UC Berkeley On That Dry Winter A Decade Ago That Hit Salmon And Steelhead Hard In Coastal Rivers

UC Berkeley released a recent study describing how the dry winter season in 2013-14 was devastating for salmon and steelhead spawning habitat in coastal rivers. Here’s more from Cal’s report:

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.

“Because of the delayed rainfall, the timing of elevated river flows was mismatched with the arrival of the fish for breeding, and we saw different impacts for different species in different places,” Carlson said. “The most extreme cases were coho salmon that spawn in coastal rivers that have so-called intermittent estuaries, where a sandbar forms across the mouth of the estuary during the dry season. There were three systems in Mendocino where the sandbar never opened the whole year, and coho salmon were lost from the entire watershed.”

In the decade since that drought, all three species have fully recovered their original ranges. This is due to both lifecycle diversity within fish populations and, in the case of the Russian River, a conservation hatchery. Salmon and steelhead can vary in how many years they spend at sea before returning home to breed; because of this, some fish from the impacted rivers were still growing at sea during the 2013-2014 season and were able to return the following year to help repopulate those rivers.