Banks Lake Fishery Evaluation Project(Project 200102800)
Matt Polacek, Project ManagerWashington 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 LakeStudy 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
• The BLFEP conducted M&E studies, examining:1. Limiting Factors and 2. Success of differing kokanee release strategies
Barrier Net Installed
1978
SMB Planted
1981
P/G UnitsOperational
(1974)
Walleye Stocked (1990's)
Net Pen kokanee rearing2002
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
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Lake
wid
e bi
omas
s (k
g *
1000
)
0
200
400
600
800
1000
1200
Con
sum
ptio
n (k
g *
1000
)
0
200
400
600
800
1000
1200
Lakewide Daphnia biomassWF Consumption KOK + WF
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 strategies1. Spring fry2. Fall fingerlings3. 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
•Tested Brood Years 2002 – 2005• Used chi-square analysis with Yates correction.
Fall fingerlings
Net pen yearlings
Spring fry
Rejected the Null Hypothesis (P < 0.001)
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
Goal for kokanee in Banks Lake: 0.5/hr; 20-30/ha; 10,000 fish harvest goal
Banks Lake Kokanee Decision Tree
Further Refine Release Success to address acute predation Address Walleye Predation Address Competition with Lake
Whitefish
Fall fingerlings
Day/shore Night/Barge
Monitor population: creel, hydroacoustics, and CPUE
Refine current bag limits to reduce the # of “teenage” walleye
Use existing data, case studies, modeling, and outreach
Monitor Population: creel and FWIN CPUE; consumption
Consumption reduced by 35% by year 5
Consumption not reduced by 35% by year 5
Implement mechanical removal program
Monitor Population: hydroacoustics and CPUE
Continue Kokanee Stocking
Discontinue Kokanee Stocking
Goal: Reduce Lake Whitefish population by 30% by year 5
Goal met or nearly met Goal not met
Continue stocking using best strategy
Goal met or nearly met Goal not met
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.