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2005 Subyearling Migration

This overview provides an analysis of the migration of subyearling fish and the effects of court-ordered summer spill in 2005. The study examines survival rates and the impact of environmental variables such as flow, spill, and temperature. The analysis compares data from 1998 to 2005 and highlights the notable changes observed in 2005 due to the provision of spill.

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2005 Subyearling Migration

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  1. 2005Subyearling Migration Fish Passage Center

  2. Overview – summer migration • Court ordered summer spill occurred from June 20 to August 31, 2005 • Question was posed to FPC if any response could be determined for the juvenile migrants • No specific studies related to spill were conducted in 2005. RT studies were conducted, but did not address reach survival of juvenile migrants. • PIT tags data were available from production marking, as well as wild fish marking and various studies (transportation, hatchery operations)

  3. Historic Data Set • PIT tags available included: production/acclimation fish, wild chinook and research/surrogate fish. • Reach survival estimates (LGR to McN) possible since 1998. This was partly due to increases in the numbers of tags released and PIT tag recapture location at JDA. • Typical hydrograph – high flows occur in late May-early June – with subsequent decreasing trend. • Summer spill prior to 2005, if spill occurred, was during late high flow periods or during periods of excess market capacity (2002).

  4. Daily Avg Q Little Goose 1998 to 2005

  5. 1998 to 2005 Conditions

  6. Preliminary Analyis • Used available PIT-tags – conduct temporal analyses similar to those conducted with yearling migrants • 2 groups separated as much as possible into before/after spill began on June 20 • Estimated LGR to MCN survival of two groups • Assigned exposure indices for environmental variables • Compared 2005 to patterns observed in other recent past years • Originally compared back to 2001

  7. Survival LGR to McN for Subyearling Chinook before and during summer spill in 2005 with 90% CI’s

  8. Survival for Subyearling Chinook LGR to McN 2001 to 2005 with 90% CI’s

  9. Updates to Preliminary Analysis • Use shorter time intervals to better match reach survivals to environmental conditions • Adds distinct pre-6/20 (at LGS-IHR), transitional, post 6/20 groups • Expanded to include 1998 to 2000 migration years • Used weighted regression (inverse variance) • Introduces higher variability in survival estimates due to lower sample sizes

  10. Lower Granite Detection date ranges for Survival Groups

  11. Percent Post LGR Detects of Fall Chinook seen as Yearlings downstream of LGR – 7 d moving average Index of increasing holdover rates by mid-July

  12. Environmental Variables • Assigned Flow, Spill, Temperature variables for each group through each reach segment (LGR to LGS, LGS to LMN, LMN to IHR, IHR to MCN) • Averaged env. variable using two-week moving “window” based on median travel time for each detection group • Then averaged these assigned variables for an exposure index related to reach survivals

  13. Detection Group date range compared to Avg Total Q at Little Goose Dam

  14. Detection Group date range compared to Avg Spill Q at Little Goose Dam

  15. Detection Group date range compared to Avg Temp C at Little Goose Dam

  16. Subyearling Survival 1998 to 2005 Lower Granite Tailwater to McNary Tailwater

  17. Subyearling Chinook Survival versus Avg Spill Percent Lower Granite Tailwater to McNary Tailwater

  18. Subyearling Chinook Survival versus Avg Total Discharge Lower Granite Tailwater to McNary Tailwater

  19. Subyearling Chinook Survival versus Avg Temperature Lower Granite Tailwater to McNary Tailwater

  20. Subyearling Chinook Survival versus Median Travel Time Lower Granite Dam to McNary Dam

  21. Correlation Matrix Subyearling Data 1998 to 2005

  22. Multivariate Analysis • Tested for significant interactions between main effects (flow, spill, temperature) • No significant interactions detectable but variability and low sample size make multivariate approach tenuous • Backward Stepwise regression AvgFlow removed from model • Final Model N=26, adj mult R2= 0.651

  23. Conclusions • Relations between survival and flow, temperature and spill were significant based on weighted linear regression at p < 0.01 • Stepwise regression resulted in Spill and Temp remaining in model; flow and temp variables were highly correlated; interactions could not be fully assessed • Trend of survival in most years since 1998 was higher early decreasing throughout the period reflecting annual patterns in flow, spill and temperature.

  24. Conclusions • The notable exceptions were 2001 and 2005. The 2001 estimates were low throughout the extreme drought year. However, the 2005 survival estimates showed a distinctly different trend with higher survival observed for the later time period. • Given the relatively low flows and relatively warm temperature, the change in survival pattern in 2005 was likely due to the provision of spill. • Similarly, travel time estimates were shorter than expected for the late group in 2005, based on flow levels that occurred in that time 2005.

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