Physiological status of coho salmon (Oncorhynchus kisutch) captured in commercial nonretention fisheries

The physical, hematological, and metabolic condition of 303 adult coho salmon (Oncorhynchus kisutch) was examined following capture with three commercial fishing gear types (seine, troll, and gill net) and a variety of methods. All fish arrived onboard in a state of severe metabolic exhaustion, and physiological differences among gear types and fishing methods were few and relatively small. Fish showed less physiological disruption with a brailing versus a ramping method of seine fishing and with a 30-min versus a 60-min net soak time for gillnet fishing. The visual ratings of physical condition (nonbleeding, vigorous, and lethargic) correlated significantly with hematocrit, plasma osmolality, plasma lactate, and plasma sodium. Fish placed in recovery boxes for 30-60 min onboard fishing vessels did not show the expected metabolic recovery; only plasma potassium recovered significantly. However, plasma lactate levels declined significantly for 125 fish placed in a net pen for 24 h, suggesting that metabolic recovery was possible after commercial capture. Because of a concern that the current recovery box design does not effect optimum recovery, we recommend that future experiments test a better-designed recovery box that orients fish into flowing water.