Factors influencing the availability of artificial hellbender ( Cryptobranchus alleganiensis ) shelters in North Carolina, USA

Abstract

The hellbender (Cryptobranchus alleganiensis) is a fully aquatic giant salamander experiencing population declines throughout the eastern United States. Hellbender declines are likely due to a loss of cover and breeding habitat, therefore artificial shelters have been designed for hellbenders to supplement breeding habitat and monitor reproductive success. Although several artificial shelter designs are currently in use throughout the hellbender range, no previous study has compared different designs in the field. We compared three shelter designs (modified boot design with an open bottom, modified boot design with a closed bottom, and a modified hydrodynamic design) to estimate their probability of availability (remaining in place and not obstructed by sediment) to hellbenders during variable stream conditions. We deployed 180 shelters of the three designs (n = 60 each) across six stream reaches in western North Carolina, measured habitat variables at installation points, and monitored shelters for sediment blockage, dislodgement, and hellbender occupancy. Shelter availability averaged 71% across all sampled occasions (67% modified boot closed, 69% modified boot open, 77% modified hydrodynamic). Blockage of shelters by sediment was responsible for the majority (96%) of occasions when shelters were deemed unavailable. Hellbenders rarely (range = 0 to 11% of occasions per site) used artificial shelters which precluded our ability to evaluate hellbender preference among shelter designs. Our findings suggest modified hydrodynamic shelters are slightly more resilient to the stream environment relative to modified boot designs, presumably due to their heavier weight and larger inner chamber. Additionally, our results highlight the need to consider site characteristics such as hellbender density and availability of natural cover before deploying artificial hellbender shelters.