Movement and Habitat Use of Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) Following Population Augmentation

Abstract

With amphibian declines at crisis levels, translocations, including population augmentations, are commonly used for amphibian conservation. Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) have declined to low densities in many areas of their range, making them ideal candidates for population augmentation. Both wild adults and captive-reared juveniles have been used for augmentations, but their suitability has never been directly compared. Herein, we use radio telemetry with Eastern Hellbenders to examine patterns of site fidelity, movement, and habitat use over a 2-yr period for adult residents, wild adult translocates, and captive-reared juvenile translocates. We used generalized linear models and generalized linear mixed models to identify temporal trends and explore the effects of residential status (resident vs. translocate) and origin/age (captive-reared juveniles vs. wild adults) on various ecological and behavioral traits relating to habitat. Site fidelity was high in adult residents and wild adult translocates, but lower in captive-reared juvenile translocates. Both adult and juvenile translocates had greater mean movement distances than residents, leading to larger home range sizes, but these differences decreased over time. Wild adult translocates had a higher probability of using artificial nest rocks than adult residents or captive-reared juvenile translocates. This pattern was most prevalent early in the study, indicating these shelters are particularly useful during the transition to release sites. Captive-reared juvenile translocates had lower site fidelity and utilized suboptimal habitat (smaller and fewer shelter rocks) compared to wild adults. Compared to previous studies, translocations had fewer negative effects on site residents or wild translocates and might be effective at promoting growth of Hellbender populations. However, translocations of captive-reared juveniles were less successful. As we are uncertain whether captive-rearing or ontogeny led to these differences, both longer head-starting times and conditioning should be explored to improve outcomes in captive-reared juvenile cohorts.

Translocation for conservation: Neonates are less suitable than adults

“…Differences in dispersal between age‐classes during translocations have been observed in other species. Captive‐bred juvenile eastern hellbenders ( Cryptobranchus alleganiensis alleganiensis ) have shown lower site fidelity in translocations compared to wild born translocated adults (60–90%, respectively; McCallen et al 2018).…”

“…A study comparing translocation of wild adult and captive‐bred juvenile eastern hellbenders found survival rates were lower in juveniles (Kraus et al 2017). Site fidelity was also lower in juvenile eastern hellbenders compared to adults (McCallen et al 2018). However, in a translocation of wild adult and captive‐reared juvenile tuatara, recapture rates were similar; 56% for juveniles and 61% for adults (Nelson et al 2002).…”

“…Studies comparing the efficacy of translocating juvenile and adult age‐classes have varied results and generally measure factors such as survival, site fidelity and habitat use (Nelson et al 2002; Sasmal et al 2015; Kraus et al 2017; McCallen et al 2018). The selection of the appropriate age‐class for translocation will largely depend on the particular species’ characteristics (Letty et al 2007).…”

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

“…Some hellbender population augmentation or reintroduction efforts have been "soft releases" (Boerner, 2014;Kocher, 2019;B. T. Kraus et al, 2017;McCallen et al, 2018). For example, eastern hellbender releases in the Allegheny River drainage in New York (Boerner, 2014;Kocher, 2019) have included soft releases using both artificial nest boxes (Briggler & Ackerson, 2012) and wire mesh cages.…”

“…Wild hellbenders are sedentary, typically spending most of their time within 30-40 m of the same stream reach (Foster et al, 2009;Nickerson & Mays, 1973). Headstart hellbenders fitted with telemetry units and tracked for short time periods have been shown to have lower site fidelity (60%) than their adult resident (100%) and translocate (90%) counterparts (McCallen et al, 2018). showed that Missouri headstarts dispersed within 550 m of release sites with most individuals dispersing <50 m. Boerner (2014) and Kocher (2019) estimated average (±SE) cumulative movement distances for New York headstarts at 653 ± 138 m and 1102 ± 267 m, respectively, and B. T. Kraus et al (2017) documented a captive reared individual moving 1.3 km from its initial release site.…”