Diets and Food Availability of 

Nonnative Trout in Bright Angel Creek, 

Grand Canyon: Implications for Native 

Fish Conservation

Daniel P. Whiting1, Jonathon J. Spurgeon1, Brian D. Healy2, 

Craig P. Paukert1

1University of Missouri, MO Cooperative Fish/Wildlife Research Unit

2Grand Canyon National Park
Changes in the Grand Canyon

Early 1900’s 2010

David Rust Photograph Collection, 

Church of Jesus Christ of Latter Day Saints, Salt Lake City, Utah

Native fish Nonnative fish
Fishes of Bright Angel Creek (BAC)

Native

Speckled dace 

Bluehead sucker

Nonnative

Brown trout

Rainbow trout 

Photo: Jeff Sorensen

Photo: Brian Healy
Native Fish Restoration

Bright Angel Creek Trout 

Reduction Project

Restore and enhance native 

fish populations in the 

Colorado River and Bright 

Angel Creek
Native Fish Restoration

Bright Angel Creek Trout 

Reduction Project

Restore and enhance native 

fish populations in the 

Colorado River and Bright 

Angel Creek

What role do nonnative trout play in Bright Angel Creek?
Questions

How much food is available to fishes in BAC?

What resources are nonnative trout consuming?

Are native and nonnative fishes consuming similar 

resources?
Objectives

How much food is available to fishes in BAC?

Quantify seasonal patterns of food availability

What resources are nonnative trout consuming?

Characterize seasonal diets of brown and rainbow trout

Are native and nonnative fishes consuming similar 

resources?

Examine potential diet overlap between native and 

nonnative fishes
Methods

Sampling periods 

November 2010

January 2011

June 2011

September 2011

Objective 1: Food availability

2 stream reaches (100 m)

Drift: 4 nets, 4 times / 24h

Benthic: 6 Hess samples 

Identified Measured Biomass
Methods

Objective 2: Diet analysis 

Backpack electrofishing

Brown trout (n=97)(68-490 mm)

Rainbow trout (n=130)(79-375 mm)

Identified Weighed Biomass

Objective 3: Diet overlap

δ 13C and δ 15N stable isotopes

Fin clips (all fish)

Invertebrates

Basal resources
Methods

Diet analysis

Short term diet trends

Piscivory rates

Identify actual items

Stable isotope analysis

Long term diet trends

Food source (δ 13C)

Trophic position (δ 15N)
Total invertebrate drift biomass

November

January

June

September

0.0

0.2

0.4

0.6

0.8

mg/m

3

Total invertebrate benthic biomass

November

January

June

September

0

500

1000

1500

2000

2500

3000

3500

mg/m

2

Objective 1: Seasonal food availability

p = 0.11 p = 0.18
Objective 1: Seasonal food availability

Source Benthic 

(mg/m2)

Drift 

(mg/m3)

Taxa

Richness

This study 1919 0.45 60

Bright Angel 

(1993)

900a - -

Colorado River 204b 0.16c 16

a Oberlin et al. 1999

b Cross et al. 2011 

c Cross et al. in revision Ecological Monographs
November

January

June

September

0

20

40

60

80

100

November

January

June

September

0

20

40

60

80

100

% Biomass

Benthic Drift

Ephemeroptera

Diptera

Megaloptera

Other Aquatic

Trichoptera

Terrestrial

Objective 1: Seasonal food availability
Objective 2: Nonnative trout diets

% of diet (biomass)

