Category Archives: Fish (general)

Yuba River Fall-Run Salmon Crash 2016-2025

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The Yuba River Fall-Run Chinook salmon population “crashed” in the last decade.  Yuba River escapement ranged only from 2000-5000 spawners counted per year (Figure 1).  Such low escapements were last encountered only during the Central-Valley-wide crash during the 2007-2009 drought.

The decade-long low escapement reflects the effects of two droughts (2013-15 and 2020-22). Though the 2023-to-2025 escapements have increased slightly1 despite the 2020-2022 drought, the higher escapement reflects the benefit of fishery closures from 2023-2025 (fisheries normally harvest more than 50% of the adult stock).  Yuba escapement also reflects substantial numbers of hatchery strays from other rivers, including the Mokelumne and American River hatcheries, the Coleman hatchery on Battle Creek in some years, as well as the Feather River (Oroville) hatchery.  Small numbers of spring-run Feather hatchery strays from release locations near the mouth of the Yuba on the Feather River are also included.

The highest number of strays in the 2020-2022 period were from one group of Mokelumne River hatchery smolts released in 2018 to Half Moon Bay on the coast south of San Francisco.  The next highest group of strays are from American and Feather hatchery smolt releases to San Francisco Bay.  The trucked hatchery smolts do very well during drought years and thus tend to bias high the Yuba returns from drought years.  That is to say, drought effects on the natural Yuba run are even worse than indicated in escapement estimates.

I categorize the decade-long decline as a “crash” based on the population spawner-recruit (S/R) relationship (Figure 2).  The S/R “curve” generally reflects a positive logarithmic relationship between spawner and recruitment numbers.  The more eggs spawned generally leads to more adult returns three years later.  The S/R ratio, at least in the Central Valley salmon populations, also reflects drought or habitat conditions wherein recruits are generally depressed from density-independent habitat factors like droughts.  The six drought years in the last decade shown in Figure 2 as red dots have led to escapement levels in the lower-left quadrant of the S/R curve – a pattern often referred to as a population crash.

Often it is difficult for a population to recover from that situation because there are not enough spawners (eggs) to get the population out of the hole.  It would take a lot of good years in sequence to make that happen, unless certain actions are taken to accelerate the recovery.  For some suggestions on how this can be accomplished, see my past post on the subject.

Because of the supplementation of recruitment from other rivers and resulting mixed bag of spawners, the Yuba run is not threatened with extinction.  However, in its present state, its poor contribution to the commercial and recreational fisheries is a problem.  The Yuba is a magnificent salmon river that should contribute more salmon.

Figure 1. Yuba River Fall-Run Chinook salmon escapement estimates 1953-2024.

Figure 2. Yuba River Fall-Run Chinook salmon spawner-recruitment relationship wherein recruits are related to recruits three years earlier. Red dots represent escapement years where two years earlier it was a drought year during rearing and outmigration.

Klamath River Coho Salmon – December 2025 Update

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This is my first update of the status of the Klamath River coho salmon population since the removal of four Klamath River dams in 2024. My initial focus was on the Chinook populations.1 The adult coho run during late fall 2024 seemed unperturbed by the effects of dam removal in 2024. Adult coho in 2024, from Broodyear 2021, came back to the Scott River in relatively good numbers. (Figures 1 and 2).

The progeny of Broodyear 2021 were in the ocean prior to the fall of 2024. They returned to the Scott River late enough in 2024 to miss the last of the high turbidity events of late summer 2024, when the remnants of the dams were removed (Figures 3 and 4).

Unlike Broodyear 2021, Broodyear 2022 was subject to the full impact of dam removal in 2024 (see Appendix). Broodyear 2022 spawned in the late fall and early winter of 2022-2023. During the first year (2023), juvenile coho from Broodyear 2022 reared in the Scott River and mainstem Klamath. They then migrated to the ocean during winter-spring 2024 freshets as yearling smolts. Winter and early spring mainstem conditions in 2024 were characterized by high turbidities (see Figure 4) from reservoir drawdown and dam removal activities, including assisted sediment evacuation in the dam-removal reach and downstream mainstem (Figure 5).

The first indication of the effects of the 2024 dam removal process is in the escapement number of Broodyear 2022 in fall 2025. Preliminary escapement estimates in fall 2025 are markedly reduced compared to recent past runs (Figures 6 and 7). Updates by CDFW of escapement numbers for the winter 2026 will provide a full assessment of Broodyear 2022 effects and initial indications of the spawning run represented by adult from Broodyear 2022.

