A Comparison of the Physiological Condition, and Fishway Passage Time and Success of Migrant Adult Sockeye Salmon at Seton River Dam, British Columbia, under Three Operational Water Discharge Rates

Abstract.—We investigated the effect of changes in water discharge from the Seton River Dam, British Columbia, on the physiological condition, passage time, and passage success of adult migrant sockeye salmon Oncorhynchus nerka. Sockeye salmon were intercepted and nonlethally biopsied for blood plasma and energy status. A subset of these fish were fitted with radio transmitters and tracked under three different operational attraction flow levels. Indices of physiological stress and exhaustive exercise (e.g., plasma cortisol, glucose, lactate, osmolality, and hematocrit) did not differ among the attraction flow discharge levels that were examined, nor did they differ appreciably from those of other adult Fraser River sockeye salmon studied during upriver migrations in areas of natural, nonregulated flows. In fact, the fish appeared relatively unstressed after dam passage. Passage time was significantly longer (19.9 h) under intermediate discharge (12.7 m3/s) than under high (15.8 m3/s) or low (11.0 m3/s) discharges (9.3 and 7.0 h, respectively) but did not differ between high- and low-discharge periods. No differences in passage success or fishway ascent time were observed among the three discharges. Though we suspect that unique flow conditions were responsibl