Brown trout Rainbow trout

Ephemeroptera Megaloptera Native fish

Other Aquatic

Trichoptera

Filamentous Algae Terrestrial

November

January

June

September

0

20

40

60

80

100

November

January

June

September

0

20

40

60

80

100

Piscivory rate 

Brown=19% 

Rainbow=4%
Objective 3: Native/nonnative diet overlap

-32 -30 -28 -26 -24

0

2

4

6

8

10

δ 15

N

δ 13C

Basal Resources

Trichoptera

Diptera

Megaloptera

BHS

BNT

SPD

RBT

Ephemeroptera Terrestrial

Carbon - Food Source

Nitrogen - trophic position
Objective 3: Native/nonnative diet overlap

-32 -30 -28 -26 -24

0

2

4

6

8

10

δ 15

N

δ 13C

Fish

Invertebrates

Basal Resources
Objective 3: Native/nonnative diet overlap

-32 -30 -28 -26 -24

0

2

4

6

8

10

δ 15

N

δ 13C

BHS

BNT

SPD

RBT

Trichoptera Diptera

Megaloptera

Ephemeroptera Terrestrial

Basal Resources

RBT – Rainbow trout

BNT – Brown trout

BHS – Bluehead sucker

SPD – Speckled dace
Objective 3: Native/nonnative diet overlap

-30 -28 -26 -24 -22

0

2

4

6

8

10

-32 -30 -28 -26 -24

0

2

4

6

8

10

-34 -32 -30 -28 -26 -24

0

2

4

6

8

10

-30 -28 -26 -24 -22

0

2

4

6

8

δ

10

15

N

δ 13C

BNT

RBT

SPD

BHS BNT

RBT

SPD BHS

BNT

RBT

SPD

BHS BNT RBT

SPD

BHS

EPH

EPH

EPH

EPH

MEG

MEG

MEG

MEG

TRI

TRI

TRI

TRI

DIP

DIP

DIP

DIP RBT – Rainbow trout

BNT – Brown trout

BHS – Bluehead sucker

SPD – Speckled Dace

EPH – Ephemeroptera

MEG – Megaloptera

TRI – Trichoptera

DIP – Diptera

November January

June September
Objective 3: Native/nonnative diet overlap

-30 -28 -26 -24 -22

0

2

4

6

8

10

-32 -30 -28 -26 -24

0

2

4

6

8

10

-34 -32 -30 -28 -26 -24

0

2

4

6

8

10

-30 -28 -26 -24 -22

0

2

4

6

8

δ

10

15

N

δ 13C

BNT

RBT

SPD

BHS BNT

RBT

SPD BHS

BNT

RBT

SPD

BHS BNT RBT

SPD

BHS

EPH

EPH

EPH

EPH

MEG

MEG

MEG

MEG

TRI

TRI

TRI

TRI

DIP

DIP

DIP

DIP

November January

June September

RBT – Rainbow trout

BNT – Brown trout

BHS – Bluehead sucker

SPD – Speckled Dace

EPH – Ephemeroptera

MEG – Megaloptera

TRI – Trichoptera

DIP – Diptera
Objective 3: Native/nonnative diet overlap

-30 -28 -26 -24 -22

0

2

4

6

8

10

-32 -30 -28 -26 -24

0

2

4

6

8

10

-34 -32 -30 -28 -26 -24

0

2

4

6

8

10

-30 -28 -26 -24 -22

0

2

4

6

8

δ

10

15

N

δ 13C

BNT

RBT

SPD

BHS BNT

RBT

SPD BHS

BNT

RBT

SPD

BHS BNT RBT

SPD

BHS

EPH

EPH

EPH

EPH

MEG

MEG

MEG

MEG

TRI

TRI

TRI

TRI

DIP

DIP

DIP

DIP

November January

June September

RBT – Rainbow trout

BNT – Brown trout

BHS – Bluehead sucker

SPD – Speckled Dace

EPH – Ephemeroptera

MEG – Megaloptera

TRI – Trichoptera

DIP – Diptera
Native and nonnative fish trophic positions

RBT BNT BHS SPD

2.0

2.5

3.0

3.5

4.0

4.5

A A AB

B

Trophic Position = [(δ 15NFish - δ 15NPetrophila) / 3.4] + 2

p< 0.001
Summary

Objective 1 – Seasonal food availability

Benthic and Drifting biomass varied seasonally

Megaloptera (hellgrammites) highest in benthos

Ephemeroptera (mayflies) & terrestrial insects highest in drift

Objective 2 – Nonnative trout diets

Diets shifted with season and differed between species

Brown trout – fish and large insects

Rainbow trout - filamentous algae and small insects

Objective 3 – Native and nonnative diet overlap

Similar trophic positions and food sources
Implications to native fish

Resource utilization

Diverse food base and high drift biomass

Rainbow trout diets likely overlap more with natives 

(algae and small bodied insects)

Niche partitioning? 

Speckled dace benthic vs. rainbow trout drift

Predation

Both brown and rainbow trout consume native fishes

Brown trout predation higher and more likely to affect natives
Future Research

Effects of trout removal on ecosystem structure/function

How will the food base and native fish populations change?

Importance of tributaries to native fish in Colorado River

Do drift inputs affect native fish assemblages?
Acknowledgements

Emily Omana-Smith – National Park Service

MU Stable Isotope Geochemistry Lab

Erin Fore – University of Missouri

Landon Pierce – University of Missouri

Dave Speas- Bureau of Reclamation 

Melissa Trammell-National Park Service

Grand Canyon Trust-Volunteers

Funding
Questions?

Food type BNT RBT 

Fish 23 6

Aquatic insects 146 100

Terrestrial insects 10 9

Organic matter 8 35

Total consumption 187 150

*Individual based model (1 yr)

*No growth assumed from estimates 

(g dry mass yr-1)

What resources are non-native trout consuming?
Food type BNT RBT 

Fish 23 6

Aquatic insects 146 100

Terrestrial insects 10 9

Organic matter 8 35

Total consumption

# fish removed

Potential resources 

“not consumed”

187 g/yr

292

54,604 g/yr

150 g/yr

541

81,691 g/yr

What resources are non-native trout consuming?
BNT RBT

Length

0 100 200 300 400 500

-28

-27

-26

-25

-24

-23

-22

0 100 200 300 400 500

3.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

5.6

0 100 200 300 400 500

-28

-27

-26

-25

-24

-23

-22

-21

-20

0 100 200 300 400 500

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

Isotopes vs. Length

r= 0.59

P < 0.001

r= 0.51

P < 0.001

r= 0.77

P < 0.001

r= 0.78

P < 0.001
-26 -25 -24 -23 -22

7

8

9

10

11

-26 -25 -24 -23 -22

7

8

9

10

11

-28 -27 -26 -25 -24 -23

7

8

9

10

11

-26 -25 -24 -23 -22

7

8

9

10

11 δ 15

N

δ 13C

BNT

RBT

BNT

RBT

BNT

RBT

BNT RBT

BHS

BHS

BHS

BHS

SPD

SPD

SPD

SPD

Are native and non-native fishes consuming similar 

resources?

November January

June September
BAC Population Estimates

October 2010 January 2011

Species No. /100m 95% CI No. /100m 95% CI

BNT 28 23-45 25 20-41

RBT 27 21-46 17 14-30

BHS - - - -

SPD 411 305-598 639 211-2947

Omana Smith, E. C., B. D. Healy, W. C. Leibfried, and D. P. Whiting. 2012. 

Bright Angel Creek trout reduction project: Winter 2010-2011 report. 

Natural Resource Technical Report NPS/GRCA/NRTR—2012/001. 

National Park Service, Fort Collins, Colorado.