For now, I can only assume that Broodyear 2022 was compromised by the events of 2024 dam removal process. The high fall and early winter flows of 2025 (Figure 8) likely led to widely dispersed spawning of Broodyear 2022 adult in the Scott River. Much of the egg/fry production will be subject to isolation and the potential of eggs/fry becoming stranded and eventually lost. Past efforts to rescue stranded fish should be redoubled in 2026 to save what is likely limited production. Mainstem Klamath flows should be carefully regulated through the summer and fall to sustain juvenile rearing and migration habitat conditions for wild and hatchery coho during 2026.

Figure 1. Source: CDFW and Scott River Watershed Council

Figure 1. Source: CDFW and Scott River Watershed Council.

Figure 2. Source: CDFW

Figure 2. Source: CDFW

Figure 3. Source: USGS.

Figure 4. Water turbidity in Middle Klamath from Iron Gate Dam to Orleans in 2024. Source: Karuk Tribe. Author added the red stress line based on coho salmon science literature.

Figure 5. Source: USGS gaging station map. The Salmon, Scott, and Shasta rivers are the main Klamath salmon spawning tributaries below Iron Gate Dam, the lowermost impassable dam removed in 2024.

Figure 6. Source: CDFW.

Figure 7. Source: CDFW.

Figure 8. Source: USGS.

Figure 9. Source: Scott River Watershed Council.

Appendix:  National Marine Fisheries Service’s 2021 Summary of Potential Dam Removal Effects:

The primary effects of dam removal on Klamath salmon were disruption of habitat conditions in 2024 affecting various life stages of Chinook and Coho salmon and steelhead brood years 2020-2024.  The following are excerpts from the National Marine Fisheries 2021 Biological Opinion on the Klamath Dam Removal Project potential effects on coho salmon.

  • Food resources for coho salmon are expected to be impacted during drawdown due to elevated SSCs as described in Section 2.5.1.2.3. Food resources may be impacted downstream as far as Orleans (about 134 miles downstream of Iron Gate) (FERC 2021a), affecting juvenile coho salmon from the Upper Klamath, Shasta, Scott, and Mid-Klamath populations. Only juveniles that rear in the mainstem during the winter or utilize the mainstem during outmigration in the spring may be exposed to conditions with fewer prey sources.
  • In a summary of literature reporting effects of suspended sediment on salmonids, Lloyd (1987) reports several studies that document stress at 300 mg/L (McLeay et al. 1984) and 50 mg/L (McLeay et al. 1987). Redding et al. (1987) found that juvenile coho salmon showed signs ofstress at high levels of suspended sediment (2000-3000 mg/L), but not at low levels (400 to 600 mg/L). Servizi and Martens (1991) found that at 18°C, 8100 mg/L was the concentration where50 percent of the exposed coho salmon juveniles died.
  • Behavioral effects resulting from elevated suspended sediment include alarm reactions, avoidance, and reduced feeding. Cederholm and Reid (1987) found that juvenile coho salmon prefer low to medium concentrations of suspended sediment, and that juvenile coho salmon prey capture success significantly declined at concentrations of 100 to 400 mg/l. Salmonids have been observed to prefer clear over turbid water (Bisson and Bilby 1982), and move vertically near the water surface (Servizi and Martens 1992) and/or downstream to avoid turbid areas (McLeay et al. 1984; McLeay et al. 1987). More than six weeks of exposure to concentrations of 100 mg/L reduces feeding success, reduces growth, causes avoidance, and displaces individuals (Spence et al. 1996).
  • All populations of coho salmon in the Klamath Basin have the potential to be exposed to elevated SSC during project implementation. All populations use the mainstem Klamath River as a migratory corridor during both the adult life stage and outmigrating smolt life stage. Additionally, some juvenile (i.e., young-of-year, subyearling, yearling) individuals from each population will use the mainstem for over-summer and over-winter rearing, although the proportion of populations using the mainstem for rearing varies.
  • Juveniles may rear in the mainstem throughout the year, and consist of sub-yearlings (0+) and yearlings (1+). Juvenile coho salmon have been observed residing within the mainstem Klamath River downstream of Iron Gate Dam throughout the summer and early fall in thermal refugia during periods of high ambient water temperatures (>22 °C). Sub-yearling juveniles may be present in the mainstem from the time they leave the tributaries to the following winter. However, most juveniles from the tributaries are assumed to rear in the tributaries. A small number of sub-yearling juveniles that successfully emerged from mainstem redds will be present in the mainstem until they redistribute in the fall. The Renewal Corporation modeled suspended sediment concentrations associated with reservoir drawdown using trap data, run timing, and location information to estimate exposure and potential risk to rearing 0+, rearing 1+, and outmigrating 1+ smolt coho salmon (Appendix H of FERC 2021a). Because coho salmon have complex life history strategies, we cannot predict with certainty the timing of exposure. Spring and seasonal redistribution of 0+ juveniles and outmigration is timed based on a variety of environmental cues. For example, the outmigration period may start in February and last into June. However, no individual fish spends that entire period of time in the mainstem.
  • Coho salmon smolts (1+ yearlings) are expected to migrate to the ocean beginning in late February, although most natural origin smolts outmigrate to the mainstem Klamath during April and May (Wallace 2003). Courter et al. (2008), using USFWS and CDFG migrant trapping data from 1997 to 2006 in tributaries upstream of and including Seiad Creek (e.g., Horse Creek, Seiad Creek, Shasta River, and Scott River), reported that 44 percent of coho salmon smolts were trapped from February 15 to March 31, and 56 percent from April 1 through the end of June. 

