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Hellbender Salamander - Cryptobranchus alleganiensis
Topic Started: Sep 10 2012, 02:56 AM (4,791 Views)
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Hellbender Salamander - Cryptobranchus alleganiensis

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Conservation status: Near threatened

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Amphibia
Subclass: Lissamphibia
Order: Caudata
Family: Cryptobranchidae
Genus: Cryptobranchus
Species: C. alleganiensis Daudin, 1803

The hellbender (Cryptobranchus alleganiensis), also known as the hellbender salamander, is a species of giant salamander that is endemic to eastern North America. A member of the Cryptobranchidae family, hellbenders are the only members of the Cryptobranchus genus, and are joined only by one other genus of salamanders (Andrias, which contains the Japanese and Chinese giant salamanders) at the family level. Hellbenders are ecologically significant for many reasons, including their uniqueness. These salamanders are much larger than any others in their endemic range, they employ an “unusual” means of respiration (which involves cutaneous gas exchange through capillaries found in their dorsoventral folds), and they fill a particular niche—both as a predator and prey—in their ecosystem which either they or their ancestors have occupied for around 65 million years.

Etymology
The origin of the name "hellbender" is unclear. The Missouri Department of Conservation says:
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The name 'hellbender' probably comes from the animal’s odd look. Perhaps it was named by settlers who thought "it was a creature from hell where it’s bent on returning". Another rendition says the undulating skin of a hellbender reminded observers of 'horrible tortures of the infernal regions'. In reality, it’s a harmless aquatic salamander.

Vernacular names include "snot otter", "devil dog", "mud-devil", "grampus", "Allegheny alligator", "mud dog", and "leverian water newt". The genus name is derived from the Ancient Greek, kryptos (hidden) and branchos (gill); a reference to oxygen absorption primarily through gills that are in a covered chamber and not lungs.

Diagnosis
The hellbender has a few characteristics that make it distinguishable from other native salamanders—these include a gigantic, dorsoventrally flattened body with thick folds travelling down the sides, a single open gill slit on each side, and hind feet that have five toes each. Easily distinguished from most other endemic salamander species simply by their size—hellbenders average up to sixty centimeters or about two feet in length—the only species that requires further distinction (due to an overlap in distribution and size range) is the mudpuppy (Necturus maculosus). This demarcation can be made by noting the presence of external gills in the mudpuppy, which are lacking in the hellbender, as well as by noting the presence of four toes on each hind foot of the mudpuppy (in contrast with the hellbender’s five). Furthermore, the average size of C. a. alleganiensis has been reported to be 45-60 cm (with some being reported as reaching up to 74 cm --30"), while N. m. maculosus has a reported average size of 28-40 cm in length, which means that hellbender adults will still generally be notably larger than even the biggest mudpuppies.

Taxonomy and physical description
The genus Cryptobranchus has historically only been considered to contain one species, Cryptobranchus alleganiensis, with two subspecies, Cryptobranchus alleganiensis alleganiensis and Cryptobranchus alleganiensis bishopi. Recent decline in population size of the Ozark subspecies Cryptobranchus alleganiensis bishopi has led to further research into populations of this subspecies, including genetic analysis to determine the best route for conservation status. Crowhurst et al., for instance, found that the “Ozark subspecies” denomination is insufficient for describing genetic (and therefore evolutionary) divergence within the Cryptobranchus genus in the Ozark region. The researchers found three equally divergent genetic units within the genus: Cryptobranchus alleganiensis alleganiensis, and two distinct eastern and western populations of Cryptobranchus alleganiensis bishopi. These three groups were shown to be isolated and are considered to most likely be “diverging on different evolutionary paths".

