In a June 2024 post, I hypothesized factors controlling the white sturgeon population in San Francisco Bay-Estuary. I concluded the major factor controlling the adult stock size was periodic recruitment of juvenile sturgeon from successful spring spawning and early rearing in the lower Sacramento River. Successful recruitment only occurs in the wettest years, when there are higher streamflows and cooler water temperatures.
Recruitment of young white sturgeon in significant numbers has only occurred in three years since 2010: 2011, 2017, and 2023. Recruitment in 2024, an above normal water year, is likely to be poor. Production of young sturgeon is likely of function of attraction of spawners from San Francisco Bay (to high winter-spring river flows – good in 2024), good spawning conditions (streamflow and water temperatures – good in 2024), and good early rearing and transport conditions in the lower Sacramento River and the north and central Delta (streamflow and water temperatures – poor in 2024).
The adult spawning stock size may not be as important as spawning conditions, given strong recruitment in wet year 2023 under a very low stock abundance (observed Bay die-off in summer of critical drought year 2022).
There are a number of measures that hold promise to protect and enhance adult stock numbers, recruitment, and survival of white sturgeon.
Spawning Conditions
Flows in the lower Sacramento River (Wilkins gage) should be 8,000 to 10,000 cfs or higher in spring.
Flow in the lower Sacramento River (Wilkins Slough) should be at least 8,000-10,000 cfs.
Early Rearing and Juvenile Transport
Sacramento River inflows to the Delta should be at least 20,000 cfs in spring.
Flow from the lower Sacramento River into the Delta (Freeport) should be at least 20,000 cfs in spring and early summer (April-July).
Delta Conditions
The net flow in the lower Sacramento River channel downstream of the entrance to Georgianna Slough should be at least 10,000 cfs in spring and early summer (April-July). This will require total Delta diversions, including local agricultural diversions and exports by the State Water Project (SWP) and Central Valley Project (CVP), to be limited to approximately 10,000 cfs.
Flow in the lower Sacramento River in the Delta below Georgianna Slough should be at least 10,000 cfs in spring and early summer (April-July).
White sturgeon recruitment is best assessed at fish salvage facilities at the water project south Delta export pumps. Young sturgeon produced in the lower Sacramento River reach the Delta in early summer as shown here in 2023. Note the high export levels of 20,000 acre-feet per day (approximately 10,000 cfs; in this figure, SWP exports are shown behind CVP exports).
Bay Conditions
Delta outflow to the Bay should be at least 10,000 cfs from spring to early fall (April-October).
Delta outflow to the Bay (DTO) and Rio Vista water temperature May-Oct, 2021-2024. Recommended Delta Outflow is a minimum 10,000 cfs (purple line).
Minimize Sturgeon Adult Harvest and Pre-Adult Fishing Mortality
Sturgeon sport fishing should be limited to the Bay only, with catch-and-release regulations, with the following further considerations:
- Fishing for sturgeon should be closed in the east Bay or north Bay if daily maximum water temperatures are expected to exceed 65ºF (18ºC) in any open water portion gage locations in either Bay portions (possible from late spring through early fall).
- CDFW could allow limited harvest through short-term regulations, limited by slot (length range) and number. (Note that slot harvest in 2024 would allow a small harvest of broodyear 2011 white sturgeon, the most recent abundant broodyear in the adult population).
Under such restrictions, the effects of sport fishing on the sturgeon population would be minimal.
In addition, sturgeon collected at south Delta export salvage facilities should be transported to an appropriate location in the Bay for release (presently, they are released in the Delta).
Population abundance and recruitment of white sturgeon are mainly a function of annual Central Valley hydrology (river flow), with abundant juvenile production occurring only in the wettest years. Past harvest has only involved a small percentage of the adult population, while watershed hydrology has orders of magnitude greater effect on recruitment and eventual adult population abundance.
Allowing a limited fishery could also help in continuing to assess the health of the population. Sport fishers should be asked to contribute important information on the sturgeon they catch.