Influence of Geomorphology on the Population Structure and Ecology of the Hellbender Salamander (Cryptobranchus alleganiensis)

Hecht-Kardasz, Kirssten

The hellbender (Cryptobranchus alleganiensis) is an imperiled salamander that has experienced declines in many parts of its range. Little knowledge of the general ecology of the larval stage exists because studies including all stage classes, particularly larvae, are rare. In 2000, a brief study in Great Smoky Mountains National Park discovered a population of C. alleganiensis where larvae were regularly encountered and few adults were captured. The authors of the 2000 study hypothesized that the size structure of hellbenders in Little River, Tennessee was potentially influenced by differences in larval hellbender habitat and crayfish abundance from other studied localities due to the geologic structure of the streambed. To further investigate this hypothesis, this study examined three main components: trends in hellbender population structure, microhabitat use of hellbender stage classes within Little River, and body condition of hellbenders in rivers with different crayfish abundances. Diurnal skin diving surveys were conducted in the summer and early fall months of 2008-2010 to locate hellbenders and collect habitat, morphometric, and diet data. Surveys conducted since 2000 in Little River suggest that the hellbender population appears stable, with abundant larvae and regular recruitment. The number of larvae in Little River appears to be much higher than in most studied hellbender populations. Flooding induced mortality of larvae may affect long-term population structure in Little River due to the influence of stream geomorphology on larval habitat use. Of the habitat variables measured during this survey, only shelter size appears to differ among stage classes, with larvae utilizing smaller shelters on average than adults and sub-adults. Very coarse gravel was positively associated with hellbender occupancy in Little River. Abundance of crayfish, based on crayfish relative frequencies, correlated to overall body condition of hellbenders in the three rivers examined. Stomach samples collected from larvae suggest that hellbenders experience an ontogenetic shift in diet, with young individuals primarily consuming aquatic insect larvae. These results help fill in knowledge gaps regarding the larval stage of the hellbender, as well as highlight the potential impacts of stream geomorphology on the ecology of a hellbender population.

Influence of Geomorphology on the Population Structure and Ecology of the Hellbender Salamander (Cryptobranchus alleganiensis)

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