Category Archives: Fish (general)

Butte Creek Spring-Run Salmon – May 2026 Update

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Central Valley Spring-run Chinook Salmon. Central Valley spring-run Chinook salmon typically return from the ocean and enter the Sacramento River system from February through June. Spawning occurs in Sacramento River tributaries from mid-September through early October with genetically distinct populations known from Clear, Mill, Deer, and Butte Creeks. Central Valley spring-run Chinook salmon also spawn in the Feather and Yuba rivers. Juveniles emigrate soon after emergence as young-of-year, or remain in or near their natal streams and emigrate as yearlings. Yearlings typically emigrate with the first flow increases in the fall and early winter. Similar to winter-run, Central Valley spring-run Chinook salmon populations have suffered significant declines in size. They are state and federally listed as threatened. CDFW

Butte Creek is a moderately sized tributary of the Sacramento River, located in California’s Central Valley near Chico, CA (Figure 1). It supports a core population of the threatened spring-run Chinook salmon native to the Central Valley and Sacramento River. Over the past decade, the Butte Creek watershed has experienced some of the largest Sierra fires of recent record.1 Prior to this period, the spring-run salmon in Butte Creek had represented a successful recovery within one of the Central Valley’s few remaining undammed streams.

I last updated the status of the Butte Creek spring-run salmon in a November 2024 post.  The spawning runs in spring-summers of 2023 and 2024 had been devastatingly low after suffering in the most recent three-year drought (2020-2022).  Some recovery in the spawning population in 2025 and 2026 brings a measure of optimism.

Problems with Recruitment

Low runs in 2023 and 2024 (Figure 2) suggest that brood years 2023 (BY23) and 2024 (BY24) will make limited contributions to runs between 2025 and 2028. Fewer eggs and any poor survival rates (e.g., from the 2024 fires or Thiamine deficiencies) will restrict recruitment of age 2-4 spawners from both brood years, limiting their contributions (recruitment into) to the future runs.

Initial survey findings show that the runs in 2025 and 2026 had fewer contributions from BY23 and BY24. Instead, most of the fish came from BY21 and BY22 spawners, whose offspring thrived during the wet years of 2023 to 2025 and gained advantages from fishery closures in those same years. Preliminary information on the 2026 run (not shown in Figure 2) indicates a low run, with only modest numbers of age-4 BY22 spawners, and lacking the normally predominant age-2 (BY 24) and age-3 spawners (BY 23).

The Cause

The cause of depressed recruitment in 2023 and 2024 was most likely poor spawning and early survival conditions during drought water years 2020-2022 that affected brood years 2020-2024.  The poor 2023 run was likely the consequence of poor survival of their source spawning adults (prespawn mortality in 2019-2021), eggs laid (2019-2021), and juveniles reared (2020-2022) of BY19-BY21 affected by the drought conditions of fall 2019 through winter-spring 2022.  For example, conditions in 2020 were very poor from low flows and high water temperatures from spring to fall (Figure 3).  The failure of PG&E’s Butte Canal in 2023 may have also been a factor.

The cause of the poor 2024 run is more complicated, because the number spawners in 2021 was high.  Drought conditions in fall 2021 and spring 2022 likely contributed to poor reproductive success and low smolt production (Figure 4).  However, the 2023 and 2024 ocean fisheries were closed, which should have more than doubled the normal run size.  The 2024 massive Park Fire may have contributed to the poor run, with lower summer-fall flows and higher water temperatures (Figure 5) and high pre-spawn mortality.

Other factors related to escapement (run size) include ocean conditions (e.g., the warm water blob and Thiamine deficiency), fishery harvest (or lack thereof), conditions in the lower Sacramento River and Bay- Delta.  All factors acting together in combination is yet another factor, with each factor potentially contributing to the other factors.

Conditions in the lower Sacramento River and Bay-Delta are changing for the worse.  For example, 2026 has been a relatively wet year, but poor snowpack and low March precipitation has led to stressful river and Bay-Delta habitat conditions in March during the peak of the adult spring-run salmon migration from the ocean.  Delta inflow was too low and water temperatures too high from mid-March to early April in 2026, almost as poor as drought year 2022 (Figures 6 and 7).  This problem led the Bureau of Reclamation to release a pulse flow from Shasta Dam in early April 2026 to help migrating salmon in the Sacramento River and its tributaries.

Solutions

The improvement of reliably robust runs of spring-run Chinook salmon is bound up in ongoing debates on how to manage Butte Creek salmon and their habitat.  Resource enhancement funds are scarce.  There is significant mitigation funding available from the PG&E 2023 flume failure that could play an important role.  More on solutions in upcoming posts.

Figure 1. Current distribution of spring-run Chinook salmon as reported by CDFG, 1998.

Figure 2. Butte Creek spring-run salmon escapement estimates by surviey 2001-2025. Source: CDFW.

