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

Seth W. Naman

Yurok Tribal Fisheries Program


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Introduction fry in the upper‑Trinity River, California 2005


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Trinity River fry in the upper‑Trinity River, California 2005Lewiston Dam to Old Lewiston Bridge

Middle of study reach


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Key features of study reach fry in the upper‑Trinity River, California 2005

  • 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


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Predation risks fry in the upper‑Trinity River, California 2005

  • 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 fry in the upper‑Trinity River, California 2005


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Basic study approach fry in the upper‑Trinity River, California 2005

  • 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 fry in the upper‑Trinity River, California 2005

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 fry in the upper‑Trinity River, California 2005

February-March (residuals)

March-May (juveniles and residuals)


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Hook and line fry in the upper‑Trinity River, California 2005

Invertebrate fly patterns


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Smoltification ratings fry in the upper‑Trinity River, California 2005

1

2

3


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Pulsed gastric lavage fry in the upper‑Trinity River, California 2005


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Residual population estimates fry in the upper‑Trinity River, California 2005

  • Mark-recapture

  • - Upper caudal clip

  • - Schnabel estimator

  • Snorkel expansion

  • - Three divers

  • - One pass


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Juvenile population approximation fry in the upper‑Trinity River, California 2005

792,861 × 0.8 = 634,289


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Juvenile population approximation fry in the upper‑Trinity River, California 2005

792,861 × 0.04 = 31,714


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Juvenile population approximation fry in the upper‑Trinity River, California 2005


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Number of fry consumed fry in the upper‑Trinity River, California 2005


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Statistical analyses fry in the upper‑Trinity River, California 2005

  • 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 fry in the upper‑Trinity River, California 2005


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Some results briefly fry in the upper‑Trinity River, California 2005

  • 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)


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Residual steelhead predation rates fry in the upper‑Trinity River, California 2005


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Juvenile steelhead predation rates fry in the upper‑Trinity River, California 2005

Mean = 0.062 (0.049-0.077)


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Hatchery STH predation studies fry in the upper‑Trinity River, California 2005

Lewis R. = 1.08, n = 48


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Residual population estimates fry in the upper‑Trinity River, California 2005


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Juvenile population approximation fry in the upper‑Trinity River, California 2005


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fry in the upper‑Trinity River, California 2005


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Steps taken to minimize estimate fry in the upper‑Trinity River, California 2005

  • 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? fry in the upper‑Trinity River, California 2005

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


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What if? fry in the upper‑Trinity River, California 2005

  • 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? fry in the upper‑Trinity River, California 2005

  • 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? fry in the upper‑Trinity River, California 2005

  • 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? fry in the upper‑Trinity River, California 2005


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Bias of Hook and Line? fry in the upper‑Trinity River, California 2005

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


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Bias of Hook and Line? fry in the upper‑Trinity River, California 2005

  • 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? fry in the upper‑Trinity River, California 2005

  • 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? fry in the upper‑Trinity River, California 2005

  • 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? fry in the upper‑Trinity River, California 2005

  • 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? fry in the upper‑Trinity River, California 2005

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.


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Conclusions fry in the upper‑Trinity River, California 2005

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 fry in the upper‑Trinity River, California 2005

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.”


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Conclusions fry in the upper‑Trinity River, California 2005

  • 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


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Recommendations fry in the upper‑Trinity River, California 2005

  • 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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Thoughts fry in the upper‑Trinity River, California 2005…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!


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Thank You fry in the upper‑Trinity River, California 2005

Jeremy Alameda

Loren Everest

Bill Pinnix

BOR

Aaron Martin

Howard Stouffer

Tim Hayden

Questions?


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