Amphibians of North Carolina

Scientific Name:	Common Name:		Family (Alpha):

NC Records
Sole representative of Cryptobranchidae in NC
Cryptobranchus alleganiensis - Hellbender

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Taxonomy

Class: Amphibia

Order: Caudata

Family: Cryptobranchidae


Taxonomic Comments: The Hellbender (Cryptobranchus alleganiensis) is an unmistakable giant salamander that inhabits cool, rocky streams in the eastern US. Taxonomists have traditionally recognized two subspecies that are best identified by geographic range and color patterns. The Eastern Hellbender (C. a. alleganiensis) occurs in central and southwestern Missouri, and from southern New York southwestward to northern Alabama and extreme northeastern Mississippi. Adults of this subspecies typically have small black spots on the dorsum and a uniformly colored chin; however, adults in southern populations are sometimes blotched (Petranka 1998). The Ozark hellbender (C. a. bishopi) occurs in southeastern Missouri and adjoining portions of Arkansas. The adults are smaller on average and have large blotches on the dorsum and a chin that is heavily mottled with dark pigmentation. Several studies have documented genetic variation in this species and have generated results that are somewhat discordant. Earlier studies using allozymes (e.g., Merkle et al. 1977) revealed remarkably little variation in protein variation throughout the range, with most alleles being fixed. Studies with mitochondrial markers (Routman et al. 1994, Sabatino and Routman 2009) found low variation within major stream drainages, but significant variation between drainages. These authors recognized eight major populations across the range of the species. Tonione et al. (2011) found similar patterns across major stream basins using both mtDNA and nuclear microsatellite data. The mitochondrial data from these studies suggest that Cryptobranchus underwent a dramatic Pleistocene range contraction to a southern refugium that was followed by a more recent range expansion. Crowhurst et al. (2011) examined genetic variation in hellbenders in Missouri using rapidly evolving microsatellite markers and found substantial differentiation among local populations of both C. a. bishopi and C. a. alleganiensis. This mostly reflected variation across major drainage basins. Three major clusters were identified that represented C. a. alleganiensis and two clusters within C. a. bishop. The two C. a. bishop clusters were as different from each other as they were when paired with C. a. alleganiensis from central Missouri. Unger et al. (2013) conducted a similar survey of genetic variation across the range of the eastern subspecies using microsatellite markers. They found two major genetic groups that consisted of one associated with the northern Ohio River drainage, and a second associated with the Tennessee River drainage to the south. A more detailed analysis of the southern group (Freake et al. 2018) revealed four strongly supported clusters which correspond to specific watersheds. Populations from western North Carolina are members of two of these groups; one in the French Broad River and a second in the Hiwassee/Little Tennessee/Little River drainage. Applegate et al. (2018) only recognized four major evolutionary lineages in the eastern subspecies. These include groups in the Ohio River drainage, the Kanawha River drainage, the Tennessee River drainage, and the Missouri River drainage. North Carolina populations are members of two of these groups. Despite significant genetic substructuring within Cryptobranchus -- and evidence that C. a. bishopi and C. a. alleganiensis are paraphyletic (Crowhurst et al. 2011, Sabatino and Routman 2009) -- taxonomists continue to recognize these subspecies. Since they are allopatric they are best recognized by range.
Species Comments:

Identification

Description: Cryptobranchus alleganiensis is a large, slimy, aquatic salamander that reaches 30-74 cm TL. The body and head are strongly flattened dorso-ventrally and the eyes are small and lidless. The skin is noticeably wrinkled, and a fleshy fold of skin occurs along each side of the body. The tail is laterally flattened and shorter than the remainder of the body. The dorsal ground color varies from greenish to yellowish brown or slate gray and is overlain with varying amounts of black spotting or blotching (Petranka 1998). Albinos and morphs with orangish ground colors have occasionally been found. Adult males develop swollen cloacal glands during the breeding season, and on average are about the same length as the females. The larvae undergo partial metamorphosis so that the adults have a single pair of circular gill openings. These are sometimes missing on one or both sides of the head (Petranka 1998).

The hatchlings are uniformly dark above and vary from 25-33 mm TL. They have conspicuous yolk sacs, small but well-developed gills, and lack functional limbs at hatching. One-month old larvae are uniformly dark above with white venters, while 6-month old larvae have large dark spots and slightly pigmented venters (Petranka 1998). The dorsal spots and blotches are most prominent in larvae 1-2 years old and in young adults (Bishop 1941).

