towards the SWP and CVP pumps (Kimmerer, 2008a). Juvenile salmon that successfully pass through the delta enter the ocean and spend one or more years there before returning to freshwater to spawn. Ocean survival is particularly dependent on the conditions the fish experience during the first few months they enter the saltwater (Lindley et al., 2009). Fish that are drawn into the central and southern delta by reverse flows are more vulnerable to predation than those that take a more direct path to the ocean, and other aspects of changed environmental conditions also expose them to predators (for more detail, see Chapter 5).
The Central Valley green sturgeon (Acipenser medirostris) is an anadromous fish that can reach 270 cm (nearly nine feet) in length with a maximum age of 60 to 70 years (Moyle et al., 2002). The historical distribution of green sturgeon is poorly documented, but they may have been distributed above the locations of present-day dams on the Sacramento and Feather Rivers (Beamesderfer et al., 2007). Information on the distribution of green sturgeon in the San Joaquin River is lacking. Mature green sturgeon enter the Sacramento River from the ocean in March and April. The Red Bluff Diversion Dam can impede their migrations (Heublein et al., 2009). After spawning, green sturgeon may immediately leave the river or hold over in deep pools until the onset of winter rains (Erikson et al., 2002; Heublein et al., 2009). Individuals then migrate back to the ocean and return to freshwater to spawn every two to four years (Erickson and Webb, 2007; Lindley et al., 2008)
Based on adult spawning behavior and the habitats required for green sturgeon embryo development, reproductive females likely select spawning areas with turbulent, high velocities near low-velocity resting areas. Green sturgeon spawning areas are presumed to be characterized by coarser substrates upstream of lower gradient reaches, which usually have slower velocities. Eggs and milt are released in turbulent water above deep, complex habitats; fertilized eggs drift into deeper areas and stick onto the substrate. Eggs require cool temperatures for development and hatch after approximately a week. Larval and juvenile green sturgeons are bottom-oriented and nocturnally active until a few months of age (Kynard et al., 2005). Juvenile green sturgeon migrate into seawater portions of natal estuaries as early as one and a half years old (Allen and Cech, 2007), and eventually emigrate to nearshore coastal waters by three years old. Subadults are migratory, spending their next 12 to16 years foraging in the coastal ocean and entering western estuaries during the summer (Moser and Lindley, 2007). In the ocean, green sturgeon inhabit the coastal shelf out to 100m depth with occa-