Oversummer Flow and Survival Study

UC Sea Grant is conducting a study to correlate flow with oversummer survival of juvenile coho. This study is being implemented through a collaborative effort known as the Russian River Coho Water Resources Partnership, which was formed in 2009 to develop a systematic approach to improve streamflow and water supply reliability in five critical Russian River tributaries. These streams include Dutch Bill Creek, Green Valley Creek, Mark West Creek, Mill Creek, and Grape Creek. 

The Partnership is working to return a viable, self-sustaining population of coho salmon to the Russian River watershed by improving spring and summer stream flow for rearing juvenile coho and coho smolts that are migrating to the ocean. Program partners work with streamside landowners to develop instream flow enhancement projects, including frost protection fans, rainwater catchment basins, off-channel storage ponds and other alternatives to water diversions during the summer months.

Our role in the Partnership is to monitor survival of juvenile coho in program streams before and after project implementation in order to evaluate whether survival is increasing as a result of Partnership projects.

Our second objective is to answer the question of how much water these fish need to survive and thrive throughout the critical summer months. In order to do this, we need to evaluate the complex relationship between flow, habitat conditions, and survival. 

To facilitate the study, two study reaches are established on each target stream, including one relatively unimpaired reach (reference) and one flow-impaired reach (treatment) where project implementation will take place . PIT tag antennas are installed at the downstream end of study reaches to monitor fish movement into and out of the study reach. Flow and water temperature gauges are installed to collect data on a continuous basis throughout the study period.

In June, approximately 500 juvenile coho are released into each study reach. Every four weeks between June and October, instream habitat condiitions are assessed and PIT tag wanding samples are conducted. Wanding is a relatively new method of sampling that allows us to count fish, and track fish distribution and movement, without handling the fish. A "wand" is a custom-made, portable PIT tag transceiver that is used to detect PIT-tagged juvenile coho in the stream habitat. When a tagged fish passes close to the head of the wand, the transceiver detects and stores the unique PIT tag number and the time that the fish passed through the field.