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

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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. Introduction. Trinity River Lewiston Dam to Old Lewiston Bridge. Middle of study reach. Key features of study reach.

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slide1

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

Seth W. Naman

Yurok Tribal Fisheries Program

slide4
Key features of study reach
  • In any given year over 50 % of all salmonid redds, upstream of the NF Trinity, are created here…extremely important spawning and rearing zone
  • Coho salmon are listed under ESA and CESA
  • In 1991, local business owners successfully lobbied CA F&G Commission to change fishing regulations to fly only and catch and release only
slide5
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)
slide7
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
slide8
Definitions

Residuals = Hatchery steelhead that spent one or more years in the river

Juveniles = Hatchery steelhead released in March of 2005

slide9
Study timeline

February-March (residuals)

March-May (juveniles and residuals)

slide10
Hook and line

Invertebrate fly patterns

residual population estimates
Residual population estimates
  • Mark-recapture
  • - Upper caudal clip
  • - Schnabel estimator
  • Snorkel expansion
  • - Three divers
  • - One pass
slide14
Juvenile population approximation

792,861 × 0.8 = 634,289

slide15
Juvenile population approximation

792,861 × 0.04 = 31,714

slide18
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
slide20
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 < 0.001)
  • No difference in the number of piscivors between smoltification groups (χ2 = 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 < 0.001)
slide22
Juvenile steelhead predation rates

Mean = 0.062 (0.049-0.077)

slide23
Hatchery STH predation studies

Lewis R. = 1.08, n = 48

slide27
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)
slide28
What if?

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

slide29
What if?
  • What if the starting number for these calculations was 60% of total smolts released?
  • 241,259 (95% CI = 153,990 – 357,683)
slide30
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%?
slide31
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)
slide33
Bias of Hook and Line?
  • Used SRS to sample 75% stomach contents data (~ 1850 records)
slide34
Bias of Hook and Line?
  • Used SRS to sample 75% stomach contents data (~ 1850 records)
  • Replaced 25% with zeros (~ 650 records)
slide35
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
slide36
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
slide37
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)
slide38
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 doesn’t include eggs, competition, etc.

conclusions
Conclusions

Predation and competition are likely important forces of mortality on naturally produced salmonids, which program partners are trying to recover

conclusions40
Conclusions

Maintaining residualized hatchery steelhead conflicts with stated goals of TRRP, CalTrout, CDFG, and others

CA F&G 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.”

slide41
Conclusions
  • Almost no naturally produced adult steelhead in this reach
  • High proportions of hatchery steelhead spawning in river and 100% hatchery broodstock are concerns…domestic selection
slide42
Recommendations
  • Better integration between TRRP and TRH
  • Reexamine mitigation goals and consider releasing fewer steelhead
  • Change fishing regulations
  • Explore possibilities for downstream release site
slide43
Thoughts…it’s 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!
slide44
Thank You

Jeremy Alameda

Loren Everest

Bill Pinnix

BOR

Aaron Martin

Howard Stouffer

Tim Hayden

Questions?

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