Contrasts in Habitat Characteristics and Life History Patterns ofOncorhynchus mykissin California's Central Coast and Central Valley

Oncorhynchus mykiss exhibit high plasticity in their life history patterns. Individual life history decisions are hypothesized to result from genetic thresholds shaped by local adaptation, with variation in environmental factors influencing the trajectories of growth and condition (e.g., Fulton's K, lipid content). We compared growth rates and life history patterns in two coastal creeks (Scott and Soquel) and two Central Valley (CV) rivers (American and Mokelumne) in California. The two regions differed markedly in habitat and physical factors, including hydrograph timing and amplitude, temperature regime, and food availability (measured as drift). Growth rates of coastal age-0 fish averaged 0.1 mm/d in summer–fall and 0.2 mm/d in winter–spring. Growth rates of CV fish were up to 10 times faster than those of fish on the coast and had the opposite seasonal pattern, in which growth in summer–fall was faster than that in winter–spring. Fish growth also differed between CV rivers; the mean growth ra...