Radio-Tracking Study Greatly Advances Central Valley Salmon Science

Over the past five years (2018-2022), federal and state biologists have undertaken a comprehensive study of salmon smolt migrations down the 350 miles of the Sacramento River from below Shasta Dam to the Delta, Bay, and ocean.  The study released thousands of radio-tagged late-fall-, spring-, fall-, and winter-run hatchery and wild smolts in the Sacramento River near Redding (RM 290), then tracked their progress and survival as they proceeded to Butte City (RM 170), the Tower Bridge in Sacramento (RM 60), and Benicia Bridge at the head of San Francisco Bay.  Each release group provides a story that is helping our understanding of salmon science in the Central Valley.  Most important are lessons learned about drought and climate change.  Much has been learned, with more to come.

An Example: Releases of Radio-Tagged Winter-Run Smolts

Radio-tagged winter-run salmon smolts from the federal Livingston Stone Fish Hatchery were released to the Sacramento River at Redding in winter of years 2018-2022.  Their signals were detected from Butte City to the Benicia Bridge at the head of San Francisco Bay.  For example, Figures 1 and 2 show detections from a release at Redding on 2/14/2019 of 650 radio-tagged smolts.  Figure 1 shows detections over the winter and early spring at Butte City, 120 river miles downstream of Redding.  Figure 2 shows detections at the Tower Bridge in Sacramento, 230 river miles below Redding.

Preliminary Findings

A summary of release-group survival in Table 1 indicates the following:

  • Survival was significantly compromised in dry years 2018, 2020, 2021, and 2022 compared to wet year 2019.
  • Survival was poor in the upper river and the Delta.
  • December late-fall-run releases during wet periods in generally dry years had relatively high survival.

Other findings include:

  • Smolts that received thiamine “boosts” in the hatchery had slightly higher survival.
  • Approximately 20-25% of smolts are diverted into the central Delta at Georgianna Slough
  • Survival among release groups within a year was often related to flow and/or water temperature after release (Figures 3 and 4).
  • Fall-run salmon grown in 2020-2021 at the Coleman Fish Hatchery on Battle Creek had significantly higher survival when released at Butte City than when released directly from the hatchery about 80 miles upstream of Butte City.

 

Table 1.  Percent survival summary for release groups by run and year.

Winter Run Hatchery Chinook – released at Redding

Year To Butte City To Sacramento To Bay
2018 18.4
2019 64.5 23.3 25.6
2020 25.8 13.2 3.5
2021 25.8 10.1 3.6

Late Fall Run Hatchery Chinook – released at Battle Creek Hatchery

Year To Butte City To Sacramento To Bay
2018 0.17
2019 23.5 4.8
2020 76.1 60.4 16.9
2021 36.6 14.3 4.7
2022 75.5 17.1

Battle Creek Hatchery fall run – released at Battle Creek Hatchery

Year To Butte City To Sacramento To Bay
2019 46.0 22.0
2020 36.4 9.1 0.1
2021 0.3 0.0

Battle Creek Hatchery fall run – paired study

Year To Sacramento To Bay
2021 at Battle Ck 1.7 0.0
2021 at Butte City 26.3 4.7

Feather Hatchery spring run – released in lower Feather River

Year To Sacramento To Bay
2019 49.4 26.2
2020 26.8 2.6
2021 28.6 2.2

Wild Chinook Red Bluff Release

Year To Butte City To Sacramento To Bay
2018 3.2
2021 2.2 0.0 0.0

American River Hatchery Chinook – lower American River release

Year To Sacramento To Bay
2018 68.1 2.0

Butte Creek Wild Spring Run – lower Butte Ck

Year To Sacramento To Bay
2018 27.2
2019 16.3 1.5
2021 0.0 0.0

Battle Creek Start-up Hatchery Winter Run Chinook to Battle Creek

Year To Butte City To Sacramento To Bay
2019 23.3 14.0
2020 17.5 9.4 0.0
2021 11.5 3.3 0.2

Figure 1. Detections at Butte City of hatchery winter run smolts released at Redding with flow at Butte City gage 2/14/2019.

Figure 2. Detections at Tower Bridge in Sacramento of hatchery winter run smolts released at Redding with lower Sacramento River flow at Wilkins Slough 2/14/2019.

Figure 3. Survival rate to Sacramento of wild Butte Creek spring run radio-tagged release groups with Butte Slough flow in 2018.

Figure 4. Survival rate to Sacramento of wild Sacramento River fall run radio-tagged smolts, Red Bluff release groups with lower Sacramento River flow and water temperature at Wilkins Slough in 2018.

Wishful Thinking on The Upcoming 2022 Salmon Season

We should be careful about wishful thinking in considering the forecasts for the 2022 California salmon season along the coast and in major rivers.1  The 2022 ocean abundance projection for Sacramento River fall Chinook, a main salmon stock harvested in California waters, is estimated at 396,500 adult salmon, a higher number than the 2021 forecasts. However, we should expect further drought-related fishery and escapement downturns in 2022 and 2023, as occurred after the 2007-2009 and 2013-2015 droughts (Figure 1). We can also expect low fishery catches, especially in rivers from low summer flows and associated high water temperatures that keep river spawners in the Bay until rivers cool in the fall.

