Assessing species- and population-level vulnerability to climate-driven phenological mismatch in Pacific salmon

Climate change is shifting the timing of life-cycle events, or phenology, of species at different rates, reshuffling species interactions, and sometimes resulting in consumer-resource mismatches, which can impact consumer fitness, survival, and population growth. Indeed, the match/mismatch hypothesis posits that a temporal mismatch between a consumer and its resource during a critical life stage will decrease consumer survival. Migratory species such as Pacific salmon move through multiple environments, experiencing different rates of climate change, and share the migratory challenge of matching with temporally limited resources that shift through time and space. For emigrating juvenile salmon smolts, survival during the critical early marine life stage may depend on matching with peak prey availability upon ocean entrance. Here I examine the vulnerability of Pacific salmon to phenological mismatches during the early marine life stage. In Chapter 2, I use a large-scale synthesis to show unpredictable patterns in phenological change across populations of Pacific salmon, which result in seemingly random rates of phenological mismatch with marine prey. In Chapter 3, I use a unique dataset of individually marked steelhead trout smolts to examine both individual and cohort marine survival across 14 years, demonstrating that size, outmigration timing, and a phenological match between smolts and annual phenology of the cold-water zooplankton community, are important predictors of marine survival. Thus, some species and populations of Pacific salmon are being exposed to phenological mismatches which negatively impact survival. In Chapter 4, using an experimental approach, I develop relationships between body condition and either prolonged swim performance or survival. Finally, in Chapter 5, I found within- and across-population variation in body condition of wild sockeye salmon smolts before and after migration. Using a bioenergetic model and the relationship between Fulton's condition factor and swim performance developed in Chapter 4, I predicted starvation resistance, that is, days to death, to demonstrate how body condition could be used as a proxy for sensitivity to starvation associated with phenological mismatch. Collectively, these studies demonstrate that salmon are resilient to infrequent phenological mismatches, but it is unclear how anthropogenic change will impact vulnerability into the future.