The flow of the Snake River downstream of Hells Canyon Dam, Idaho, frequently fluctuates as dam operators alter the amount of electrical load generated in response to momentto-moment power needs (termed load-following). Flow fluctuations due to load-following have the potential to increase the energy used by juvenile white sturgeon Acipenser transmontanus that move to avoid unfavorable habitat or that alter swimming speed to maintain position over a range of velocities. Following laboratory respirometry experiments, a field study using electromyogram (EMG) and sonic telemetry was conducted to determine whether movement (area and distance), swimming speed, or oxygen consumption of juvenile white sturgeon responded to the operation of Hells Canyon Dam during three study periods when flows were artificially fluctuated to resemble extreme load-following operation (192-836 m 3 /s), held high and stable (442-629 m 3 /s), or held low and stable (275-284 m 3 /s). Respirometry results confirmed that the oxygen consumption of juvenile white sturgeon increased with swimming speed, was temperature dependent, and when corrected for fish mass, ranged from 140.2 to 306.5 mg O 2 · kg Ϫ1 · h Ϫ1 . The telemetry study showed that the distance sturgeon moved and the area used were similar at all flows. However, when flows were held low and stable, swimming speed and oxygen consumption decreased compared with the other study periods. Although the overall trend was for swimming speed and oxygen consumption to be less during the study period when flows were low and stable, the differences between study periods appeared to be due to differences in water temperature and light levels, which changed during the investigation. The results suggest that high flows, even those of relatively short duration such as occur during load-following operations, restrict the movement of juvenile white sturgeon. However, high flows do not result in an increase of energy expenditure, possibly because of morphological and behavioral adaptations to living in a high-velocity environment.

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