Onboard respirometry in a marine recreational fishery reveals predictors of post-capture recovery in adult coho salmon

Annually, billions of fish are captured and released under the assumption that they will recover and survive, which may not occur. Fishing-induced stressors require subsequent recovery, characterized by increased energy expenditure, greater vulnerability to predation and disease, and lost opportunities for critical activities such as feeding and migration. This study examined the physiological responses of adult coho salmon (Oncorhynchus kisutch) to interactions with fishing gear in coastal British Columbia, Canada. Collaborating with recreational fishers, we used novel onboard respirometers to measure metabolic recovery for 1 h, alongside blood sampling to assess physiological status. We examined how angling-induced injuries (scale loss, line wrap, fin and eye damage) and intrinsic and extrinsic factors (fork length, sex, preexisting wounds, temperature, capture duration) affect post-capture recovery. Fish with greater scale loss or line wrap incurred higher recovery costs and more acidic blood, respectively, while smaller fish and longer fight duration demonstrated greater acidosis and lactate accumulation. Comparisons with lab-based chase protocols on the same individuals revealed that standard lab methods underestimated aerobic capacity and short-term recovery, underscoring the value of the novel methodology for fisheries management and conservation.