Monitoring Humpback Chub in the Little 

Colorado River and Colorado River, 

Grand Canyon

Maria Dzul1, David Van Haverbeke2, Charles B. Yackulic1, Mariah 

Giardina1, Mike Pillow2, Pilar Rinker2

1U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, Flagstaff, AZ

2U.S. Fish and Wildlife Service, Arizona Fish and Wildlife Conservation Office, 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 Not for Citation or Distribution.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: Humpback Chub (HBC, Gila cypha) Population 

Dynamics throughout the Colorado River Ecosystem

 Project elements and objectives:

 G.1: HBC population modeling

 G.2 Annual spring/fall HBC abundance estimates in the lower 13.6 km of 

the Little Colorado River (LCR)

 G.3. Juvenile HBC monitoring near the LCR confluence

 G.4 Remote PIT tag array monitoring in the LCR

 G.5. Monitoring HBC aggregation relative abundance and distribution

 G.6. Juvenile Humpback Chub Monitoring - West

 G.7. Chute Falls HBC translocations

 Funding Amount and Source: $1,015,966 AMP ($978,126 spent)

 Cooperators: USGS, USFWS

 Resource Goals: Humpback Chub, Other Native Fish

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 Not for Citation or Distribution.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

(Project G)

 Little Colorado River (LCR) aggregation

 Humpback chub abundance estimates 

 LCR 

 Juvenile chub monitoring (JCM) -east

 Implications of warm water temperatures & fast growth

 Total adults & triggers

 Chute Falls translocations

 Western Grand Canyon

 Humpback chub aggregations monitoring & seining

 Abundance estimation in western Grand Canyon

 JCM-west

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 Not for Citation or Distribution.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

Grand Canyon

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 Not for Citation or Distribution.

Map by Tom Gushue

LCR 

aggregation
Life history of humpback chub in LCR aggregation

Colorado River

Little Colorado 

River

resident

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 Not for Citation or Distribution.

migrants
Presentation outline

(Project G)

 LCR aggregation

 Humpback chub abundance estimates 

 LCR

 JCM-east

 Implications of warm water temperatures & fast growth

 Total adults & triggers

 Chute Falls translocations

 Western Grand Canyon

 Humpback chub aggregations monitoring & seining

 Abundance estimation in western Grand Canyon

 JCM-west reach

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

(sizes are mm total length)

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

0

<100

100-149

150-199

200-249

>250

Juvenile

Small subadult

Large subadult

Small adult

Large adult
* 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

Age-0 abundances in the LCR

Abundance

*

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

Year
18,000

Annual Sept/Oct HBC age-0 abundance 

(grey) and the following April/May age-1 

abundance (red). Note age-0 in 2022 is 

not particularly high

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022

Abundance

Year born (cohort)

Abundance <106 mm fall Abundance 91-161 mm the next spring

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Annual spring abundances of large subadult HBC in lower 13.6 km of LCR 

No sampling spring 2020, Mean in circle = 1,248, 

trigger is 1,250

4,500

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

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

May/June 2001

April/May 2002April/May 2003April/May 2004April/May 2005April/May 2006April/May 2007April/May 2008April/May 2009

May/June 2010May/June 2011

April/May 2012April/May 2013April/May 2014April/May 2015April/May 2016

April/June 2017

April/May 2018April/May 2019April/May 2020

April/May2021

April/May 2022

Abundance estimate

Year
Annual spring abundances of adult 

HBC in lower 13.6 km of LCR

0

2,000

4,000

6,000

8,000

10,000

12,000

2001200220032004200520062007200820092010201120122013201420152016201720182019202020212022

Abundance

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Annual fall abundances of adult HBC in 

lower 13.6 km of LCR

0

2,000

4,000

6,000

8,000

10,000

12,000

2001200220032004200520062007200820092010201120122013201420152016201720182019202020212022

Abundance

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

(Project G)

