A Protocol for Quantifying Hellbender Abundance and In-Stream Habitat

摘要

Effective habitat and species monitoring programs require robust and repeatable estimates derived from standardized protocols. Hellbenders (Cryptobranchus alleganiensis) are large, long-lived salamanders endemic to highland streams in central and eastern North America. Based on historical data, it is apparent that Hellbender populations are undergoing significant, wide-spread declines; however, the ability of researchers to detect declines is limited because there has been little effort to standardize surveys and virtually no quantitative habitat data are collected during surveys. Here, we assess the efficacy of a spatially constrained transect-based method to capture Hellbenders and describe habitat conditions among years. We compared results to conventional snorkel/ rock-turning surveys and tested the consistency of habitat parameters using intra-class correlations. Although the differences were not statistically significant, spatially constrained surveys captured 25% more animals and produced relative abundance estimates that were 107% higher than unstandardized surveys. By constraining surveys and carefully recording effort, we ensured technicians would search study reaches more effectively and find Hellbenders in habitats that may have been overlooked by unconstrained surveys. Intra-class correlations demonstrated that some physical habitat conditions remained consistent between years whereas others were much more variable reflecting the year-to-year variability inherent to stream ecosystems. By constraining Hellbender surveys in time and space, researchers can provide more informative estimates of abundance and habitat suitability that will improve the ability of monitoring programs to detect changes in the range and population sizes of these large but cryptic aquatic salamanders.