Effects of Warm-Water Invasive Species 

on Native Colorado River Fishes

David Ward

Grand Canyon Monitoring and Research Center

Southwest Biological Science Center

Project I.

LTEMP Resource Goal – Minimize impacts of 

Invasive Species
Non-native fishes
Incompatibility of native and nonnative fishes

Marsh and Pacey 2005

Clarkson et al. 2005

Mueller 2005
Fundamental Question?

Why are they incompatible?

• Why don’t predators cause the extinction 

of prey in all cases?

• How does any prey persist?
Answer:

In co-evolved predator prey relationships the 

prey species have:

Morphology, Physiology and Behavior –

That render some individuals less vulnerable
Often the key to Effective 

Management is understanding 

• Morphology

• Physiology

• Behavior
Behavioral Ecology

Traditional Ecological

Knowledge
Assessing the morphology, physiology and 

Behavior of fish is often more difficult
Ward and Figiel 2013, Journal of Fish and Wildlife Management
Reduced movement makes sense

In the historic Colorado River
Reduced movement only works if you have:

1. High Turbidity

2. Sight feeding predators

Turbidity increases predation effectiveness of 

catfish.

RZ suckers and catfish are Immiscible !

Differences in behavioral response 

• Chub move away from threats

• Razorback suckers avoid movement

?
These predator avoidance 

behaviors and morphologies

were shaped over a 

3 million-year period
Colorado Pikeminnow shaped

the behavior and morphology of 

The Fish Community
Predator Gapes
A Comparison of Predator Gapes

Total Length (mm)

50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800

Maximum Anatomical Gape (mm)

0

10

20

30

40

50

60

70

80

90

100

Smallmouth Bass

Brown Trout

Rainbow trout

Colorado Pikeminnow

Flathead Catfish

Striped Bass

Black Bullhead Catfish

Body Depth/Gape Relationships
• Behavior

• Morphology

Lets apply what we know to the 

introduced warm-water fish
Catfish !!!

Historically - Nothing similar in 

Colorado River

Prior to Glen Canyon Dam

Most abundant fish in the Colorado River

(Dill 1944 surveys)
What has changed in 

Western Grand Canyon in the last 15 years?
Channel Catfish in the Little Colorado River
Channel Catfish in the Little Colorado River (Angling 2018)

 May 20-24

Total Length (mm)

100 200 300 400 500 600 700

Frequency

0

1

2

3

4

32 fish Average = 1 fish/hr
Channel Catfish in the Little Colorado River (Angling 2019)

4 Trips May - June

Channel Catfish in the Little Colorado River 2019

Total Length (mm)

100 200 300 400 500 600

Frequency

0

2

4

6

8

10

N=82

Average size = 408 mm TL (Range = 261-630 mm TL)
2019 Summary – Channel Catfish Angling in LCR

• 82 Fish caught and PIT tagged (109 angler-hours of effort)

• Mostly large adults (Average 16+ inches)

• Only 2 recaptures – no population estimate - Population is 

likely large – or moves a lot

• Widely distributed - Confluence - Atomizer Falls (Rkm 13.5)

• Catch is temperature dependent

• Found in deep water, under boulders
Laboratory Predation Studies



CCF with Humpback chub

Treatment

Clear Muddy Marl

Number surviving in 24-hours

0

2

4

6

8

10

12

14

Channel Catfish Mean = 320 mm TL

Razorback sucker 40-50-mm TL
Small CCF With Razorback sucker

Treatment

Clear Muddy Marl

Number of HBC surviving after 24-hours

0

2

4

6

8

Channel Catfish Mean = 260 mm TL

Humpback chub 35-50-mm TL
Probability that a juvenile chub will survive predation 

by smallmouth bass at 20 °C at 3 different sizes.

Probability of survival (%) 

0%

20%

40%

60%

80%

100%

140 160 180 200 220 240 260 280

Smallmouth Bass TL

 

 

 
BD/Gape: Able to calculate size of fish 

Smallmouth Bass consumed
Smallmouth bass on average will not consume chub 

with body depths more than 40% of their gape

Laura Tennant MS Thesis, NAU

64%
A graph showing percent survival of humpback chub in the presence of green sunfish

Juvenile humpback chub total length (mm)

10 20 30 40 50 60

Percent survival of humpback chub in the presence 

of 80 mm Green Sunfish

0

20

40

60

80

100

Green Sunfish
Percent (%) probability that a juvenile chub will survive predation by a 285 

mm rainbow trout as chub size increases from 45-85 mm TL at 10, 15 and 

20 °C, with trout size held constant at 285 mm TL. 

 

 

Chub Total Length (mm)

45 50 55 60 65 70 75 80 85

Probability of Survival (%)

0

20

40

60

80

100

10 °C

15 °C

20 °C

Rainbow Trout
Green Sunfish consume chub with 

body depths more than 54% of their gape

Juvenile humpback chub total length (mm)

10 20 30 40 50 60

Percent survival of humpback chub in the presence 

of 80 mm Green Sunfish

0

20

40

60

80

100
130 mm

45 mm



Why Green Sunfish?

• Group hunting behavior

• Aggressive predator

• Small size allows them to access prey

• Highly fecund

• Spread with flood events

• Typically overtake natural systems
Why Channel Catfish?

• Incompatible with most native fish

– Nocturnal, more effective in turbid water, large gape

• Live in Little Colorado River

• Highly vulnerable to predation

• Appears to be little recruitment
Questions?