The findings, published in the journal Ecosphere, add important context to the general scientific understanding that more water in the river improves fish survival. Previous studies, the authors explain in their paper, have demonstrated that more juvenile salmon migrating toward the sea complete their journey when the Sacramento River system contains more water. Just how much water has been the source of much controversy among user groups. “These studies have not explored the potential nonlinearities between flow and survival, giving resource managers the difficult task of designing flows intended to help salmon without clear guidance on flow targets,” write the authors, led by Cyril Michel of the Institute of Marine Sciences at UC Santa Cruz. Studying migrating Chinook salmon smolts under a wide range of hydrologic conditions, they found that fewer than three percent of fish carrying acoustic tags were detected after release at flows weaker than about 4,260 cubic feet per second. However, survival jumped to 19 percent at flows ranging between 4,260 and 10,700 cfs; they jumped again to more than 50 percent when the river was carrying between 10,700 and 22,870 cfs. However, fish survival did not improve at even greater flows. “It looks like survival plateaus beyond a certain point,” Michel says. “You can get a lot more bang for your buck if you aim for these thresholds.” Notably, the researchers calculated that achieving these key flow rates could be possible in most years without adding any extra water to the system by holding reservoir water back at times to release in pulses during heavy migration periods. However, Michel and his team did conclude that just a little extra water—about 150,000 acre-feet per year dedicated to the river system—would be helpful. Michel says he hopes his research will provide a productive guideline for agencies that manage reservoir releases and Delta pumping.

Pearls in the ocean of information that our reporters didn’t want you to miss
Preparing to tag a juvenile salmon. Photo: Cyril Michel
 

New research indicates that survival of juvenile Chinook salmon in the Sacramento River system can be significantly boosted by achieving key thresholds for river flow.

The findings, published in the journal Ecosphere, add important context to the general scientific understanding that more water in the river improves fish survival. Previous studies, the authors explain in their paper, have demonstrated that more juvenile salmon migrating toward the sea complete their journey when the Sacramento River system contains more water. Just how much water has been the source of much controversy among user groups. “These studies have not explored the potential nonlinearities between flow and survival, giving resource managers the difficult task of designing flows intended to help salmon without clear guidance on flow targets,” write the authors, led by Cyril Michel of the Institute of Marine Sciences at UC Santa Cruz. Studying migrating Chinook salmon smolts under a wide range of hydrologic conditions, they found that fewer than three percent of fish carrying acoustic tags were detected after release at flows weaker than about 4,260 cubic feet per second. However, survival jumped to 19 percent at flows ranging between 4,260 and 10,700 cfs; they jumped again to more than 50 percent when the river was carrying between 10,700 and 22,870 cfs. However, fish survival did not improve at even greater flows. “It looks like survival plateaus beyond a certain point,” Michel says. “You can get a lot more bang for your buck if you aim for these thresholds.” Notably, the researchers calculated that achieving these key flow rates could be possible in most years without adding any extra water to the system by holding reservoir water back at times to release in pulses during heavy migration periods. However, Michel and his team did conclude that just a little extra water—about 150,000 acre-feet per year dedicated to the river system—would be helpful. Michel says he hopes his research will provide a productive guideline for agencies that manage reservoir releases and Delta pumping.

About the author

A native to San Francisco, Alastair Bland is a freelance journalist who writes about water policy in California, rivers and salmon, marine conservation and climate change. His work has appeared at NPR.org, Smithsonian.com, Yale Environment 360 and News Deeply, among many other outlets. When he isn't writing, Alastair is likely riding his bicycle uphill as fast as he can.

Related Posts

A large pulse of water sent through the Yolo Bypass in summer 2016 boosted phytoplankton biomass and food web conditions in Cache Slough and the lower Sacramento River, a new report confirms.

 “Our goal was to improve estuarine habitat by increasing net flows through the Cache Slough Complex to enhance downstream transport of lower trophic-level resources, an important driver for fish such as the endangered Delta Smelt,” write the authors—including esteemed (and recently retired) California Department of Water Resources lead scientist Ted...

Electrofishing is a powerful but underutilized tool for monitoring Delta fish, particularly species favoring “structured” habitats that are difficult to sample using more common methods like trawls and seines.

By analyzing fish catch data from past surveys, researchers Ryan McKenzie, of the US Fish and Wildlife Service, and Brian Mahardja, of the US Bureau of Reclamation, determined that electrofishing resulted in better detection rates for many native and non-native species than net-based surveys. Although electrofishing is currently restricted to...

The robust monitoring programs established to track now-rare Delta smelt could benefit other native fishes, too.

Decades ago, resource managers first learned of declining Delta smelt numbers not through surveys targeting the once-abundant native fish, but rather as a byproduct of long-term monitoring programs for non-native striped bass. Now, the authors of a new study published in the March 2021 issue of San Francisco Estuary and...