Both males and females grow to an adult length of 24 centimetres (9.4 in) to 40 centimetres (16 in) from snout to vent, with a total length of 30 centimetres (12 in) to 74 centimetres (29 in) making it the third largest aquatic salamander species in the world (next to the Chinese giant salamander and the Japanese giant salamander) and the largest in North America. An adult weighs 1.5 kilograms (3.3 lb) to 2.5 kilograms (5.5 lb). Hellbenders reach sexual maturity at about five years of age, and may live thirty years in captivity.

C. alleganiensis have flat bodies and heads, with beady dorsal eyes and slimy skin. Like most salamanders, they have short legs with four toes on the front legs and five on their back appendages, and their tails are keeled to propel them through water. The hellbender has working lungs, but gill slits are often retained although only immature specimens have true gills; the hellbender absorbs oxygen from the water through capillaries of its side-frills. They are blotchy brown or red-brown in color, with a paler underbelly.
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Distribution
Hellbender species are present in a number of eastern states that stretch “from southern New York to northern Georgia,” including parts of Ohio, Pennsylvania, Maryland, West Virginia, Virginia, Kentucky, Illinois, Indiana, Tennessee, North Carolina, South Carolina, Alabama, Mississippi, Arkansas, Missouri, and even a small bit of Oklahoma and Kansas. The subspecies (or species, depending on the source) Cryptobranchus alleganiensis bishopi is confined to the Ozarks of northern Arkansas and southern Missouri while Cryptobranchus alleganiensis alleganiensis is found in the rest of the aforementioned states.

Some hellbender populations—namely a few in Missouri, Pennsylvania, and Tennessee—have historically been noted to be quite abundant, but several anthropogenic maladies have converged on the species such that it has seen serious population decline throughout its range. Hellbender populations were listed in 1981 as already extinct or endangered in Illinois, Indiana, Iowa, and Maryland, decreasing in Arkansas and Kentucky, and were noted as being generally threatened as a species throughout their range by various human activities and developments.

Ecology
The hellbender salamander is considered to be a “habitat specialist”—in other words, it has adapted to fill a specific niche within a very specific environment. It is labeled as such “because its success is dependent on a constancy of dissolved oxygen, temperature and flow found in swift water areas,” which in turn limits it to a narrow spectrum of stream/river choices. As a result of this specialism, hellbenders are generally found in areas with large, irregularly shaped and intermittent rocks and swiftly moving water, and tend to avoid wider, slow moving waters with muddy banks and/or slab rock bottoms. This specialism likely aided the decline in hellbender populations, as collecting was made easier by being able to easily spot their specific habitat selection. One collector noted that before in the ecosystems natural condition, “one could find a specimen under almost every suitable rock,” but that after years of collecting, the population had declined significantly. The same collector noted that he “never found two specimens under the same rock,” corroborating the account given by other researchers that hellbenders are generally solitary—they are only thought to gather during the mating season.

Both species, C. a. alleganiensis and C. a. bishopi undergo a metamorphosis after around a year and a half of life. It is at this point—when they are roughly 13.5 centimeters in length—that they lose the gills that were present during their larval stage, and develop toes from lobes on their front limbs and “paddle-shaped” hind limbs. Until this point, they are easily confused with mudpuppies, and can be differentiated often only through toe number. After this metamorphosis, hellbenders have to be able to absorb oxygen through the folds in their skin, which is largely behind the need for fast moving, oxygenated water. If a hellbender ends up in an area of slowly moving water, not enough water will pass over its skin in a given time period, making it difficult to garner enough oxygen to support necessary respiratory functions. Likewise, a below favorable oxygen content can make life just as difficult. Hellbenders are preyed upon by multiple different predators, including various fish and reptiles (including both snakes and turtles). Cannibalism of eggs is also considered to be a common occurrence.

Life History and Behavior
Behavior
Once a hellbender finds a favorable location, it generally does not stray too far from it—except occasionally for breeding and hunting—and will protect it from other hellbenders both in and out of the breeding season. While the range of two hellbenders may overlap, they are noted as rarely being present in the overlapping area when the other salamander is in the area. The same researchers claim the species is at least somewhat nocturnal, with peak activity being reported by one source as occurring around “two hours after dark” and again at dawn (although the dawn peak was recorded in the lab and could be misleading as a result). Nocturnal activity has been found by at least one set of researchers to be most prevalent in early summer, perhaps coinciding with highest water depths.

