Drought Effects on the Availability of Spawning Habitat for Fall-run Chinook Salmon in the Tuolumne River Watershed

The main run of Chinook Salmon (Oncorhynchus tshawytscha) of the Tuolumne watershed is the Fall run. These fish enter the streams in early fall and spawn from October through December in the Tuolumne River below La Grange Dam. Much of the historic spawning habitat of the salmon has been lost due to anthropogenic activity, mainly the building of dams. With the drought conditions of 2012-2015, this loss in habitat has been exacerbated. Drought is a prolonged period of time in which there is extremely low water inflow and availability (Lake, 2003). The current drought is considered supra-seasonal, persisting beyond a season and continuing to decrease in precipitation and water availability (Lake, 2003). Decreased precipitation leads to lower water levels and consequently fewer available spawning sites. Drought-reduced seasonal flows disrupt habitat conditions along the Tuolumne River, decreasing the availability of spawning sites. Data from 1992 through 2004 from the Lodi Fish and Wildlife office show a 62% decline, despite restoration efforts, among Chinook Salmon in the San Joaquin River basin, one of the largest decreases among the Central Valley populations. Based on past declines, one could expect extended drought conditions to have a negative impact on the already-declining Fall run Chinook Salmon in the Tuolumne River. As such, there are many options available that may aid in restoring much of the lost habitat, such as gravel augmentation, adjusting flow regime, and releasing water from La Grange dam during key periods of time for salmon spawning