Rapid recovery of exhausted adult coho salmon after commercial capture by troll fishing

To reduce mortality in the by-catch of commercial salmon fisheries, techniques are being explored to revive fish before live release and improve survival. By measuring blood and muscle variables, we demonstrated that capture of coho salmon (Oncorhynchus kisutch) by commercial trolling methods resulted in severe exhaustion and stress, e.g., muscle lactate reached 46.1 mmol·kg–1while muscle phosphocreatine (PCr) decreased to 6.1 mmol·kg–1. Nevertheless, coho salmon recovered rapidly by swimming in a cage alongside the vessel while fishing activity continued. In particular, there were significant increases in muscle glycogen and PCr levels, and a decrease in muscle lactate after two hours. Notably, and in contrast to when exhausted fish are held stationary during recovery, plasma lactate remained low (<4 mmol·L–1) during recovery, a phenomenon observed in earlier laboratory studies with rainbow trout (Oncorhynchus mykiss). There was no postcapture delayed mortality after 24 h. Therefore, we have established that postexhaustion activity promotes a rapid recovery in wild salmon and this result might find application in nonretention commercial and recreational fishing.