Monitoring Humpback Chub in the Little Colorado 

River and Colorado River, Grand Canyon 

Maria Dzul1, Mike Pillow2, Pilar Rinker2, John Fennell3, 

C harles B. Yackulic1, David Ward2

, David Rogowski3 

1U.S . Geological S urvey, S outhwest Biological S cience C enter, Grand C anyon Monitoring and Research C enter, Flagstaff, AZ 

2U.S . Fish and Wildlife S ervice, Arizona Fish and Wildlife C onservation Office, Flagstaff, AZ 

3Arizona Department of Game & Fish, Research Branch, Flagstaff, AZ 
 

 

 

 

 

 

This information is preliminary and is subject to 

revision. It is being provided to meet the need for 

timely best science. The information is provided on the 

condition that neither the U.S. Geological Survey nor 

the U.S. Government shall be held liable for any 

damages resulting from the authorized or 

unauthorized use of the information. 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Project G Presentation outline: 

• Little Colorado River (LCR) aggregation 

• LCR 

• HBC abundance estimates 

• Juvenile Chub Monitoring (JCM) – east 

• HBC abundance estimates 

• Implications of warm temperatures & fast growth 

• Total adults & triggers 

• Chute Falls translocations 

• Western Grand Canyon 

• Humpback Chub aggregations monitoring 

• Hoop net relative abundance 

• Abundance estimates in western Grand Canyon 

• JCM – west 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
Fixed site monitoring in eastern Grand Canyon 

Map by Tom Gushue, USGS 

LCR 

aggregation 

 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
Size chart 

indicator 

(sizes are mm total length) 

Juvenile 

Small subadult 

Large subadult 

Small adult 

Large adult 

0 

 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

<100 

100-149

150-199

200-249

>250
 

Life history of Humpback Chub in LCR aggregation: 

Colorado River 

Little Colorado River 

resident 

migrants 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Project G Presentation outline: 

• Little Colorado River (LCR) aggregation 

• LCR 

• HBC abundance estimates 

• Juvenile Chub Monitoring (JCM) – east 

• HBC abundance estimates 

• Implications of warm temperatures & fast growth 

• Total adults & triggers 

• Chute Falls translocations 

• Western Grand Canyon 

• Humpback Chub aggregations monitoring 

• Hoop net relative abundance 

• Abundance estimates in western Grand Canyon 

• JCM – west 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

Large, prolonged flood in LCR in 2023 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

 

 

 

Age-0 abundances in the LCR 

* Abundance estimate 

from 2020 is based on 

expanding from a small 

proportion of the spatial 

area (near the 

confluence) and may not 

be fully representative 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
Annual Fall HBC age-0 (gray) and age-1 

(red) abundance by hatch year shows a 

large 2023 cohort. 

* 

 

 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

Fall age-0 

Spring age-1 

*No sampling

spring 2020
 

 

Annual spring abundances of large sub-adult HBC 

in lower 13.6 km of LCR remains above the 

trigger. 

2021-2023 

 

Abundance (N ± 95% CI) 

150-199 mm TL 

3-year average: 

1,418 

1,250 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
2023 spring adult (≥ 200 mm) abundance shows

highest point estimate recorded in LCR 

Spring 

 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. Abundance (N ± 95% CI) 
Spring 

Fall 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

Fall adult (≥ 200 mm) abundance of LCR resident

HBC in 2023 is stable in recent years 

( Abundance 

N

± 95% CI) 
 

 

Project G Presentation outline: 

• Little Colorado River (LCR) aggregation 

• LCR 

• HBC abundance estimates 

• Juvenile Chub Monitoring (JCM) – east 

• HBC abundance estimates 

• Implications of warm temperatures & fast growth 

• Total adults & triggers 

• Chute Falls translocations 

• Western Grand Canyon 

• Humpback Chub aggregations monitoring 

• Hoop net relative abundance 

• Abundance estimates in western Grand Canyon 

• JCM – west 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Juvenile Chub 

Monitoring - east 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

Artwork by Randy Van Haverbeke 
Juvenile abundance in the JCM East 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

Was there mainstem production in Eastern Grand Canyon in 

2022? 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
Small subadult abundances in JCM-east 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

are higher than in years 
Large subadults in JCM-east are bel ow

the trigger 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
Small subadults grow fast when water 

temperatures are warm 

 

