Decline of a giant salamander assessed with historical records, environmental DNA and multi‐scale habitat data

Abstract

Freshwater species are declining rapidly but more complete data are needed for determining the extent and cause(s) of population declines and extirpations. Integrating newer survey techniques, freely available data, and traditional field work may allow for more effective assessment of population decline. We used detailed historical species records and environmental DNA (eDNA) survey methods to identify changes in population distribution of a long‐lived, imperiled stream salamander, the eastern hellbender (Cryptobranchus alleganiensis alleganiensis: Cryptobranchidae). We used logistic regression with Bayesian inference to test whether selected environmental variables may be good predictors of hellbender population persistence and extirpation. Hellbenders persisted in only 42% of the 24 historical record sites. The best fit model indicated electrical conductivity (EC) was the strongest predictor of hellbender population persistence (EC < 278 μS/cm) and extirpation. Conductivity was strongly negatively correlated with canopy cover within the total watershed (r = −0.83, n = 21, p < 0.001) and riparian buffer of the watershed (r = −0.77, n = 21, p < 0.001). Electrical conductivity tends to increase following deforestation, and may inhibit sperm motility and thus limit recruitment of hellbenders and other aquatic vertebrate species with external fertilisation. By integrating historical data, eDNA, field data, and freely available high resolution remote sensing data, our study design allowed for rapid assessment of predictors of and changes in hellbender distribution over a relatively broad geographic area. This cost‐ and time‐effective approach may be used for evaluating other rare aquatic species.

Using environmental DNA and occupancy modelling to identify drivers of eastern hellbender (Cryptobranchus alleganiensis alleganiensis) extirpation

“…Variable flow conditions of lotic systems have been shown to influence environmental DNA detection probabilities (Jane et al., ). Further, hellbenders have been negatively associated with high conductivity, which could impede reproduction (Pitt et al., ). We collected water quality data using a Hanna Instruments HI98196 Multiparameter probe (Hanna Instruments, Woonsocket, RI).…”

“…Specifically, we used eDNA to examine current hellbender occupancy at locations that historically supported hellbender populations. We used a single species, single season SODM framework with catchment and riparian‐scale predictors of occupancy that included hydrogeomorphic, current land cover, and historical mining data to determine possible drivers of extirpation (Pitt et al., ; Wenger, Peterson, Freeman, Freeman, & Homans, ). We assumed that populations were extirpated when the species no longer occupied a historical site.…”

Assessing the effect of landscape features on pond colonisation by an elusive amphibian invader using environmental DNA

“…The spatial distribution of habitat patches and the features of the matrix determine the colonisation probability at the site scale (Hanski & Ovaskainen, 2003;Ray, Lehmann, & Joly, 2002;Rudnick et al, 2012), and connectivity at the landscape scale. The lack of eDNA-based studies that aimed to identify landscape predictors of population occupancy and colonisation is surprising, considering the potential insight into freshwater ecosystems this approach can provide (Pitt et al, 2017). Because of their capacity to detect species at low densities (Dejean et al, 2012), eDNA surveys are of high interest to investigate site occupancy, especially for taxa in which overland movements are difficult to investigate.…”

“…While fish presence and pond hydroperiod play a role in predicting site occupancy of other species of amphibians(Amburgey, Bailey, Murphy, Muths, & Funk, 2014;Fuller, Pope, Ashton, & Welsh, 2011;Pitt et al, 2017), their effects on X. laevis presence in a pond are yet to be tested. Conversely, smaller agricultural ponds are widespread across the TWI range and often lack fishes.…”

Spatial Convergence in Major Dissolved Ion Concentrations and Implications of Headwater Mining for Downstream Water Quality

“…Further, stream conductivity can remain elevated for decades following fill construction (Merricks et al 2007). Mayflies (Ephemeroptera) have proven particularly sensitive (Pond 2010;Johnson et al 2015) to elevated TDS, and evidence indicates that stream salamanders may also be impacted (Muncy et al 2014), including potentially threatened eastern hellbenders (Cryptobranchus alleganiensis alleganiensis; Pitt et al 2017). Mayflies (Ephemeroptera) have proven particularly sensitive (Pond 2010;Johnson et al 2015) to elevated TDS, and evidence indicates that stream salamanders may also be impacted (Muncy et al 2014), including potentially threatened eastern hellbenders (Cryptobranchus alleganiensis alleganiensis; Pitt et al 2017).…”