In 2007, low returns of Sacramento River Fall run Chinook (SRFC) to spawning grounds prompted the closure of the state’s largest salmon fishery. Examination into the cause of low escapement suggested that although the proximate cause was poor ocean conditions, the ultimate cause was diminished genetic and life history diversity among the populations comprising the stock. The Fellow will evaluate how much increased life history diversity could have reduced variability at the aggregate stock level through a maximized portfolio effect and whether that would have prevented closure of the SRFC fishery. She will also explore an alternative mechanism of greater stock variability through a strengthened cohort resonance effect. The cohort resonance effect quantifies population sensitivity to a varying environment and is magnified by decreased survival from fishing. By modeling and comparing the impact of these effects on overall stock variability, the Fellow will develop a better understanding of the underlying mechanisms and management actions that have the potential to stabilize the SFRC stock and other fisheries under changing environmental conditions.
Quantifying the roles of environmental variability and the portfolio effect in the population dynamics of the Sacramento River Fall Chinook salmon stock