Seth W' Naman

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Predation by hatchery-reared steelhead on natural
salmonid fry in the upper-Trinity River,
California 2005

• Seth W. Naman
• Yurok Tribal Fisheries Program

2
Introduction
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Trinity RiverLewiston Dam to Old Lewiston Bridge
Middle of study reach
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Key features of study reach

• In any given year over 50 of all salmonid
  redds, upstream of the NF Trinity, are created
  hereextremely important spawning and rearing
  zone
• Coho salmon are listed under ESA and CESA
• In 1991, local business owners successfully
  lobbied CA FG Commission to change fishing
  regulations to fly only and catch and release only

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Predation risks

• Spatial and temporal overlap of predator and
  prey
• High concentrations of predator and prey
• Size overlap of predator and prey
• Low turbidity
• Limited fry rearing habitat (TRFE)

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Methods
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Basic study approach

• Pump stomachs of hatchery steelhead to estimate
  the amount of salmon fry per stomach
• Estimate the number of hatchery steelhead in the
  study reach
• Multiply the two

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Definitions
Residuals Hatchery steelhead that spent one or
more years in the river Juveniles Hatchery
steelhead released in March of 2005
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Study timeline
February-March (residuals) March-May (juveniles
and residuals)
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Hook and line
Invertebrate fly patterns
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Smoltification ratings
1
2
3
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Pulsed gastric lavage
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Residual population estimates

• Mark-recapture
• - Upper caudal clip
• - Schnabel estimator
• Snorkel expansion
• - Three divers
• - One pass

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Juvenile population approximation
792,861 0.8 634,289
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Juvenile population approximation
792,861 0.04 31,714
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Juvenile population approximation
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Number of fry consumed
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Statistical analyses

• T-tests, chi square, ANOVA, etc. performed using
  Minitab and SAS
• Fry per stomach data modeled using WinBugs
• -non-informative priors
• -Used DIC to compare models

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Results
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Some results briefly

• Differences in fork length between all
  smoltification groups were significant,
  non-smolting juvenile were larger
  (ANOVA, F2, 2,476  24.13, P lt 0.001)
• No difference in the number of piscivors between
  smoltification groups (?2 0.202)
• No difference in fork length between juvenile
  piscivores and non-piscivores (T 0.90 P
  0.815)
• Significant difference in fork length between
  residual piscivores and non-piscivores (T 3.83
  P lt 0.001)

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Residual steelhead predation rates
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Juvenile steelhead predation rates
Mean 0.062 (0.049-0.077)
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Hatchery STH predation studies
Lewis R. 1.08, n 48
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Residual population estimates
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Juvenile population approximation
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Steps taken to minimize estimate

• Chose a conservative gastric evacuation model
• 158,572 (20) hatchery juvenile steelhead not
  included in calculations
• Used twilight hours instead of 24 hours in
  calculations (correction of 0.5)

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What if?
What if the starting number for these
calculations was 60 of total smolts released?
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What if?

• What if the starting number for these
  calculations was 60 of total smolts released?
• 241,259 (95 CI 153,990 357,683)

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What if?

• What if the starting number for these
  calculations was 60 of total smolts released?
• 241,259 (95 CI 153,990 357,683)
• 40?

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What if?

• What if the starting number for these
  calculations was 60 of total smolts released?
• 241,259 (95 CI 153,990 357,683)
• 40?
• 189,900 (95 CI 116,765 268,779)

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Bias of Hook and Line?
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Bias of Hook and Line?

• Used SRS to sample 75 stomach contents data (
  1850 records)

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Bias of Hook and Line?

• Used SRS to sample 75 stomach contents data (
  1850 records)
• Replaced 25 with zeros ( 650 records)

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Bias of Hook and Line?

• Used SRS to sample 75 stomach contents data (
  1850 records)
• Replaced 25 with zeros ( 650 records)
• 119 fry consumed for 2,479 records

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Bias of Hook and Line?

• Used SRS to sample 75 stomach contents data (
  1850 records)
• Replaced 25 with zeros ( 650 records)
• 119 fry consumed for 2,479 records
• Overall mean of 0.048

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Bias of Hook and Line?

• Used SRS to sample 75 stomach contents data (
  1850 records)
• Replaced 25 with zeros ( 650 records)
• 119 fry consumed for 2,479 records
• Overall mean of 0.048
• 215,661 (95 CI 129,474 - 344,024)

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Does it matter?
Chinook 3889 redds 3000 eggs 0.4
survival 4,606,800 Coho 1041 redds 3000 eggs
0.4 survival 1,249,200 312,802/5,856,000 100
5.3
Remember, this doesnt include eggs, competition,
etc.
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Conclusions
Predation and competition are likely important
forces of mortality on naturally produced
salmonids, which program partners are trying to
recover
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Conclusions
Maintaining residualized hatchery steelhead
conflicts with stated goals of TRRP, CalTrout,
CDFG, and others
CA FG Commission policy Resident fish will not
be planted or resident fisheries developed in
drainages of steelhead waters, where, in the
opinion of the Department, such planting or
development will interfere with steelhead or
salmon populations.
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Conclusions

• Almost no naturally produced adult steelhead in
  this reach
• High proportions of hatchery steelhead spawning
  in river and 100 hatchery broodstock are
  concernsdomestic selection

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Recommendations

• Better integration between TRRP and TRH
• Reexamine mitigation goals and consider
  releasing fewer steelhead
• Change fishing regulations
• Explore possibilities for downstream release site

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Thoughtsits not about 300,000 fry

• Consider the cumulative effects of competition
  and predation over a year, or a decade, from
• Residuals (individuals consumed up to 60 eggs),
• plus smolts
• plus anadromous hatchery steelhead (1.12
  fry/stomach)
• plus brown trout. Incremental effects add up!

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Thank You Jeremy Alameda Loren Everest Bill
Pinnix BOR Aaron Martin Howard Stouffer Tim
Hayden
Questions?