Predation and disease limit population recovery following 15 years of headstarting an endangered freshwater turtle

Abstract

Recovery strategies for endangered species vary in scope and scale, and uncertainties regarding their effectiveness make it necessary to implement evidence-based methods to ensure best management practices and the most efficient use of limited conservation dollars. Assessing recovery actions for species with slow life histories requires decades of study. We quantitatively assessed the putative recovery of two populations (PopA, PopB) of globally endangered Wood Turtles (Glyptemys insculpta) after 30 years of mark-recapture study and 15 years of headstarting implemented in response to a 57% reduction in population size attributed to poaching. We modeled population-specific demographic parameters to evaluate recovery efforts to date, and determine the next phase of management. Both populations showed limited recovery despite the release of 490 headstarted turtles. Recovery has been hindered by lower than expected 1-year post-release survivorship of headstarts (36%, 52% in each population, respectively), and only moderate (for turtles) adult survivorship (89%, 93%). Six headstarted turtles have, however, reproduced suggesting both populations may eventually become self-sustaining. From 2015 to 2018, subsidized predators killed 11 adult turtles, and we detected three diseases (mycotic shell disease, ranavirus, Glyptemys herpesvirus 2) in the headstarts. Our population viability analysis projected that both populations would recover if a predator-management strategy were implemented. Headstarting alone is not enough to save at-risk populations from local extinction when they face multi-faceted problems, including the cascading effects of landscape-scale habitat modification, for which management is challenging.