December 2, 2025 — Many thousands of fall-run Chinook salmon migrated beneath the Golden Gate Bridge into the upper Sacramento River to spawn this fall. About 100 of the adult fish carried small tags that signaled their location as they went.
A monitoring network tracked the fish, showing their progress online in real time as part of a joint project by scientists at NOAA Fisheries and UC Santa Cruz. They followed adult salmon through the Sacramento-San Joaquin River Delta into Central Valley Rivers and their tributaries. The scientists want to know what affects salmon survival and how many fish reach their spawning grounds.
“Are the salmon burning too much energy, and what factors affect this?” asked Miles Daniels, who leads the project for NOAA Fisheries’ Southwest Fisheries Science Center. The center operates a research laboratory adjacent to UC Santa Cruz, focusing on salmon. Adult salmon need cold water; they may stop if they hit water that is too warm. Since they do not eat on the way back upriver, delays could deplete the energy they need to complete their migration and spawn.
The research is funded by California’s State Water Board to learn more about how water temperatures influence the salmon that support valuable commercial and recreational fisheries. Officials are interested in whether water can be managed to benefit fish while still supplying Central Valley farms with irrigation water. Irrigation is vital to the production of billions of dollars worth of produce and other agricultural products every year.
Fall Chinook salmon are among today’s most abundant California salmon and have long formed the backbone of West Coast salmon fisheries. However, low numbers of returning salmon have closed California ocean waters to most recreational and all commercial salmon fishing for the last 3 years.