Habitat Preferences, and Population Structure and Stability, in an Eastern Hellbender Population in the West Branch of the Susquehanna River

Abstract

We collected habitat and population data over two field seasons (2012 and 2014) for an eastern hellbender (Cryptobranchus alleganiensis) population in a tributary of the West Branch of the Susquehanna River. Analyses of population data show that the population has been stable across the sample years, with no significant change in linear density. Analyses of habitat use show that hellbenders take up residency in or near the thalweg, where the majority of cover rocks are located. Peripheral cover rocks are only rarely used by hellbenders. We found a positive relationship between the size (total body length) of hellbenders and the size (length) of the cover rock. Population size/age structure and sex ratios were similar between the two sample years. During the second field season (2014), we observed American eels (Anguilla rostrata) beneath cover rocks, but in no case did we find eels and hellbenders beneath the same cover rock. We observed no eels in the study area in 2012. Recent eel introductions in the watershed likely explain the sudden appearance of eels in the study reach. The precipitous co-occurrence of eels and hellbenders raises the concern that eels may compete with hellbenders for rock cover and for a limited food resource that consists mainly of Allegheny crayfish (Orconectes obscurus). Significant competition for food and cover, and eel predation on hellbender eggs, larvae and juveniles, could potentially initiate a decline in an otherwise stable hellbender population