Cryptobranchus alleganiensis alleganiensis

See taxonomic comments under full species. Collins (1991) elevated this form to species status. Molecular data presented by Crowhurst et al. (2011) do not support the monophyly of the subspecies, but no formal change in the taxonomy was suggested (Crother 2017). It exhibits low range-wide allozyme diversity and high between-population mtDNA variation (Routman 1993). A mtDNA phylogeny by Routman et al. (1994) indicated that "the two subspecies of hellbenders are paraphyletic with respect to one another. Hellbenders found in the southern Ozarks (C. a. bishopi) are either most closely related to populations of C. a. alleghaniensis inhabiting the Tennessee River drainage or are so divergent that phylogenetic affinities are undetectable. Extremely low levels of divergence among mtDNA haplotypes found in populations from Pennsylvania, Indiana, Illinois, and the northern Missouri Ozarks suggest a recent, probably post-Pleistocene, invasion of this region from a refugium in one of these areas." Hence, recognition of the nominal subspecies appears to be unwarranted.

This species has undergone significant declines in population size, extent of occurrence, and area of occupancy. It depends on cool, flowing, well-oxygenated water, and it needs a coarse (rocky) substrate. It therefore faces significant threats from dams, sedimentation, and water pollution.

Alabama, Georgia, Indiana, Illinois, Kentucky, Maryland, Mississippi, Missouri, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia.

The range extends from southern Illinois (Brandon and Ballard 1994, Phillips et al. 1999), southern Indiana (Minton 1972), Ohio (Pfingsten and Downs 1989), Pennsylvania (McCoy 1982), and southern New York (Bishop 1941), Missouri, Mississippi, Alabama (Mount 1975), northern Georgia (Mitchell and Gibbons 2010), western Carolinas (Martof et al. 1980), western Virginia (Tobey 1985), West Virginia (Green and Pauley 1987), and Maryland (Phillips and Humphries 2005).

No estimates are available, but there are many occurrences in several dozen rivers, and genetic analyses suggest there is sub-drainage structuring to populations (Unger et al. 2013). The eastern hellbender is known from 183 8-digit hydrologic units.

The principal threat is degradation of habitat, including impoundments, channelization, ore and gravel mining, silt and nutrient runoff (e.g., from timber harvest, agriculture, faulty septic and sewage treatment systems), other water pollution, and den site disturbance due to recreational uses of rivers (Nickerson and Mays 1973, Mount 1975, Bury et al. 1980, Williams et al. 1981, Minton 2001, Mayasich et al. 2003). The subspecies depends on cool, flowing, well-oxygenated water, and it needs coarse (rocky) substrate. In agricultural regions, most of the former rocky habitat has been buried under silt (Phillips et al. 1999). Hellbenders appear to be intolerant of heavy recreational use of the habitat (Wheeler et al. 2003). In particular, temporary dam building or wading pool construction can cause direct mortality to adults and juveniles (Unger et al. 2017). Siltation, water chemistry, and water quality alterations impact the occurrence and prevalence of hellbenders (Keitzer et al. 2013, Bodinof Jachowski et al. 2016, Pitt et al. 2017).

Overexploitation (collection and illegal or unintentional harvest) may be a threat to declining populations, whose viability may be reduced by removal of relatively few adults.

Many populations have become reduced to the point at which the usual problems associated with small population size come into effect. Fragmentation of populations as a result of habitat loss/degradation is making it increasingly unlikely that extirpated populations can be reestablished through natural dispersal.

Some recent studies found open sores, tumors, and missing limbs and eyes in hellbenders (see Wheeler et al. 2002). Approximately 68% of hellbenders in an Indiana study found evidence of abnormalities (missing digits, scars, open wounds, and abnormal or missing eyes) (Burgmeier et al. 2011). A hellbender that tested positive for amphibian chytrid fungus showed severe anemia and undetectable protein levels (hypoproteinemia) (Burgmeier et al. 2011).

An exceptionally large flood event may have contributed to the decline in the Spring River, Arkansas population (Trauth et al. 1992).