Salmonids select spawning sites in the river or stream where suitable water velocities, depth and substrate are present. Substrate particle (gravel) size and quantity is critical to spawning habitat. Sufficiently high water velocities are necessary to provide inducement for spawning and flow through salmon redds for egg incubation. Once laid in the river gravels, eggs and larvae must receive oxygenated water of suitable temperature and free from toxic contaminates or an abundance of fine particles.
Stressors
- Habitat Quantity and Quality – The construction of on-stream reservoirs during the past century has blocked salmon passage and a large amount of habitat in the Sacramento
River basin was eliminated, resulting in large-scale reductions in physical habitats for all runs of salmon and all freshwater life stages. The dams also eliminate the recruitment of spawning gravel in downstream reaches. - Water Temperature and Flows – The timing and quantity of releases from Shasta Dam in
particular have been tied to egg mortality. Changes in reservoir operations that further
alter the operation of the projects can impact the availability and temperature of water in a manner that is detrimental to incubating salmon eggs.
