Summer Streamflow and Fish Survival
Oversummer flow and survival study
CA Sea Grant is conducting 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, including rainwater catchment basins and other alternatives to water diversions 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. Follow these links to learn more about our methods and study outcomes.
The Partnership has also developed Streamflow Improvement Plans for Mill, Grape and Dutch Bill creeks, and is working on one for Green Valley Creek. This effort 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 stream reaches where juvenile coho and steelhead are rearing become intermittent or dry, leading to high mortality rates. 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 wetted habitat conditions, 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, the driest year in recent record, only 39% of the habitat where young fish were observed rearing remained wet into September. See the right side of this page for all maps by year.
In 2017, we received a grant from the Wildlife Conservation Board to conduct wet/dry mapping on three life-cycle monitoring streams--Dutch Bill, Green Valley and Mill creeks--at two-week intervals over the summer season. Past and ongiong wetted habitat conditions are documented in the 2017 and 2018 map books. 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.