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Recruitment Failure

Recruitment Failure. Diagnosis Analysis Remediation. Recruitment failure (a.k.a. collapse). What are the “true” recruitment histories of the dam affected populations (Nechako, Columbia, Kootenay)

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Recruitment Failure

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  1. Recruitment Failure • Diagnosis Analysis Remediation

  2. Recruitment failure (a.k.a. collapse) • What are the “true” recruitment histories of the dam affected populations (Nechako, Columbia, Kootenay) • What information can we learn from historic recruitment (diagnosis) • Lab studies examining potential mechanisms of recruitment failure (analysis) • Pathway forward to field testing of remediation measures (remediation)

  3. Recruitment collapse– Kootenay • Many factors likely affecting recruitment (dams, dykes) in this system. Libby effects were the “final straw” (Note: M=0.07) • Sand substrates present at current spawning location

  4. Recruitment collapse - Nechako • Recruitment collapse coincides with the arrival of a sand wave downstream of the spawning site

  5. Nechako substrate change • Substrate changes identified in air photos between 1960-80 • Timing of substrate change at Vanderhoof WSC gauge coincides with timing of recruitment failure

  6. Recruitment collapse - Columbia

  7. Arrow Lakes Reservoir Kootenay River AR HKD KL Brilliant Dam Hugh Keenleyside Dam KOOT Columbia River WAN CAN. USA ROOS Pend d’Oreille River Waneta Dam Roosevelt Reservoir

  8. Recruitment collapse - Columbia • Lag between upstream (KOOT/HLK) and downstream groups (ROOS)

  9. Recruitment collapse - Columbia • Slope difference between KOOT/HLK/ROOS and Ft.Sheperd/Waneta groups

  10. Recruitment collapse - Columbia • Groupings are based on genetics and movement – NOT CONFIRMED • Multiple patterns complicate, but lags and slope differences are apparent • Cause likely related to slag either physically or contaminant loads (waterborne unlikely)

  11. Recruitment history caveats • Aging inaccuracy and imprecision can affect patterns (further work needed, though effect should be diminished on the age of fish critical to this diagnosis) • Confirmation of Columbia genetics critical (delayed. Should be completed spring 2006) • SUMMARY – causal connection with substrate change has some support, lesser evidence for contaminants

  12. Analysis - emerging link to substrates, but what is the mechanism • Strongest recruitment effect should be in young (most likely <1 mo.) • Juvenile studies don’t show substrate preferences

  13. Analysis – lab flume studies • Previous work by Bennett (in press) showed preference for pea gravel (1/2”) which subsides by day 12 • Present plot shows downstream movement greater with sand substrate (>>6 days at higher velocity) • Other studies have shown increased yolk resorption and greater mortality with sand substrates (Gessner 2005 – Atlantic sturgeon)

  14. Proposed work – 2006 and beyond • Expand substrate preference tests • Greater variety of substrates, including impacted • Presence of predator • Examine energetic effects • Artificial substrates preferred by larvae • Undertake field trials • Kootenay testing rip rap additions • Nechako planning pilot test of scarification and gravel addition • Need to look into larval releases, i.e <1 year old (Columbia,Kootenay)

  15. The end

  16. Field test – small scale (2006) • Small substrate alterations in the Nechako River at Vanderhoof • e.g. 3 substrates, 8 replicates, 1m^2 test sections (total 24m^2) • CHALLENGES • How to quantitatively sample larvae (1 cm) in a large river (2-4m, >1 m/sec) • Natural bed movement may cover test samplers • In 2004 we caught 1 • A risk that small scale tests may be futile (no/small effect size)

  17. New sand sheet overtopping an old sheet

  18. Assessment - Specific gauge analysis • Slow degradation 1952-68 • Accumulation 1968-93 • Degradation 1993 onward • Field notes indicate significant sand and gravel inputs in 1972 • No changes seen at Isle Pierre

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