Online Photos: Google iNaturalist

AmphibiaWeb Account

Distribution in North Carolina

Distribution Comments: Cryptobranchus alleganiensis is found east of the Mississippi River from southern New York southwestward through the Appalachian region to northern Georgia, Alabama and extreme northeastern Mississippi, and westward to Tennessee, Kentucky, and southern Illinois. Two disjuncts occur west of the Mississippi River in Missouri and northern Arkansas. Populations in North Carolina are found in medium to larger streams and rivers at lower elevations in the mountains.
Distribution Reference: Beane et al. 2010
County Map: Clicking on a county returns the records for the species in that county.


GBIF Global Distribution

Key Habitat Requirements

Habitat: Hellbenders inhabit large, rocky, fast-flowing streams that are well oxygenated. They are generally found at elevations below 762 m (2500’) and are most commonly found beneath large rocks or rocky shelves in or near shallow rapids (Hillis and Bellis 1971, Nickerson and Mays 1973a). Suitable rocky habitats are often patchily distributed along stream stretches and may be interspersed with large reaches of unsuitable habitat that lack the adults and larvae. Crayfishes and small fishes are important prey, and streams with healthy prey populations, minimal sediment input, and numerous large, unembedded rocks provide ideal conditions. Rossell et al. (2013) examined the characteristics of shelters that were used by 41 hellbenders in western North Carolina. All of the animals were found beneath large rocks that typically had flat bottoms, deep cavities, and sand and gravel substrates. The shelter rocks were significantly larger than nearby rocks that were not used.

The larvae have been found under large rocks and boulders that are frequented by the adults, but also beneath small stones in gravel beds, in cobble, and in interstitial spaces in gravel beds (Applegate et al. 2018, Nickerson and Krysko 2003, Nickerson and Mays 1973a, Petranka 1998). Unger et al. (2020a) found that larvae prefer loose cobble relative to gravel, and that larvae have a difficult time burrowing into cobble that is embedded in sediment.

Environmental and Physiological Tolerances: Hellbenders primarily obtain oxygen through their skin and will engage in rocking behavior when oxygen-stressed (Harlan and Wilkinson 1981). Rocking the body back and forth helps to distribute oxygenated water across the skin surface. Local populations appear to be restricted to cool, well-oxygenated streams due to physiological limitations associated with cutaneous respiration.

Biotic Relationships: The natural predators of hellbenders are poorly documented. The adults produce very slimy skin secretions that are noxious to some predators, and their large size limits losses from gape-limited predators. Nonetheless, this species is occasionally preyed upon by large fish, turtles, and watersnakes (Petranka 1998). The eggs and larvae are frequently eaten by conspecifics, and hatchlings and small larvae undoubtedly are taken by many aquatic predators.

See also Habitat Account for Montane Rocky Rivers

Life History and Autecology

Breeding and Courtship: The breeding season in most local populations last for 3-4 weeks and varies among populations depending on the location and local site conditions. Breeding can occur anytime between mid-August and mid-November, but most populations appear to breed from mid-August through mid-September, including those in North Carolina (Petranka 1998, Unger et al. 2020b). Peterson et al. 1989a documented an exceptional population in the Spring River of Arkansas that breeds primarily in January when populations throughout the remainder of the range have ceased breeding. Sex ratios in most Ozark populations are usually close to 1:1 (Nickerson and Mays 1973a, Peterson 1987), but males frequently outnumber females in eastern populations (e.g., Hillis and Bellis 1971, Pfingsten 1990).

Unlike most salamanders, Cryptobranchus has external fertilization. The males produce a milky seminal fluid rather than spermatophores and deposit the seminal fluid directly on the eggs as they are being laid. Both sexes tend to become restless shortly before mating. They frequently move about the stream bed during the day and prod with their noses beneath crevices under rocks in search of mates (Petranka 1998). In some instances as many as 6-12 adults may congregate on the stream bottom.

Shortly before mating each male moves to a brooding site. This is usually an excavated depression beneath a large rock, log, or plank, with the entrance positioned on the downstream side of the depression (Bishop 1941, Nickerson and Mays 1973a, Petranka 1998). Males remain posed with their heads emerging from entrances in wait of females. As a gravid female approaches an entrance, the male often guides or drives her into his burrow, and becomes attracted to the female soon after eggs begin to emerge from her cloaca (Smith 1907). As eggs are laid by the female, they are sprayed with seminal fluid that is often produced in stringy cords. During this process the male sways his body laterally and lowers and raises his hind limbs, which helps to disperse sperm over the eggs (Petranka 1998).

Reproductive Mode: Females lay their eggs in beaded strings in depressions within the males' burrows (Nickerson and Mays 1973a, Smith 1907). The freshly-laid ova are pale to light yellow, 5-7 mm in diameter, and are surrounded by two gelatinous envelopes. Freshly laid eggs with the surrounding envelopes are 18-20 mm in diameter and are separated from adjoining eggs by short cords that are 5-10 mm in length (Petranka 1998).

