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Snake River steelhead Management goals. Rishi Sharma Columbia River Intertribal Fish Commission Portland, OR. Overview of the talk. Stock status. Pre and Post Dam effects (1976 cut-off). Assessment of optimal spawning stock size.
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Snake River steelhead Management goals Rishi Sharma Columbia River Intertribal Fish Commission Portland, OR
Overview of the talk • Stock status. • Pre and Post Dam effects (1976 cut-off). • Assessment of optimal spawning stock size. • Assessment of SAR and its effect on optimal spawning stock size. • Rebuilding targets and in river management. • Conclusions.
Dam effect Where R=recruits, S=spawners and t is equal to 0 for the years before the completion of Lower Granite Dam (1976) and 1 after.
1968 was Lower Monumental • 1972 was Little Goose dam • 1975 was Lower Granite
Conclusions from dam analysis • We can’t mix data from pre and post 1976 (LGR was completed in 1975). • For rebuilding reference point’s we decided to use the pre 1976 data and use two models, the Beverton-Holt and the Ricker model. • Performed an analysis to use both models using Bayesian inference.
Assessing Uncertainty in Parameter estimates (juvenile data)
Conclusions from this analysis • Fit using the adult data was extremely poor (r2 was less than 0.1) • Decided we should use the juvenile data. • However, how do we assess smolt to adult return (SAR) in our adult management goal? • Simulated 4 SAR’s (encapsulating both passage and climate induced return rates) using observed smolt data and low, average, highest and rebuilding survival estimates. • Re-ran the analysis on adults simulated and used both models with an integrated goal.
Goals based on varying survival (passage and ocean/climate effect) • Low survival (17,000, CV=0.8). • Medium survival (21,000, CV=0.9). • Highest ever observed survival (27,000, CV=0.12). • Rebuilding target based on return rates from the Keogh River in BC (60,000, CV=0.11)
Implicit assumptions for rebuilding • Juvenile productivity is high. • Increase passage survival (adult mortality on average through the dams (14-60% mortality through dams for adult stage). • As long as SAR is low, management targets need to be low. • Rebuilding can only be attained through improving survival and/or increasing available habitat.
Overall conclusions • Dams had an effect on productivity pre and post 1975. • Current management targets should not be greater than 27,000 adults. • Rebuilding target of 60,000 adults can be attained through increasing productivity and/or capacity. Functions are different depending on which model we choose to use. • Aggregated goals for all Snake River steelhead are probably biased low, but the data resolution is unavailable at the sub-species or sub-population level.
Acknowledgements • Henry Yuen, USFWS my co-author in this work. • David Graves, CRITFC for the GIS based maps. • Charlie Petrosky, IDFG for sharing his juvenile data with us. • Technical Advisory Committee (TAC) for checking the validity of the data. • Dr. Nate Mantua and Dr. Bob Francis for influencing me to think about climatic effects on management goals.