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.