Flow and Survival Study

Oversummer flow and survival study

UC Sea Grant is conducting a study to correlate flow and environmental conditions with oversummer survival of juvenile coho, in collaboration with 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, including rainwater catchment basins and other alternatives to water diversions during the summer months. 

Our role in the Partnership is to evaluate whether survival of juvenile coho is increasing as a result of Partnership projects and to contribute to a better understanding of how much water coho need to survive and thrive throughout the dry summer months. In order to do this, we examine the complex relationships between flow, habitat conditions, and survival by carefully monitoring PIT-tagged coho salmon and environmental conditions in reference and treatment reaches. Click here to learn more about our methods. 

To date, this multi-year study has been conducted on Green Valley, Mill, Dutch Bill, and Grape Creeks, and the Partnership has completed numerous flow-enhancement projects. This work also led us to develop Streamflow Improvement Plans for both Mill and Grape Creeks. The Partnership is generously funded by the National Fish and Wildlife Foundation, with additional support from the Sonoma County Water Agency.

Late summer wetted habitat surveys

Insufficient instream flow is a primary limiting factor to Russian River coho populations. By late summer, many of the tributary streams have dried or only have intermittent pools remaining, both of which can lead to high mortality rates for the young coho and steelhead rearing there. UC Sea Grant has been documenting late-summer wetted habitat conditions on high priority tributaries since 2011, through our work with the Partnership and the Russian River Coho Salmon Captive Broodstock Program. Biologists walk each stream to document wet (continuous flow), intermittent (isolated units with no connected flow) and dry points, then compare the resulting maps to the locations where adult salmon and steelhead were observed spawning the previous winter and juvenile fish were observed in early summer.

The maps to the right show 2015 conditions for Mill Creek and its tributaries. Only 17% of the stream reaches where salmon and steelhead spawned and 14% of the reaches where young fish were observed earlier in the summer remained wet into September. On average, for all 14 streams surveyed in 2015, only 17% of the habitat where adult salmonids were observed spawning and 39% of the habitat where young fish were observed rearing remained wet into September. Click here for maps of all streams surveyed in 2015 and here for those surveyed in 2016.