Challenges of monitoring reintroduction outcomes: Insights from the conservation breeding program of an endangered turtle in Italy

•We analyzed monitoring data for 7 years of releases of captive-bred turtles.•Estimated survival was similar for 3-5 year-old turtles, but varied among sites.•Initial uncertainty regarding the age class to release has been resolved.•Key uncertainty now shifts to site suitability and breeding in the wild.•Monitoring data should be collected with a clear link to management uncertainty.

Captive breeding and reintroduction programs remain a powerful but divisive tool for management of threatened species, with a proven potential to avoid extinction, but low long-term success rates and high resource requirements. Monitoring the results of reintroductions is critical to be able to assess short- and long-term success, adjusting management decisions as new information becomes available. In this study, we assessed the first 15 years of the captive breeding and restocking program for the European pond turtle Emys orbicularis in Liguria, northern Italy. We estimated survival of released turtles by modelling mark-recapture monitoring data. We then used those estimates to update our prior expectations about long-term outcomes, and to adjust management decisions about the age of individuals to release. Modelling results suggest released turtles had sufficiently high survival, matching prior expectations, such that local extinction has been averted in the short-term. Survival was similar among candidate age classes for releases, suggesting the release of younger individuals can provide positive outcomes while reducing management costs. On the other hand, survival varied among sites, indicating the need for ongoing in-situ habitat management to ensure long-term persistence. Moreover, the late onset of sexual maturity in the species means reproduction of released animals cannot yet be determined with certainty. Captive breeding and reintroduction programs normally require long-term efforts; therefore, focused monitoring that is clearly linked to decision-making is necessary to continually refine and adjust management strategies.