Effort, in person-hours, was recorded as in and in Mark-recapture estimates of hellbender abundance ranging from 0. Peterson captured adults in a m2 study site in the Niangua River in Missouri during Humphries conducted a mark-recapture study from —'99 in the West Fork of the Greenbrier River in West Virginia. An abundance estimate of 31 individuals was found within a m stretch of stream.
The density in this section was 0. Four streams in the White River drainage of Missouri were surveyed in Ziehmer, Numbers encountered and effort were recorded as follows: This is the only evidence of decline in a hellbender population that has been documented rigorously in the literature.
- More Information.
- AmphibiaWeb - Cryptobranchus alleganiensis?
- 10 Slimy Facts About Hellbenders.
The suggestion by Alexander that male hellbenders move many km to reach their breeding grounds in the fall has not been supported by recent research. Most authorities agree that no actual breeding migration takes place, although males may move short distances within their home ranges to brooding sites. The breeding season is variable but occurs mainly in September and October, although evidence of breeding activity as late as December and January has been reported for the Spring River in Arkansas Peterson et al. Only a few specific breeding dates are given in the literature.
Smith reported egg-laying dates from 28 August—8 September in six consecutive years starting in in northwestern Pennsylvania. Swanson stated that egg-laying takes place about the 1 September in Venango County, Pennsylvania. The release of milt from captured males and the presence of gravid females was documented between 7 September—11 October during two years of study in the Blue River of Indiana Kern, b. Dundee and Dundee noted a nest containing eggs in the Niangua River, Missouri, on 14 November, and Johnson noted a clump of eggs in the same river on 19 September. Green reported the spawning season of the hellbender in the vicinity of Elkins, West Virginia, to be from the middle of August to early September.
The beginning of the breeding season is marked by a change in behavior of hellbenders, especially males. They leave their routine hiding places and move around the stream bottom, even during daylight, exploring cavities under flat rocks and crevices or holes in the bedrock Smith, Eventually a male occupies a suitable site and may actively prepare a nest by moving gravel to create a saucer-shaped depression Bishop, b. Peterson also reported males using a hole in a mud-gravel bank for nesting.
The males lie at the opening of their nests, frequently with their heads exposed, waiting for gravid females. Females may enter nest sites voluntarily or they may be forced into the cavity by the male. As soon as the female starts to deposit eggs, the male moves alongside or slightly above the female and sprays the eggs with snowy-white seminal fluid that may take the form of a cloudy mass or ropy chunks Smith, Deposited eggs are often eaten by both males and females Smith, ; Bishop, b.
The eggs are yellow, round, approximately 6 mm in diameter, and surrounded by two transparent envelopes. The inner envelope is attached as a solid rope from egg to egg resulting in long egg strings Nickerson and Mays, a. The eggs swell with water and eventually increase to 18 mm in diameter Smith, a.
Males usually remain in the nest cavity with the eggs, and both Smith and Bishop b witnessed episodes of active nest guarding by males. Bishop b also observed a brooding male swaying from side to side over the eggs, which may increase the oxygen supply to the eggs. The duration of this brooding period varies, but Smith , a,b found males attending nests that contained embryos about 3 wk old. Bishop b estimated the incubation period at 68—84 d for western New York and Pennsylvania. Peterson encountered hatchlings in the Niangua River, Missouri, that he believed to be no more than 45 d old.
Temperature undoubtedly plays a major role in determining length of embryonic period. Smith provides the most comprehensive data on embryonic development and should be consulted for details. Newly hatched larvae are approximately 30 mm TL and are well pigmented dorsally and on the tail.
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The venter is unpigmented except for the yellow of the yolk sac. The mouth and eyes are conspicuous, the gills are short and flattened, the front limbs terminate in two lobes, and the hindlimbs are paddle-shaped and unlobed Bishop, b. Development is rapid, and hatchlings double their size during the first year Bishop, b. Larvae normally lose their external gills in the second summer after hatching, at — mm TL Smith, ; Bishop, b; Nickerson and Mays, a. The diet of larval hellbenders has not been studied but probably includes invertebrates.
Nickerson and Mays a reported that larval hellbenders utilize small stones and chert for cover. They also reported an anecdotal account of a larval hellbender taken from the interstices of a gravel bed in an area of subsurface percolation. The scarcity of records for larval hellbenders compared to adults supports this suggestion Kern, c; Petranka, The major morphological features of hellbender metamorphosis are the loss of the external gills and the attainment of adult color pattern. Adult hellbenders are found in fast-flowing streams containing abundant cover in the form of large flat rocks, bedrock shelves and crevices, and logs Bishop, b; Nickerson and Mays, a.
