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Population Genetics of the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) across Multiple Spatial Scales
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Conservation genetics is a powerful tool to assess the population structure of species and provides a framework for informing management of freshwater ecosystems. As lotic habitats become fragmented, the need to assess gene flow for species of conservation management becomes a priority. The eastern hellbender (Cryptobranchus alleganiensis alleganiensis) is a large, fully aquatic paedamorphic salamander. Many populations are experiencing declines throughout their geographic range, yet the genetic ramifications of these declines are currently unknown. To this end, we examined levels of genetic variation and genetic structure at both range-wide and drainage (hierarchical) scales. We collected 1,203 individuals from 77 rivers throughout nine states from June 2007 to August 2011. Levels of genetic diversity were relatively high among all sampling locations. We detected significant genetic structure across populations (Fst values ranged from 0.001 between rivers within a single watershed to 0.218 between states). We identified two genetically differentiated groups at the range-wide scale: 1) the Ohio River drainage and 2) the Tennessee River drainage. An analysis of molecular variance (AMOVA) based on landscape-scale sampling of basins within the Tennessee River drainage revealed the majority of genetic variation (∼94–98%) occurs within rivers. Eastern hellbenders show a strong pattern of isolation by stream distance (IBSD) at the drainage level. Understanding levels of genetic variation and differentiation at multiple spatial and biological scales will enable natural resource managers to make more informed decisions and plan effective conservation strategies for cryptic, lotic species.
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Importance of demographic surveys and public lands for the conservation of eastern hellbenders Cryptobranchus alleganiensis alleganiensis in southeast USA
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Comparisons of recent and historic population demographic studies of eastern hellbenders Cryptobranchus alleganiensis alleganiensis have identified significant population declines and extirpations associated with habitat degradation, poor water quality and disease, leading to nomination as a candidate for listing under the Endangered Species Act. However, populations in the southern Appalachian region of the range have received less attention despite relatively high levels of watershed protection due to the establishment of federally protected National Forest and National Park public lands. These watersheds likely represent some of the best remaining available habitat, yet the lack of published studies make assessment of population stability and viability very difficult. Our objectives were to (1) conduct a capture-mark-recapture (CMR) demographic study and a point transect survey on the Hiwassee River in Tennessee which is designated a National Scenic River, and is largely contained within the Cherokee National Forest, (2) quantify the size structure of the population, (3) compare abundance, survival and recruitment with historic and contemporary hellbender populations across the range, (4) assess the importance of this population and the significance of National Forest and National Park lands in the context of hellbender population conservation in the southeastern United States. We detected all age classes present, with larval hellbenders comprising 21.5% of captures. Using a combination of static life table and CMR methods, we determined that survival rates during the first year were low (~10%), but were high (68–94%) for taggable sized hellbenders. Density of hellbenders at the study site was very high (84 taggable sized hellbenders per 100m of river) compared to recent demographic studies conducted in other regions of the range. We detected hellbenders over ~28 km of river, with a mean density of 23 taggable sized hellbenders per 100m of river, and a total population estimate of 6440 taggable hellbenders. National Forest and National Park lands are likely to continue to play a particularly important role in providing suitable habitat for hellbenders in the southern Appalachians. In fact, only six of 21 known hellbender locations in Tennessee appear to show consistent larval recruitment, all of which are located within or adjacent to National Forest or National Park land.
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Pathogenic Chytrid Fungus Batrachochytrium dendrobatidis, but Not B. salamandrivorans, Detected on Eastern Hellbenders
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Recent worldwide declines and extinctions of amphibian populations have been attributed to chytridiomycosis, a disease caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd). Until recently, Bd was thought to be the only Batrachochytrium species that infects amphibians; however a newly described species, Batrachochytrium salamandrivorans (Bs), is linked to die-offs in European fire salamanders (Salamandra salamandra). Little is known about the distribution, host range, or origin of Bs. In this study, we surveyed populations of an aquatic salamander that is declining in the United States, the eastern hellbender (Cryptobranchus alleganiensis alleganiensis), for the presence of Bs and Bd. Skin swabs were collected from a total of 91 individuals in New York, Pennsylvania, Ohio, and Virginia, and tested for both pathogens using duplex qPCR. Bs was not detected in any samples, suggesting it was not present in these hellbender populations (0% prevalence, 95% confidence intervals of 0.0–0.04). Bd was found on 22 hellbenders (24% prevalence, 95% confidence intervals of 0.16 ≤ 0.24 ≤ 0.34), representing all four states. All positive samples had low loads of Bd zoospores (12.7 ± 4.9 S.E.M. genome equivalents) compared to other Bd susceptible species. More research is needed to determine the impact of Batrachochytrium infection on hellbender fitness and population viability. In particular, understanding how hellbenders limit Bd infection intensity in an aquatic environment may yield important insights for amphibian conservation. This study is among the first to evaluate the distribution of Bs in the United States, and is consistent with another, which failed to detect Bs in the U.S. Knowledge about the distribution, host-range, and origin of Bs may help control the spread of this pathogen, especially to regions of high salamander diversity, such as the eastern United States.
