The consequences of angling, beach seining, and confinement on the physiology, post-release behaviour and survival of adult sockeye salmon during upriver migration

Abstract

Few studies have examined the effects of fisheries capture on wild fish, particularly in the context of evaluating the sustainability of capture and release methods for Pacific salmon ( Oncorhynchus spp.) during upriver migration. This study examined the physiological condition, post-release behaviour and survival of adult migrating sockeye salmon ( O. nerka) in the Fraser River, British Columbia, Canada. Fish were captured by either beach seine or angling and released immediately, or were captured by angling and released following a 24-h recovery period in a net pen. Before release, all salmon were biopsied or tagged with radio telemetry transmitters. Capture by either angling or beach seine with immediate release resulted in >95% survival 24 h after release, whereas net pen recovery after angling resulted in ∼80% survival. This differential in survival was similarly expressed in the percentage of released fish reaching natal sub-watersheds, with 52.2% and 36.3% of fish immediately released by beach seine and angling reaching natal sub-watersheds, respectively, compared with 2.9% of fish released after angling and net pen recovery. Blood plasma stress indices reflected the 10-fold difference in survival, with a ∼4-fold higher plasma cortisol, a ∼2-fold higher plasma glucose and significantly depressed plasma ions and osmolality relative to fish sampled upon capture. Plasma lactate did not differ among groups. Collectively, these results suggest that a 24 h recovery in net pen following angling failed to promote post-release survival experienced with immediate release after angling or beach seining.