The issues relate primarily to remaining stocks of Chinook salmon, not to the nearly extinct endangered Coho. The 2022 season also relates mostly to the availability of brood year 2019 salmon from Central Valley rivers, not coastal streams. Finally, it is important to remember that most of the adult salmon in 2022 will come from hatcheries on the Klamath, Trinity, Sacramento, Feather, American, Mokelumne, and Merced rivers, especially those hatcheries that truck and barge salmon to the Bay or coast.

Hatchery returns, the backbone of California salmon fisheries, are likely to be lower in 2022 than expected. Near 40 million Chinook salmon smolts from brood year 2019 were released from California federal and state hatcheries in 2020. Of the total, about 26 million were raised at Sacramento River watershed hatcheries, 9 million at San Joaquin River hatcheries, and 4 million at Klamath-Trinity hatcheries. Most of the releases were fall-run (34 million), with about 4 million spring-run, 1 million late-fall-run, and 0.4 million winter-run. Their returns of jacks and adults are likely to be lower in 2022 than expected because of low Delta inflows and outflows (Figure 2) and low Klamath-Trinity flows (Figures 3 and 4) in winter-spring 2020 and 2021, which are likely to result overall in relatively poor returns from river and Bay releases of hatchery smolts.2

Wild salmon stocks, already severely depressed, are going to further decline and contribute even less to fisheries. Natural production of brood years 2019 and 2020 was likely poor because wild smolts faced dry-year conditions in winter-spring 2020 and 2021, respectively.

Adult salmon that return to spawn in 2022 will face warm rivers, as they did in 2021 (Figures 5 and 6). They will be delayed, and many will die before spawning.

In summary, we must be careful about wishful thinking about the future based on the recently released ocean abundance estimate for 2022. Many other factors point in a downward direction. Perhaps the most immediate question is whethersalmon will simmer again in what looks to be a dry, hot summer.

Figure 1. Sacramento River Basin fall-run salmon escapement 1975-2020.

Figure 2. Sacramento-San Joaquin Delta outflow 2014-2022.

Figure 3. Klamath River flow at Orleans 2014-2022.

Figure 4. Trinity River flow at Hoopa 2014-2022.

Figure 5. Flow and water temperature in the lower Sacramento River at Wilkins Slough in 2021. Red line is 20ºC (68F) water quality standard and safe upper level for salmon.

Figure 6. Water temperature at Wilkins Slough in 2021 and recent historical average.

Salmon Released from Central Valley Hatcheries

Hundreds of thousands of smolts of endangered salmon are being released to the lower Sacramento River from federal and state hatcheries this winter, the San Francisco Chronicle reported on March 2.1 It is a drought year, and most of the young salmon will likely perish in the jaws of predators on their 300-mile journey to the ocean through the river, Delta, and Bay. Without the protection of adequate river flow, cold water, and turbidity for the journey, there is little hope. Reservoir storage is depleted from the past two years of overzealous water deliveries. What little rain and snowmelt there has been in the Valley is being stored in reservoirs. Warm weather has come early. The 400 thousand smolts released on March 2 could use some help, but they have not received it and are not likely to get it.

River Flow

Flow from Shasta Reservoir to the upper river via Keswick Dam has been minimal (Figure 1, KWK). 40 miles downstream at the Bend (BND) gage near Red Bluff, the river received some snowmelt from tributaries in January, but even that tapered off by the end of January. Flow into the Delta from the Sacramento Valley at Freeport (FPT) reached minimal levels by the end of January. Delta outflow (Figure 2) settled at its minimal prescribed level near 12,000 cfs after some January export taking.

Water Temperature

Warm weather and low flows have allowed water temperatures in the lower Sacramento River and north Delta migration corridor to reach the mid-fifties (Figure 3), temperatures that activate lower river predators like striped bass, resident trout, and pikeminnow.

Turbidity

Turbidities (Figure 4) are now at seasonal lows from the upper river near Red Bluff (RDB) to the Delta near the Rio Vista Bridge (RVB), reflecting clear waters needed by sight-feeding predators like striped bass.

Delta Salmon Salvage

Hatchery salmon smolts released in December at least reached the Delta during the December storms (Figure 5). It remains to be seen if the February and March smolt releases even reach the Delta.

What’s Needed

The article in the Chronicle mentioned that only one of the 140 radio-tagged hatchery smolts released in February has reached the Delta. The March 2 release of 400,000 smolts could use a pulse of cold turbid water from Shasta, Oroville and Folsom reservoirs to help them reach the Bay. So far, only Oroville releases have increased, from 3500 to 5500 cfs in recent days, with the added 2000 cfs showing at Freeport (Figure 1). While this helps near the Delta, it does little for the upper 200 miles of river the smolts have yet to transit.

Figure 1. River flows near Keswick (River Mile-RM 300), Bend (RM 250), and Freeport (RM 50) in winter 2022.

Figure 2. Delta outflow in tidally averaged daily cfs in winter 2022.

Figure 3. Water temperature in Sacramento River near Bend (RM 250), Wilkins Slough (RM 140) and Freeport (RM 50) in winter 2022.

Figure 4. Water turbidity in Sacramento River near Bend (RM 250), Red Bluff (RM 240), Freeport (RM 50), and Rio Vista (RM 30) in winter 2022.

Figure 5. Salmon salvage observed at Delta Fish Facilities in water year 2022.