Sturgeon 2025 – A Retrospective

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Tom Cannon December, 2025

In a 9/12/25 post, I warned of poor summer conditions in the Bay for sturgeon.  This came on the heels of a poor population status assessment by CDFW.

From the Department of Fish and Wildlife: “Recent results from white sturgeon monitoring surveys by the California Department of Fish and Wildlife (CDFW) suggest the white sturgeon (Acipenser transmontanus) population has continued to decline. CDFW fisheries biologists now estimate there are approximately 6,500 white sturgeon between 40-60 inches long in California — down sharply from the previous estimate of approximately 30,000 fish in that size range, based on the 2016-2021 survey average.” https://mavensnotebook.com/2025/07/10/cdfw-scientific-surveys-show-continued-decline-in-white-sturgeon-population/

Not only was the recent adult sturgeon population survey estimate down, but the products of sturgeon reproduction in 2025 were nearly non-existent, a pattern inconsistent with an above-normal water year.   During the wet year 2023, white sturgeon reproduction in the Bay-Delta population was up sharply, as shown by numbers salvaged at the south Delta pumping plant fish salvage facilities (Figure 1).  In contrast, sturgeon salvage numbers were very low in summer of above-normal water year 2024.  In above-normal water year 2025, no sturgeon were collected in the south Delta salvage surveys.

Figure 1. Number of juvenile sturgeon salvaged at south Delta state and federal pumping plant fish screens in wet year 2023. Source: https://wildlife.ca.gov/Conservation/Delta/Salvage-Monitoring

A big reason for the unsuccessful sturgeon reproduction in water years 2024 and 2025 was poor conditions in the spring spawning and early rearing reach of the middle Sacramento River (Figure 2).  Water temperatures were above optimal (>65oF) and at times stressful (>68oF) or even lethal (>72oF) in 2024 and 2025.  Few juvenile sturgeon survive to reach the Delta under these habitat conditions.  This was one of the factors that led the State Water Board and USEPA to set 68oF as the water quality standard for the Sacramento River two decades ago. This standard is also a condition of the State Water Board water right permits for the state and federal water projects.

The water temperature standard could be met if river flows are maintained in the 8000-10,000 cfs range at the Wilkins Slough gage (WLK) located upstream of the mouth of the Feather River (river mile 120). (Note the water temperature benefit of higher flows in the May and June flow pulses in 2025.)

Figure 2. Lower Sacramento River flow and water temperature at Wilkins Slough gage (RM 120) Apr-Jul 2023-2025. Stress on egg and larval sturgeon occurs above 65ºF, whereas mortality begins at 70-72ºF.

The residual adult sturgeon population within their Bay summer habitat also experienced unfavorable elevated temperature conditions (>20ºC, 68ºF; Figure 3).

Figure 3. Water temperature and salinity in Suisun Bay at the Benecia Bridge gage, Aug-Nov 2025. Water temperature spike in mid-September occurred with Delta draining in super moon cycle and low Delta outflow (without Fall X2 Action).

For further detailed discussion of the status of sturgeon in the Central Valley see:  https://calsport.org/fisheriesblog/?cat=20 .

Sacramento River Salmon Redd Dewatering – Fall 2025

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I have previously reported on the dewatering of fall-run salmon redds in the upper Sacramento River near Redding during the early fall spawning season. Redd dewatering has a significant negative effect on salmon egg and fry production that translates to lower annual escapement and significantly contributes to the multi-decade decline in the population (Figure 1).

Figure 1. Escapement to the upper Sacramento River natural spawning area 1952-2024.

