Concurrent visual encounter sampling validates eDNA selectivity and sensitivity for the endangered wood turtle...

Area of Science:

• Ecology
• Conservation Biology
• Molecular Ecology

Background:

• Environmental DNA (eDNA) is a powerful tool for detecting species, especially cryptic or declining ones like the wood turtle.
• Traditional survey methods for wood turtles are limited by imperfect detection rates, necessitating novel monitoring approaches.
• Wood turtles are a declining semi-aquatic chelonian species requiring effective distribution and abundance monitoring.

Purpose of the Study:

• To assess the efficacy of eDNA for detecting the presence of wood turtles in northern Virginia streams.
• To validate eDNA results against visual encounter surveys (VES) using an occupancy-modelling framework.
• To investigate factors influencing eDNA detection probability for wood turtles in aquatic environments.

Main Methods:

• Conducted eDNA sampling and repeat visual encounter surveys (VES) across 37 stream reaches in northern Virginia.
• Employed occupancy modelling to compare detection and occupancy probabilities between eDNA and VES.
• Analyzed environmental variables (e.g., rainfall, temperature, discharge) associated with eDNA detection.

Main Results:

• Wood turtle occupancy probability was comparable between eDNA (0.55) and VES (0.54).
• eDNA detected wood turtles at 76% of VES-confirmed sites and three additional known-occurrence sites.
• Higher eDNA detection was linked to greater turtle density, recent rainfall, lower temperatures, and lower discharge.

Conclusions:

• eDNA sampling is a promising method for monitoring aquatic chelonians, including the wood turtle, in various stream conditions.
• Validation with traditional methods and quantification of sampling error are crucial for reliable eDNA-based monitoring.
• eDNA offers a viable alternative or complement to VES for assessing wood turtle distribution and potentially abundance.