Diet
Studies have been performed in which hellbenders were captured, transported back to the lab, and then dissected to determine dietary habits. Stomach pumping of living specimens has also been performed to determine diet. These studies demonstrated quite clearly that C. alleganiensis feeds primarily on crayfish and small fish. One report, written by a commercial collector in the 1940s, noted a trend of more crayfish predation in the summer during times of higher prey activity, whereas fish made up a larger part of the winter diet while crayfish are less active. There seems to be a specific temperature range in which hellbenders feed, as well: between 45 and 80°F. Several researcher note that cannibalism—mainly on eggs—has been known to occur within hellbender populations, and one researcher claims that perhaps density is maintained—and density dependence in turn created—in part by intraspecific predation.

Reproduction
The hellbenders' breeding season begins in late August or early- to mid-September and can continue as late as the end of November, depending on region. They exhibit no sexual dimorphism, except during the fall mating season, when males have a bulging ring around the cloaca glands. Unlike most salamanders, the hellbender performs external fertilization. Before mating, each male excavates a brood site, a saucer-shaped depression under a rock or log with its entrance positioned out of the direct current, usually pointing downstream. The male remains in the brood site awaiting a female. When a female approaches, the male guides or drives her into his burrow and prevents her from leaving until she oviposits.

Female hellbenders lay 150-200 eggs over a two- to three-day period; the eggs are 18–20 mm in diameter, connected by 5–10 mm cords. As the female lays eggs, the male positions himself alongside or slightly above them, spraying the eggs with seminal fluid while swaying his tail and moving his hind limbs, which disperses the sperm uniformly. The male often tempts other females to lay eggs in his nest, and as many as 1,946 eggs have been counted in a single nest. Cannibalism, however, leads to a much lower number of eggs in hellbender nests than would be predicted by ovarian counts.

After oviposition, the male drives the female away from the nest and guards the eggs. Incubating males rock back and forth and undulate their lateral skin folds, which circulates the water, increasing oxygen supply to both eggs and adult. Incubation lasts from 45–75 days, depending on region. Hatchling hellbenders are 25 millimetres (0.98 in) to 33 millimetres (1.3 in) long, have a yolk sac as a source of energy for the first few months of life, and lack functional limbs.

Adaptations
Hellbenders are superbly adapted to the shallow, fast-flowing, rocky streams in which they live. Their flattened shape offers little resistance to the flowing water, allowing them to work their way upstream and also to crawl into narrow spaces under rocks. Although their eyesight is relatively poor, they have light-sensitive cells all over their bodies. Those on their tail are especially finely tuned and may help them position safely under rocks without their tail poking out to give the game away. They have a good sense of smell and will move upstream in search of food such as dead fish, following the trail of scent molecules. Smell is possibly their most important sense when hunting. They also have a lateral line similar to that of fish, with which they can detect vibrations in the water.
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Conservation status
Research throughout the range of the hellbender has shown a dramatic decline in population abundance in the majority of locations. Many different anthropogenic sources have helped to create this decline, including the siltation and sedimentation, blocking of dispersal/migration routes, and destruction of riverine habitats created by dams and other development, as well as pollution, disease and overharvesting for commercial and scientific purposes. As many of these detrimental effects have done irreversible damage to hellbender populations, it is important to conserve the remaining intact populations through protecting habitats and—perhaps in places where the species was once endemic and has been extirpated—by augmenting numbers through reintroduction. Due to sharp decreases that have been seen in the Ozark subspecies, researchers have been looking at trying to differentiate C. a. alleganiensis and C. a. bishopi into two management units. Indeed, researchers found significant genetic divergence between the two groups, as well as between them and another isolated population of C. a. alleganiensis. This could be reason enough to ensure work is done on both denominations, as preserving extant genetic diversity is of crucial Ecological importance.

