Smallmouth Bass Population Modeling 

and Implications 

Drew Eppehimer1, Charles B. Yackulic1, Kate Behn1, Maria Dzul1, 

Pilar Rinker2, Brian Healy1, and Laura Tennant3 

1 US Geological Survey, Southwest Biological Science Center, 

Grand Canyon Monitoring and Research Center 

2 US Fish and Wildlife Service 

3 Grand Canyon National Park 

Annual Reporting Meeting 

Jan 23, 2024 

Phoenix, AZ 

Preliminary data, subject to change, do not cite 
Acknowledgements 

Interagency Smallmouth Bass Taskforce 

Glen Canyon Dam Adaptive Management Program 

L. Bruckerhoff, J. Wang, K. Young, B. Mihalevich, K. Bestgen, & J. Schmidt 

P. Budy, B. Friesen, D. Ward, B. Healy, W. Pine, R. Valdez, A. Schultz, G. Anderson, 

G. Chong, & E. Rumpf 

Southwest Climate Adaptation Science Center 
 

 

Introduced fishes do not pose equal risks 

• NPS Risk Levels (2021 update): 

• Smallmouth Bass (Very High) 

• Walleye (Very High) 

• Brown Trout (Very High) 

• Green Sunfish (High) 

• Rainbow Trout (High) 

• Common Carp (Med.-low) 

• Fathead Minnow (Low) 

NPS Risk levels (n=29 species)

Very High (4) 

14% 

High (6) 

21% 

Medium-high (1) 

3% 

Medium (6) 

21% 

Medium-low 

(5) 

17% 

Low (7) 

24% 

Preliminary data, subject to change, do not cite 
 

 

2023 Grand Canyon Nonnative Fishes 

*Does not include NPS 

targeted SMB removals 

Preliminary data, subject to change, do not cite 
Channel Catfish Smallmouth Bass 

Black Crappie 

Green Sunfish 

Threadfin Shad 

Bluegill Fathead Minnow 

Bullhead Catfish 

Plains Killifish 

Walleye Mosquitofish 

Striped Bass 

 

Grand Canyon Nonnative Fishes 

Nonnative species that have increased in catch more than 100% in last 3 years 

compared to 2000-2019: 
 

Grand Canyon Nonnative Fishes 

Nonnative species that have increased in catch more than 100% in last 3 years 

compared to 2000-2019: 

Potential for self-sustaining population

Channel Catfish 

Walleye Bullhead Catfish 

Smallmouth Bass 

and high piscivory 

Black Crappie 

Green Sunfish 

Striped Bass Bluegill Fathead Minnow 

Threadfin Shad 

Plains Killifish 

Mosquitofish 
Lake Mead 

Lake Powell 

Colorado River 

N 

10 30 70 

miles 
Lake Powell 

1982-1989 

stocked Lake Mead 

Colorado River 

N 

10 30 70 

miles 
Lake Powell 

miles 

1982-1989 

stocked Lake Mead 

2000 

1st Capture 

Colorado River 

N 

10 30 70 
Lake Powell 

2003 

1st Capture 1982-1989 

stocked 

miles 

Lake Mead 

2000 

1st Capture 

Colorado River 

N 

10 30 70 
Smallmouth bass capture locations in the 

Grand Canyon 

 

 

 

Routine, Interagency Monitoring 

2003 - 2021: 

22 SMB caught 

12 from Lees Ferry 

N 

Figure: J. Boyer, AZGFD 

*Spatial distribution of effort differs through time D. Rogowski, AZGFD 
Glen Canyon Dam 

Lake Powell 

Lees Ferry 

3470 ft: Penstocks 

3370 ft: Bypass Jet Tubes 

Warmer Water 

Colder Water 

Colder 
Glen Canyon Dam 

Lake Powell 

Warmer Water 

Colder Water 

Lees Ferry 

Warmer 

3470 ft: Penstocks 

3370 ft: Bypass Jet Tubes 
Smallmouth bass modeling 

1. Propagule Pressure from Lake Powell 

-Entrainment (fish passage through dam) 

 Elevation dependent 

2. Population Growth 

-Reproduction, survival, recruitment 

 Thermal suitability 

 Elevation dependent 
Smallmouth bass modeling 

1. Propagule Pressure from Lake Powell 

-Entrainment (fish passage through dam) 

 Elevation dependent 

2. Population Growth 

-Reproduction, survival, recruitment 

 Thermal suitability 

 Elevation dependent 
Modeling: Smallmouth Bass Propagule Pressure

Conceptual Model of Entrainment Risk 

 

 

 

 

Fish Distribution by 

Depth 

Reservoir elevation drives 

penstock depth 

# of SMB Available 

for Entrainment 

Lake Powell 

Elevation 

Penstock Entrainment 

(numbers of fish passed through dam) 

Survival 

Rate 

SMB Abundance in 

Lees Ferry at 

Beginning of Year 

SMB Abundance in 

Lees Ferry at End of 

year 

Survival 

Rate 
Survival 

Rate 

Statistical Model of 

Entrainment Risk 

Elevation 

S

Inflows 

Outflows 

(Bank Storage, 

Evaporation) 

