Species Description
Eastern Hellbenders are one of the largest salamanders in the world, with a maximum length of 74 centimeters, although more typically large adults measure 45 to 55 cm. Along with the Ozark Hellbender subspecies, they are the only remaining North American member of the family Cryptobranchidae, with the other two species occurring in China and Japan. The Cryptobranchid family is an ancient group of salamanders, with fossils from 40 million years ago that are very similar to Hellbenders we see today. So in this way, hellbenders can be considered “living fossils.”
The range of Eastern Hellbenders is centered on the Appalachian Mountains from southern New York to Georgia, as well as additional populations outside the Appalachians as far west as Missouri. The Ozark Hellbender is only found in a small area of Missouri and Arkansas.
Hellbenders are completely aquatic, with a flattened body and rudder-like tail that allows them to seek refuge under rocks and navigate efficiently in the fast-moving rivers and streams that they inhabit. Hellbenders take in 90 percent of their oxygen through their skin, and they have folds along the side of the body that allow them to take up oxygen more efficiently. Hellbenders produce skin secretions that give them a slimy appearance—while the secretions are distasteful, they are not poisonous (a common myth about hellbenders).
Taxonomy
Hellbenders are currently divided into two subspecies: the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) and the Ozark Hellbender (Cryptobranchus alleganiensis bishopi). The species was first described by Daudin in 1803. Cryptobranchus means “hidden gills”—in fact, adult Hellbenders completely lack gills. The species name alleganiensis refers to the Allegheny Mountain portion of the Appalachian chain, which is where the species was first discovered.
Habitat
Hellbenders are restricted to cold rivers and streams with adequate flow, high dissolved oxygen and low levels of sedimentation. They spend much of their time under large rocks that have spaces underneath for the animal to take refuge and to use as egg-laying sites. Individuals are rarely found in the open. Larvae tend to use smaller rocks and cobble on the margins and rivers, and they often hide in spaces within the stream bottom. The presence of surrounding forest is also very important for Hellbender populations, which is likely related to reduced soil erosion into streams in these areas.
Movement and Home Range
In general, Hellbenders do not move frequently and do not have large home ranges. Individuals can often be found under the same rock from year to year, and movements rarely range more than 100 to 200 meters along a stream, although in rare cases, individuals have been found to move more than a kilometer.
Diet
Like all salamanders, Hellbenders are carnivorous and are capable of eating a wide variety of prey. However, crayfish make up the vast majority of their diet, and it is likely that other prey items are only taken when crayfish availability is low. Many fishermen believe that Hellbenders are detrimental to sport-fish populations, which is untrue. Hellbenders rarely eat fish, and when they do, they are typically small fish like minnows and suckers. Hellbenders will scavenge, which is why they are sometimes caught by fishermen attempting to eat their bait. Finally, Hellbenders occasionally cannibalize on smaller individuals or eat other Hellbender eggs.
Reproduction
Hellbenders have external fertilization, which is very unusual in salamanders. Hellbenders lay their eggs under large rocks (known as nest rocks) that males prepare and control. The breeding season typically occurs in late summer or early fall, and during this time male Hellbenders are especially aggressive while fighting for control of nest rocks. Females will go under nest rocks to lay eggs, which are then fertilized by the attending male. The males fertilize eggs by releasing milt (which contains sperm) into the water and using their body to direct it towards the eggs. Once the female lays her eggs, she leaves the nest rock and the male remains to attend to the eggs. Multiple females will use the same nest rock, and there can be thousands of eggs at one nest rock. Eggs typically hatch in late fall. Hellbenders have a larval stage in which larvae have gills until age two, although individuals may not reach sexual maturity until eight years of age.
Conservation Concerns
Hellbenders are important both symbolically and ecologically. They are one of the last survivors of an ancient group of salamanders—the loss of this species would mean the loss of a genus and the only members of its family that occurs in North America. They are important predators of crayfish, and while detailed studies are lacking, they likely play a role in keeping crayfish populations in control in streams.
Hellbenders are declining throughout their range, which is believed to be due to a number of factors. The most important factor is probably increased silt and sediment in rivers due to increased soil erosion. Siltation leads to spaces being filled in on the stream bottoms, and therefore Hellbenders cannot go under rocks for refuge, nests get filled in and larvae lack spaces in the stream bottom that are critical for survival at that young age. Increased erosion also tends to lead to increase pollutants into rivers, which Hellbenders may absorb directly through their skin, and it reduces the dissolved oxygen in the water which is essential for them to breathe.
Dams and other alterations to rivers have also reduced habitat suitability for Hellbenders not only by creating barriers to movement, but more importantly, creating stretches of river that no longer have the flow necessary to maintain Hellbender populations. This eliminates habitat and isolates populations. Humans also exert some direct pressure on Hellbenders—for example, river recreation often leads to rocks that Hellbenders use being moved around, and humans will sometimes kill Hellbenders based on misconceptions and fear. Disease could also be a factor, although there is not yet direct evidence for this.
Many sites still have older adult Hellbenders but lack larvae or young individuals. Such patterns suggest that Hellbenders are most vulnerable at these early stages, and improving survival of young Hellbenders may be the most important conservation action. Hellbenders also probably have limited ability to respond or adapt to disturbance as they have very low levels of movement.