UC Berkeley

The complex and seasonal landscape of the California Central Valley produces a mosaic of habitat niches for Chinook salmon (Oncorhynchus tshawytscha) to occupy. Diversity in life history enables Chinook salmon to widely distribute across habitats and over time, reducing competition and hedging against environmental disturbances, resulting in overall more abundant and stable populations. Human activity including habitat alteration and resource extraction can eliminate ecological niches available to Chinook salmon and reduce their life history diversity. Maintaining this important element in the face of natural resource demands and climate change requires understanding how human activities influence life history expression and the various life history types. Hatcheries artificially producing salmon to supplement natural populations are pervasive in the Central Valley. Practices during the breeding, rearing, and release process can result in trait divergence between hatchery and natural-origin salmon. Trait differences can result in differential impacts from human activity and potentially bias inferences drawn directly from hatchery fish data for managing the natural or combined population. Throughout the dissertation, I compared the life history of hatchery- and natural-origin fish and evaluated how their distinct traits could influence impact from human activity. For each chapter, I explored how life history shapes population dynamics and affects assessment tools used in managing Chinook salmon. In Chapter 1, I found that natural-origin Sacramento River winter-run Chinook salmon use the basin far more extensively than hatchery-origin fish when migrating to the ocean and have greater habitat needs than what would be suggested from hatchery fish data alone. In Chapter 2, I found winter-run hatchery fish return from the ocean to spawn at earlier and more homogenous ages, which suggests natural-origin fish may be more impacted by ocean fisheries because of their later maturation ages. In Chapter 3, I found trends in maturation schedules for Sacramento River fall-run Chinook salmon over time have contributed to forecast error in management models used to guide harvest policies. Overall, this dissertation demonstrates that understanding life history diversity and population dynamics can help natural resource managers make well-informed and cost-effective decisions that maintain the integrity and long-term persistence of threatened salmon populations.