October is the peak in the fall-run Chinook salmon spawning season (Figure 2).  During early November 2024, the Bureau of Reclamation reduced Keswick Dam releases from the October average of 7000 cfs to 4000 cfs.  The flow reduction reduced water levels in the upper river spawning grounds below Keswick Dam from approximately the 11-ft water surface elevation (stage) to about the 8.5 ft level, a drop of about 2.5 feet.  In 2025, nearly identical flow management led to the same redd dewatering conditions (Figure 3). With most of salmon redds constructed in the 1-to-3 ft depth range, most were dewatered or only slightly watered and thus susceptible to high-egg-mortality conditions (low flow, warm water, low oxygen, and sedimentation).

The flow management strategy was also employed in recent wet years 2017 and 2019, although a more benign strategy was employed in historical wet year 2011 (Figure 4).  The issue has attracted inter-agency study and mention, but actions necessary to reduce the problem have been limited.

Figure 2. Stage and water temperature in the Sacramento River below Keswick Dam in fall 2024. Grey box denotes period when most fall run salmon spawn in the upper Sacramento River.

Figure 3. Stage and water temperature in the Sacramento River below Keswick Dam in fall 2025. Grey box denotes period when most fall run salmon spawn in the upper Sacramento River.

Figure 4. Stage and water temperature in the Sacramento River below Keswick Dam in fall of wet years 2011, 2017, and 2019.

American River Salmon Update – Spawning Season, November 2025

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In a 10/19/2023 post and a 11/21/2024 post, I discussed how the lack of access to Folsom Reservoir’s deep cold-water pool results in delayed natural and hatchery spawning of American River fall-run salmon.  Delays, and spawning in warmer water, cause reductions in spawning success, smolt production, recruitment into harvestable fishery stocks, and spawning escapement (run size) to the American River.  Lower salmon contributions from the American River significantly reduce California coastal and river salmon fishery stocks.  Poor production in the American River contributed to the closure of California salmon fisheries in 2023-2025.

During the 2020-2022 drought, Reclamation released water from the lower-level power bypass (sacrificing hydropower production) to provide the cold water (<55ºF) salmon needed for spawning in the ten-mile spawning reach from Nimbus Dam (near Fair Oaks gage) to the William Pond gage (Figure 1).  This is the prime spawning reach for salmon in the lower American River.  However, in the fall of the wetter years 2023-2025, Reclamation did not use the power bypass to release cold water (Figures 2 and 3), despite higher storage levels than during the drought (Figure 4).  The lack of cold water delayed natural spawning and hatchery egg taking, to the detriment of egg viability, fry production, and smolts reaching the ocean.

Ultimately, the number of adult salmon returning to the American River to spawn (escapement) is the important measure of success.  There are many factors that may contribute to the number of returns.  Recent returns are up (Figure 5).  The 2023 and 2024 returns were good despite having been the product of the 2020-2022 drought reproduction (Figurer 6).  Closed fisheries in 2023 and 2024 contributed to higher escapements.

I also believe efforts to improve fall water temperatures below Folsom during the drought improved both the wild and hatchery components of escapement.  I remain concerned that a return to warmer fall water temperatures will hinder future escapement.

I am also concerned with apparent efforts to sustain higher fall 2025 reservoir levels (see Figure 4) by reducing tailwater stream flow rates (Figure 7).  Such low flows reduce the quantity and quality of salmon spawning habitat.  Many critical spawning side channels become dewatered at such low flows1.  Main channel velocities, substrate, and depths are also compromised at low flow rates.

Reclamation  also reduced funding for the salmon hatchery and for river habitat projects in 2025, and will likely do the same in subsequent years.  This strategy will not help to recover American River salmon stocks to levels that once again can contribute toward commercial and recreational salmon fisheries.

Figure 1. Map of three CDEC gaging stations on the lower American River.

Figure 2. Average daily water temperatures in Nov-Dec period at William Pond gage 2021-2025. Red line (55ºF) denotes upper safe level for Chinook spawning.

Figure 3. Average daily water temperatures in November period at Fair Oaks gage 2021-2025. Red line (55ºF) denotes upper safe level for Chinook spawning.

Figure 4. Late summer and fall Folsom Reservoir water storage (acre-feet) 2021-2025.

Figure 5. Adult salmon escapement estimates for the American River 1975-2024. Source: Grand Tab.

Figure 6. American River spawner/recruit relationship – { log10(escapement) -3.5]. Number is year of escapement (recruits). Color denotes water year type two years prior. Red is dry, green is normal, and blue is wet. Note escapement in 2023 and 2024 are red, denoting spawning and rearing occurred two years earlier in dry water years.

Figure 7. Streamflow (daily average) in the American River at Fair Oaks gage Aug-Nov period 2021-2025.