Summer Streamflow and Survival

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 funded by the National Fish and Wildlife Foundation, with additional support from the Sonoma County Water Agency.

Summer wetted habitat surveys

Insufficient summer streamflow is the single biggest limiting factor to recovery of Russian River coho populations. By late summer, many of the tributary streams where juvenile coho and steelhead rear have dried or become intermittent, which can lead to high mortality rates for the young coho and steelhead rearing there. Sea Grant has been documenting late-summer wetted habitat conditions in relation to fish distribution on high priority tributaries since 2012. Biologists walk each stream in September to document wet, intermittent (isolated pools with no connected flow) and dry channel, then overlay the resulting maps with adult spawning observations from the previous winter and juvenile fish observations from early summer to determine the impact of stream drying on salmonids.

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 39% of the habitat where young fish were observed rearing remained wet into September. Click here for 2015 habitat and fish distribution maps and here for 2016.

In 2017, we received a grant from the Wildlife Conservation Board to document wetted habitat conditions on three life-cycle monitoring streams--Dutch Bill, Green Valley and Mill creeks--at two-week intervals over the summer season. You can see the 2017 maps here. Our partners at UC Berkeley will use data from this effort to build a predictive model of surface water recession to help guide resource management decisions.