Understanding Snake River Salmon Migration & Age Tactics

1. Migration pathway, age at ocean entry, and SARs for Snake River Basin fall Chinook prior to summer spill at LGR, LGS, and LMN dams

2. Prehistorical Metapopulation - Subyearling ocean entrants Core Area

3. Contemporary Subpopulations -Subyearling and yearling ocean entrants

4. Subyearling inter-annual mean 59% Yearling inter-annual mean 41% 100 90 80 (65) 70 (55) (101) (92) (126) (305) (444) 60 Percentage of annual sample 50 40 30 20 10 (2) (6) 0 2001 2004 2005 1998 2000 2003 1999 2002 2006 Return Year Fig 1. - Age at ocean-entry for random samples of wild Snake River Basin full-term fall Chinook salmon adults (i.e., II-Salts) collected at Lower Granite Dam.

5. Briefly explore the complex and diverse juvenile life history of Snake River Basin fall Chinook salmon; • Describing migration pathways and the subyearling and yearling tactics (a.k.a., ages at ocean entry) • Summarizing the limited information on SARs for the migration pathways and subyearling and yearling tactics

6. Data Collected during Non-spill years (1992 to present) PIT-tag detection histories Validated scale pattern analysis

7. A complete data set describing migration pathway, age at ocean entry, and SARs for wild Snake River Basin fall Chinook Salmon does not exist • Therefore, existing data are subject to interpretation and this requires some generalization and speculation

8. #1 Migration Pathway = Transportation • Subyearling ocean entrants • winter at sea (prevalent in • summer barged groups) • Yearling ocean entrants • winter below Bonneville • Dam (prevalence increases in • fall trucked groups) • Subyearling ocean entrants are • numerically • dominant

9. Prevalence of yearling ocean entry increases Fig 2.- Smolt-to-adult return rates (full-term adults detected at LGR / number of smolts transported system-wide) for surrogate and run-at-large Snake River subyearlings (brood year 2001) transported from a collector dam in 2002.

10. Size and Timing of Release Downstream of Bonneville Dam Summer transport75-100 mm FL Fall transport175-200 mm FL (or larger)

11. #2 Migration Pathway = Inriver Migration • Subyearling ocean • entrants winter at sea • (prevalent for Snake • River subpopulation) • Yearling ocean entrants • winter above or below • Bonneville (prevalent • for Clearwater River • subpopulation) • Active subyearling • migrants are numerically • dominant

12. Clearwater Radio tags Snake Mostly subyearling 120 Mostly yearling 100 PIT-tag detection All yearling (reservoir types) system typically 80 dewatered Estimated number passed 60 Never detected group (reservoir types) Dewatering 40 20 0 05/01/2006 08/01/2006 11/01/2006 02/01/2007 06/16/2006 09/16/2006 12/17/2006 03/19/2007 Passage date at Lower Granite Dam Fig 3.-Seasonal migration patterns in 2006-2007 for wild fall Chinook salmon juveniles (brood year 2005) from the Snake River Basin upstream of Lower Granite Reservoir.

13. Yearlings Yearlings prevalent Subyearlings prevalent Yearlings prevalent Fig 4.- Smolt-to-adult return rates (full-term adults detected at LGR / smolts detected and bypassed system-wide) for surrogate subyearlings released into the Snake River in 2002 (i.e., brood year 2000) that migrated to the sea inriver.

14. Size at Bonneville Dam Passage Subyearling inriver100-125 mm FL Yearling inriver 200-225 mm FL

15. 95% of Smolts Avg. SAR 3.4% 5% of Smolts Avg. SAR 0.4% Fig 5.- Smolt-to-adult return rates for surrogate and run-at-large subyearlings by migration pathway in 2002 (i.e., brood year 2001) given with the percentage of smolts detected using each migration pathway.

16. Discussion • Diversity increases fitness • There will be a “Darwinian Debt” to pay if the population evolves completely to the yearling tactic (e.g., Williams et al. in press; Evolutionary Applications)

17. Discussion (Cont) Summer spill (2005 to 2007) Will summer spill increase the SARs of active inriver migrants destined to enter the ocean as subyearlings, thereby balancing juvenile life history diversity in the population?

18. Conclusions • The juvenile life history of Snake River Basin fall Chinook salmon is complex and diverse; unlike Snake River Basin spring Chinook salmon, this complexity and diversity is exhibited within the hydropower system and the estuary • The relatively large number of active early migrants destined to become subyearling ocean entrants likely compensates for the relatively low SARs for active early migrants • The relatively high SARs for late migrants destined to become yearling ocean entrants compensated for the relative small number of fish that likely survive to become yearling ocean entrants • Consequently, both the subyearling and yearling tactics contribute largely to the return of full-term adults