OCCURRENCE OF A SUITE OF STREAM-OBLIGATE AMPHIBIANS IN TIMBERLANDS OF MENDOCINO COUNTY, CALIFORNIA, EXAMINED USING ENVIRONMENTAL DNA

Abstract/Summary

Stream-obligate amphibians are important indicators of ecosystem health in the Pacific Northwest, but distributional information to improve forest management is lacking in many regions. We analyzed archived DNA extracted from water samples in 60 pools within streams in private timberlands in Mendocino County, California, for 3 California Species of Special Concern—Coastal Tailed Frogs (Ascaphus truei), Foothill Yellow-legged Frogs (Rana boylii), and Southern Torrent Salamanders (Rhyacotriton variegatus)—to better understand their distributions in the region. Both Coastal Tailed Frog and Foothill Yellow-legged Frog occurrence was affected by whether silt or organic matter was a dominant substrate in the sampled pool, and Foothill Yellow-legged Frog occurrence also was affected by water temperature. Foothill Yellow-legged Frog occurrence had a strong, positive association with water temperature, with occurrence unlikely below 14°C and very likely above 16°C, and a positive association with silt or organic substrates in pools, which was likely an indicator of higher-order stream reaches. In contrast, Coastal Tailed Frogs had a negative association with silt or organic substrates. Historical visual detections were generally congruent with findings using eDNA, but differences highlight important areas for further study. Detection probabilities of eDNA of both frogs was positively affected by water temperature. We did not detect Southern Torrent Salamanders using eDNA at any sites. Our study reinforces that ecological relationships of these species are varied and indicates the importance of maintaining the integrity of streams with diverse characteristics for conserving stream amphibians.