Modeling chinook salmon with SALMOD on the Sacramento River, California

Four races of Pacific salmon crowd the Sacramento River below a large reservoir that prevents access to historical spawning grounds. Each race is keyed to spawn at specific times through the year. A salmon population model was used to estimate: (1) the effects that unique run timing, interacting with seasonal river flows and water temperatures, have on each race; and (2) which habitats appeared to be the most limiting for each race. The model appeared to perform well without substantive calibration. Late fall, winter, and spring run Chinook do not appear to have the same production potential as fall run Chinook even though fall run production is more variable than that for the other three races. Spring fish have the lowest production on average, and production appears to be declining through time, perhaps making that race harder to recover should the population become more depressed. Rearing habitat appears to be the factor most limiting production for all races, but water temperature is responsible for most year-to-year production variation.