Hellbender - Wikipedia
Home range has been reported in various forms for several populations of hellbenders. Using minimum area convex polygon in Missouri, average home range size was 28 m2 for females and 81 m2 for males Peterson and Wilkinson, Coatney calculated an elliptical home range of 90 m2 for seven Ozark hellbenders radio-tracked nocturnally for 2 wk. In Pennsylvania, average inter-captured distance was The mean activity radius for this population was Calculated as a circular home range, the average home range was Linear distance between captures in Tennessee ranged from 5—60 m Casey et al.
Topping and Peterson provided evidence for size-specific movement in hellbenders in Missouri. They demonstrated a tendency for upstream movements ranging from 2. In contrast, Peterson detected no net movement upstream or downstream in the Niangua River, Missouri. Mean linear movement of hellbenders in a West Virginia stream was Home ranges of hellbenders overlap Peterson and Wilkinson, , but they apparently avoid being in the area of overlap at the same time Coatney, However, hellbenders have been observed in close proximity to each other at night without conflict between individuals Humphries, Hellbenders will utilize rocks recently vacated by other individuals Hillis and Bellis, ; Peterson and Wilkinson, ; Humphries, Male hellbenders become extremely territorial during the breeding season and will defend nest holes or rocks Smith, ; Bishop, b; Peterson, Blais reported that during the breeding season in New York, male hellbender's home ranges tended to overlap more than those of females.
Not reported; however, Green stated that hellbenders in West Virginia moved to deeper holes in summer to find colder water. See "Breeding migrations" above. Like most salamanders, it has short legs with four toes on the front legs and five on its back limbs, and its tail is keeled for propulsion.
What the Heck Is a Hellbender—And How Can We Make More of Them?
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. Hellbenders reach sexual maturity at about five years of age, and may live 30 years in captivity. The hellbender has a few characteristics that make it distinguishable from other native salamanders, including a gigantic, dorsoventrally flattened body with thick folds travelling down the sides, a single open gill slit on each side, and hind feet with five toes each. The genus Cryptobranchus has historically only been considered to contain one species, C.
They found three equally divergent genetic units within the genus: These three groups were shown to be isolated, and are considered to most likely be "diverging on different evolutionary paths". The subspecies or species, depending on the source C. Some hellbender populations—namely a few in Missouri, Pennsylvania, and Tennessee—have historically been noted to be quite abundant, but several man-made maladies have converged on the species such that it has seen a serious population decline throughout its range. Hellbender populations were listed in as already extinct or endangered in Illinois, Indiana, Iowa, and Maryland, decreasing in Arkansas and Kentucky, and generally threatened as a species throughout their range by various human activities and developments.
This specialization likely contributed to the decline in their populations, as collectors could easily identify their specific habitats. Until then, they are easily confused with mudpuppies, and can be differentiated often only through toe number. If a hellbender ends up in an area of slow-moving water, not enough of it will pass over its skin in a given time, making it difficult to garner enough oxygen to support necessary respiratory functions. A below-favorable oxygen content can make life equally difficult. Hellbenders are preyed upon by diverse predators, including various fish and reptiles including both snakes and turtles.
Cannibalism of eggs is also considered a common occurrence. 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. 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.
One report, written by a commercial collector in the s, 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, when crayfish are less active. There seems to be a specific temperature range in which hellbenders feed, as well: Cannibalism—mainly on eggs—has been known to occur within hellbender populations. One researcher claimed perhaps density is maintained, and density dependence in turn created, in part by intraspecific predation.
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 their cloacal 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. As the female lays eggs, the male positions himself alongside or slightly above them, spraying the eggs with sperm 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, [22] 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 egg 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 to 75 days, depending on region. 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 tails are especially finely tuned and may help them position safely under rocks without their tails poking out to give themselves away. They have a good sense of smell and 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 those of fish, with which they can detect vibrations in the water. Research throughout the range of the hellbender has shown a dramatic decline in populations in the majority of locations. Due to sharp decreases seen in the Ozark subspecies, researchers have been trying to differentiate C.
Indeed, researchers found significant genetic divergence between the two groups, as well as between them and another isolated population of C. This could be reason enough to ensure work is done on both subspecies, as preserving extant genetic diversity is of crucial ecological importance. 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.
Louis Zoo's captive hellbender population between March and April , tests began to be conducted on wild populations. The disease has been detected in all Missouri populations of the Ozark hellbender.