Adult Salmon Migrations in the Umatilla River Basin: Balancing Water Use for Irrigation and Fish

Large hydropower projects in the Columbia River basin have been demonstrated as impediments to upstream migration of adult salmonids, but low-elevation dams and irrigation diversions may also impact migration as fish approach spawning areas in smaller tributaries.  The Umatilla River has seven low elevation dams that may obstruct Chinook salmon and steelhead access to historically productive spawning areas.  The timing of migration, particularly of steelhead, during high-flow, turbid times of year, makes traditional counting methodologies difficult to employ. We used radio telemetry to examine fallback rates, passage routes, rates, and delays, holding and spawning locations, and maximum upstream distribution of Chinook salmon and steelhead in the Umatilla River basin (Oregon). Analyses focused on the effects of project modifications on salmonid passage, and on overall system use by fish.  Detections at fixed receivers and mobile tracking of 116 tagged steelhead, 28 spring Chinook salmon, and 82 fall Chinook salmon in 2010 provided data for these analyses. Recent project modifications at individual diversion structures have resulted in marked improvements in fish passages times. Species show preference for different aspects of the modifications; for example, jump pools are used by spring Chinook much more than steelhead. No diversions now stand out as targets for focusing modification energy with respect to adult salmonid passage. System passage times have also been markedly reduced. Locating key holding and spawning areas will provide information for additional habitat and restoration needs.  The determination of upstream distribution and spawning of hatchery fish will allow managers to better assess the use of hatchery releases to supplement historical spawning areas.