Migration pathway, age at ocean entry, and SARs for Snake River Basin fall Chinook prior to summer s

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Migration pathway, age at ocean entry, and SARs
for Snake River Basin fall Chinook prior to
summer spill at LGR, LGS, and LMN dams
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Prehistorical Metapopulation - Subyearling ocean
entrants

Core Area
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Contemporary Subpopulations -Subyearling and
yearling ocean entrants

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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.
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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

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

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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

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

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Radio tags
Clearwater
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.
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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.
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Size at Bonneville Dam Passage
Subyearling inriver100-125 mm FL
Yearling inriver 200-225 mm FL
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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.
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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)

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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?
  

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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