| Summary: | The primary goal of this research was to predict how changes in water temperature affect
the swimming performance and energetic cost of transport in adult pink salmon (Oncorhynchus
gorbuscha) and sockeye salmon (O. nerka), thus contributing to their ability to reach natal
streams and spawn successfully. The prolonged swimming performance (U[sub crit]), minimum and
maximum metabolic rate (Mo[sub 2-min] and Mo[sub 2-max]), oxygen cost of transport (COT) for upper
Fraser River pink salmon were assessed across a range of naturally occurring temperatures using
Brett-type swim tunnel respirometers and compared with values for sockeye salmon. To reduce
mortality in senescing fish we minimized holding time and, therefore, thermal acclimation to as
little as 48 hours before experiments. Therefore, we also used a salmonid model, the cutthroat
trout (O. clarki clarki), to examine the effects of 48-hour and 3-week temperature acclimation
periods on U[sub crit]. The length of the acclimation period had no significant effect on either the first
or second U[sub crit] or on the recovery ratio (the quotient of U[sub crit-2]/U[sub Crit-1])- These results indicate that a
48-h acclimation to experimental temperatures may be sufficient in studies of swimming
performance with this species. Contrary to previous beliefs, pink salmon were capable of similar
relative critical swimming speeds as sockeye salmon (2.25 FL•s⁻¹), but sockeye salmon swam to a
higher absolute U[sub crit](125.9 cm•s⁻¹) than pink salmon (116.4 cm•s⁻¹) because of their larger size.
However, some individual pink salmon swam faster than all the sockeye salmon tested.
Metabolic rate increased exponentially with swimming speed (P < 0.01) in both species and was
higher for pink than sockeye salmon (P = 0.01), although swimming efficiency (was not
significantly different between the species at their optimal swimming speeds minimum cost of
transport; COT[sub min]) . The upper and lower limits of metabolism also increased exponentially with
temperature (Mo[sub 2-min] P = 0.01; Mo[sub 2-max] , P < 0.01, respectively) but were not different between
species (Mo[sub 2-min] P = 0.93; Mo[sub 2-max] , P = 0.38). The relationship between Mo₂ and swimming speed
was positively affected by temperature in pink salmon (P = 0.01), but average and minimum
COTs were independent of temperature over the range tested (9-22 ºC) in both species. Overall, a
higher degree of inter-individual variability and thermal insensitivity in pink salmon suggest that
this species might not be as locally adapted to particular upriver migrations as are sockeye
salmon.
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