Importance of Water Level Management to Kokanee

and Bull Trout in Lake Pend Oreille

Lake Pend Oreille

Pend Oreille River

Cabinet Gorge Dam

Clark Fork River

Albeni Falls Dam

Bayview

Hope

Sandpoint

10 Km

Idaho

Montana

Idlewild Bay

Scenic Bay

Size = 38,300 ha, Maximum Depth = 351m

624

625

626

627

628

629

Ja

nF

eb

Ma

rA

pr

Ma

Ju

nJ

ul

Au

Se

pO

ct

No

vD

ec

Ja

nF

eb

Ma

rA

pr

Ma

Ju

nJ

ul

Au

Se

pO

ct

No

vD

ec

1935 1936

Lak

e el

evat

ion

(m)

Natural elevations for Lake Pend OreilleNatural elevations for Lake Pend Oreille

624

625

626

627

628

629

Ja

nF

eb

Ma

rA

pr

Ma

Ju

nJ

ul

Au

Se

pO

ct

No

vD

ec

Ja

nF

eb

Ma

rA

pr

Ma

Ju

nJ

ul

Au

Se

pO

ct

No

vD

ec

1935 2002 1936 2003

Lak

e el

evat

ion

(m)

204720492051205320552057205920612063

Lak

e el

evat

ion

(ft)

Natural and Managed Lake LevelsNatural and Managed Lake Levels

Natural

Managed

Why are kokanee important to bull trout?

•60-80% of their diet is kokanee.

•Without kokanee, lake trout and bull trout would be in direct competition for a limited food supply.

0

1

2

3

4

5

6

7

8

9

1052 56 60 64 68 72 76 80 84 88 92 96 00 04

Kok

anee

abu

ndan

ce (m

illio

ns)

Estimates of Adult Kokanee Abundance

1952 dams were built

Year

1966 consistently deep lake drawdowns begin

Spawning habitat is the

limiting factor

Gravel at Farragut March 2004

Water line

Shoreline at low pool

Larger rocks

Can we show that a varied winter water level will increase kokanee

egg survival?

2048

2049

2050

2051

2052

2053

2054

2055

2056

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

Year

Ele

va

tio

n (

ft)

Winter Elevations in Lake Pend Oreille

Experimental years

Methods

Trawling

Hydroacoustics

Fry net used on trawler

Kokanee Fry Abundance

0

2

4

6

8

10

12

14

16

19

99

20

00

20

01

20

02

20

03

20

04

Year

Nu

mb

er o

f F

ry (

mil

lio

ns)

Fry Net

Hydroacoustics

Results

0

2

4

6

8

10

12

0 200000 400000 600000 800000

Female kokanee spawners

Wild

egg

-to-

fry

surv

ival

(%

)

Lowered lake level

Wild egg-to-fry survival

0

2

4

6

8

10

12

0 200000 400000 600000 800000

Female kokanee spawners

Wild

egg

-to-

fry

surv

ival

(%

)

Wild egg-to-fry survival

Raised lake level

0

2

4

6

8

10

12

0 200000 400000 600000 800000

Female kokanee spawners

Wild

egg

-to-

fry

surv

ival

(%

)

Lowered lake level

Wild egg-to-fry survival

Raised lake level

0

2

4

6

8

10

12

0 200000 400000 600000 800000

Female kokanee spawners

Wild

egg

-to-

fry

surv

ival

(%

)

Lowered lake level

Wild egg-to-fry survival

Raised lake levelP< 0.05

2.4 fold increase

1. Vary winter lake level 4 ft in different years.

2. Maintain a higher winter pool level for 3 years, then lower lake to replenish gravel.

3. Time full drawdown to coincide with years when kokanee numbers are low.

Lake Level Management

2051’ 2055’

Yes

Start

Is there a declared power emergency ?

YesNo

Rainfall prediction for Nov -Jan for Columbia River Basin

Are female kokanee spawners above 70k?

Was lake at 2051’ the previous year?

Was lake at 2055’ each of 3 previous years?

Was lake at 2051’ each of previous 2 yrs?

Below normal

No Yes

Yes NoYes No

Are female kokanee spawners above 70k?

No Yes

Was lake at 2051’ the previous year?

Yes No No

Equal chance, normal, or above normal

Was the previous year successful for chum salmon spawning (< ? % of redds dewatered)?

NoYes Will this be the second year in a row the lake is lowered to 2051’?

Yes

No