Both males and females often prey upon their own eggs and those of others. Smith (1907) collected a female that regurgitated 80 eggs soon after capture while three others contained 10, 22, and 23 eggs in their stomachs. Most hellbenders examined during the breeding season contained between 15-25 eggs in their stomachs. Males in other populations frequently regurgitate eggs, and females sometimes eat their own eggs while ovipositing them (Petranka 1998). Unger and Williams (2017) verified through DNA analyses that guarding males will eat eggs that they fertilized.

Females leave the nesting sites soon after laying their eggs, and the males remain behind to aerate the eggs and guard them from marauding conspecifics and predatory fishes. Unger et al. (2020b) used underwater camaras to study the behavior of guarding males at several sites in western North Carolina. Males spent the majority of time actively guarding the shelter entrance. They defended their eggs with a variety of agonistic behaviors towards conspecifics that included defensive posturing, biting, and prolonged bite-holds. Nonetheless, both males and females often intruded and entered guarded burrows.

The number of eggs in nests is often much lower than the number of enlarged ovarian eggs. This likely reflects both egg predation by conspecifics and the fact that females often do not lay their entire ovarian complement. Egg counts for nests with eggs from a single female vary from 138-334, but communal nests have been found with nearly 2,000 eggs (Petranka 1998). The number of enlarged ovarian eggs in Missouri females varied from about 150-750 and averaged between 400-500 (Topping and Ingersol 1981). However, females appeared to only lay about 75% of these and reabsorbed the remainder after the breeding season. The mean number and range of mature ova in females examined by Peterson et al. (1988) from four rivers in Arkansas and Missouri were 365 (215-452), 429 (95-481), 450 (159-687), and 480 (296-908). The number of ova was positively correlated with TL and age in all four of these populations.

The incubation period is 68-75 days in Pennsylvania and New York populations and about 45 days in a Missouri population, with hatching typically occurring in November (Petranka 1998).

Aquatic Life History: Hatchlings have conspicuous yolk sacs and presumably rely on yolk as an energy source for the first few months after hatching (Petranka 1998). Hatchlings in New York grow 35-40 mm during their first year of life and reach 68-70 mm TL when 1-year old (Bishop 1941). The larvae partially transform and lose their external gills after reaching 100-130 mm TL and 1.5-2 years of age (Bishop 1941, Nickerson and Mays 1973a, Smith 1907, 1912).

Many populations that are in decline in the eastern US have disproportionately few larvae and young juveniles. Unfortunately, we know relatively little about the ecology of the early life-history stages. Nickerson and Mays (1973a) found that larvae and small transformed individuals use small stones in chert-gravel beds and suspected that hatchlings and very small larvae use interstitial areas in gravel. Smith (1912) found larvae under small stones in shallow water. The diet is poorly documented for the larvae. Larvae that Hetch et al. (2017) examined from Tennessee consumed mayflies, caddisflies, stoneflies and other aquatic insects, as well as crayfishes and a Eurycea larva. Unger et al. (2020c) used DNA barcoding to determine dietary items of specimens from two western North Carolina streams and found that the larvae feed heavily on mayflies. Other prey included stoneflies, a chiromonid larva and an earthworm.

Individuals mature sexually when 5-8 years old, and males normally mature at a smaller size and a younger age than the females (Petranka 1998). Females in most Missouri populations mature sexually when 37-39 cm TL and after 6-8 years post-hatching. The males mature when about 30 cm TL and after 5-6 years of growth. Males and females in western Pennsylvania become sexually mature when 33 and 35 cm TL (Petranka 1998). Individuals can live for 25-30 years or more and growth rates decline steadily with age after metamorphosis. Animals at 18 months grow about 60-70 mm TL per year while those approaching 25-30 years of age grow only 1 mm per year (Peterson et al. 1983, 1988, Taber et al. 1975).

The adults remain beneath rocks or other cover during the day and are mostly active outside of cover at night. They tend to be more diurnally active during the breeding season and on very overcast days. The adults show a preference for large, flat rocks for cover, but occasionally use rock shelves or submerged logs. Although adults sometimes move long distance, most remain within a restricted home range (Peterson 1987, Petranka 1998). Hillis and Bellis (1971) found that marked animals rarely move > 10-20 m from their point of release. The median size of the home ranges in their study was about 113 m2. Nonbrooding adults will defend rocks from conspecifics and rarely share home rocks with other individuals (Hillis and Bellis 1971, Nickerson and Mays 1973a). Nickerson and Mays (1973b) estimated that the North Fork of the White River in Missouri supported an estimated 428 mature hellbenders/km of stream and a biomass of 156 kg/km of stream. Peterson et al. (1988) estimated densities of 1-6 hellbenders/100 m2 of stream in four populations in Arkansas and Missouri.

