Small Dams, Big Impacts; Adult Salmonid Migrations in the Umatilla River Basin

Like large hydropower counterparts in the Columbia River, low-elevation dams and irrigation diversions may impede adult salmonid migrations 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 historic spawning areas.  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 overall system use by fish.  Detections at fixed receivers and mobile tracking of 326 tagged steelhead, 130 spring Chinook salmon, and 206 fall Chinook salmon from 2009-2011 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 more than steelhead. 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.