Wednesday February 26, 2025
PhysOrg —
For young salmon, the journey along the San Joaquin River in Central California is no small feat. Every spring and fall, thousands of these fish—each as long as a pinky finger—embark on a 350-mile race, swimming day and night and dodging predators along the way to reach the Pacific Ocean.
But less than 5% survive the journey, and in some years, hardly any make it. Elevated water temperatures, dams and poor water quality all endanger the animal, but human-introduced predators, including striped and largemouth bass, kill most of them.
In a new CU Boulder-led study, researchers reveal how these salmon learn to swim in different parts of the river at different times of day to avoid predators and conserve energy. The study was published in the journal Ecology Letters.
“The salmon fishery in the San Joaquin River delta area is on the verge of collapsing,” said Mike Gil, the paper’s first author and assistant professor in the Department of Ecology and Evolutionary Biology. “We know these juvenile salmon are getting wiped out on their migration to sea. We need to know why and how this is happening, and if there are opportunities to leverage conservation practices.”