# Evaluating the Use of Environmental DNA as a Method to Determine Occupancy and Distribution of Coeur d'Alene Salamanders in Montana

## TL;DR

This study evaluates using environmental DNA (eDNA) to detect Coeur d'Alene salamanders in Montana, finding it effective when paired with specific sampling conditions.

## Contribution

The study introduces a species-specific eDNA assay and recommends a protocol for detecting Coeur d'Alene salamanders with high accuracy.

## Key findings

- eDNA sampling is viable for detecting Coeur d'Alene salamanders under specific conditions like nighttime and low water flow.
- Five 5-L water samples are needed to achieve a detection rate above 79%.
- Combining eDNA with visual searches is recommended due to the high cost of eDNA analysis.

## Abstract

Coeur d'Alene salamanders (
Plethodon idahoensis
) are found in small, isolated populations in the mountains of Montana, Idaho, and British Columbia. Effective conservation of this species hinges upon understanding population distribution and connectivity; however, identifying occupied Coeur d'Alene salamander (CDL) sites is challenging. Surveys in Montana have been haphazard and have involved biologists searching potential sites during rainy nights in the early summer. To evaluate alternative survey methods, we sampled water at known‐occupied CDL sites across western Montana to evaluate the efficacy and applicability of using environmental DNA (eDNA) to detect CDLs, as well as covariates that impacted CDL detection. We first developed a species‐specific eDNA Taqman quantitative PCR assay. We then used repeated eDNA sampling to evaluate how different environmental covariates would impact detection probability of CDLs and used these results to recommend a survey protocol. We found that optimal eDNA sampling conditions for CDLs occurred at night, within 50 m of the downstream extent of preferred salamander habitat, and at lower water flow rates. Under these conditions, five 5‐L water samples were required to achieve a detection rate above 79%. The results of this study revealed that eDNA analysis is a viable method to estimate CDL occupancy at potential sites across their range; however, eDNA analysis can be costly, so combining this method with visual searches is advised.

The purpose of this project was to evaluate the efficacy of eDNA sampling to determine occupancy of Coeur d'Alene salamanders, an “imperiled” species in Montana. Previous methods used to identify occupied sites were haphazard with no measure of detection probability. Due to the unique habitat used by these salamanders (seeps and waterfall spray zones), it was unclear if eDNA sampling would be an effective tool. Our work suggests that indeed eDNA sampling is viable for determining occupancy, and we propose a protocol that may be employed to achieve a high rate of detection.