Field Report: The State of California Chinook Salmon Populations

By Michael O’Farrell, Nate Mantua and Steve Lindley

On April 6, 2023, the Pacific Fishery Management Council (PFMC) adopted a near-complete closure of ocean salmon fisheries south of Cape Falcon, Oregon. Management measures allow for no fishing in California, and minimal fisheries in Oregon, which will be primarily focused on hatchery coho.

The widespread closures for 2023 stemmed from very low abundance forecasts for two key stocks: Klamath River and Sacramento River fall Chinook salmon. Both stocks are major contributors to harvest in California and Oregon ocean fisheries, yet also frequently limit ocean fishing opportu- nity. Figure 1 shows the highly variable but generally declining abundance of these stocks. The 2023 abundance forecasts (dots) are near record lows.

Why have abundances declined in recent years? A convergence of longterm stressors, climate extremes, and higher than anticipated ocean harvest, has brought us to this point.

California has recently been plagued by hot drought conditions. Droughts in 2012-2016 and 2020-2022 reduced stream flows and depleted water stored in reservoirs, resulting in warm temperatures and low flows during critical parts of the freshwater life stages. In the ocean, the California Current experienced heat waves from 2014-16 and

2019-21. Much of the Oregon and California coast featured poor conditions for salmon, while pockets of good conditions could be found in some coastal areas with localized upwelling. Widespread thiamine deficiency was discovered in Central Valley Chinook stocks in 2020, and has persisted into early 2023, coincident with, and likely caused by, record abundance of anchovies in central and southern California’s coastal waters. Additionally, the efficiency of the commercial salmon fishery in California has been anomalously high, with catches exceeding expectations for the past five years.

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While the salmon fishery closures were brought about by low abundance of fall run stocks from the Sacramento and Klamath rivers, other California salmon stocks have experienced more pronounced declines over time. These stocks include winter, spring, and latefall run Chinook in the Sacramento Basin, and spring Chinook in the Klamath Basin. Coho salmon populations have also declined in California despite a ban on coho fishing since 1993.

The underlying causes of the longer term declines include habitat loss and degradation, in some cases due to unresolved conflicts over water management that intensify during droughts. Fish hatcheries are intended to mitigate these habitat problems and increasingly are relied upon to mitigate drought impacts, but they have some unintended negative effects. These include loss of phenotypic and genetic diversity, support of harvest rates that are likely unsustainable for naturallyspawning populations, and increased disease prevalence. In combination, these trends are increasing the reliance on hatchery production and the overall productivity of these systems has declined while becoming more volatile.

Despite the aforementioned issues, there may be a bump in abundance following California’s exceptional winter. A massive snowpack, saturated landscape, and full reservoirs after a cold and wet winter should dramatically improve this year’s freshwater conditions and up the odds for increased adult salmon and steelhead abundance 1 to 3 years from now. On the other hand, expectations for El Niño-related warming of the California Current later this year may limit ocean productivity in the next year or two.

California salmon are in a dire situation. Rebuilding populations and fisheries will require major actions to restore diversity and resilience in the freshwater production system. Continuing ongoing work to better align hatchery and harvest policies with long-term recovery goals will also be needed. Existing stressors that have been limiting the quality, quantity, connectivity, and diversity of habitat options needed to boost population resilience must be addressed if we hope to make space for California’s salmon to adapt to our warming and increasingly variable climate.

For more information:

Pacific Fishery Management Council salmon fishery planning documents: https://www.pcouncil.org/salmon-management-documents/

Thiamine Deficiency in California salmon: https://www.fisheries.noaa.gov/featurestory/researchers-probe-deaths-central-valley-chinook-possible-ties-oceanchanges

Michael O’Farrell leads the Fisheries Assessment Modeling Team at NOAA’s Southwest Fisheries Science Center in Santa Cruz, CA and participates in the annual ocean salmon season setting process as chair of the Pacific Fishery Management Council’s Salmon Technical Team.

Nate Mantua leads the Landscape and Seascape Ecology Team at NOAA’s Southwest Fisheries Science Center in Santa Cruz, CA. This team is focused on science in support of salmon, steelhead and sturgeon recovery in California. Prior to 2013 he was at the University of Washington’s Climate Impacts Group for 17 years, with the last 6 on the faculty in the School of Aquatic and Fishery Sciences.

Steven Lindley is the Director of the Fisheries Ecology Division at NOAA’s Southwest Fisheries Science Center in Santa Cruz, CA. The Fisheries Ecology Division conducts science to support sustainable groundfish and salmon fisheries and conservation of protected fish species and the habitats upon which they depend. Much of his research at NOAA has focused on salmon, steelhead, and sturgeon that spawn in California’s Central Valley.

West Coast Salmon and Steelhead 5year Status Reviews: https://www.fisheries.noaa.gov/westcoast/endangered-species-conservation/report-card-recovery-reviews-asse ss-28-salmon-and

Recovery Through Reintroductions for California’s Central Valley Salmon: https://www.fisheries.noaa.gov/westcoast/endangered-species-conservation/recovery-through-reintroductionscalifornias-central-valley-salmon https://www.fisheries.noaa.gov/about/so uthwest-fisheries-science-center

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