Adult Green Sturgeon and General Life History –  Source

The Southern Green Sturgeon is an anadromous fish species that spawns in the upper Sacramento River near Red Bluff CA.  It is a state and federal listed endangered species.  Adults migrate from the ocean to spawn in April-May in gravel/cobble riffles and pools.¹  The eggs hatch in approximately 12 days.  The young larval or fry are susceptible to stress and mortality if water temperature warm too quickly into the 65-70^oF range.  Optimal water temperatures for embryos and larvae are 60-65^oF.²  Survival declines at higher temperatures, with 68^oF considered lethal.

The fry grow quickly and begin moving downstream from mid-May to mid-July, as shown by screw trap collections at the Red Bluff Diversion Dam (Figures 1 and 2).  It is the reaches below Red Bluff downstream into the middle river near Wilkins Slough where larvae-fry are vulnerable to excessive spring-season water temperatures.  There are minimal available records of juvenile survival in the middle and lower river, although some data indicate they do not move to the Delta and Bay until the first fall rains.

Juvenile production measured at Red Bluff is lower in drought years (Figure 2) as a consequence of low flows and high water temperatures. With water temperatures already high in early May 2021 (Figure 3), the prognosis for young green sturgeon production is not good.

Figure 1. Screw traps at Red Bluff Diversion Dam in Sacramento River. USFWS photo.

Figure 2. Green sturgeon collections in Red Bluff screw traps 2003-2012. Note poor survival in drought years 2007 through 2009. Source.

Figure 3. Water temperature of the Sacramento River at Red Bluff (RDB rm 240) and Wilkins Slough (WLK rm 125) April-June in 2014, 2015, and 2021. Note the lethal water temperature for green sturgeon larvae is considered to be 68^oF.