in the alpine zone? and 2. How does a long-lived, large-bodied, and viviparous skink respond to translocation into a fenced sanctuary with mouse irruptions?
To understand life-history traits and environmental variables associated with skink presence in the alpine, I collected demographic data for 71 skinks and conducted habitat surveys. Adult female skinks had significantly longer snout-vent-lengths than adult males. Habitats with high vegetation cover, especially near large sheltering rocks, are important components of habitat used by adult and juvenile skinks in the alpine zone.
To assess the success of the translocation, I modified specific success indicators based on standardised criteria, used historical lizard-monitoring data to detect trends in the catch rate over time, and conducted photo ID surveys to reveal Otago green skinks’ post-translocation responses in Orokonui Ecosanctuary. Eight years following translocation, Otago green skinks met the taxon-specific success criteria for a viable, established population. That is, the population grew from a founder population of 40 skinks to a minimum of 56 individuals, 34% of skinks were juveniles, and only 5% were founder animals, indicating successful recruitment and population growth. The average catch per unit effort increased 300% over eight years, some individuals moved into new territories, and on average the skinks showed improvement in body condition, all metrics adding support to the report of a successful translocation outcome.
My research reveals valuable ecological information for this declining, data-poor lizard which can be used to improve targeted searches aimed at identifying new populations. My outcome evaluation shows that Otago green skinks thrive when protected from most mammals, paving the way for using translocation as a conservation tool for other ecologically similar skinks, including the other three members of the green skink complex, all of which are threatened.