Dworshak Fisheries Research

1
Dworshak Fisheries Research
Researchers Melo Maiolie Eric Stark Ric
Downing Larry Jones
Funding by Bonneville Power Administration
2
Dworshak Reservoir

• completed in 1973
• flood control reservoir
• min 80ft drawdown

3

• 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.

4
Density of catchable-size kokanee
Fish / ha
Goal of sustainable densities 11 inch average.
5
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.
6
(No Transcript)
7

• Project Tasks
• Strobe light testing
• Monitor entrainment
• Monthly hydroacoustic forebay density surveys
• Annual hydroacoustic kokanee density
  population estimate survey
• Annual kokanee spawner counts

8

• Entrainment problems for kokanee
• Libby Dam in Montana
• Banks Lake in Washington
• Grand Coulee Dam in Washington
• Dworshak Dam in Idaho

9

• Possible solutions to reducing entrainment
• Barrier nets
• Sound
• Lights
• Electric weirs
• To date, there has been no proven technique to
  stop
• fish entrainment in large reservoirs.

10

• Strobe light success stories
• Coho and Chinook (Nemeth and Anderson 1992)
  (Fields and Finger 1956) (Ploskey and Johnson
  2001)
• Alewife, rainbow smelt, gizzard shad, white
  perch, spot, Atlantic menhaden (Patrick and
  Christie 1985)
• Salmon smolts (Johnson et al. 2001)
• American shad (Taft 1990)

11

• Strobe light failures
• Alden Labs, Electric Power Research Institute,
  Northern States Power Company (1998)
• Johnson et al. (2002), in press
  strobe lights attract fish

12

• Strobe Light Testing
• Phase 1. Off-site testing
• Phase 2. Testing at single turbine intake
• Phase 3. Testing at multiple turbine intakes
  (higher discharges - turbine 3)
• Phase 4. Testing at the reservoir outlets
• Phase 5. Develop recommendations for
  implementation submit to Army Corps of
  Engineers

13
Off-site testing Spirit Lake Lake Pend Oreille
14
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
15

• Phase 1 Results
• Kokanee densities were reduced 72 - 100
  (plt0.001)
• All seasons of the year, all age classes of
  kokanee.
• Flash rates from 300 to 450 f/min worked.
• Effectiveness correlated
  with water clarity.

16
Phase 2 Tests at a single Turbine Intake
Spill gates
Underwater (fishs eye view)
Reservoir Outlets
17

• steel barge holds shelter which houses strobe
  light powerhead, computer, generator and cable
  spools
• 2 whorls of 4 lights at 90 to each other and
  single down hanging light
• lights lowered raised with winch

18
Side View
Transducer
Dam
Strobe light platform
Boat
Turbine Intake
Selector Gate
19
Turbine 1 Discharge 37 m3/s (1,300 cfs)
Spillway Outlets
Reservoir Outlets
20
88 reduction in densities between the average
lights off transects and lights on transects
Lights off
Lights on
21
Results of On-Site Tests
Lights off 107 fish/ha, Lights on 13
fish/ha 88 reduction in fish densities, p .009
22
Phase 4 Testing at the Reservoir Outlets
23
Reservoir Outlet Strobe Tests (Fishs Eye view of
Dworshak Dam)
All 3 Reservoir Outlets operating Discharging 40
m3/s each (1400 cfs) water velocity 1.7 m/sec
24
Reservoir Outlet (RO) Tests

• Statistically non- significant (p0.207)
• 66 reduction in density still highly effective
• reduced power limited by only 3 replicates
• limited by duration of operation of ROs to test
  
• limited by testable kokanee densities

25
Tests at Reservoir Outlets
66 reduction in densities, p 0.21, df 2
26

• Ancillary Data (strobe tests)
• Forebay water velocity spatial distribution
• 90 megawatt turbine (s 1 2)
• 220 megawatt turbine (3)
• Reservoir Outlets (R.O.s) under spill
  discharge
• Discharge rates
• Water withdrawal depths (selector gate mode)
• Water Clarity (Secchi)

27
Affects of Water Clarity
28
Strobe Light Testing Summary

• Reduced kokanee densities during the night near
  turbine intakes (88) and R.O.s (66).
• No sign of fish habituation to lights during a
  night, nor after repeated nights.
• On-going testing will assess effectiveness near
  R.O.s, simultaneously at multiple turbine
  intakes, under higher discharges with more
  turbid water.
• To date, appear effective enough to reach
  objective of a 50 reduction in entrainment.

29

• Entrainment Sampling
• minimum of one 24-hour hydroacoustic sample
  period per month
• Divided each sample into 4 strata
• (dawn, day, dusk, night)
• Other factors
• (discharge, depth
• selector gate mode)
• Entrainment measured as fish/hr

30
Entrainment Results
Higher entrainment rate through reservoir outlets
than turbines
Higher entrainment rate during dusk and nighttime
periods
31
Entrainment Assessment Summary

• Behavioral analysis revealed fish actively
  seeking intake opening (not pulled in by high
  velocities)
• Entrainment occurs at even the lowest of
  discharges (chronic)

• Acute losses mainly through Reservoir Outlets
  (R.O.s) especially at higher discharges
• Deeper intake depths entrain more fish because
  of alignment with kokanee layer depth

32

• Entrainment Sampling Improvements
• provide a more accurate assessment of strobe
  light effectiveness
• testing phase
• post-implementation monitoring

Turbine Intake
33
Forebay Kokanee Densities (2001-2003)
34
Kokanee Population Estimates (2002)
35

• Operational Changes
• make recommendations on selector gate
  operations
• change depth of water withdrawal based upon known
  depth distribution of kokanee
• thereby minimize entrainment potential within
  constraints of Hatchery water temperature needs

36
On-going Future Work

• Strobe Tests
• 2 turbines simultaneously, at higher flows
• reservoir outlets (more replicates)

• Entrainment
• installed transducers at multiple intakes
• greatly increased sampling efficiency (temporally
  spatially)

• Other
• enhanced accuracy of annual population estimate
  with new hydroacoustic equipment trawling

37

• Benefits of stable kokanee population
• Consistent fishery
• Reduce reliance on hatchery supplementation
• Benefits to reservoir river ecosystems