November 2, 2021 — In drought years and when marine heat waves warm the Pacific Ocean, late-migrating juvenile spring-run Chinook salmon of California’s Central Valley are the ultimate survivors. They are among the few salmon that survive in those difficult years and return to spawning rivers to keep their populations alive, according to a study published October 28 in Nature Climate Change.
The trouble is that this late-migrating behavior hangs on only in a few rivers where water temperatures remain cool enough for the fish to survive the summer. Today, this habitat is primarily found above barrier dams. Those fish that spend a year in their home streams as juveniles leave in the fall. They arrive in the ocean larger and more likely to survive their one to three years at sea.
Researchers led by first author Flora Cordoleani, associate project scientist with the Institute of Marine Sciences at UC Santa Cruz and NOAA Fisheries, based their findings on an analysis of the ear bones of salmon, called otoliths. These bones incorporate the distinctive isotope ratios of different Central Valley Rivers and the ocean as they grow sequential layers.
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