 LCR aggregation

 Humpback chub abundance estimates 

 LCR 

 JCM-east

 Implications of warm water temperatures & fast growth

 Total adults & triggers

 Chute Falls translocations

 Western Grand Canyon

 Humpback chub aggregations monitoring & seining

 Abundance estimation in western Grand Canyon

 JCM-west

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

Artwork by Randy Van Haverbeke

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Juvenile abundance in the JCM East

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

are very low

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

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

Large subadults in JCM-east are 

below the trigger

Year
Very high growth for subadults in 

JCM-East during 2022

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Growth of subadults in JCM-East

 Juvenile & subadult humpback chub grew 60-100mm from 

Oct 2021-Oct 2022

 Humpback chub in 2022 spent less than a year as small 

subadults and(or) large subadults

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Subadult numbers in JCM-east are low but...

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

Small subadults Large subadults













Prior to 2020 (cold water – slow growth):

~3 years for large subadults to become adults

Large subadults comprised of three cohorts

In 2022 (warm water – fast growth):

~1 year for large subadults to become adults

Large subadults comprised of one cohort

Faster growth means fewer subadults
Presentation outline

(Project G)

 LCR aggregation

 Humpback chub abundance estimates 

 LCR 

 JCM-east

 Implications of warm water temperatures & fast growth

 Total adults & triggers

 Chute Falls translocations

 Western Grand Canyon

 Humpback chub aggregations monitoring & seining

 Abundance estimation in western Grand Canyon

 JCM-west reach

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.

Year
Tier for humpback chub trigger* 

(Metric 3.1)

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

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

*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:
Catch of channel catfish was very high in 

JCM-East in Oct 2022

• Small channel catfish

Ictalurus punctatus

(~20mm) also captured 

in the LCR during July 

2022 sampling trip

• Increase presumably 

due to warmer water 

temperatures in the 

main-stem

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

LCR & JCM East

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

Artwork by Lindsay Hansen

 Adult estimates remain high

 Subadult numbers are low

 Warm water temperatures are changing things!

 Fast growth = fewer subadults 

 More non-native fishes (channel catfish?)

 Mainstem spawning near the LCR? (now possible)
Presentation outline

(Project G)

 LCR aggregation

 Humpback chub abundance estimates 

 LCR 

 JCM-east

 Implications of warm water temperatures & fast growth

 Total adults & triggers

 Chute Falls translocations

 Western Grand Canyon

 Humpback chub aggregations monitoring & seining

 Abundance estimation in western Grand Canyon

 JCM-west reach

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Translocations and Chute Falls Monitoring

Preliminary Information - Subject to 

Revision. Not for Citation or 

Distribution.
Number of HBC translocated annually (black 

bars) and annual abundances of adult HBC 

above Chute Falls (red and grey bars) 

0

100

200

300

400

500

600

700

20032004200520062007200820092010201120122013201420152016201720182019202020212022

Abundance estimate or number of fish

Year

Translocated fish Monte Carlo (N) Chapman Petersen (N)

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Length frequencies of HBC in Chute Falls 

and Atomizer reaches (2013-2021)

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Summary: Chute Falls 

Translocations

 To address reaching the “trigger” in the mainstem in 

2020, we increased the number of HBC translocated 

to above Chute Falls to 535 in 2021.

 To address reaching the “triggers” in the JCM in 2022, 

we suggest conducting an additional HBC 

translocation to above Chute Falls in spring 2023. 

 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.
Presentation outline

(Project G)

 LCR aggregation

 Humpback chub abundance estimates 

 LCR 

 JCM-east

 Implications of warm water temperatures & fast growth

 Total adults & triggers

 Chute Falls translocations

 Western Grand Canyon

 Humpback chub aggregations monitoring & seining

 Abundance estimation in western Grand Canyon

 JCM-west

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
2022 seining trip

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Humpback Chub catches via seining by river 

mile

0

10

20

30

40

50

60

70

80

90

0-14 15-29 30-44 45-59 60-74 75-89 90-104 105-119120-134135-149150-164165-179180-194195-209210-224225-239

# seine hauls or # fish 

River mile

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Length frequencies of Humpback Chub 

captured via seining

0

20

40

60

80

100

26-3046-5066-7086-90

106-110126-130146-150166-170186-190206-210226-230246-250266-270286-290306-310326-330346-350366-370386-390

