Monthly Archives: August 2024

White Sturgeon Recruitment to San Francisco Bay-Estuary in 2024

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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:

  1. 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).
  2. 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.

Park Fire – Spring-Run Salmon’s Worst Nightmare

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The fire that started on July 24 has burned most of the lower foothill and middle reaches of the affected streams as of August 8th.  It is now actively encroaching on the mountain spawning reaches of Mill and Deer creeks on the south slopes of Mt Lassen, the two most important of the affected spawning streams (see maps below).  It will likely slow only when it reaches the boundary of the 2021 Dixie Fire and its lower levels of fuels.

Map of Park Fire in northeast Sacramento Valley dated 8/3/2024.  Red arrows indicate further fire growth as of 8/6, mainly in the upper Mill and Deer creeks watersheds.  Green stripes indicate spring-run salmon summer holding and fall spawning reaches.

Spring-run salmon populations in the Central Valley, including the core Battle, Mill, Deer, and Butte Creeks populations, are at recent historic lows.  It is essential to rehabilitate previously burned watersheds as soon as possible.  The California Department of Fish and Wildlife should expand the Deer Creek Spring-Run Conservation Hatchery Program begun in 2023 at UC Davis to include the other spring-run salmon streams in the Sacramento Valley. 

At the same time, it is important to attack the causes of poor survival of juveniles migrating to the ocean and poor survival of adults returning to the spawning grounds.  In this regard, comments on the Environmental Impact Statement for the Long-Term Operations of the Central Valley  Project and the State Water Project are due on September 9.  Operations of these water projects play a major role in the survival of Central Valley salmon to and from the ocean.  With the acceleration of climate change, it is important to re-evaluate the present and future effects of these water projects and potential operational changes to protect salmon under this new climate change baseline.

For more on Mill and Deer creek salmon see:  https://www.facebook.com/CaliforniaDFW/videos/spring-run-chinook- salmon/306327998810027/

Park Fire active zone moving northeast in the upper Mill Creek watershed on August 8th, 2024.  CALFIRE hopes to stop the Park Fire advance at highways 32/36 and the boundary of 2021 Dixie Fire (see next map).

Park Fire active zone moving northeast in the upper Mill Creek watershed on August 8th, 2024.  CALFIRE hopes to stop the Park Fire advance at highways 32/36 and the boundary of 2021 Dixie Fire (see next map).

Western boundary (extent) of Dixie Fire in summer 2021.

Klamath River Update – July 2024

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It is the first summer without the reservoirs on the Klamath River.  Upper river flows at Iron Gate are now at summer lows (900 cfs, Figure 1).   The flow, water temperature, and turbidity in the river without the reservoirs (the dams have not all been removed) is shown in the following figures.  Two major concerns are sporadic turbidity events from dropping flows and higher water temperatures that are a consequence of unshaded former reservoir reaches and loss of cold-water dam releases.

Extensive gaging data are available for the lower Klamath River from the USGS and Karuk Tribe (Figure 2).  The focus here is on the reach below the four-dam-removal project where the dams were drained in early 2024, leaving the river free-flowing.

Late spring and early summer gage data show the upper reaches below Iron Gate had the warmest water in 2024 (Figures 3-5).  Water temperatures reached 25oC/77oF, lethal to salmonids.  Further downstream, water temperatures were gradually cooler as the river progressed toward the mouth, generally remaining in the 68-70oF maximum range after receiving cool tributary water and cooler air temperatures.  Further upstream above Iron Gate, water temperatures were similar those immediately below Iron Gate (Figure 6).

Prior to dam removal, the upper reaches below Iron Gate had the lowest water temperatures in 2022 and 2023 (Figure 7 and 8), reflecting the release of cold water from the bottom of Iron Gate Reservoir.  Without this source of cold water, the upper reaches are now significantly warmer in late spring and summer. 

Because the water temperatures were similar in 2024 above and below the former Iron Gate Reservoir (see Figures 4 and 6), there seems to be little warming in the unforested former Iron Gate reservoir reach.  The upper reach of river below Iron Gate Dam now generally reflects historic warm water characteristics of the 6-dam project reach between Klamath Lake and Iron Gate Dam.  Future riparian forest restoration of the three former reservoir reaches may lead to some cooling of the upper river in the future.

Finally, the drop in river flow in early July 2024 (see Figure 1) appears to have caused additional reservoir-footprint erosion and scouring, leading to high turbidity levels below Iron Gate (Figure 9).  Such turbidities like the warm water are generally lethal to salmonids.

Figure 1.  Upper Klamath River flow at Iron Gate gage in June and early July 2024.

Figure 2.  Lower Klamath River gauging stations from Klamath Lake downstream to mouth.  Blue marker denotes gage below JCBoyle Dam.  Numbers in green and yellow circles denote multiple gage locations.

Figure 3.  Water temperatures in lower Klamath River in June 2024.  Iron Gate Dam is uppermost location and Turwar Gage is lower-most location near mouth.  Note greatest water temperatures were recorded from the two uppermost reaches:  Iron Gate and Walker Bridge.

Figure 4.  Water temperature recorded at Iron Gate gage 6/15-7/7 2024.

Figure 5.  Water temperature recorded at Walker Bridge gage 5/20-7/7 2024.

Figure 6.  Water temperature recorded at Fall Creek gage 6/1-7/7 2024.

Figure 7.  Water temperatures in lower Klamath River in June-July 2022.  Iron Gate Dam is uppermost location and Turwar Gage is lower-most location near mouth.  Note lowest water temperatures were recorded from the two uppermost reaches:  Iron Gate and Walker Bridge.

Figure 8.  Water temperatures in lower Klamath River in June-July 2023.  Iron Gate Dam is uppermost location and Turwar Gage is lower-most location near mouth.  Note lowest water temperatures were recorded from uppermost reach: below Iron Gate.

Figure 9.  Turbidity (suspended sediment) concentrations measured at Iron Gate Gage in 2024.  Note original reservoir drawdown and subsequent reservoir sediment deposit erosion January-