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

Abstract

Population declines and local extirpation trends are widespread among freshwater species, but the responsible drivers of these trends are poorly understood. Identifying the potential drivers of population declines is essential to effective conservation planning. However, conventional detection methods used to monitor cryptic and elusive freshwater species are inefficient. Integrating new surveying and modelling techniques may allow for a more comprehensive assessment of population declines. We used environmental DNA (eDNA) sampling methods and detailed historical records to identify drivers of local extirpation in a declining, long‐lived giant salamander, the eastern hellbender (Cryptobranchus alleganiensis alleganiensis) in West Virginia, U.S.A. We used a site occupancy and detection modelling framework (SODM) to test the influence of current land use, historical mining, hydrogeomorphic and water quality variables on model‐based predictions of hellbender extirpation and detection. We failed to detect hellbender eDNA at 51% (naïve 1 – Ψ) of historical sites, suggesting local extirpation at a broad spatial scale in West Virginia. Our best‐supported SODM model suggested catchment‐scale road density was the best predictor of hellbender extirpation, and that 38% (predicted 1 – Ψ) of historical sites may be locally extirpated. Estimates of hellbender occupancy probability were extremely low in highly developed catchments. Water turbidity and conductivity were the best predictors of eDNA detection, both negatively influencing detection probability. Roads can increase sedimentation rates and alter water chemistry of freshwater ecosystems, identifying landscape alteration/human development and water quality declines as possible drivers of hellbender extirpation trends in West Virginia. Our findings also suggest that water conductivity and turbidity may act as polymerase chain reaction inhibitors and decrease eDNA detection in lotic systems. This study emphasises the negative impacts of urban development on freshwater ecosystems and the sensitivity of long‐lived amphibian species to rapid environmental change. Our findings may aid in conservation planning by providing a sampling framework that integrates eDNA data within a SODM framework to rapidly and accurately assesses relational changes in aquatic species' occupancy at historical sites.

Environmental DNA improves Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) detection over conventional sampling methods

“…This study was also part of a larger study examining hellbender occupancy across West Virginia using eDNA (Wineland et al, 2019). We selected random sites by generating random points every 2 km on stream line features and performed a selection by location in ArcMap 10.4 (ESRI, Redlands, CA) based on proximity to access via trails or roads.…”

“…Therefore, field samples that had a minimum of two-third qPCR replicates amplify with concentrations above 0.08 ng/µl were used as an indicator of hellbender presence (Wineland et al, 2019). We determined that the deionized tap water was contaminated at the source by filtering three samples of it in a separate laboratory using all single-use equipment, along with three samples of nuclease-free water for comparison.…”

“…To account for any possible false presences in this study, we considered that contaminated negative field controls from all three sampling periods had only one-third qPCR replicates amplify, and all DNA concentration values were below 0.08 ng/µl. Therefore, field samples that had a minimum of two-third qPCR replicates amplify with concentrations above 0.08 ng/µl were used as an indicator of hellbender presence (Wineland et al, 2019).…”

“…Range-wide population declines and range constrictions have been reported (Briggler et al, 2007;Foster, McMillan, & Roblee, 2009;Gates, Hocutt, Stauffer, & Taylor, 1985;Graham et al, 2011;Keitzer, Pauley, & Burcher, 2013;Pfingsten, 1990;Pitt et al, 2017;Quinn, Gibbs, Hall, & Petokas, 2013;Wheeler, Prosen, Mathis, & Wilkinson, 2003;Wineland et al, 2019) resulting in mounting conservation concern for the species. For example, The U.S.…”

“…Conventional hellbender sampling methods suffer from low detection rates due to the logistical constraints of physically searching under large rock cover in swiftly-flowing streams, often by lifting the rocks and disturbing habitat structure. Recent studies have successfully employed eDNA methods to detect hellbender presence using this noninvasive method (Pitt et al, 2017;Spear et al, 2015;Wineland et al, 2019). However, studies that aim to monitor population demography often use conventional sampling methods, which can result in nest and/or shelter abandonment (Nickerson & Krysko, 2003;Olson, Briggler, & Williams, 2012;Pugh, Hutchins, Madritch, Siefferman, & Gangloff, 2016).…”