Implementation

During the summer of 2019, project partners excavated an alcove at the downstream end of the oxbow (pictured above). The goal was to move the cooler spring groundwater concentrated in the oxbow into the alcove to provide a cool water refuge for adult salmon as they migrate up the warmer reaches of the lower Yakima River. Large wood was added to the alcove, conditions created to restore fish passage to the downstream end of the oxbow channel, and the channel was planted to protect the cool water.

The project area also included an adjacent northerly side channel that is fully-connected to the river but is impacted by sediment accumulation and Water stargrass colonization. The side channel, oxbow, and springs were included in the description of river features identified as high priorities for enhancement in the Assessment of the Lower Yakima River in Benton County, Washington (Appel et al. 2011).

Fish Monitoring

To document use of the alcove by native fish we worked Yakama Nation Fisheries to develop a PIT tag monitoring site at RM 25 during 2021. This monitoring site will make use of the thousands of Yakima basin salmonids implanted each year with passive integrated transponders (PIT tag) by other monitoring projects. If one of these tagged fish enters the alcove their tag will be read by one of the two arrays installed within the alcove. When a tagged salmonid registers on either array its time/date stamp is then stored on a data logger.

The use of two arrays is crucial to gain a better understanding of how fish are using the alcove. Each array can pick up a PIT tag that comes within 8 inches of it. If a fish is detected on only the first array (red) investigators can assume it passed by the alcove however it cannot be said that they utilized the alcove for any great length of time. If a tagged fish registers on both arrays it demonstrates definitively that the fish utilized the alcove. Additionally, when a tagged fish registers on the array, that information is recorded with a time and date stamp so it will be possible to estimate how long a tagged fish remained in the alcove. This site will be monitored for 12 months and the results will help fisheries organizations better understand how fish use thermal refuge project.

Juvenile salmonid monitoring was accomplished using the established program of hatchery tagged fish being release upstream. In 2024, we detected 25 hatchery Coho on the project site antennas that were released at Prosser. Over one million Coho were released in March 2024, which shows a miniscule percentage of fish getting detected utilizing the alcove in any fashion. This project was not able to determine actual fish usage increases in the project area as data are not available to determine survival rates of juveniles within the lower Yakima River.

Of the 28 total fish detected in 2024, the average usage rate of the alcove was roughly 5 hours and carried by 7 fish whom were detected at the alcove for more than 1 day. 17 fish from first and last detection spent less than 10 minutes within the alcove.

The small percentage of detected fish on the pit tag antenna suggests a minimal usage of salmonids in this portion of the Yakima River for rearing. However, it also highlights that some juvenile or out migrating fish utilizing the fringe habitat for refuge with some opting to stay longer than others. This is also highlighted by the time individuals travel from release site to this detection site. Some fish were detected as soon as a day after release, while other individuals were detected up to 2-week post release. No fish were detected at McNary, however 4 tags were retrieved on Badger Island. This recovery percentage highlights a large predation trap exists between RM 25 and McNary.

Detection rates in early 2021 also indicated usage by Chinook and Coho juveniles prior to damage of the PIT Tag array by beaver in late spring of 2021.

Project Partners

The project was funded with support from the McNary Mitigation Fund, WA Department of Ecology's Husseman Fund, the WA Association of Conservation District's Voluntary Stewardship Program, the Yakima Basin Integrated Plan, and Regional Fisheries Enhancement Group funds.