Intra- and inter-population variation in sensitivity of migratory sockeye salmon smolts to phenological mismatch

Certain consumer traits may influence sensitivity to phenological mismatches between consumers and their prey, and understanding the variation in these traits across or within populations could be helpful in predicting if and how a consumer population will respond to climate change. Here, we quantify intra- and inter-population variation in traits of sockeye salmon (Oncorhynchus nerka) smolts that may influence sensitivity to starvation associated with phenological mismatch. We asked 2 questions: (1) What is the magnitude of intra- and inter-population variation in physical and energetic condition at different stages of emigration? (2) How would this trait influence survival during periods of starvation? We collected sockeye salmon smolts from 3 populations before and 8 populations after riverine migration within the Skeena River watershed, BC, and measured condition-specific traits such as size and energetic condition. We discovered among-population variation was lower after migration: before migration traits differed between populations, but after-migration traits were more similar across populations. We estimated starvation resistance, the number of days until predicted death, using a previously developed model. Mean starvation resistance varied between 18 and 33 d across populations and varied within each population to as low as 6 d. These results reveal substantial within- and across-population sensitivity to starvation which may be associated with phenological mismatch. Thus, factors other than phenology (e.g. freshwater ecosystem dynamics that influence smolt condition) have the potential to influence sensitivity to phenological mismatch and, potentially, marine survival.