In a 10/31/17 post, I described record low spring-run Chinook salmon runs in Sacramento Valley rivers in 2017, with emphasis on the Feather River, the largest component of the Central Valley spring-run population. In this post, I update information on Central Valley spring-run. The combined Central Valley runs of spring Chinook salmon were indeed at record low levels in 2017 (Figure 1). The run total includes escapement to all Central Valley streams that host spring-run salmon, including Battle Creek, Clear Creek, Butte Creek, Antelope Creek, Big Chico Creek, Cottonwood Creek, Mill Creek, Deer Creek, Antelope Creek, Feather River-Yuba River, and the mainstem Sacramento River.1
I plotted these numbers in a spawner-recruit relationship, with spawners being recruits three years earlier (Figure 2). The water year type during the first winter-spring following spawning is shown in Figure 2 by color. Winter-spring conditions reflect early rearing and emigration conditions in spawning rivers, as well as conditions in rivers downstream an in the Bay-Delta.
Factors contributing to poor recruitment in the eight critically dry years in the observed period include low river flows, high water temperatures, excessive predation, loss at water diversions, and low turbidity, all factors that are inter-related. Poor ocean conditions and hatchery operations also were likely factors, which may also be related directly or indirectly to river flows.
Most recent recovery efforts and planning have focused on habitat restoration.2 My own focus has been on poor river conditions (low flows and high water temperatures) and related predation.3 My reasoning is based on escapement trends over the past decade that indicate sharply dropping escapement during dry year low-flow conditions in most of the spawning rivers (Figures 3-5).