A comparison of juvenile life histories among selected Snake River steelhead populations Brett Bowersox, Timothy Copeland, and Alan Byrne Idaho Department of Fish and Game

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A comparison of juvenile life histories among
selected Snake River steelhead populationsBrett
Bowersox, Timothy Copeland, and Alan ByrneIdaho
Department of Fish and Game
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Steelhead in Idaho

• Present in Snake, Clearwater, and Salmon River
  drainages
• Provide valuable fishery
• Well documented variation in ocean life history
  (A vs B run)
• High variation in freshwater habitat
  characteristics
• Freshwater life history not extensively studied
  in Idaho
• ESA listed in 1997

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ESA Status Assessments

• Abundance
• How many of them are there?
• Productivity
• How well do they reproduce survive?
• Spatial structure
• Where are they?
• Diversity
• What are they like?

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Technical Recovery Team Efforts

• No population specific data
• Used aggregate A-run, B-run data for adults at
  Lower Granite Dam
• Divided abundance to population within run-type
• Assumed all had same run-type productivity
• Limited information on life history or spatial
  structure

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Objectives

• Compare/contrast freshwater life history data
• Examine implications for population productivity

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Study Populations
East Fork Potlatch River
Big Bear Creek
Crooked Fork Creek
Fish Creek
Rapid River
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Technical Recovery Team Populations
Lower Clearwater (A-run)
Lochsa (B-run)
Little Salmon (A-run)
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Environmental Variation
Stream Elevation (ft) Annual Precipitation (in) Geology Land use
Big Bear Creek 1200-4983 22-30 Loess/volcanic ash Agriculture
East Fork Potlatch River 2685-4400 22-45 Volcanic ash/loess Forestry
Fish Creek 2000-6540 30-55 Volcanic ash/granite Limited Forestry
Crooked Fork Creek 3442-6340 35-55 Volcanic ash/granite Forestry
Rapid River 2100-8660 14-30 Colluvium/ basalt Wilderness
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Methods

• Use 2008 emigrant data from screw traps
• Abundance, scale samples, PIT tags
• Metrics
• Emigrant abundance
• Timing from natal stream
• Age composition
• Length at age
• Detections in Snake/Columbia hydrosystem

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Objective 1

• Compare/contrast freshwater life history data

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2008 Abundance Estimates
Stream Spring Summer Fall
Big Bear Creek 3,492 1,245 670
East Fork Potlatch River 1,912 2,706 3,749
Fish Creek 751 3,236 11,960
Crooked Fork 63,679 37,879 3,431
Rapid River 2,380 1,121 1,664
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Seasonal Outmigration Variability
Spring
Summer
Fall
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Age Distribution
Age -0
Age -1
Age -2
Age -3
Age -4
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Length at Age
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Detection rates in Hydrosystem
Stream Spring tags Summer tags Fall tags
Big Bear Creek 0.54 0.16 0.13
East Fork Potlatch River 0.27 0.20 0.16
Fish Creek 0.40 0.35 0.43
Crooked Fork Creek 0.62 0.41 0.55
Rapid River 0.54 0.04 0.33

• Spring tags detected in year of tagging (Sp
  2008)
• Summer and fall tags detected year after tagging
  (Sp 2009)

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Objective 1 Summary

• A variety of life history strategies observed
  between the populations
• Juvenile rearing completed within natal streams
  and downstream reaches
• Lower elevation populations have younger age
  structure than high elevation

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Objective 2

• Examine implications for population productivity

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Relative Productivity Model

• Use abundance, age structure, assumed survival
  to estimate initial fry abundance
• Use abundance apparent migration survival to
  LGD to estimate smolt production
• Productivity measure is smolts per fry

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Fry to Smolt Survival
Natal Stream Annual Survival Natal Stream Annual Survival
Stream S 0.5 S 0.33
Big Bear Creek 0.138 (1.00) 0.066 (1.00)
EFK Potlatch River 0.083 (0.60) 0.045 (0.68)
Fish Creek 0.106 (0.77) 0.042 (0.63)
Crooked Fork 0.074 (0.54) 0.019 (0.29)
Rapid River 0.058 (0.42) 0.017 (0.26)

• Survival Relative to Big Bear Creek in
  parentheses

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Objective 2 Summary

• Productivity differences within Technical
  Recovery Team populations
• (Fish Cr v. Crooked Fk / Big Bear v. EFK
  Potlatch)
• Decreasing natal stream survival increases
  relative advantage of Big Bear EFK Potlatch
• B-run populations need increased smolt-adult
  survival fecundities to make up for older age
  structure

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Summary

• Variation in freshwater life history important to
  population stability
• Low elevation populations very resilient
• Results similar to genetic parr density studies
• High value of habitat restoration projects for
  lower elevation populations
• Further investigations of high elevation
  Salmon River populations

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Questions