Downstream Passage of Steelhead Kelts through Hydroelectric Dams on the Lower Snake and Columbia Rivers

Abstract

AbstractAfter spawning, iteroparous steelhead Oncorhynchus mykiss from the Columbia River basin must navigate several hydroelectric dams on their way to the Pacific Ocean. We used radiotelemetry to investigate migration rates, downstream passage routes, and success of adult steelhead kelts migrating past lower Snake River and Columbia River dams during the springs of 2001 and 2002. Seaward‐migrating kelts were collected, radio‐tagged, and volitionally released from the juvenile bypass facilities at Lower Granite Dam (LGR) on the Snake River and at McNary Dam (McN) and John Day Dam (JDD) on the Columbia River. Migration success rates from LGR to the study area exit (8 km east of Portland, Oregon) were poorer during the low‐flow nonspill conditions of 2001 (4.1%) than in the more typical flow year of 2002 (15.6%). Kelts tagged and released at Columbia River dams had substantially higher migration success than those released on the Snake River; 59.6% and 62.3% of the kelts released at McN and 63.6% and 80.0% of those released at JDD were contacted at the study area exit during 2001 and 2002, respectively. Kelt dam passage was predominately via spillways and surface flow routes, and during periods of spill 90.0% or more kelts typically passed via nonturbine routes. Only 47.2% of kelts were guided out of turbine intakes by screen systems during nonspill periods. Turbine passage, the primary alternative route during nonspill periods, may be a substantial source of kelt mortality. The poor migration success rate of Snake River kelts in both 2001 and 2002 suggests that additional management (i.e., kelt reconditioning, transportation, or both) may be warranted to boost iteroparity rates in this population.