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.

Run reconstruction (Snake Steelhead)

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Snake River escapement

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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.

lo g ( )e

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•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 (adult data)

Beverton-Holt Ricker

Figure 3. Likelihood profiles for Beverton-Holt estimates of productivity and capacity, and for Ricker estimates of productivity and parameter B, all based on adult-return data.

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Assessing Uncertainty in Parameter estimates (juvenile data)

Figure 3. Likelihood profiles for Beverton-Holt estimates of productivity and capacity, and for Ricker estimates of productivity and parameter B, all based on smolt-recruit data.

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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.

Figure 6. Posterior probability distribution of Smsy from Ricker and Beverton-Holt curves using smolt recruit data and three levels of average ocean survival. Combined posterior probablity distribution using Bayesion methods.

6.4% ocean survival

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Posterior Beverton-Holt (Juvenile)

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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)

Rebuilding and Fish Management 101

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.