Penstock Entrainment 

(numbers of fish passed through dam) 

MB abundance in

Lees Ferry at 

beginning of year 

SMB abundance in 

Lees Ferry at end of 

year 

Survival 

Rate 
Assumes 

7.48 maf outflows 

Modeling: Smallmouth Bass Propagule Pressure Lake Powell Starting Elevation (ft)

Propagules / year 
Modeling: Smallmouth Bass Propagule Pressure Lake Powell Starting Elevation (ft) 

7.48 maf outflows Match inflows and outflows 

Propagules / year 
Modeling: Smallmouth Bass Propagule Pressure 

Out of sample prediction for 

2022 and 2023 entrainment 
Smallmouth bass modeling 

1. Propagule Pressure from Lake Powell 

-Entrainment (fish passage through dam) 

 Elevation dependent 

2. Population Growth 

-Reproduction, survival, recruitment 

 Thermal suitability 

 Elevation dependent 
 

 

 

 

 

 

 

 

 

Modeling: Smallmouth Bass Population Growth

(Assumes Allee Effect threshold is surpassed) 

Population Growth Rate (lambda) 

Based on thermal suitability 

Daily River Temperature (mainstem only) 

-Lake Powell depth profiles 

-Lake Powell elevation 

-Downriver temp model (Dibble et al. 2021) 

Smallmouth Bass and Temperature 

-Spawn/hatch (16C spawning threshold) 

-Age 0 growth 

-Age 0 overwinter survival 

Parameters were derived from Breton et al. 

(2015) and Bruckerhoff et al. (in prep) 
 

Modeling: Smallmouth Bass Population Growth

(Assumes Allee Effect threshold is surpassed) 

Population Growth Rate (lambda) 

Based on thermal suitability 

Daily River Temperature (mainstem only) 

-Lake Powell depth profiles 

-Lake Powell elevation 

-Downriver temp model (Dibble et al. 2021) 

Smallmouth Bass and Temperature 

-Spawn/hatch (16C spawning threshold) 

-Age 0 growth 

-Age 0 overwinter survival 

Parameters were derived from Breton et al. 

(2015) and Bruckerhoff et al. (in prep) 
Inflow strength changes thermal profile 

Bigger inflows = warmer water deeper 

Depth to 16C can 

change by >100ft! 
Lake Powell temperature model Depth below surface (ft) 

Example: 5 maf inflow 

50 

100 

150 

200 

250 

7.48 maf 

outflows 

3,550 ft starting 

elevation 
Lake Powell temperature model Depth below surface (ft) 

Example: 12 maf inflow 

50 

100 

150 

200 

250 

7.48 maf 

outflows 

3,550 ft starting 

elevation 
Predicted vs observed water temperature Water Temperature (C) 

20 

15 

10 

Out of sample prediction for Lees Ferry 2023 

Predicted 

Observed 

RMSE= 1.28 

Error 
 

 

 

 

 

 

 

 

 

Modeling: Smallmouth Bass Population Growth

(Assumes Allee Effect threshold is surpassed) 

Population Growth Rate (lambda) 

Based on thermal suitability 

Daily River Temperature (mainstem only) 

-Lake Powell depth profiles 

-Lake Powell elevation 

-Downriver temp model (Dibble et al. 2021) 

Smallmouth Bass and Temperature 

-Spawn/hatch (16C spawning threshold) 

-Age 0 growth 

-Age 0 overwinter survival 

Parameters were derived from Breton et al. 

(2015) and Bruckerhoff et al. (in prep) 
 

 

Smallmouth Bass and temperature 

Yampa River Data: Smallmouth Bass Hatch 

First day over 16C 

Figure: Bestgen & Hill, 2016 
 

 

Smallmouth Bass and temperature 

Data: Shuter et al, 1980; Figure: Dudley & Trial, 2014 

Age-0 Smallmouth Bass Growth 

Very slow growth at 

temperatures <16C 
Lake Powell Starting Elevation (ft) 

Lees Ferry 

Assumes 7.48 maf 

outflows 

Modeling: Smallmouth Bass Population Growth 
Lees Ferry 

Assumes 7.48 maf 

outflows 

Modeling: Smallmouth Bass Population Growth Lake Powell Starting Elevation (ft)

2024 
Modeling: Smallmouth Bass Population Growth 

Lees Ferry 

7.48 maf outflows 

Lake Powell Elevation (ft) 

Lees Ferry 

Match inflows and outflows 
Downriver suitability? 

