1 Assessment of Risks to Sierra Nevada Populations of Foothill Yellow-Legged Frogs (Rana boylii) Under Varying Snow-Melt Hydrograph Recession Rates in Rivers

• Foothill yellow-legged frogs (FYLF) breed, lay eggs (oviposit), and tadpoles develop during the spring and summer of each year in a variety of stream environments from small creeks to large rivers. • In the Sierra Nevada, FYLF have evolved with and are adapted to the snow-melt run-off/recession period and typically oviposit during the middle to the tail end of that period (e.g., Figure 1) • Cues for breeding/oviposition appear to be a combination of day length, water temperature, and local habitat suitability (e.g., water velocity and depth). • The primary risks during the snow-melt recession period are scouring and stranding. Scouring can occur if water flows increase substantially after eggs have been laid. Stranding can occur if recession rates are too fast relative to water depth and egg development time. Here we focus on stranding risk only. • This assessment focuses on the egg mass lifestage only within relative large Sierran rivers. This lifestage would be present from approximately mid-April through mid-July, depending on water year conditions. • Recession rates are defined in this assessment as change in stage per week at representative oviposition sites. When evaluated with data on the channel morphology of oviposition sites in a given river reach, this recession rate can be translated to a change in discharge over time for that reach. Lind and Yarnell- FYLF and snow-melt recession rates- 24 March 201