Energetic Responses of Salmon to Temperature. A Study of Some Thermal Relations in the Physiology and Freshwater Ecology of Sockeye Salmon (Oncorhynchus nerkd)

SYNOPSIS. Studies on the relation of temperature to tolerance,preference, metabolic rate, performance, circulation, and growthof sockeye salmon all point to a physiological optimum in theregion of 15°C. Natural occurrence is limited in time andspace at temperatures above 18°C despite being able to tolerate24°C. Forms of physiological inadequacy can be demonstratedwhich account for such restrictions in distribution. Predictivepower for locating and accounting for concentrations of youngfish in thermally stratified lakes appeared to provide "proof"for the controlling influence of the physiological optimum temperature.Early literature on the ecology of sockeye supported this view.Recent studies using midwater trawls and sonar detection reveala diurnal behavior pattern which points to a more subtle interactionof biotic andabiotic factors governing vertical distributionin which the controlling force appears to be bioenergetic efficiency.It is concluded that a mechanism of behavioral thermoregulationhas evolved which favorably balances daily metabolic expendituresin order to conserve energy when food is limited.