Attributes of Shelters Selected by Eastern Hellbenders (Cryptobranchus a. alleganiensis) in the French Broad River Basin of North Carolina

Abstract

We investigated the attributes of shelters used by Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) in two 500-m stretches of the French Broad River basin in North Carolina during June 2010. We quantified attributes at each Hellbender shelter and at a corresponding unoccupied shelter located <25 m away to determine whether the attributes selected differed from those available in the surrounding environment. We identified 41 Hellbender shelters, each occupied by a single animal. Hellbenders selected shelters that had larger cover rocks and deeper cavities than the unoccupied shelters. No other attributes differed between occupied and unoccupied shelters, and there were no significant relationships between total length of Hellbenders and size of the cover rock or cavity depth. All Hellbender shelters were formed by large rocks with flat bottoms. Most had a single entrance that was oriented downstream and a cavity floor consisting of sand and gravel. Shelters were generally located in shallow, fast-flowing water with <10% of their surface area embedded in the substrate. Our results suggest that Hellbenders prefer shelters with attributes that maximize cavity space. Larger cavities likely provide greater protection from predators and greater concealment from sunlight. In addition, larger cavities allow more space for Hellbenders to rock back and forth to maximize oxygen uptake through their skin during periods of low flow when oxygen levels drop.