April 4, 2025 — A single severely dry winter temporarily, but dramatically, altered the ranges of three fishes — Chinook salmon, coho salmon, and steelhead trout — in California’s northern waterways.
In a new study, published this week in the journal Proceedings of the National Academy of Sciences, biologists found that the unusually dry winter of 2013-2014 caused some salmon and steelhead to temporarily disappear from individual tributaries and even entire watersheds along the northern California coast.
“California is at the southern end of the range for several species of salmon and trout, and because of a whole host of impacts, from colonization and engineered control of western rivers to climate change, these populations have been decimated,” said study lead author Stephanie Carlson, the A.S. Leopold Chair in Wildlife Biology at the University of California, Berkeley. “Our findings provide a glimpse into how an individual extreme event can trigger the widespread and sudden collapse of multiple populations and species and potentially result in longer term range shifts.”
During California’s historic multi-year drought of 2012-2016, the 2013-2014 winter was remarkable for having both very little rain and an extremely late start to the rainy season. By the time the first large rainstorms arrived in late January and early February 2014, many streams and rivers in Northern California were very low, and in some, the mouths had dried up completely, preventing salmon and steelhead from completing their annual voyages upriver to spawn.
The study examined how the drought affected Chinook salmon, coho salmon and steelhead trout, all part of the genus known as “salmonids,” in 13 coastal watersheds ranging from Marin to Humboldt counties. While all three fish species were impacted, Chinook salmon were able to cope by shifting their breeding activities downstream. However, fish monitoring data from the summer of 2014 revealed that steelhead trout had been eliminated from a number of individual tributaries, and coho salmon disappeared entirely from three coastal watersheds.