Physiological responses of free-swimming adult coho salmon to simulated predator and fisheries encounters

The responses of free-swimming adult coho salmon (Oncorhynchus kisutch) to simulated predator and fisheries encounters were assessed by monitoring heart rate (f(H)) with implanted data loggers and periodically taking caudal blood samples. A 10- or 30-min corralling treatment was conducted to simulate conspecifics being cornered by a predator or corralled by fisheries gear without physical contact. Corralling rapidly doubled f(H) from ～31 beats min(-1) to a maximum of ～60 beats min(-1), regardless of the duration of the corralling. However, recovery of f(H) to precorralling levels was significantly faster after the 10-min corralling (7.6 h) than after the 30-min corralling (11.5 h). An exhaustive-exercise treatment (chasing for 3 min, with physical contact) to simulate a predator chasing a fish to exhaustion or a fish becoming exhausted after encountering fisheries gear resulted in increased f(H) (to 60 beats min(-1)), plasma lactate, glucose, sodium, osmolality, and cortisol (males only) and a significant decrease in mean corpuscular hemoglobin concentration. Recovery of f(H) and most blood variables was complete about 16 h after exhaustive exercise and handling. The results illustrate a clear relationship between the intensity of exercise and the duration required for recovery of f(H). Changes in f(H) were significantly correlated with those in plasma lactate, chloride, and sodium at 1 h after the exercise treatment protocols. Thus, measurements of f(H) may provide an accurate indication of the general physiological response of salmonids to exhaustive exercise in the natural environment.