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

—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 m/s) than under high (15.8 m/s) or low (11.0 m/s) discharges (9.3 and 7.0 h, respectively) but did not differ between highand 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 responsible for the longer passage time during intermediate discharge, a detailed hydraulic analysis is needed to further interpret our results. The proliferation of dams during the latter half of the 20th century resulted in the alteration of many formerly unconstrained river systems (Dynesius and Nilsson 1994; Rosenberg et al. 2000; Nilsson et al. 2005). At some dam sites, fish bypass systems (e.g., fishways, fish lifts) were installed in order to provide a means of connectivity for fish between upstream and downstream habitats (Clay 1961; Odeh 1999). Though the earliest fish bypass structures were often poorly designed for local hydraulic conditions and fish species, designs began to accommodate biologically relevant factors by the early 1900s, and by the middle of the 20th century, design criteria became increasingly based on rigorous fish passage research (Odeh 1999). An important part of effective fishway design is the provision of a means for fish to be able to locate and enter the structure in a timely manner and without undue physiological stress (Andrew and Geen 1960; Clay 1961; Powers et al. 1985; Larinier 1998). * Corresponding author: [email protected] Received May 7, 2008; accepted March 18, 2009 Published online September 3, 2009 1195 North American Journal of Fisheries Management 29:1195–1205, 2009 Copyright by the American Fisheries Society 2009 DOI: 10.1577/M08-114.1 [Article]