Oral Presentation Society for Freshwater Science 2026 Annual Meeting

Spatial and temporal variation in occupancy of stream-associated amphibians. (135751)

Tiffany Garcia 1 , Jake Verschuyl 2 , AJ Kroll 3
  1. Oregon State University, Corvallis, OR, United States
  2. National Council for Air and Stream Improvement, Anacortes, Washington
  3. Rocinante Consulting, Corvallis, Oregon

Forest management regulations often require riparian buffer protections, with buffer length and width generally determined by fish presence. New forest practices rules in Oregon add buffers to streams without fish and increase buffer width on larger fish-bearing streams. Several species predicted to benefit from these added habitat protections are headwater stream amphibians such as the Columbia torrent salamander (Rhyacotriton kezeri), southern torrent salamander (Rhyacotriton variegatus); coastal giant salamander (Dicamptodon tenebrosus); Cope’s giant salamander (Dicamptodon copei); and coastal tailed frog (Ascaphus truei). To inform management efforts, we estimated site-level occupancy for these species across the northern Oregon Coast Range during summer low flow to quantify species status as a function of forest management and streamflow conditions. We completed visual and environmental DNA sampling at 80 randomly selected 3rd order basins that vary in forest management intensity in 2026-2025. Sampling occurred on six 100-meter reaches (one 3rd-order, two 2nd-order, and three 1st-order) in each basin. We observed Dicamptodon species in 76/80 basins with detections throughout all stream orders; Ascaphus in 54/80 basins, also across all stream orders; and Rhyacotriton species most frequently in 1st order streams in 51/80 basins. We developed an eDNA metabarcoding assay to estimate occupancy of our target amphibian species and to compare across physical and eDNA sampling methodologies to maximize sampling efficiency. Preliminary results on 2024 sampling show that our metabarcoding assay detected all amphibian species observed using visual survey methods. Further, in samples without method agreement, eDNA surveys identified species that were not detected with visual surveys. This study establishes a baseline for assessing responses of headwater amphibians to forest management and streamflow conditions over time, explores species distributions within headwater stream reaches and across Oregon's northern coast range, and identifies appropriate survey methodologies as a function of environmental conditions.