A1261684805lECTG

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Dworshak Research Project
Researchers Melo Maiolie Eric Stark Ric
Downing
ISRP Proposal Presentation August 15th, 2001
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• Dworshak Reservoir
• completed in 1973
• flood control reservoir
• 155 ft drawdown

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Objectives 1. Maintain a kokanee population of
30-50 adults/ha on an annual basis by reducing
entrainment losses. 2. Establish baseline bull
trout population indices, and increase the
threatened population by reducing entrainment
losses. 3. Improve kokanee size to 380 mm at
densities of 30-50 adults/ha by enhancing
reservoir productivity.
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Kokanee in Dworshak Reservoir

• First stocked in 1972
• Continue to provide valuable fishery, of over
  200,000 fish harvested

• Fish spawn during September in tributary
  streams, primarily at age 2.
• Adults range in size from 250 to 400 mm but
  generally average 300 mm.
• Variable population makes management difficult.

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Density of catchable-size kokanee
Fish / ha
Goal of sustainable densities 11 inch average.
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Problem Entrainment losses make the fishery
highly variable. Ex An estimated 95 of age
1 2 kokanee were lost in 1996, and the
population took 3 years to recover after
restocking. .
Solution Minimizing entrainment will help to
sustain stable densities of kokanee.
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Off-site Strobe Tests
Depth (m.)

• deterred fish 30-40 m.
• more effective in clear
• water during winter
• (up to 100 m. deterrence)

Lights Off
Lights On
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Top of Dworshak dam
Maximum pool elevation 1600 ft
Spill gates
Selector gates
Turbine intakes
R.O.s
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(No Transcript)
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Tasks (Stage 1)

1. Monitor entrainment seasonally under a broad
   range of dam operations.
2. Test effectiveness of strobe lights to deter
   kokanee from turbine intake and thereby reduce
   entrainment rate.
3. Survey forebay water velocities to determine
   spatial extent of critical entrainment velocities
4. Annual hydroacoustic survey to determine kokanee
   density and population estimate.

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Tasks (Stage 2)

1. Monitor and survey entrainment and water
   velocities of multiple turbine intakes including
   turbine 3.
2. Expand strobe light testing to include multiple
   turbine intakes (higher discharges).
3. Survey water velocities in front of reservoir
   outlets to determine extent of critical
   velocities under spill discharges.

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Methods

• stationary (entrainment rate)
• mobile transects
• (distance and density)

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Tasks (Stage 3)
Dependent on effectiveness of strobe lights in
front of the turbine intakes, progress to testing
in front of reservoir outlets (R.O.s) under high
discharge events.
Tasks (Stage 4)
If strobe lights prove effective at turbine
intakes and R.O.s, develop and recommend
implementation plan to the Army Corps of
Engineers.
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Objective 2 Establish baseline bull trout
population indices, and increase the threatened
population by reducing entrainment losses.
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• Tasks
• Monitor BT abundance and survival trends.
• 2. Monitor BT movements utilization of
  reservoir, specifically w/in the forebay,
  spatial temporal vulnerability to entrainment.
• 3. Dependant on severity, develop methods to
  deter entrainment.

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• Methods
• in cooperation w/ IDFG Fish Management bull
  trout collection and tagging
• anesthetize surgically implant radio or
  combined acoustic/radio tags (CART)
• acoustic detection in lower reservoir (deeper)
  with system of wireless hydrophones near forebay

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Methods
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Objective 3 Improve kokanee average size to
380mm at densities of 30-50 adults/ha.
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• Tasks
• Collect seasonal limnological samples throughout
  reservoir to serve as input values in mass
  balance equations to model the effect of changes
  in nutrients conentrations on
• primary secondary production
• kokanee avg. size, fecundity, density

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• Methods
• limnological sampling stations - 12 throughout
  reservoir (April-Nov.)
• D.O., turbidity, temp
• TDS, NO3, Ortho-P, Total-P
• algal composition, density, biomass chl A,
  primary production
• zooplankton density, composition, biomass
• 2. length, weight, scale, kokanee stomach
  samples

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• Tasks (continued)
• 2. Evaluate feasibility of nutrient enhancement
  to improve kokanee growth average size
• bioenergetic results
• cost-benefit of fertilization
• benefit to native species
• catch to the creel.

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• Benefits of stable kokanee population
• Consistent fishery
• Reduce reliance on hatchery supplementation
• Benefits to native species