Determining Presence of Rare Amphibian Species: Testing and Combining Novel Survey Methods

Abstract

Abstract. Data deficiencies exist for ∼20–25% of amphibian and reptile species worldwide, typically excluding them from conservation consideration and funding opportunities. Current species status is often unknown at historic locations or previously unsurveyed areas. We present an iterative study to assess and optimize novel survey methods for a declining amphibian species (Boreal Toad, Anaxyrus boreas boreas) using a combination of methods. We found that if toads are present in a drainage, searching riparian areas multiple times during the active season is an efficient way of detecting the occurrence of previously unknown breeding populations. Once a breeding population has been located, traditional visual encounter surveys yield high probabilities of species detection for monitoring efforts (vis ≈ 0.80). Supplementing streamside surveys when toads are not detected with other survey methods (e.g., environmental DNA [eDNA] samples) at suitable breeding locations can help confirm the species is absent, provided ≥10 eDNA samples are collected. Moreover, employing both visual surveys and eDNA samples can simultaneously yield distributional information on amphibian species and target pathogens, if pathogen presence is evaluated for all captured amphibian species and environmental samples are tested for both amphibian and pathogen DNA. Our iterative process of designing, testing, optimizing, and combining sampling methods to determine current species distribution should serve as a model for other rare amphibian and reptile species and provide managers better information with which to plan mitigation and conservation efforts.