Anomalous ocean conditions in 2015 may bode poorly for juvenile Chinook salmon survival

According to researchers from Oregon State University and the National Oceanic and Atmospheric Administration, ocean conditions were historically bad in the spring of 2015, when migrating yearling fish that will comprise the bulk of this spring's adult Chinook salmon run first went out to sea. In fact, Pacific Decadal Oscillation values – which reflect warm and cold sea surface temperatures – suggest it was one of the warmest nearshore oceans encountered by migrating Chinook salmon dating back to at least 1900.

The lack of food for the salmon in 2015 may have resulted in significant mortality that will show in this year's run of Columbia River springers. One way or another, it will provide new information on fish survival and whether juvenile salmon prey data can help resource managers predict future returns.

Results of the research, which was funded by the Bonneville Power Administration and NOAA, have just been published in the journal Marine Ecology Progress Series.

About 80 percent of a typical spring Chinook run on the Columbia River come from fish that went out to sea as yearlings two years earlier, according to lead author Elizabeth Daly, a senior faculty research assistant with the Cooperative Institute for Marine Resource Studies, jointly operated by OSU and NOAA out of the Hatfield Marine Science Center in Newport.

"When juvenile salmon first enter the ocean, it is a critical time for them," Daly said. "They are adjusting to a salt-water environment, they have to eat to survive, and they have to avoid becoming prey themselves. When we sampled juvenile salmon in May and June of 2015, the fish were much smaller and thinner than usual, and many of them had empty stomachs. There just wasn't anything for them to eat."

Read more at phys.org