Sex-specific differences in physiological recovery and short-term behaviour following fisheries capture in adult sockeye salmon (Oncorhynchus nerka)

Abstract

Numerous laboratory and field studies have found that female Pacific salmon have higher mortality than males during their once-in-a-lifetime upriver spawning migration. However, the proximate cause(s) of this increased mortality are poorly understood. This study exposed sockeye salmon (Oncorhynchus nerka) to a mild capture and tagging stressor and evaluated physiological recovery and movement behaviour at 1 and 4 h postrelease. Female sockeye salmon did not expend more anaerobic energy in response to the stressor but did have higher plasma lactate levels 4 h after the stressor, indicating that females took longer to physiologically recover compared with males. In addition, female salmon had lower plasma glucose but higher plasma cortisol, plasma K+, and cardiac lactate levels compared with males. Male and female salmon had markedly different postrelease behaviours within the first hour of release; males were more likely to hold position within the staging area. Two potential mechanisms leading to increased mortality in female salmon were identified in this study: (a) prolonged recovery duration (possibly mediated by elevated plasma cortisol levels) and (b) insufficient oxygen delivery to the heart.