Reanalysis and Interpretation of 25 Years of Snake–Columbia River Juvenile Salmonid Survival Studies

Abstract

Tagging studies to estimate salmonid smolt survival during out-migration have been an integral component of hydroproject mitigation programs for decades in the Snake–Columbia River basin. Fifty-three smolt survival investigations from 1971 to 1996 were reexamined to identify general patterns for survival of smolts through turbines, spillbays, and river reaches. Average survival that measured both direct and indirect effects from turbine passage was based on 102 Kaplan turbine replicate releases. Average Kaplan turbine survival was estimated to be Ŝ = 0.873. However, direct mortality estimated from 9 Kaplan turbine balloon tag replicate releases was Ŝ = 0.933. For spillways, passage survival was estimated to be 1.005 from 45 different replicate releases. However, survival of smolts through non-deep-plunge spillways (Ŝ = 1.030) was significantly higher than through deep-plunge spillways (Ŝ = 0.842). Also, smolts of steelhead Oncorhynchus mykiss had lower spillway survival (Ŝ = 0.910) relative to other salmonid smolts. Our meta-analysis provides within-year and between-year variance components that can be used in the design of future smolt survival studies.