A decision analysis of flow management experiments for Columbia River mountain whitefish (Prosopium williamsoni) management

High spawning flows from Hugh Keenleyside Dam (HKD) on the Columbia River results in dewatering of eggs in mountain whitefish (Prosopium williamsoni) populations, but the ultimate effect on adult abundance depends on the shape of the egg-to-adult recruitment curve. Our decision analysis assessed the benefits of alternative flow experiments while accounting for uncertainties in this relationship and in flows in the Columbia and Kootenay rivers. The value of experimenting depended on the true recruitment relationship, how we quantified experimental benefits, and experimental design. With current uncertainty, the optimal HKD spawning flow (out of 11 alternative flows) was 1699.2 m3·s–1. Spawning flows below 1699.2 m3·s–1 did not improve egg survival because lower flows rendered highquality spawning habitat unavailable and increased scour mortality. Two experimental designs, both with higher precision monitoring, had a high probability of detecting the true recruitment curve at reasonable cost. Information from these experiments suggested an optimal spawning flow of 1699.2 m3·s–1 if adult abundance were sensitive to egg mortality or 1982.4 m3·s–1 if the population were insensitive.