A new NOAA Fisheries report identifies late-migrating juvenile spring-run Chinook salmon of California’s Central Valley as the ultimate survivors in drought years and when marine heat waves warm the waters of the Pacific Ocean. They are among the few salmon returning to spawning rivers in such difficult years to keep these populations alive, according to research published in early November in the journal Nature Climate Change.
“Some years the late migrants were the only life-history strategy that was successful,” according to Flora Cordoleani, lead author of the research and associate project scientist with NOAA Fisheries and the University of California Santa Cruz. These fish, Cordoleani said, can survive difficult drought conditions because they come from the few remaining rivers with accessible high-elevation habitats where water is cool enough through the summer.
The findings, NOAA Fisheries research scientist Rachel Johnson said, underscore the importance of providing secure cool-water habitat for fish so they can survive difficult conditions during drought and ocean warming.
“Most salmon blocks from their historical habitats appear to migrate just too early and perish once they encounter the warmer water temperatures during droughts,” Johnson explained.
The study also projected that river temperatures in the Central Valley would rise with climate change, leaving just a few higher-elevation rivers cool enough to sustain salmon. Many of these areas lie above existing dams without fish passage.
NOAA Fisheries has outlined a plan for reintroduction of salmon to cold water rivers above dams as a critical recovery strategy for endangered Sacramento River winter-run Chinooks. The reintroduction of threatened spring-run Chinooks to the San Joaquin River watershed has already taken hold and offspring of reintroduced spring-run kings are now returning from the ocean, the report said.
NOAA Fisheries is also advancing the reintroduction of spring-run Chinooks to the upper Yuba River upstream of Englebright Dam. The study also found that temperatures would stay cool enough for salmon to survive in the north Yuba River as climate changes.
“What’s needed now is to reconnect salmon to their historical habitats so they can draw from their own climate-adapted bag of tricks to persist in a warming world,” Johnson said.
By growing for a year in their home river, the later-migrating fish head for the ocean larger than others and in cooler temperatures, allowing for more to survive and return to their home rivers to spawn when marine heatwaves warm the ocean and depress salmon survival.