Lake Powell 

Lake Mead 

Lees Ferry 

Little Colorado River 

Colorado River 

Diamond Creek 

N 

10 30 70 

miles 
Modeling: Smallmouth Bass Population Growth 

Downriver warming 

Lees Ferry LCR Confluence DC Confluence 

Lake Powell Starting Elevation (ft) 

(RM 0) (RM 61) (RM 225) 
Testing assumptions and learning from two years of 

data collection 

• Suitable water temperatures 

• Sufficient food 

• Sufficient spawning habitat 

• Suitable water turbidity 
Smallmouth Bass and temperature 

Spawning initiation (observed eggs in nest) 
 

 

Smallmouth Bass and temperature 

Data: Shuter et al, 1980; Figure: Dudley & Trial, 2014 

Age-0 Smallmouth Bass Growth 

Very slow growth at 

temperatures <16C 
 

 

Smallmouth Bass and temperature 

Data: Nonnative fish database 

Preliminary data, subject to change, do not cite 
 

Smallmouth Bass and temperature 

Data: Shuter et al, 1980; Figure: Dudley & Trial, 2014 

Age-0 Smallmouth Bass Growth 

2023 

2022 

Preliminary data, subject to change, do not cite 
 

 

 

may limit population size, but unlikely to

limit establishment

infrequent, high turbidity could limit

downriver reproduction in some years

Testing assumptions and learning from two years of 

data collection 

• Suitable water temperatures 

• Sufficient food 

• Sufficient spawning habitat 

• Suitable water turbidity 
Courtesy of Kate Behn, GCMRC; preliminary data, subject to review and change, do not cite. 

2022 Fall Juvenile SMB from the mainstem Smallmouth Bass Diets Total n=53, non-empty n= 40 

Frequency of occurrence Prey by % biomass 

Preliminary data, subject to change, do not cite 
Smallmouth Bass Diets 2023 Summer Juvenile SMB from the mainstem 

Total n=42, non-empty n= 25 

Courtesy of Kate Behn, GCMRC; preliminary data, subject to review and change, do not cite . Preliminary data, subject to change, do not cite 
Smallmouth Bass Diets 2023 Summer Adult SMB (mainstem and slough) 

Total n=10, non-empty n= 6 

Preliminary data, subject to change, do not cite 
Testing assumptions and learning from two years of 

data collection 

• Suitable water temperatures 

• Sufficient food 

• Sufficient spawning habitat 

• Suitable water turbidity 
Lake Mead 

Grand Canyon 

10 30 70 

miles 

Lees Ferry Velocity Map 

Baseline operations (6-12k CFS) 

19.63 ha (0.2 km2) 

5x5m pixels 

Spawning Habitat (<0.1 m/s) 

Preliminary data, subject to change, do not cite 

Lake Powell 

(Kaplinski et al., 2022a; 2022

N 

b; 

Nelson et al., 2016) 

Discharge/Velocity model: 

S. Wright, J. Korman, P. Grams 
Lake Mead 

Grand Canyon 

 N 10 30 70 

miles 

Lake Powell 

Lees Ferry Velocity Map 

Baseline operations (6-12k CFS) 

19.63 ha (0.2 km2) 

5x5m pixels 

Spawning Habitat (<0.1 m/s) 

-12 mile Slough 

Preliminary data, subject to change, do not cite 

(Kaplinski et al., 2022a; 2022b; 

Nelson et al., 2016) 

Discharge/Velocity model: 

S. Wright, J. Korman, P. Grams 
 

15k CFS 

20k CFS 25k CFS 

30k CFS 

10k CFS 

40k CFS 

Preliminary data, subject to change, do not cite 
 

What about downriver spawning habitat? 

No discharge-velocity model exists 

Potential surrogate: 

cobble, gravel, talus, or debris fan adjacent to an eddy 

Analysis currently underway 
 

infrequent, high turbidity could limit

downriver reproduction in some years

Testing assumptions and learning from two years of 

data collection 

• Suitable water temperatures 

• Sufficient food 

• Sufficient spawning habitat 

• Suitable water turbidity 
 

 

Colorado River Turbidity Log 10 Turbidity 

10000 

1000 

100 

10 

1 

Proportion exceedance 

CR at cameo Cr at stateline GR at GR Diamond SJ bluff SJ farmington SJ four corners 

0 0.2 0.4 0.6 0.8 1 1.2 

Ex: 2021-2022 

Colorado River at 

Diamond Creek 

(09404200) 

Colorado River at Cameo 

(09095500) 

Colorado River at 

Stateline (09163500) 

Green River at Green 

River (09315000) 

San Juan River at 

Bluff (09379500) 

San Juan River at 

Farmington (09365000) 

San Juan River at Four 

Corners (09371010) 

Preliminary data, subject to change, do not cite 
 

Conclusions 

• Smallmouth Bass entrainment model predicted catch of adults in 2022 

and 2023 and suggests entrainment was only modestly elevated. 

• Smallmouth Bass lambda model predicted reproduction in 2022 and 

2023, and growth was consistent with model assumptions. 

• Smallmouth bass diet are consistent with literature but have provided 

some system specific surprises. 

• Studies to address uncertainties are ongoing. 
Photo Credit: Richard McLeish 

Drew E. Eppehimer 

deppehimer@usgs.gov 

Charles B. Yackulic 

cyackulic@usgs.gov