Although insects and other invertebrates such as worms and mollusks have been documented in the diets of the adults, crayfishes and small fish are the dietary staples. Crayfishes appear to be particularly important (Petranka 1998). Other miscellaneous prey include salamanders, anurans, aquatic reptiles, and even a small mammal (Green 1935, Nickerson and Mays 1973a).

General Ecology

Population Ecology: Factors that regulate local populations are poorly understood, but competition for large rocks that are used for cover and brooding may set an upper limit on population size. Unger et al. (2013) conducted a survey of genetic variation across the range of the eastern subspecies and found that populations in different reaches of the same stream often showed significant genetic differences and exhibited genetic isolation by stream distance. This likely reflects the fact that suitable rocky habitats are patchily distributed in streams and that individuals do not disperse long distances within streams. Most genetic variation that was observed across the range of the species (>93%) reflected within stream variation of this sort, with only a small percentage due to higher hierarchical levels.

Community Ecology: Although the natural history of Cryptobranchus is well documented, the ecological interactions of Cryptobranchus with other community members and its functional role in communities are poorly understood. This species appetite for crayfishes suggests that it may play an important role in regulating crayfish populations in some streams.

Adverse Environmental Impacts

Habitat Loss: Cryptobranchus requires fast-flowing water to survive. The construction of dams and large reservoirs has eliminated many miles of suitable habitat and caused populations to become fragmented and isolated.

Status in North Carolina

NHP State Rank: S3

Global Rank: G3

Status in North Carolina: SC

Global Status: PS,E,UR

Populations: Resurveys of historical collection sites indicate that Cryptobranchus has undergone extensive declines in many areas of its range. For example, Graham et al. (2011) surveyed 45 sites in 29 streams in northern Alabama and were unable to find a single hellbender, while Wineland et al. (2018) estimated that about 38% of known populations in West Virginia have been extirpated. In addition to being lost, many extant populations have undergone dramatic demographic shifts to older individuals with little recruitment of juveniles into the populations. Applegate et al. (2018) reported that -- of 570 populations have been documented throughout the range -- around 40% have been extirpated. Of the remaining extant populations, an estimated 37% are healthy and the remainder are in decline. Applegate et al. (2018) predicted that these trends will continue and many more populations will be lost in the future. Western North Carolina is one of the few regions in the eastern US where populations appear to be mostly healthy and not in precipitous decline. The status of these populations could change as the region undergoes rapid urbanization in the future.

Environmental Threats: Numerous factors have been implicated in the loss and decline of populations, including river impoundment, stream sedimentation and pollution, persecution from anglers, illegal collecting, and disease (see a comprehensive review by Applegate et al. 2018). Of these, excessive sedimentation associated with agriculture, silviculture, and urbanization appear to be the most important factor. Excessive sedimentation can suffocate eggs, destroy or degrade habitat for larval and juvenile hellbenders, bury shelter and nest rocks for adults, and depress the numbers of invertebrates and crayfishes that are used as food resources. Nutrient and organic enrichment from livestock, waste water treatment plants, agricultural fields, and urban run-off can enhance algae growth and reduce oxygen levels in streams. Other losses have come from anglers who kill them after being caught on hook and line, and the illegal pet trade. Climate change that results in stream warming and extreme droughts may ultimately eliminate many populations.

Photo Gallery for Cryptobranchus alleganiensis - Hellbender		8 photos are shown.
	Recorded by: D. Rodgers, A. Fraley, S. Fraley, TR Russ, A. Leslie, J. Shimel, P. Bailey, D. Blatny, A. Dillard, J Alleghany Co.	Recorded by: Todd Pierson Transylvania Co. Comment: An orangish morph from Transylvania County.
	Recorded by: E. Corey, J. Humphries, J. Wilson, and P. Bailey Ashe Co.	Recorded by: Kelly McCoy Ashe Co. Comment: A unusual orangish morph that is occasionally seen in North Carolina population.
	Recorded by: Gabrielle Graeter, Mountain Wildlife Diversity BiologistNC Wildlife Resources Commission172 Dave Ashe Co. Comment: A large male that was moving about during the day.	Recorded by: E. Corey, NERI staff, Davidson College personnel Ashe Co.
	Recorded by: S. Lambiase,B. Strong Ashe Co.	Recorded by: P. Bailey, S. Lambiase, B. Strong, D. Alleghany Co.

Cryptobranchus alleganiensis - Hellbender

Photo Gallery for Cryptobranchus alleganiensis - Hellbender

8 photos are shown.