Research Document - 2012/163

Knowledge of fish physiology used to set water temperature thresholds for in-season closures of Atlantic salmon (Salmo salar) recreational fisheries

By C. Breau

Abstract

In a number of rivers in Eastern Canada, water temperatures may exceed 25°C during the summer, and often in combination with low water levels. During these high temperature events, salmonids which cannot escape the high temperatures must cope in order to survive. Temperature tolerance is species and life-stage specific with adult salmon being less tolerant than juveniles. As temperatures increase from optimal temperature (T_opt) to  critical temperature (T_crit) values, thermal tolerance of fish decreases. During stress, metabolic byproducts accumulate in the white muscle of the fish. Concentrations of these byproducts must return to lower and specific levels for metabolic recovery. This document presents information on fish physiology to develop temperature thresholds that could be used to trigger in-season closures of the Atlantic salmon recreational fisheries. Catch and release angling imposes additional stress on the fish and the goal is to determine a temperature threshold above which this additional stress should be managed. Information with which to define T_opt and T_crit for adult Atlantic salmon is lacking. As a result, information from juvenile Atlantic salmon and other salmonid species were used to define these temperature thresholds for adult salmon. The probability of full metabolic recovery is reduced when the minimum nighttime water temperature remains above 20°C.

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