Number of Fish

Total Length (mm)

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

Seining vs. Hoop netting

Nonnatives

Seining Hoop netting

Bluegill 1

Black Crappie 5

Bullhead 1

Channel Catfish 38 5

Carp 33 7

Fathead Minnow 612 16

Green Sunfish 54

Gizzard Shad 4

Plains Killifish 287

Rainbow Trout 81 14

Stiped Bass 55

Threadfin Shad 3

Totals 1,174 42

Natives

Bluehead Sucker 8 3

Flannelmouth Sucker 5,185 5,929

Flannelmouth x Razorback 3

Humpback Chub 485 1,340

Speckled Dace 1,666 231

Totals 7,344 7,506

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Hoop netting sample sites on 2022 aggregation trip

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Annual CPUEs of Humpback Chub and 

Flannelmouth Sucker on aggregation trips 2000 

and 2010-2022 

-2

0

2

4

6

8

10

12

14

16

18

20

22

0

100

200

300

400

500

600

700

800

Mean CPUE (captures/set)

Hoop Nets (n)

Aggregation trip by year

Hoop nets

Humpback Chub

Flannelmouth Sucker

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Annual CPUEs of Humpback Chub at sample 

sites above Havasu Rapids 2010-2022

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Annual CPUEs of Humpback Chub at sample sites 

below Havasu Rapids 2010-2022

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Length frequencies of HBC above and 

below Havasu aggregation (RM 156)

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

Canyon (Havasu to Pearce Ferry)

 1) conduct mark-recapture studies to gain capture 

probability data.

 2) Apply capture probability data to catch data to 

estimate densities of adult Humpback Chub within 

sample reaches.

 3) Extend densities between sample reaches and refine 

estimates by accounting for habitat variability, potential 

movement, effects of turbidity, temp, etc. 

 4) Spatial & habitat effects account for non-random 

sampling

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Do fish swim to get to the bait?

Or the “superpopulation” (what area are we sampling?)

Area sampled 

= sampling site

Area sampled > 

sampling site

Area sampled >> 

sampling site

Preliminary Information - Subject to 

Revision. Not for Citation or 

Distribution.
Abundance estimates of HBC in western Grand 

Canyon (Havasu Rapids to Pearce Ferry) 

2017-2022

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
An example of density (fish/mile) estimation in 

western Grand Canyon – the 2022 pattern

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

 Since ~2017, western Grand Canyon has been 

populated by Humpback Chub representing all size 

classes. 

 Highest densities of adults appear to consistently be 

between Lava Falls and Separation Canyon (RM 

180-240). 

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

(Project G)

 LCR aggregation

 Humpback chub abundance estimates 

 LCR 

 JCM-east

 Implications of warm water temperatures & fast growth

 Total adults & triggers

 Chute Falls translocations

 Western Grand Canyon

 Humpback chub aggregations monitoring & seining

 Abundance estimation in western Grand Canyon

 JCM-west

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

Grand Canyon (JCM-west)

Preliminary Information - Subject to Revision. Not for Citation or Distribution. Photo by Lindsay Hansen

Map by Tom Gushue

JCM-west

LCR agg
Colorado River

Little Colorado 

River

resident

LCR migrants = slow life history

LCR residents = fast life history

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Annual apparent survival of 

humpback chub in JCM-west

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

Apparent survival = probability of survival and not emigrating from the study site
Fast growth of humpback chub in JCM-west

JCM-west growth is more comparable to the LCR than JCM-east

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Movement of HBC is likely high in 

JCM-west

Transience is the probability a fish captured in the sampling reach is just 

swimming through (i.e., only remains in sampling reach for 1 occasion)

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Summary: Humpback chub in JCM-west

 JCM-west is unique

 not similar to LCR-residents or LCR-migrants

 High subadult survival and fast subadult growth

 Fast population turnover rates

 Low adult survival or high movement?

 Need more information about movement in western Grand 

Canyon!

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

Artwork by Lindsay Hansen 

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