In a paper published online last week in the journal Biological Conservation, a team of California researchers revealed a surprising finding: Juvenile winter-run Chinook aren’t just using the Sacramento River as rearing habitat; after hatching, they also venture in large numbers into the river’s tributaries, including creeks that feed into it below Redding, as well the Feather and the American rivers.
Winter-run Chinook are a distinct species of salmon that return each year to spawn and die in the Sacramento River near Redding. As recently as the 1960s, tens of thousands of adult fish used to make the one-way journey.
Now, as little as a few dozen come back. The population’s steep decline has forced federal water managers to cut back water deliveries from Shasta Dam to farms and cities in some years to preserve cold water the fish need to spawn. Commercial salmon-fishing seasons also have been restricted. Researchers say their findings may eventually lead to greater protections for waterways that hadn’t been considered vital to the survival of the species. …
Sturrock’s team was surprised to discover that the isotope data found in ear bone samples taken from adult fish in 2007 through 2009 revealed that up to 65 percent of the fish had traveled off the main Sacramento River channel as youngsters.
The study’s lead author, Corey Phillis of the Metropolitan Water District of Southern California, recalls thinking at first the readings were wrong.
“But then we started presenting this work at conferences, and we keep having (researchers) come up to us and saying, ‘Oh yeah, we would catch (young) fish that are far too large at that time of year to be anything other than winter-run,’” he said.
The findings come at a critical time for the winter-run Chinook. Cut off by dams from the spring-fed, cold-water tributaries in which the species used to spawn, the fish now lay their eggs in the heat of the summer in a short stretch of the Sacramento River below Shasta Dam.