Survival and Body Condition of Captive-Reared Juvenile Ozark Hellbenders (Cryptobranchus alleganiensis bishopi) Following Translocation to the Wild
We used radiotelemetry and recapture to monitor survival and body condition of 36 captive-reared Ozark Hellbenders (Cryptobranchus alleganiensis bishopi) released at two sites on the North Fork of the White River, Missouri, from May 2008 to August 2009. At the end of our study 16 salamanders were alive, 13 had died, and the fate of seven could not be determined. Captive-reared hellbenders released at a site with densely arranged boulders exhibited approximately 1.5-fold higher annual survival (0.7467; daily survival = 0.9992 ± 0.0004 95% CI) than hellbenders released at a site where boulders were patchily distributed (0.4816; daily survival = 0.9980 ± 0.0007 95% CI). When compared to log-transformed length–mass relationships developed for wild hellbenders from the same river in the 1970s, mean body condition of hellbenders at the patchy boulder site was about average at the end of the study (mean residual distance = −0.0273 ± 0.0234 SE, n = 7; range = −0.1375–0.0486), while mean body condition of hellbenders at the dense boulder site was above average (mean residual distance = 0.0423 ± 0.0402 SE; n = 8; range = −0.0374–0.1088). In addition to lower survivorship and body condition, a greater proportion of hellbenders at the patchy site accrued physical abnormalities (6 of 13 vs. 2 of 14), carried leech parasites (9 of 16 vs. 4 of 14), and carried the fungus Batrachochytrium dendrobatidis (3 of 11 vs. 1 of 13). A ‘site only’ model of survival was most supported, though additional supported models suggested increased mass at release may have increased daily survivorship. While more work is needed to determine the impact of translocation on long-term population dynamics of Ozark Hellbenders, our study demonstrated that about half of a translocated population of captive-reared hellbenders can survive while maintaining or increasing in body condition during their first year post-release, given release sites are well selected.
Survival rate over one year for captive-reared Ozark Hellbenders (Cryptobranchus alleganiensis bishopi) translocated to the upper (A) and lower (B) sites on the North Fork of the White River, Missouri, USA, 2008–2009. The solid line represents the survival estimate and the dashed lines represent the 95% confidence intervals.
Daily survival (survival from one day to the next) of captive-reared Ozark Hellbenders (Cryptobranchus alleganiensis bishopi) translocated to the upper (A) and lower (B) sites on the North Fork of the White River, Missouri, USA, 2008–2009, based on days from the time of surgery to release. The solid line represents the predicted survival estimate and the dashed lines represent the 95% confidence intervals.
Daily survival (survival from one day to the next) of captive-reared Ozark Hellbenders (Cryptobranchus alleganiensis bishopi) translocated to the upper (A) and lower (B) sites on the North Fork of the White River, Missouri, USA, 2008–2009, based on mass (g) at time of release. The solid line represents the predicted survival estimate and the dashed lines represent the 95% confidence intervals.
Comparison between length–mass associations for captive-reared Ozark Hellbenders (Cryptobranchus alleganiensis bishopi) translocated to the upper (white circles) and lower (dark circles) sites on the North Fork of the White River, Missouri, USA, 2008–2009, and historic length–mass associations (regression lines) developed separately for male (M), female (F), and pooled gender (U) wild Ozark Hellbenders from the same river in the late 1970s. Regression lines represent log-transformed length–mass relationships developed by Peterson et al. (1983). Residuals around the line in ‘pre-release’ plots represent all 36 captive-reared hellbenders released, and in the ‘end of study’ plots represent the seven upper and eight lower site hellbenders recaptured at the end of the study.
The number of captive-reared Ozark Hellbenders (Cryptobranchus alleganiensis bishopi) predicted to be surviving in years post-release, based on estimates of daily survival for hellbenders released at 125 g (short dash), 225 g (long dash), and 325 g (solid line). Daily survival estimates are based on the ‘site × mass’ model of daily survival developed for captive-reared Ozark Hellbenders released at the lower site on the North Fork of the White River, Missouri, 2008–2009.
Contributor Notes
Associate Editor: M. J. Lannoo.