Building Eastern Hellbender (Cryptobranchus a. alleganiensis) Populations through Reintroduction of Head-Started Individuals

Abstract

Abstract Freshwater biodiversity is declining at a fast pace despite significant efforts directed towards the management and conservation of aquatic systems. Specifically, amphibians are among the most threatened taxa, with loss of aquatic habitat and alteration of habitat quality among important drivers of decline. Eastern Hellbenders are one of North America’s most iconic stream amphibian species, a sentinel of stream health, and are experiencing rapid population declines throughout most of their range. Common conservation strategies include headstarting (raising animals in captivity from wild eggs until 3–4 years old) and releasing them into streams. However, the success of this strategy for rebuilding hellbender populations and the most optimal release scenarios have largely been unassessed. In this study, we use a cohort of 205 headstart animals released in several Ohio watersheds in 2018 to evaluate the success of headstarting and reintroduction efforts over 3 years. Using PIT-tag surveys over 25 occasions between July 2018 and November 2021 and capture-recapture models, we found that 3-year apparent survival post-release was 0.162 ± 0.061, with lower survival in the first year (0.383 ± 0.058) and higher in years 2 (0.696 ± 0.086) and 3 (0.609 ± 0.154). We used demographic simulations integrating survival data from this study and from the literature to evaluate the number of releases and timing of releases required for building self-sustaining populations. We found that, given the low survival post-release, releasing cohorts of N = 100 individuals at fewer suitable sites several times (e.g., 3 releases, 2 or 3 years apart) would be a better strategy to achieve a high number of breeding adults compared to single release events across multiple sites. In addition, Eastern Hellbender headstarting programs using wild eggs are highly beneficial in producing more animals reaching adulthood (up to 7 times) compared to allowing eggs to develop in the wild. This study emphasizes the need to monitor the success of reintroduction programs, particularly for species with cryptic lifestyles. It also provides evidence that headstarting can be a viable strategy for rebuilding Eastern Hellbender populations, particularly if implemented in tandem with other management actions such as improving habitat and water quality and mitigating other threats.