Temperature effects on swimming performance, energetics, and aerobic capacities of mature adult pink salmon (Oncorhynchus gorbuscha) compared with those of sockeye salmon (Oncorhynchus nerka)

We assessed the prolonged swimming performance (U-crit), metabolic rate (M-dotO(2-min) and M-dotO(2-max)), and oxygen cost of transport (COT) for upper Fraser River pink salmon (Oncorhynchus gorbuscha (Walbaum, 1792); 53.5 +/- 0.7 cm FL) and sockeye salmon (Oncorhynchus nerka (Walbaum, 1792); 59.3 +/- 0.8 cm FL) across a range of naturally occurring river temperatures using large Brett-type swim tunnel respirometers. Pink salmon were capable of similar relative critical swimming speeds (U-crit) as sockeye salmon (2.25 FL center dot s(-1)), but sockeye salmon swam to a higher absolute U-crit (125.9 cm center dot s(-1)) than pink salmon (116.4 cm center dot s(-1)) because of their larger size. Nevertheless, three individual pink salmon (Ucrit-max = 173.6 cm center dot s(-1)) swam faster than any sockeye salmon (Ucrit-max = 157.0 cm center dot s(-1)), indicating that pink salmon are far better swimmers than has been previously assumed. Metabolic rate increased exponentially with swimming speed in both species and was highest for pink salmon, but swimming efficiency (i.e., COT) did not differ between species at their optimal swimming speeds. The upper and lower limits of metabolism did not differ between species and both M-dotO(2-min) and M-dotO(2-max) increased exponentially with temperature, but aerobic costs of transport were independent of temperature in both species. Strong thermal dependence of both swimming performance and COT were expected but not demonstrated in either species. Overall, a higher degree of inter-individual variability in pink salmon swim performance and capacity suggests that this species might not be as locally adapted to particular river migration conditions as are sockeye salmon.