ABSTRACT Introduced salmonids can impact aquatic ecosystems through direct predation and indirect effects. We explored the effects of introduced Cutthroat Trout ( Onchoryncus clarki) on Boreal Toad ( Anaxyrus boreas boreas ) survival and habitat use during two aquatic life stages, the embryo and tadpole, at Boreal Toad breeding sites with and without Cutthroat Trout. We found no difference in embryo survival and higher tadpole survival at the site with Cutthroat Trout. Cutthroat Trout are unlikely to use the shallow areas where Boreal Toad eggs are deposited; however, during the tadpole stage, Cutthroat Trout and tadpoles overlap broadly in near-shore aquatic habitats. Frequency of tadpole habitat use is lower in Cutthroat Trout–used areas, but we observed no behavioral or temporal avoidance of Cutthroat Trout by tadpoles. Our results suggest that Cutthroat Trout do not have a negative effect on Boreal Toad embryo or tadpole survival in wild settings and that Cutthroat Trout presence does not preclude tadpoles from using habitats.

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 ( p̂ vis ≈ 0.80). Supplementing streamside surveys when toads are not detected with other survey methods (e.g., environmental DNA [ e DNA] samples) at suitable breeding locations can help confirm the species is absent, provided ≥10 e DNA samples are collected. Moreover, employing both visual surveys and e DNA 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.

We used an occupancy modeling framework to test the relative importance of upland habitat composition (proportion of different types of vegetation and development) and pond characteristics (water chemistry and vegetation) in determining the occurrence of two species of pond-breeding salamanders, the Marbled Salamander ( Ambystoma opacum ) and Mabee's Salamander ( Ambystoma mabeei ), in an urban nature reserve in southeastern Virginia, USA. Of 55 ponds surveyed in 2009, we found A. opacum larvae in 17 (30.9%) ponds and A. mabeei larvae in seven (12.7%) ponds. We found a strong positive relationship between A. opacum larval occupancy probability and pH; salamanders were more likely to occupy less acidic waters. Sampled ponds were highly acidic, with pH values ranging between 3.36 and 4.41, but A. opacum occupied only ponds with pH values >3.66. Ambystoma mabeei was more tolerant of the highly acidic conditions and was more likely to occupy larger ponds with fewer trees and scrubs. Landscape-level models were not well supported. Although pond acidification is generally dismissed as a cause of amphibian declines, our results suggest that pH can be an important, species-specific factor in determining occupancy of pond-breeding amphibians.