San Francisco Estuary and Watershed Science

California’s salmonids are at the southern limits of their individual species’ ranges, and display a wide diversity of strategies to survive in California’s highly variable climate. Land use changes after statehood in 1850 eliminated important habitats, or blocked access to them, and reduced the abundance, productivity, and distribution of California’s salmon. Habitat simplification, fishing, hatchery impacts, and other stressors led to the loss of genetic and phenotypic (life history, morphological, behavioral, and physiological) diversity in salmonids. Limited diversity and habitat loss left California salmon with reduced capacity to cope with a variable and changing climate. Since 1976, California has experienced frequent droughts, as were common in the paleo-climatological record, but rare in the peak dam-building era of 1936–1976. Increasing temperatures and decreasing snowpacks have produced harsher conditions for California’s salmon in their current habitats than they experienced historically. The most likely way to promote salmon productivity and persistence in California is to restore habitat diversity, reconnect migratory corridors to spawning and rearing habitats, and refocus management to replenish the genetic and phenotypic diversity of these southernmost populations.