The effects of experimental energy depletion on the physiological condition and survival of adult sockeye salmon (Oncorhynchus nerka) during spawning migration

In 2005 and 2006, adult sockeye salmon (Oncorhynchus nerka) were captured en route to spawning grounds and placed in either a slow (similar to 0.1 m center dot s(-1)) or fast (similar to 0.4 m center dot s(-1)) water velocity treatment for 18 days in order to assess how migrational energy depletion during the final stages of maturation affected physiological condition and survival. Fish in the fast treatment utilized more energy than the slow treatment in 2005 (0.91 MJ kg(-1) vs. 0.43 MJ kg(-1); P = 0.010), and 2006 (0.72 MJ kg(-1) vs. 0.37 MJ kg(-1); P = 0.021). Non-treatment fish captured upon arrival at spawning grounds showed energy levels intermediate to the two treatments in 2005 and lower than both in 2006, suggesting that energy use during the treatments were within levels normally experienced by this population. No differences in survival were found between treatments (P > 0.05), although females had lower survival than males in both years (both P < 0.01). After 18 days, surviving fish from the fast treatment showed signs of elevated physiological stress relative to fish from the slow treatment. Specifically, plasma osmolality was lower in fast fish in 2005 (P < 0.001), as was plasma chloride in both years (both P < 0.02). In 2006, plasma lactate was higher (P = 0.014) in fast fish. Within the ranges of energetic depletion that were examined here, a more energy-intensive migration can have a substantial influence on the physiological condition and stress of adult sockeye salmon, but not on survival.