Figure 3. Butte Creek water temperature and streamflow at USGS BCK-gage near Chico Feb-Oct 2020. Water temperatures above 18-20C are stressful to migrating and holding adult salmon.

Figure 4. Butte Creek water temperature and streamflow at USGS BCK-gage near Chico Aug 2021 to Jun 2022. Water temperatures above 18-20C are stressful to migrating juvenile salmon and holding adult salmon.

Figure 6. Flow in the Sacramento River at Freeport at the entrance to the north Delta in spring 2022-2026. Red line is recommended minimum Freeport flow. Source: CDEC.

Figure 7. Water temperature(F) in the Sacramento River at Freeport in the north Delta in spring 2022-2026. Red line is recommended maximum Freeport water temperature for spring salmon migrations. Source: CDEC.

Once again, Sturgeon overlooked in Spring 2026

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Water temperatures are reaching lethal levels (22oC) for the newly spawned sturgeon eggs and fry in the lower Sacramento River. To save this broodyear of sturgeon, resource managers must immediately increase flows in the lower Sacramento River. Right now, those flows are unusually low.

The San Francisco Bay-Delta watershed is home to two native sturgeon species: white sturgeon and green sturgeon. White sturgeon are popular among sport fishers in major rivers and the Bay-Delta. Green sturgeon are less common and are protected under state and federal endangered species laws, making their harvest illegal.

Both species migrate from the ocean or Bay into rivers to spawn—a behavior known as anadromy. Green sturgeon tend to spend more time in marine environments and travel further upstream to reproduce. White sturgeon are larger and sought after by anglers. Both types feed along river and bay bottoms, often attracted by bait that has a strong scent. The introduction of non-native clams has given sturgeon an abundant food source, potentially boosting their growth. However, they are sensitive to warm water and thrive best in cooler, saltier environments below 68°F (20°C).

Spawning poses significant challenges for sturgeon. They use stored energy in late winter and spring to reach clean, cool, fast-flowing rivers with deep, rocky bottoms where they lay sticky eggs. After several days, these eggs hatch. The young fry drift down to the Delta and Bay over about a month, feeding and growing along the way. Their survival depends on river conditions—low flow and warm water can be fatal in dry years. During wetter years, strong currents help them safely reach the Bay.

Once in the Bay, sturgeon can take 10 to 15 years to mature before returning upstream to spawn. Unlike salmon, sturgeon live long lives and can reproduce multiple times.

The frequency of wet years and the quality of Bay conditions both affect how many adult sturgeon persist in the population. Recently, recreational fishing has removed about 5–10% of adults annually. Droughts pose bigger risks—especially to white sturgeon—by warming Bay waters and encouraging algae blooms that deplete oxygen, sometimes causing mass die-offs during the summer.

Measures needed to support sustainable sturgeon populations amidst climate change include maintaining adequate river flows and suitable water temperatures in the Sacramento River, Delta, and Bay. This is especially important during spring and early-summer spawning and rearing periods.

Under current water management, most young sturgeon fail to survive the Delta due to poor flows, high temperatures, predation, and entrainment into water diversions. Summer is a critical season in the Bay, where most sturgeon reside, and healthy conditions are vital. Some years, large tides associated with Super Moons bring warm water into the Bay, triggering harmful algal blooms. Consistent freshwater inflow is necessary to support the food web and keep the Bay cool and oxygenated.

During consecutive dry years, population maintenance involves options like hatchery releases, rescuing stranded sturgeon, and stricter controls on fishing. The top priorities should be protecting breeding adults over 15 years old, ensuring adequate recruitment of younger subadults, and improving the survival of eggs and juveniles. Achieving these goals requires enhanced scientific monitoring and assessment of both the fish and their habitats, as is commonly recommended for other native fish like salmon and steelhead.

The current status of sturgeon is less well documented than other species like salmon, steelhead, smelt, and striped bass. Unlike others, there is no formal recovery plan for sturgeon. There are increasing calls to end the sport fishery and list white sturgeon as endangered. However, some scientists and resource managers argue that more pressing threats should be addressed first, and recommend focusing on gathering data from the fishery and data on population abundance.

In my last post on the sturgeon (February 2026), I hypothesized that the 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.  Water temperatures were above optimal (>65oF) and at times stressful (>68 oF) or even lethal (>72 oF) in spring 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 68 oF 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.

Once again, during a relatively wet winter-spring, both the sturgeon and the water quality standard seem to be overlooked (see Figure 1).

To save this broodyear of sturgeon, resource managers must immediately increase flows in the lower Sacramento River. Right now, those flows are unusually low.

For more on white sturgeon science, monitoring, and fisheries management see https://wildlife.ca.gov/Conservation/Fishes/Sturgeon/White-Sturgeon.

Figure 1. Sacramento River streamflow and water temperature at Wilkins Slough in the lower prime spawning reach of white sturgeon in spring 2026.

Figure 1. Sacramento River streamflow and water temperature at Wilkins Slough in the lower prime spawning reach of white sturgeon in spring 2026.

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 .