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Movement and Habitat Use of Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) Following Population Augmentation
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With amphibian declines at crisis levels, translocations, including population augmentations, are commonly used for amphibian conservation. Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) have declined to low densities in many areas of their range, making them ideal candidates for population augmentation. Both wild adults and captive-reared juveniles have been used for augmentations, but their suitability has never been directly compared. Herein, we use radio telemetry with Eastern Hellbenders to examine patterns of site fidelity, movement, and habitat use over a 2-yr period for adult residents, wild adult translocates, and captive-reared juvenile translocates. We used generalized linear models and generalized linear mixed models to identify temporal trends and explore the effects of residential status (resident vs. translocate) and origin/age (captive-reared juveniles vs. wild adults) on various ecological and behavioral traits relating to habitat. Site fidelity was high in adult residents and wild adult translocates, but lower in captive-reared juvenile translocates. Both adult and juvenile translocates had greater mean movement distances than residents, leading to larger home range sizes, but these differences decreased over time. Wild adult translocates had a higher probability of using artificial nest rocks than adult residents or captive-reared juvenile translocates. This pattern was most prevalent early in the study, indicating these shelters are particularly useful during the transition to release sites. Captive-reared juvenile translocates had lower site fidelity and utilized suboptimal habitat (smaller and fewer shelter rocks) compared to wild adults. Compared to previous studies, translocations had fewer negative effects on site residents or wild translocates and might be effective at promoting growth of Hellbender populations. However, translocations of captive-reared juveniles were less successful. As we are uncertain whether captive-rearing or ontogeny led to these differences, both longer head-starting times and conditioning should be explored to improve outcomes in captive-reared juvenile cohorts.
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FOREST REMOVAL AND THE CASCADE OF EFFECTS CORRESPONDING WITH AN OZARK HELLBENDER POPULATION DECLINE
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Populations of the endangered Ozark Hellbender salamander (Cryptobranchus alleganiensis bishopi) in the North Fork of the White River (NFWR) in Missouri and other streams have declined precipitously in recent decades. Deforestation of the riparian and nearby upland habitat has corresponded with in-river habitat changes and other interacting stressors that coincide chronologically with the precipitous decline. We review the cascade of effects, including changes in water quality, benthic habitat, illegal and scientific harvesting, and introduced and reintroduced species occurrence that followed deforestation in the context of their impacts on hellbenders and relationship with other stressors such as climate change. In-river habitat changes since the 1960s include benthic microhabitat alterations associated with redistribution of gravel, siltation, and sedimentation and, in part, increases in nuisance vegetation, including periphyton. Deforestation of riparian and nearby upland habitats increased access and opportunities for human activities such as recreation, wildlife collection, and development. The subsequent degradation of stream habitat and water quality following deforestation reducedthe carrying capacity for the NFWR Ozark Hellbender population and had negative consequences on population health.
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Environmental DNA improves Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) detection over conventional sampling methods
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Effective conservation planning relies on accurate species detection. However, conventional sampling methods used for detecting rare and cryptic aquatic species suffer from low probabilities of detection. Environmental DNA (eDNA) has emerged as an innovative and powerful sampling tool for detecting aquatic species, with previous studies suggesting a detection advantage over conventional sampling. However, comparative studies often fail to consider the appropriate sampling frameworks to adequately compare sampling methodologies and account for the influence of environmental variables on eDNA detection probabilities. In this study, we paired two detection methods (eDNA and physical sampling) at 22 sites in West Virginia, USA, to compare the probability of detecting a cryptic, elusive, and imperiled species of giant salamander, the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis). We used a multimethod occupancy modeling framework to compare method‐specific detection probabilities using a suite of predictor variables based on environmental conditions thought to influence hellbender detection. We detected hellbenders at 19/22 sites using eDNA and at 13/22 sites using physical sampling methods. The best supported model indicated that detection probability for eDNA (0.84 ± 0.06) was three times higher than conventional methods (0.28 ± 0.07). Water turbidity was the best predictor of hellbender detection and negatively impacted our ability to detect eDNA. We failed to detect an association between eDNA concentration and hellbender catch per unit effort. Our study supports previous findings that suggest eDNA sampling methods greatly increase the probability of detecting aquatic species. However, with little known about the influence of environmental variables on eDNA detection, our results highlight the negative influence turbidity and other physiochemical factors have on eDNA detection and suggest that further research on eDNA detection in turbid environments is needed.
