Study Shows Obstacles California Salmon Face Enroute From Rivers To Sea
A new study from the University of Colorado reinforced the struggles that king salmon can have on their journey from Central Valley rivers through the Delta and then into San Francisco Bay and the Pacific. According to the project’s abstract to the full study:
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.
Here’s more from the CU report:
Gil and his team placed trackers in 424 juvenile Chinook salmon, as well as 23 striped bass and 17 largemouth bass. Using detectors placed along the riverbanks, the team monitored the activities of salmon and their predators, including when and where predators attack the most, for two months as they traveled through the San Joaquin River.
They found that salmon migrate over a much longer distance at night, a behavior that scientists had previously observed without fully understanding why.
The team’s data showed that during the day, predatory bass tend to concentrate and attack more frequently mid-river, where salmon prefer to swim. There, the currents flowing toward the sea are stronger, so salmon can ride the water downstream, saving energy.
To avoid those bass, young salmon have adapted to migrate mid-river at night. Meanwhile, by day, they seek refuge near the riverbanks— even though that means expending more than double the energy to swim the same distance.
“Intuitively, one would think these fish should just be taxiing right down the middle of the river all the time, so they can get out to the ocean and get away from all these terrifying predators as fast as possible. But that’s not what we saw,” Gil said. “Our study suggests that bass activities are forcing these fish to adopt a different strategy.”
Coming off a second straight year where all California salmon fishing was canceled, the California Department of Fish and Wildlife hosts a virtual meeting on Wednesday to discuss salmon escapement numbers and 2025 projections.
The Pacific Fishery Marine Council is set to meet in early March to discuss salmon management possibilities for the West Coast. PFMC will also soon determine if ocean fishing will be canceled again for a third straight year, which would surely also be the case in inland waters.