 

 

* Water temperatures in 2023 

were approximated (no data 

available) 

Growth was high in 2023, but 

not as high as in 2022 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Project G Presentation outline: 

• Little Colorado River (LCR) aggregation 

• LCR 

• HBC abundance estimates 

• Juvenile Chub Monitoring (JCM) – east 

• HBC abundance estimates 

• Implications of warm temperatures & fast growth 

• Total adults & triggers 

• Chute Falls translocations 

• Western Grand Canyon 

• Humpback Chub aggregations monitoring 

• Hoop net relative abundance 

• Abundance estimates in western Grand Canyon 

• JCM – west 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

Adult abundances in the LCR aggregation 

are above the trigger 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

 

 

 

Tier for Humpback Chub trigger* 

(Metric 3.1) 

*for more info on triggers, see: U.S. Bureau of Reclamation. 2016. Record of decision, Glen Canyon Dam long-term 

experimental and management plan, final environmental impact statement. U.S. Department of the Interior, Bureau of 

Reclamation, Salt lake City, Utah, National Park Service, Lakewood Colorado, Dec. Available 

at: https://ltempeis.anl.gov/documents/docs/LTEMP_ROD.pdf 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Take-home points: LCR & JCM East 

 2023 was a good reproduction year in the LCR 

 Large, prolonged flood 

 Small body size of age-0 fish 

 High age-0 abundance in the Colorado River 

 Subadult numbers are low BUT 

 Slight increases in the last few years 

 Partly due to warm water (fast growth) 

 Adult estimates remain high 

Artwork by Lindsay Hansen 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Project G Presentation outline: 

• Little Colorado River (LCR) aggregation 

• LCR 

• HBC abundance estimates 

• Juvenile Chub Monitoring (JCM) – east 

• HBC abundance estimates 

• Implications of warm temperatures & fast growth 

• Total adults & triggers 

• Chute Falls translocations 

• Western Grand Canyon 

• Humpback Chub aggregations monitoring 

• Hoop net relative abundance 

• Abundance estimates in western Grand Canyon 

• JCM – west 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
Humpback Chub Translocation and 

Chute Falls Monitoring 

Chute Falls 

Little Colorado River 

Translocation 

Monitoring 

Reach 
 

 

Annual HBC Translocations above Chute Falls 

2023: 173 (63-117mm) 

2003-2023: 4,871 (50-155mm) 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
Spring adult abundance above Chute Falls shows 

increasing trend and highest estimates recorded in 

2022-23 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
42% of HBC captured above Chute Falls in 2023 

were not translocated there 

 

Translocated 

n = 199 

Not Translocated: 

n = 140 

Upstream Migrants:

n = 2 

42% 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
The proportion of local (not translocated) HBC above 

Chute Falls has increased substantially since 2011 

 

 

 

1% 1% 

9% 5% 5% 

4% 14% 14% 

14% 24% 42% 

1% 

Translocated 

Not Translocated 

% Local 

*12 HBC have been documented moving above Chute Falls from below between 2007-2023 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

Summary: Chute Falls Translocations 

• Adult HBC abundance in the translocation reach remains 

high. 

• Some evidence of local reproduction and upriver expansion 

• 173 HBC were translocated above Chute Falls in 2023 

• 4,871 total fish have been translocated since 2003 

• To address reaching the “trigger” in the JCM reach in 2023, 

we suggest conducting two HBC translocations to above 

Chute Falls in 2024. 

• Other options may need to be considered in the future (e.g., 

continue translocating higher #’s above Chute Falls, 

transporting juvenile HBC from western Grand Canyon?). 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Project G Presentation outline: 

• Little Colorado River (LCR) aggregation 

• LCR 

• HBC abundance estimates 

• Juvenile Chub Monitoring (JCM) – east 

• HBC abundance estimates 

• Implications of warm temperatures & fast growth 

• Total adults & triggers 

• Chute Falls translocations 

• Western Grand Canyon 

• Humpback chub aggregations monitoring 

• Hoop net relative abundance 

• Abundance estimates in western Grand Canyon 

• JCM – west 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

2023 Mainstem HBC aggregation trip sampled 15 sites with hoop 

nets between 20-mile and Columbine Falls (RM 275) in the fall 

20-Mile 

Nautiloid 

60-Mile 

Cardenas Cremation 

103-Mile 

Middle Granite 

Gorge Below Havasu 

Above Lava 

Big Bar 

JCM West 

Ghost 

243-Mile 

250-Mile 

Columbine 

Western Grand Canyon Eastern Grand Canyon 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