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Noninvasive Method for a Statewide Survey of Eastern Hellbenders Cryptobranchus alleganiensis Using Environmental DNA
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Traditional survey methods of aquatic organisms may be difficult, lengthy, and destructive to the habitat. Some methods are invasive and can be harmful to the target species. The use of environmental DNA (eDNA) has proven to be effective at detecting low population density aquatic macroorganisms. This study refined the technique to support statewide surveys. Hellbender presence was identified by using hellbender specific primers (cytochrome b gene) to detect eDNA in water samples collected at rivers, streams and creeks in Ohio and Kentucky with historical accounts of the imperiled eastern hellbender (Cryptobranchus a. alleganiensis). Two sampling protocols are described; both significantly reduced the amount of water required for collection from the previously described 6 L collection. Two-liter samples were adequate to detect hellbender presence in natural waterways where hellbenders have been previously surveyed in both Ohio and Kentucky—1 L samples were not reliable. DNA extracted from 3 L of water collected onto multiple filters (1 L/filter) could be combined and concentrated through ethanol precipitation, supporting amplification of hellbender DNA and dramatically reducing the filtration time. This method improves the efficiency and welfare implications of sampling methods for reclusive aquatic species of low population density for statewide surveys that involve collecting from multiple watersheds.
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Prevalence of Batrachochytrium dendrobatidis in Eastern Hellbender (Cryptobranchus alleganiensis) Populations in West Virginia, USA
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The eastern hellbender (Cryptobranchus alleganiensis alleganiensis) is a North American salamander species in decline throughout its range. Efforts to identify the causes of decline have included surveillance for the chytrid fungus Batrachochytrium dendrobatidis (Bd), which has been associated with global amphibian population losses. We evaluated the prevalence of Bd in 42 hellbenders at four sites in West Virginia, US, from June to September 2013, using standard swab protocols and real-time PCR. Overall prevalence of Bd was 52% (22/42; 37.7–66.6%; 95% confidence interval). Prevalence was highest in individuals with body weight ≥695 g (χ2=7.2487, df=1, P=0.007), and was higher in montane sampling sites than lowland sites (t=−2.4599, df=44, P=0.02). While increased prevalence in montane sampling sites was expected, increased prevalence in larger hellbenders was unexpected and hypothesized to be associated with greater surface area for infection or prolonged periods of exposure in older, larger hellbenders. Wild hellbenders have not been reported to display clinical disease associated with Bd; however, prevalence in the population is important information for evaluating reservoir status and risk to other species, and as a baseline for investigation in the face of an outbreak of clinical disease.
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Improving the Utility of Artificial Shelters for Monitoring Eastern Hellbender Salamanders (Cryptobranchus alleganienses alleganiensis)
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Artificial shelters show great promise as novel, non-invasive tools for studying
hellbenders, but their use thus far has faced several challenges. During initial trials in multiple
river networks, artificial shelters routinely became blocked by sediment and dislodged during
high stream discharge events, and were rarely used by hellbenders. We sought to determine
whether these complications could be overcome via alternative shelter design, placement, and
maintenance. Between 2013 and 2018, we deployed 438 artificial shelters of two different
designs across ten stream reaches and three rivers in the upper Tennessee River Basin. We
assessed evidence for several hypotheses, postulating broadly that the availability, stability, and
use of artificial shelters by hellbenders would depend on how shelters were constructed,
deployed, and/or maintained. We found that maintaining shelters at least once every 40 days
limited sediment blockage, and building ~ 40 kg shelters with 3-4 cm thick walls and recessed
lids improved their stability during high discharge events. Additionally, we found that
hellbenders most frequently occupied and nested in artificial shelters when they were deployed
in deeper (~50+ cm) portions of reaches with high adult hellbender densities. Our results suggest
that artificial shelters can serve as effective tools for studying hellbenders when designed,
deployed, and maintained with these advancements, but also highlight some limitations of their
use.
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Artificial Nest Box Research
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Evaluating artificial shelter arrays as a minimally invasive monitoring tool for the hellbender (Cryptobranchus alleganiensis)
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Hellbenders Cryptobranchus alleganiensis are critically imperiled amphibians throughout the eastern USA. Rock-lifting is widely used to monitor hellbenders but can severely disturb habitat. We asked whether artificial shelter occupancy (the proportion of occupied shelters in an array) would function as a proxy for hellbender abundance and there by serve as a viable alternative to rock-lifting. We hypothesized that shelter occupancy would vary spatially in response to hellbender density, natural shelter density, or both, and would vary temporally with hellbender
seasonal activity patterns and time since shelter deployment. We established shelter arrays (n = 30 shelters each) in 6 stream reaches and monitored them monthly for up to 2 yr. We used Bayesian mixed logistic regression and model ranking criteria to assess support for hypotheses concerning drivers of shelter occupancy. In all reaches, shelter occupancy was highest from June–August each year and was higher in Year 2 relative to Year 1. Our best-supported model indicated that the extent of boulder and bedrock (hereafter, natural shelter) in a reach mediated the relationship between hellbender abundance and shelter occupancy. More explicitly, shelter occupancy was positively correlated with abundance when natural shelter covered <20% of a reach, but uncorrelated with abundance when natural shelter was more abundant. While shelter occupancy should not be used to infer variation in hellbender relative abundance when substrate composition varies among reaches, we showed that artificial shelters can function as valuable monitoring tools when reaches meet certain criteria, though regular shelter maintenance is critical.
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Artificial Nest Box Research