The Ozark hellbender has been listed as an endangered species under the Endangered Species Act by the U.S. Fish and Wildlife Service on Oct. 5, 2011. This hellbender subspecies inhabits the White River and Spring River systems in southern Missouri and northern Arkansas, and its population has declined an estimated 75% since the 1980s, with only about 590 individuals remaining in the wild. Degraded water quality, habitat loss resulting from impoundments, ore and gravel mining, sedimentation, and collection for the pet trade are thought to be the main factors resulting in the amphibian's decline.

The Ozark hellbender was successfully bred in captivity for the first time at the St. Louis Zoo, in a joint project with the Missouri Department of Conservation, hatching on Nov. 15, 2011. The decade-long collaboration has yielded 63 larvae.

Fossil record
Extant species in the Cryptobranchidae family are the modern-day members of a lineage that extends back millions of years—the earliest fossil records of a basal species date back to the Middle Jurassic and were found in volcanic deposits in northern China. (This reported estimated Middle Jurassic age for the fossils has been reputed and defended multiple times, and the debate is still not fully settled). These specimens are the earliest known relatives of modern salamanders, and together with the numerous other basal groups of salamanders found in the Asian fossil record, they form a concrete base of evidence for the fact that “the early diversification of salamanders was well underway” in Asia during the Jurassic period. Interestingly, little has changed in the morphology of the Cryptobranchidae since the time of these fossils, leaving researchers to note “extant cryptobranchid salamanders can be regarded as living fossils whose structures have remained little changed for over 160 million years.”

As the fossil record for the Cryptobranchidae shows an Asian origin for the family, the story of how these salamanders made it to the eastern U.S. has been a point of scientific interest. Research has led to a dispersal via land bridge-based theory, and scientists have gone on to note the waves of adaptive radiation that seem to have swept the Americas from north to south.
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Edited by Taipan, Sep 16 2012, 02:39 PM.
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U.S. Giant Salamanders Slipping Away: Inside the Fight to Save the Hellbender
Two-foot-long amphibian declining due to unhealthy streams, disease.


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A scientist displays a hellbender in Pennsylvania's Casselman River in an undated photo.

Jane J. Lee
National Geographic
PUBLISHED DECEMBER 19, 2013

Snot otters. Lasagna lizards. Allegheny alligators. With nicknames like these, you'd think the actual animal, a salamander more commonly known as a hellbender, would be a natural poster child for endangered wildlife.

Instead, hellbenders live quiet lives tucked away under large rocks in the mountain streams of eastern North America, from Arkansas to New York. Ranging in color from mottled olive-gray to chocolate brown with rust-colored splotches, the nocturnal amphibians can easily be mistaken for rocks, if they're seen at all.

But that rarity is what concerns researchers. There are two varieties or subspecies of hellbenders—the Ozark hellbender (Cryptobranchus alleganiensis bishop) and the eastern hellbender (Cryptobranchus alleganiensis alleganiensis)—and both have been quietly slipping away since about the 1980s.

The U.S. government currently considers the eastern hellbender a species of concern, while the Ozark subspecies was federally listed as endangered in 2011. The International Union for Conservation of Nature's Red List of Threatened Species classifies the hellbender as near threatened, although their total number is unknown.

In New York State, researchers began to see small declines in their eastern hellbender population starting in the 1980s, said Ken Roblee, senior wildlife biologist with the New York Department of Environmental Conservation.

But it wasn't until a 2005 survey that scientists saw a 40 percent reduction in the number of adults at monitoring sites, perhaps due to predation or disease—researchers are still trying to figure out the causes. "That got us really concerned," Roblee said.

