Summer Streamflow and Fish Survival
Oversummer flow and coho survival
Since 2010, California Sea Grant has conducted a study to correlate flow and environmental conditions with oversummer survival of juvenile coho, through a collaboration known as the Russian River Coho Water Resources Partnership. The Partnership, formed in 2009, is working to improve streamflow for fish and water supply reliability for landowners in five Russian River tributaries deemed critical to coho salmon recovery: Dutch Bill, Green Valley, Mark West, Mill and Grape creeks.
Partners work with landowners to develop streamflow enhancement projects to augment or forebear streamflow during the dry summer months. Sea Grant's role is to evaluate whether survival of juvenile coho is increasing as a result of those projects and to contribute to a better understanding of how much water coho need to survive throughout the dry summer months. The number of days that pools were disconnected from surface flow was the most important predictor of fish survival, with survival decreasing the longer pools were disconnected. If you're interested, you can learn more about our methods here and study outcomes.
Through a grant from the Wildlife Conservation Board, researchers at UC Berkeley were able to analyze the summer survival data at a finer scale (i.e., habitat-unit-scale survival at all sample intervals, versus reach-scale oversummer survival). Once again, days of disconnection stood out as the most important predictor of fish survival, followed by percent cropland cover within the watershed and pool volume. The study overview and preliminary outcomes can be seen in the second half of this slideshow.
The Partnership has also developed Streamflow Improvement Plans for Mill, Grape, Dutch Bill and Green Valley creeks, and is currently working to complete one for Green Valley Creek. This effort is funded by the National Fish and Wildlife Foundation, with additional support from Sonoma Water.