Successful recovery of the physiological status of coho salmon on board a commercial gillnet vessel by means of a newly designed revival box

Successful application of fish-revival techniques in commercial fishing prior to release of nontarget species requires clear evidence that recovery devices do indeed improve physiological status and minimize postcapture delayed mortality. This study provides such evidence for a newly designed recovery box (Fraser box) that assisted gill ventilation. Immediately after capture by gillnet, adult coho salmon (Oncorhynchus kisutch) were in a state of severe metabolic exhaustion and stress, based on a comprehensive analysis of plasma and muscle tissue. However, when placed in a Fraser recovery box for 1-2 h, both lethargic and vigorous fish showed significant metabolic recovery and their ability to swim was also quickly restored. An emphatic demonstration of the benefit of the Fraser box was the successful revival of > 90% of fish that appeared dead at capture. Furthermore, postcapture delayed mortality was only 2.3% after a 24-h observation period. Therefore, in the context of commercial salmon gillnet fishing, revival of nontarget coho salmon in a Fraser box, in combination with a soak time (total time the gillnet is in the water) less than or equal to 70 min and careful fish handling to minimize physical trauma, could improve physiological status, restore swimming ability, and markedly reduce postcapture delayed mortality.