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Partial migration in Oncorhynchus mykiss : A spatially and sexually explicit approach

Analyzing the spatial and sexual dynamics of Oncorhynchus mykiss migration through predictive models based on broad-scale environmental data. The study focuses on female anadromy patterns and local variability to understand the drivers of migration. Various factors such as stream size, water temperature, and biological organization are considered in predicting migration behavior. The research highlights the predictability of female anadromy and emphasizes the importance of stream size in determining migration patterns.

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Partial migration in Oncorhynchus mykiss : A spatially and sexually explicit approach

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  1. Partial migration in Oncorhynchus mykiss: A spatially and sexually explicit approach J. McMillan photos Justin Mills, USGS/OSU (MS, 2008) Jason Dunham, USGS-FRESC Chris Jordan, NOAA-Fisheries Gordie Reeves, USFS-PNW John McMillan, USGS/OSU (MS 2009) Chris Zimmerman, USGS

  2. Sex and migration J. McMillan photos

  3. Space: John Day River

  4. Study objectives • Broad-scale measures of female anadromy • Predict patterns of female anadromy • Assess potential importance of local variability

  5. Study design Collect juvenile O. mykiss Test for non-random distribution Determine maternal origin Collect water samples Sites with anadromy Tests of model performance Broad-scale environmental variable(s) Predictive model Test for residual spatial variation

  6. 2.4 2.2 2 1.8 Sr/Ca ratio 1.6 1.4 1.2 1 0 200 400 600 Distance from centrum (microns) Collection and maternal origin Four otoliths Two fish + water sample P. Stratis photos

  7. Anadromy was common, widespread Anadromy at 52 of 72 sites Two rainbow trout offspring One of each Two steelhead offspring

  8. R S = Rainbow trout offspring = Steelhead offspring How is maternal origin distributed? S R R R R S S S R S S R R R S R R R S R S S S S S S S S R S S S R S S S S S R S S R R S Random distribution Numerical dominance or spatial segregation

  9. Maternal origin was clustered ² = 11.15, df = 1, P < 0.001 n = 47 sites; only those with 2 juveniles < 2 years old

  10. Objective 2: Predictive model Sites with anadromy Tests of model performance Broad-scale environmental variable(s) Predictive model Test for residual spatial variation

  11. Stream size and anadromy • Associated with many ecological and physical processes • Sediment transport • Water temperature • Biological organization • Readily used in spatial statistics • Simple to estimate for large area

  12. 2000 1500 1000 Elevation (m) 500 0 -5 -4 -3 -2 -1 0 1 2 Log(mean annual runoff; m3/s) Rainbow trout offspring Steelhead offspring Anadromy varied with stream size

  13. Autocorrelated residuals A B ΔResidual ΔDistance Mantel test for spatial autocorrelation Euclidean distance Stream network distance

  14. 1.0 0.8 0.6 ΔResiduals 0.4 0.2 0.0 0 100 200 300 400 500 600 ΔStream network distance (km) No spatial autocorrelation • Mantel tests non-significant • Spatial gradients accounted for by model Subset of 1/5 of pairwise distances

  15. Bottom lines • Sampling approach proved useful • Female anadromy was predictable • Stream size accounted for most of the broad-scale variability in female anadromy • Local factors potentially source of remaining variability J. McMillan photos

  16. Improvements • Model improvements • Redd counts • Combined probabilistic predictions • Local factors • Bioenergetics • Species interactions • Community effects • Ecosystem processes • Doesn’t address males • Doesn’t address resident females

  17. Discussion • The process: critical periods, sexual tension, and everything in-between • The evidence: observation, model, experiment – correlation vs causation? • The relevance: ESA listing, modeling, monitoring, recovery du les sauvages?

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