Characterizing the fish a

Lake Powell forebay: 

potential for nonnative 

through Glen Canyon D

lower Colorad

Barrett Friesen, Phaedra Bud

Gary P. Thie
Historical conditions: withdrawal from hypolimnion

Epilimnion

Hypolimnion

flow
Current conditions: withdrawal from epilimnion

Epilimnion

Hypolimnion

flow

Current level: 3535 ft

Lake level has risen 12 ft since April TWG meeting 
Objectives

1. Characterize the potentially ‘entrainable’ fish population in Lake 

Powell

• Space, depth, and seasons (time)

2. Determine the likelihood that a fish that does get entrained, 

will survive the journey
Efforts to date

• November pilot sampling

• March and June full sampling

• Temperature and Oxygen Profile

• Gill netting

• Minnow trapping

• Larval fish tows

• BoR TSC = Hydroacoustics

• Sensor Fish deployment planning (dam 

tour)

• Ultrasonic network planning/permitting
Sample locations

Wahweap

Confluence

Forebay

Each location sampled 

3 times per visit 
What’s changed since March?

Lake temperature/stratification

Forebay fish community composition
Warmwater fish 

movement into 

forebay
SMB in forebay

(shallow)
Carp by trash rack 
Forebay profile - temp

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20

Depth (m)

Temp (C)

Series1
Forebay profile - temp

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20

Depth (m)

Temp (C)

Series1 Series2
Forebay profile - temp

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20

Depth (m)

Temp (C)

Series1 Series2 Series3
Forebay profile - temp

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20

Depth (m)

Temp (C)

Series1 Series2 Series3

Top 10 m: 

protoepilimnion?
Forebay gillnets – species composition change

3

1

4

1 2 3

count

March 2022

n = 8

CPUE: 0.021 

fish/net hr
Forebay gillnets – species composition change

11

14

16

11

12

2

1 2 3 4 5 6

count

June 2022

n = 66

CPUE: 0.156 fish/net hr

3

1

4

1 2 3

count

March 2022

n = 8

CPUE: 0.021 

fish/net hr
Forebay gillnets – how deep are the fish?

0

2

4

6

1 2 3 4 5 6 7 8 9

count

Depth (m)

March 2022

n = 8
Forebay gillnets – how deep are the fish?

0

2

4

6

1 2 3 4 5 6 7 8 9

count

Depth (m)

March 2022

n = 8 0

10

20

30

1 2 3 4 5 6 7 8 9

count

Depth (m)

June 2022

n = 66
Forebay gillnets – how deep are the fish?

0

2

4

6

1 2 3 4 5 6 7 8 9

count

Depth (m)

March 2022

n = 8 0

10

20

30

1 2 3 4 5 6 7 8 9

count

Depth (m)

June 2022

n = 66

0

2

4

6

1 2 3 4 5 6 7 8 9

count

Depth (m)

SMB - June 2022

n = 11
Minnow traps (all GSF)

0

5

10

15

20

1 3 5 7 9 11 13 15 17 19 21

count

TL (mm)

March 2022

n = 48

Mean TL: 46 mm

CPUE: 0.026 fish/trap hr
Minnow traps (all GSF)

0

5

10

15

20

1 3 5 7 9 11 13 15 17 19 21

count

TL (mm)

March 2022

n = 48

Mean TL: 46 mm

CPUE: 0.026 fish/trap hr

0

5

10

15

20

25

30

35

1 3 5 7 9 11 13 15 17 19 21

count

TL (mm)

June 2022

n = 137

Mean TL: 51 mm

CPUE: 0.063 fish/trap hr
Next steps

• Next full sample August & Autumn

• Ultrasonic telemetry August

• Transmitters and receiver network

• Depths 

• Movement
Next steps

Likelihood of fish dam passage survival?

• Sensor Fish instruments August & Autumn

• Varying wicket gate opening• Varying pressure head Sensor Fish

90 mm

TemperaturePressureGyroscope (orientation)Tri‐axial accelerometer (chan
Acknowledgment

Bureau of Reclamation

• Clarence Fullard

• Kerri Pedersen

• Mike Horn

• Mark McKinstry

• Kato Miyagishima

Utah State Univers