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Banks Lake Fishery Evaluation Project
(Project 200102800)
Matt Polacek, Project Manager
Washington Department of Fish and Wildlife
Objective and Purpose
• To re-establish a once popular and successful
kokanee fishery in Banks Lake to provide a
salmonid fishery above the blocked area.
• Established as an
M&E program for kokanee
planted by the Ford
Hatchery (200102900).
Banks Lake
Study Area
Project History
• This Project was funded by BPA in 2001 to
evaluate game fish populations in Banks Lake.
• Identifying limiting factors to kokanee became
the primary objective due to their popularity
in regional fisheries.
• Baseline data collections
began in 2002.
Historical Kokanee Fisheries
80
P/G Units
Operational
(1974)
SMB
Planted
1981
Harvest (x 1000)
70
60
50
Barrier Net
Installed
1978
Walleye
Stocked
(1990's)
Net Pen
kokanee
rearing
2002
40
30
20
10
0
1971 1972 1975 1977 1978 1980 1981 1982 1983 1985 1995 2001 2002 2003 2004 2005 2006 2008 2009 2010
Year
• The BLFEP conducted M&E studies, examining:
1. Limiting Factors and 2. Success of differing kokanee release strategies
Limiting Factors
• Evaluate factors that limit kokanee survival
– Exploitation (creel)
– Zooplankton availability
– Water conditions and quality
– Entrainment
– Predatory impacts (bioenergetics modeling)
Results - Limiting Factors
• HIGH IMPACTS
– Prey Availability - Whitefish consumption exceeded
Daphnia biomass in the winter and summer months
– Whitefish abundance is of concern (90% composition)
– Predation - Walleye predation was the leading source of
mortality based on diet analysis and bioenergetics
modeling.
• LOW IMPACTS
– Water quality
– Exploitation (< 2,000)
– Entrainment (< 3,000)
Results – Prey Availability
1200
Lakewide Daphnia biomass
WF Consumption
KOK + WF
Consumption (kg * 1000)
1000
1000
800
800
600
600
400
400
200
200
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Month
Aug
Sep
Oct
Nov
0
Dec
Lakewide biomass (kg * 1000)
1200
Walleye Predation on Kokanee
• Bioenergetics Modeling
• Over 8 million grams of kokanee were
consumed in one year
• Equates to an estimate of over 950,000 fry
– Age 2 (size 12” – 14”) – consume 35%
– Age 3 (14” – 19”) – consume 31%
– Age 4 (19” – 22”) – consume 16%
– Age > 4 (up to 32”) – consume 18%
• Acute predation during releases is substantial
Kokanee Release Strategies
• Maximize hatchery kokanee survival
– Differing release and rearing strategies
1. Spring fry
2. Fall fingerlings
3. Net pen yearlings
• Each group was differentially marked using
thermal otolith marking or fin clips
• Null Hypothesis: The proportions of each
release group is not significantly different than
the proportions collected in the fall as adults.
Release Strategy Results
Rejected the Null Hypothesis (P < 0.001)
Fall fingerlings
Net pen yearlings
Spring fry
•Tested Brood Years 2002 – 2005
• Used chi-square analysis with Yates correction.
Adaptive Management
We recognize that the “status quo” is not working
– Predation issue
– Lake whitefish competition issue
– Recruitment to the creel is not meeting expectations
Therefore,
We propose to build on
past results to implement
new strategies to increase
kokanee survival
Banks Lake Kokanee Decision Tree
Goal for kokanee in Banks Lake: 0.5/hr; 20-30/ha; 10,000 fish harvest goal
Further Refine Release Success
to address acute predation
Night/Barge
Use existing data, case studies,
modeling, and outreach
Consumption reduced
by 35% by year 5
Monitor population: creel,
hydroacoustics, and CPUE
Goal met or
nearly met
Continue
stocking using
best strategy
Address Competition with Lake
Whitefish
Refine current bag limits to reduce
the # of “teenage” walleye
Fall fingerlings
Day/shore
Address Walleye Predation
Consumption not reduced
by 35% by year 5
Implement mechanical
removal program
Goal: Reduce Lake Whitefish
population by 30% by year 5
Monitor Population:
hydroacoustics and CPUE
Monitor Population: creel and
FWIN CPUE; consumption
Goal not met
Goal met or
nearly met
Continue Kokanee
Stocking
Goal not met
Discontinue Kokanee
Stocking
Continue to
monitor water
quality and
zooplankton
The Future of Kokanee in Banks Lake
• Continued stocking of kokanee will depend on
how close goals are met
•If not kokanee, then WDFW managers will
implement a new strategy (i.e. increase rainbow
trout production) to provide a salmonid fishery
above the blocked areas.
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