Estimating the Impacts of Reservoir Elevation Changes on Kokanee Emergence in Flaming Gorge Reservoir, Wyoming–Utah

Abstract

Flaming Gorge Reservoir, like many western North American reservoirs, is managed to release water during the winter months to allow for water storage associated with melting snow and rain during spring. Decreases in reservoir elevation during winter can cause mortalities of kokanee Oncorhynchus nerka spawned along the shoreline the previous fall. This study compared data on depth distribution of embryos and depth-adjusted survival to estimate the relative survival of emergent kokanee at different depths and the effect of winter drawdown on the proportion of deposited eggs that survive to emergence. Estimates of decreases in kokanee survival to emergence were 8.3% and 38.1% for reservoir elevation reductions of 1.0 m and 5.0 m, respectively.