AGFD river-wide hoop net CPUE shows an increase in 

spring HBC relative abundance since 2017 

(spring sampling) 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

 

Overall HBC fall relative abundance at highest level on 

record, a large increase from 2022 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

0 

2 

4 

6 

8 

10 

12 

Mean CPUE (captures/set) 

(fall sampling) 

Aggregation trip by year 
 

 

 

This increase is primarily driven by captures in the 

western Grand Canyon, below Havasu Creek 

* * * * * 

*LCR Aggregation not sampled 

* 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

AGFD and HBC Aggregations find most HBC 

between 200-240 mile 

Downstream 

Eastern Grand 

Canyon 

Western Grand 

Canyon Eastern Grand 

Canyon 

Western Grand 

Canyon 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

Relative abundance increase is driven primarily by 

small sub-adults 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
Age-0 HBC were 

found in 

backwaters along

Colorado River in 

July (high water)

and September

(low water) 

Summer 

Backwater Seining 

Eastern Grand 

Canyon Fall 

Backwater Seining 

 

20 40 60 80 100 120 140 160 180 200

0 

50 

100 

150 

0 

50 

100 

150 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. Total Length (mm) 
 

 

Project G Presentation outline: 

• Little Colorado River (LCR) aggregation 

• LCR 

• HBC abundance estimates 

• Juvenile Chub Monitoring (JCM) – east 

• HBC abundance estimates 

• Implications of warm temperatures & fast growth 

• Total adults & triggers 

• Chute Falls translocations 

• Western Grand Canyon 

• Humpback Chub monitoring 

• Hoop net relative abundance 

• Abundance estimates in western Grand Canyon 

• JCM – west 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

 

Abundance estimation in western Grand Canyon 

(Havasu to Pearce Ferry) 

1) Mark-recapture to obtain capture probability 

2) Capture probability & catch to estimate density 

-effects of turbidity, temp, etc. 

3) Spatial & habitat effects account for non-random 

sampling 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
HBC Abundance in western Grand 

Canyon 2017-2023

(Havasu Rapids to Pearce Ferry) 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

Summary: HBC Aggregations: 

• HBC relative abundance in Grand Canyon 

increased substantially in 2023 

• Driven by small sub-adults (100-149 mm) 

• Adult abundance below Havasu Rapid has also 

been increasing since 2018 

• In order to update our capture probabilities 

with the changing river conditions, we suggest

conducting two-pass mark-recapture event in 

2024 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

Project G Presentation outline: 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

• Little Colorado River (LCR) aggregation

• LCR

• HBC abundance estimates

• Juvenile Chub Monitoring (JCM) – east

• HBC abundance estimates

• Implications of warm temperatures & fast growth

• Total adults & triggers

• Chute Falls translocations

• Western Grand Canyon

• Humpback Chub monitoring

• Hoop net relative abundance

• Abundance estimates in western Grand Canyon

• JCM – west
 

 

 

Fixed site monitoring in western 

Grand Canyon (JCM-west) 

Photo by Lindsay Hansen 

Map by Tom Gushue 

JCM-west 

LCR agg 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

High juvenile abundance in JCM-west in 

2022 & 2023 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

HBC adult abundance in JCM-west 

compared to western Grand Canyon 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Apparent survival = probability of survival and not emigrating from the study site 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

Apparent survival of HBC 
 

 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

* Water temperatures in 2023 were approximated (no data available) 

Growth of HBC is faster in JCM-W 

than JCM-E 
 

 

 

 

 

 

Summary: Humpback Chub in Grand Canyon 

• Eastern Grand Canyon 

• High abundance of small, age-0 fish in the LCR & JCM-East 

• Subadults low, but faster growth 

• High abundance of adults 

• Chute Falls translocations: some evidence of reproduction? 

• Western Grand Canyon 

• Adult abundance at its highest 

• High age-0 abundance in 2022 & 2023 

• Growth & survival different from Eastern Grand Canyon 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 
 

 

Artwork by Lindsay Hansen 

Preliminary Information - Subject to Revision. Not for Citation or Distribution. 

Thank You