Scaling of the Portfolio Effect in Central Valley Chinook Salmon: Trends and Implications

R/SF-61
Start/End: July, 2014 to December, 2015

Is bigger always better? Recently published research suggests that bigger out-migrating young salmon are more likely to survive poor ocean conditions than smaller salmon of about the same age. But, does this size advantage hold true for all salmon populations under all freshwater conditions? The fellow will explore this question for juvenile Chinook salmon in the Central Valley. Abundance and size data from juveniles exiting their natal rivers and caught in traps will be analyzed and compared with size-at-outmigration reconstructions of adults that returned to their natal rivers to spawn, to see who really survives. The reconstructions will be based on analyses of otoliths (earbone-like structures) collected during salmon carcass surveys. Strontium isotope signatures in the otoliths will be used to determine where a fish was born, its size upon leaving its natal stream and upon entering the ocean. Scientists will compare patterns across a range of spatial and temporal scales (rivers, basins, runs, years and hydrologic regimes) to explore the importance of size-selective mortality and life-history diversity for juvenile salmon in the Central Valley. Results will be evaluated in the context of the portfolio effect, which argues that maintaining multiple and diverse salmon stocks will dampen boom-bust cycles in adult salmon returns and increase population persistence.

Research mentor: Stephanie Carlson, University of California Berkeley

Community mentor: Rachel Johnson, National Marine Fisheries Service