Restoring eastern hellbender (Cryptobranchus a. alleganiensis) populations through translocation of headstarted individuals

Abstract

Freshwater biodiversity is declining at a fast pace despite significant efforts directed toward the management and conservation of aquatic systems. 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; however, the success of this strategy for rebuilding hellbender populations and the most optimal release scenarios have largely been unassessed. We use a cohort of 205 animals released in several Ohio watersheds 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 year 1 (0.383 ± 0.058) and greater in years 2 (0.696 ± 0.086) and 3 (0.609 ± 0.154). Using demographic simulations, we found that 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 compared to single release events across multiple sites. Additional simulations showed that eastern hellbender headstarting programs using wild eggs can be highly beneficial in producing more animals reaching adulthood (up to 7 times, if survival in captivity is assumed to be 100%) compared to development in the wild. This study emphasizes the need to monitor the success of reintroduction programs and provides evidence that headstarting can be a viable strategy for rebuilding eastern hellbender populations.