Fig 1.
(A) Range map of hellbenders. Light blue shaded area indicates the distribution of hellbenders Cryptobranchus alleganiensis, used with permission from the IUCN Red List [38]. The Tennessee border is indicated in red, and the Hiwassee study site location is shown by a dark blue filled circle. (B) Hiwassee river with the study area highlighted in red. Shaded green area corresponds to National Forest public lands. Detailed location information is withheld to limit the risk of disturbance or illegal collection (see Ethics and Permits below).
Fig 2.
Size frequency distribution of eastern hellbenders (n = 466) averaged over annual surveys conducted 2004–2008, Hiwassee River, Tennessee.
Fig 3.
Shelter rock use by eastern hellbenders in the Hiwassee River, Tennessee, 2004–2008.
(A) Regression analysis indicates a significant relationship (p < 0.001) between hellbender total length and maximum horizontal dimension of shelter rock (n = 147). (B) Box plots illustrating shelter rock size used by larvae (n = 35), subadults (n = 31) and adults (n = 81). Box boundaries indicate interquartile ranges, heavy line within box indicates the median, whiskers indicate 1.5x interquartile range and solid black dots indicate outliers. The mean is illustrated with white diamonds, and arrows between boxes illustrate pairwise comparisons using Tukey’s honest significant difference test.
Table 1.
Capture-recapture matrix for Hiwassee hellbenders caught and released within the focal site core area, Hiwassee River, Tennessee, 2004–2008.
Table 2.
POPAN parameterization of Jolly-Seber model rankings, Hiwassee River, Tennessee, 2004–2008.
Parameters are survival (φ), capture (p) and entry (b) probabilities. The parameters may be time dependent (t) or constant (.). Only the four best supported models are shown.
Table 3.
Population parameter estimates and 95% confidence intervals derived from POPAN Jolly-Seber model-averaged estimates.
Parameter estimates include apparent survival, capture probability, superpopulation size, net abundance, and entry probability. Hiwassee River, Tennessee, 2004–2008.
Fig 4.
Map of public lands overlaying contemporary and historic eastern hellbender populations in Tennessee.
Shaded areas show National Park (dark green), National Forest (mid green), and State Wildlife Management Areas (light green). Purple squares indicate locations for which there are historic (1915–2000) eastern hellbender occurrences, but no contemporary (post 2000) sightings. Orange and red lines indicate the extent of contemporary eastern hellbender populations based on verified captures from 2001 to 2015. In the red populations, a range of age classes including larvae, juveniles and adults have been observed during this period, while in orange populations only adults have been documented.
Table 4.
Comparison of studies estimating eastern hellbender population densities or relative abundances, organized by date of publication.
Densities are expressed as number of hellbenders per 100 m2 of river. Relative abundance is given by catch per unit effort (CPU), which is the number of hellbenders caught per person hour searching. Adapted with permission from Burgmeier et al. [21].