"A vitamin deficiency likely killed as many as half of newly hatched fry of endangered winter-run Chinook salmon in the Sacramento River in 2020 and 2021. These new findings were published in the Proceedings of the National Academy of Sciences [led by CWS Senior Researcher Rachel Johnson].

The deficiency of thiamine, or Vitamin B1, is linked to large-scale shifts in the ocean ecosystem. These shifts changed the prey adult salmon consume before they return to West Coast rivers to spawn, scientists reported. They said the longtime loss of habitat and water has already weakened many California salmon populations. Further declines from thiamine deficiency or other impacts may lead to their extinction.

The deficiency syndrome can also affect salmon runs like the Central Valley’s fall-run that once supported valuable commercial fisheries across California. They have since dwindled to the point that commercial ocean salmon fishing in California has been closed for the last 3 years.

“Salmon in California have endured one blow after another,” said Nathan Mantua, research scientist at NOAA Fisheries’ Southwest Fisheries Science Center. “They have lost habitat, water, and access to higher elevations. Many are maintained in hatcheries. There is really no safety net left. Any new impact could be the final blow, especially if it continues over an extended period.”

The new research reports on the cause, extent, and impact of thiamine deficiency in salmon in California’s Central Valley. It found endangered winter-run Chinook and commercially valuable fall-run Chinook vulnerable. The problem has also been noted in some salmon in the Klamath River in Northern California. [...]"

From: "Anchovy Dominated Diets off the West Coast Pose New Dangers for Salmon". June 2025. NOAA Fisheries Feature Story: Southwest Fisheries Ecology News. https://www.fisheries.noaa.gov/feature-story/anchovy-dominated-diets-west-coast-pose-new-dangers-salmon 

Read the full NOAA Feature Story here