Importance of demographic surveys and public lands for the conservation of eastern hellbenders Cryptobranchus alleganiensis alleganiensis in southeast USA

Abstract

Comparisons of recent and historic population demographic studies of eastern hellbenders Cryptobranchus alleganiensis alleganiensis have identified significant population declines and extirpations associated with habitat degradation, poor water quality and disease, leading to nomination as a candidate for listing under the Endangered Species Act. However, populations in the southern Appalachian region of the range have received less attention despite relatively high levels of watershed protection due to the establishment of federally protected National Forest and National Park public lands. These watersheds likely represent some of the best remaining available habitat, yet the lack of published studies make assessment of population stability and viability very difficult. Our objectives were to (1) conduct a capture-mark-recapture (CMR) demographic study and a point transect survey on the Hiwassee River in Tennessee which is designated a National Scenic River, and is largely contained within the Cherokee National Forest, (2) quantify the size structure of the population, (3) compare abundance, survival and recruitment with historic and contemporary hellbender populations across the range, (4) assess the importance of this population and the significance of National Forest and National Park lands in the context of hellbender population conservation in the southeastern United States. We detected all age classes present, with larval hellbenders comprising 21.5% of captures. Using a combination of static life table and CMR methods, we determined that survival rates during the first year were low (~10%), but were high (68–94%) for taggable sized hellbenders. Density of hellbenders at the study site was very high (84 taggable sized hellbenders per 100m of river) compared to recent demographic studies conducted in other regions of the range. We detected hellbenders over ~28 km of river, with a mean density of 23 taggable sized hellbenders per 100m of river, and a total population estimate of 6440 taggable hellbenders. National Forest and National Park lands are likely to continue to play a particularly important role in providing suitable habitat for hellbenders in the southern Appalachians. In fact, only six of 21 known hellbender locations in Tennessee appear to show consistent larval recruitment, all of which are located within or adjacent to National Forest or National Park land.

Using environmental DNA and occupancy modelling to identify drivers of eastern hellbender (Cryptobranchus alleganiensis alleganiensis) extirpation

“…Further, we could not include forest cover at both spatial scales in our analysis because it was highly correlated with road density, indicating that hellbender extirpation in WV may not be attributable to singular landscape‐scale factors, rather the possible synergistic effects of deforestation and urban development (Price, Dorcas, Gallant, Klaver, & Willson, ; Surasinghe & Baldwin, ). Although we could not include the percentage of catchment area covered by public land in our models because it was highly correlated with forest cover and road density, recent research highlights the importance of highly forested catchments within public lands to preserve water quality and hellbender populations (Bodinof Jachowski & Hopkins, ; Freake & DePerno, ). Based on our analysis of historical locations, current hellbender occupancy in WV may be constricted to high‐quality headwater streams within and around the Monongahela National Forest, identifying this tract of managed public land as an important conservation area for hellbenders.…”

“…Range‐wide hellbender population declines, often described as enigmatic, are just now being fully investigated using eDNA to determine the loss of area occupied by the species. Combining eDNA sampling with detailed demographic surveys to assess changes in population demography could provide a more mechanistic understanding of population declines (Bodinof Jachowski & Hopkins, ; Freake & DePerno, ; Pitt et al., ). Hellbender range constriction trends warrant timely conservation action to ensure continued persistence of remaining hellbender populations.…”

“…Although we could not include the percentage of catchment area covered by public land in our models because it was highly correlated with forest cover and road density, recent research highlights the importance of highly forested catchments within public lands to preserve water quality and hellbender populations (Bodinof Jachowski & Hopkins, 2018;Freake & DePerno, 2017).…”

“…Hellbenders inhabit streams with fast flow, cobble/boulder rock cover, and good water quality (Nickerson & Mays, 1973). Current research has focused on identifying quantitative relationships among suspected land use, habitat, and water quality variables associated with the species presence and changes in population demography (Bodinof Jachowski & Hopkins, 2018;Bodinof Jachowski, Millspaugh, & Hopkins, 2016;Freake & DePerno, 2017;Pitt et al, 2017). Causal agents of population declines are suspected to be habitat loss via siltation and filling of interstitial spaces because of anthropogenic landscape disturbances and water quality declines that impede successful reproduction via a lack of recruitment (Pitt et al, 2017).…”

Environmental DNA improves Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) detection over conventional sampling methods

“…All four observers watched for any hellbenders emerging from under rocks. To increase the probability of detecting all size classes, we also turned small cobble in riffle/run areas while snorkeling to search for larval individuals that often go undetected (Freake & DePerno, 2017). Lifted rocks were carefully placed back to their original resting position to limit substrate and hydrologic disturbance.…”