Declining populations have prompted conservation efforts in New York, as well as in states across the hellbender range, including Ohio and Missouri.

These programs aim to study the biology of North America's largest salamander—which can reach a length of 2 feet (0.6 meter)—as well as to try and reintroduce the animals to the wild.

Murky Future

Salamanders are vulnerable for a few reasons. First, "they are really closely tied to their environment," said Kim Terrell, a conservation biologist with the Smithsonian's National Zoo in Washington, D.C., who studies hellbender immune systems.

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"Unlike a lot of other salamanders, [hellbenders] breathe entirely through their skin," she explained. That means the fully aquatic amphibians need clean, cold, oxygen-rich freshwater to live.

Because of that, hellbenders thrive only in areas with good water quality, Terrell said.

"Imagine if you're in a river, and you're dragging your lungs around behind you—things are not going to go well if that river is polluted or muddy or murky," the conservation biologist explained.

And declining hellbender numbers are mirroring the declining health of their habitats. (Read about vanishing amphibians in National Geographic magazine.)

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Map of the eastern half of the United States showing the range of the hellbender salamander.

Changing land use, such as an increase in agriculture, is causing greater loads of dirt and sediment to pile up in streams throughout the hellbenders' range, reducing water quality. What's more, many of these streams also contain harmful toxins and chemicals. Both developments are driving this unassuming amphibian into the ground.

Mysterious Disease

Unknown diseases may also be afflicting hellbenders, and researchers are ramping up monitoring efforts to try to understand why the animals are getting hit with chronic skin conditions. For example, several biologists are swabbing hellbenders and cataloguing any potential disease-causing organisms they find.

"We know that hellbenders are really sensitive to disease," Terrell said. "And we find animals that have evidence of skin disease quite often in the wild. But we don't know what's causing it."

One particularly nasty infection can cause some hellbenders to lose one or more of their feet. "Something is eating that foot tissue, and you'll find animals with exposed bone, missing feet," explained Terrell. "That's pretty serious for a group of animals that tend to have incredible healing abilities."

Experts thought at first that the chytrid fungus—responsible for demolishing frog populations around the world—was causing the hellbender skin disease.

The fungus is found in hellbender habitats, and on the animals themselves, said Thomas Floyd, a wildlife biologist with the Georgia Department of Natural Resources.

Previous research has found that chytrid can also hide out in crayfish—hellbenders' favorite food—showing that the fungus can persist in other species before it jumps to an amphibian.

But based on skin swabs from hellbenders, "there's no indication it's a problem yet," Floyd said.

Healthy Hellbenders

Floyd and his colleagues are working hard to ensure their hellbender populations remain safe.

The state has perhaps some of the healthiest populations of hellbenders in the country, Floyd explained, and they regularly monitor the wild animals to make sure they stay that way.

That often involves donning a mask and snorkel and rooting under rocks in water as chilly as 60°F (16°C) to look for the animals.

"[In Georgia], if you look at areas where they're doing really well, they're on public land," which tends to have more intact forests, he explained. "There's a direct correlation between forest cover and habitat quality."

That's because forests are natural barriers against erosion, preventing sediments from washing into mountain streams and clogging up the waterways.

Hellbenders in the Empire State

Unfortunately, hellbenders in New York aren't doing as well.

"We have them in only two watersheds in New York State—the Allegheny River watershed and the Susquehanna watershed," said New York State's Roblee.

"The hellbenders in Susquehanna have nearly disappeared, and we don't know the reasons for the decline," he said. Researchers have seen only two hellbenders in this watershed over the past three years.

A team of biologists and students tried searching for the wrinkly creatures again this year, with no luck. "The situation there is quite dire," said Roblee.

The wildlife biologist and his colleagues are instead concentrating their efforts on the Allegheny, "where the hellbenders are doing better, thankfully," Roblee said.

Population numbers in the Allegheny River seem to have stabilized in the past two years: Surveys in 2012 found between 60 and 100 hellbenders at various monitoring sites, and those numbers seem to be holding.

Luckily, "no severe health problem has shown up," he added.

Even so, the Allegheny populations have declined 40 percent since the 1980s.

The problem could be due to the fact that not enough young hellbenders are making it to adulthood, Roblee said. "Many of the monitored sites only had large adults."

So the biologist and his colleagues decided to give young hellbenders a leg up.

A Head Start

By hatching and raising hellbenders in captivity, Roblee and colleagues hoped to give the amphibians a refuge to grow to a size—around 9 inches (23 centimeters)—that makes them less vulnerable to predators.

Once the animals get big enough, they're released back into streams in the Alleghenies.

A 2009 grant from the U.S. Fish and Wildlife Service enabled Roblee and colleagues at the Buffalo Zoo in New York to collect 744 eggs from a hellbender nest in the wild.

The team successfully hatched 610 of the eggs, but soon realized they needed help raising all those animals. Luckily the Bronx Zoo; the Seneca Park Zoo in Rochester, New York; and the Seneca Nation of Indians expressed interest in taking some of the amphibians in, and each soon had their own colonies of young hellbenders.

The first release of hellbenders occurred in 2011, when 46 young salamanders bearing tiny radio-tracking tags were released into streams in the Alleghenies. The scientists released another hundred tagged animals in 2012.

But the results have been mixed. When researchers went back to check on the tagged amphibians released in 2011, only 4 percent of the animals remained where scientists had released them. Of the 2012 reintroduction, only 8 percent were found in the original area.

Roblee explained that they've observed some of the hellbenders moving farther downstream, up to about 3,000 feet (900 meters) away.

This wanderlust may be a problem, because when young hellbenders travel, they're leaving the protection of their rocks and exposing themselves to predators.

So this year, when the biologists released another 250 young hellbenders, they tried enclosing the amphibians' rocks in vinyl wire cages to keep the animals from wandering too far from safety. But the salamanders escaped.

Several of the 2013 animals ended up dead—suggesting predators including raccoons, mink, and otter are eating them.

But the researchers aren't giving up yet: They have 150 hellbenders left in captivity, which are slated for release in 2014. "We're modifying the cage design to keep [the hellbenders] securely inside to reduce the predation we're seeing," Roblee said.

The hope is that the cages will keep the salamanders in place long enough for them to become accustomed to their new homes—enough time so they won't feel the need to leave.

Salamander Saviors

Roblee has had a much easier time working with the landowners who live among hellbenders.

Initially, most weren't aware that they even had these giant salamanders on their property, he said. But once they learned about the animal and what researchers were doing, they were willing to work with the scientists.

One campground owner is even helping the Smithsonian's Terrell collect data on how changing temperatures affect hellbenders.

The volunteer kayaks out to collect temperature sensors scattered in the stream, sends the data to Terrell, and then returns the sensors to the river, said Roblee.

The fascination with the salamander and a willingness to work with conservation efforts is something Will Miller, chief conservation officer with Seneca Nation Fish and Wildlife, has noticed during his outreach efforts.

The Seneca Nation originally got interested in hellbenders because of a cultural connection, Miller said. Tribe historians say some of the Nation's stories are connected to the hellbender, he said.

In addition to monitoring the Seneca Nation's territory for hellbenders and raising 20 of the amphibians for the reintroduction program, Miller and his colleagues travel to hunting shows and local schools to help the public understand the salamander's situation.

Their efforts were rewarded this year when fishers sent Miller a cellphone picture of a hellbender they had accidentally caught but then released once they realized what it was.

New York State's Roblee hopes to capitalize on that appreciation to save the amphibian from extinction.

"As a society, as we move forward in time, we'd like to take the hellbenders with us," he said, "and not be responsible for their demise."

http://news.nationalgeographic.com/news/2013/12/131220-hellbender-salamander-conservation-endangered-animals-science/
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