Fisheries Review: Annual Reporting FY2023 

Maria Dzul* 

with help from 

Charles Yackulic, Drew Eppehimer, Dale Fonken, Josh Korman, David Ward, David 

Rogowski, Mariah Giardina, Mike Pillow, Pilar Rinker, Lucas Bair, Brian Healy, and 

many more 

*U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center; 

mdzul@usgs.gov 

U.S. Department of the Interior 

U.S. Geological Survey 
Thank you! 

Numerous biologists, volunteers, logistics crew, boatmen,

database managers 

Glen Canyon Dam Adaptive Management Program 

Thank you to the 

Grand Canyon 

Native American 

Tribes! 

In this presentations: all fish illustrations by Joe Tomelleri 
Presentation outline 

 Non-native species

 Smallmouth Bass (SMB) in Glen Canyon

 Brown Trout (BNT) in Glen Canyon

 Rainbow Trout (RBT) fishery

 Growth, abundance in Glen Canyon

 Angler catch

 Humpback Chub (HBC)

 Abundances

 Triggers (see 2016 BiOp)
Non-native species: 

SMB background – when Lake Powell is high 
Non-native species: 

SMB background – when Lake Powell is low 

entrainment 

reproduction 
Non-native species: 

Models suggest adult SMB entrainment is low 

*Does not include NPS targeted SMB removals
 

 

Non-native species: 

Models suggest adult SMB entrainment is low 

Models suggest only 

modest entrainment of 

adult SMB in 2022 and 

2023 

Modeling suggests 

greater entrainment at 

Lake Powell elevations 

<3,525 ft.

*Does not include NPS targeted SMB removals
 

Non-native species: 

Models suggest some potential for SMB 

population growth in 2024 

Eppehimer et al., 2024

Population growing 

Population stable or 

declining 

Eppehimer et al., 2024 

16C 

Lees Ferry LCR Confluence 

2/23 traces with λ > 1 8/23 traces with λ > 1 

Using historic inflows from 2000-2022 

λ > 1 

λ ≤ 1 

2024 2024 
 

Non-native species: 

Models suggest some potential for SMB 

population growth in 2024 

Using historic inflows from 2000-2022 

Lees Ferry λ > 1 LCR Confluence Population growing 

λ ≤ 1 Population stable or 

2/23 traces with λ > 1 8/23 traces with λ > 1 declining 

16C 

2024 2024 Eppehimer et al., 2024 Eppehimer et al., 2024

Predictions for 2024: 

• Water temp likely >16C in Lees Ferry but SMB success will be 

limited because: 1) temp >16 C late in year, 2) only slightly >16C 

• If -12 mile slough remains in current condition, temperatures will 

likely be suitable for SMB reproduction in Lees Ferry. 
 

Non-native species: 

Juv. SMB are eating a wide variety 

of food items 

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. 
 

 

 

 

Non-native species: 

SMB are eating a wide variety of 

food items 

Less common outside of Lees 

Ferry (LF) 

2023 Summer Juvenile 

SMB from the mainstem 

Total n=42 

Non-empty n=25 

SMB are eating some prey 

items common only in LF, 

but they are also eating 

prey found throughout the 

CRe 

Courtesy of Kate Behn, GCMRC; preliminary data, subject to review and change, do not cite. 
Non-native species: 

BNT in Glen Canyon have stabilized since peak in 

2020-2021 

 

 

~-14 - -12 mile ~-4 - -3 mile 

Abundance (1000s) per 3 km of river 

12 

Courtesy of Josh Korman, Ecometric Research, preliminary data, subject to review and change, do not cite. 
 

 

 

Non-native species: 

BNT in Glen Canyon had low condition/slow growth in 2023 

Brown Trout growth @ 300g 

Growth/condition is low even in spring 2023 when temp 

& dissolved oxygen were favorable – prey limitation? 

Courtesy of Josh Korman, Ecometric Research, preliminary data, subject to review and change, do not cite. 
 

 

 

Non-native species: 

Brown trout declined in 2023 

Drop due to incentivized 

harvest or poor env. 

conditions/ lack of 

recruitment? 

Preliminary data, do not cite. 
 

Non-native species: 

BNT declined mostly due to poor env. 

conditions, but incentivized harvest helped 

Observed 

Back calculated 

(if harvest had 

not occurred) 

Preliminary data, do not cite. 
Non-native species: 

Increased catch of Green Sunfish 

Other native fishes: 

Increased catch of 

Flannelmouth Sucker 
 

 

RBT fishery: 

Poor RBT recruitment over last few years 

Courtesy of Josh Korman, Ecometric Re

 ~-14 - -12 mile ~-4 - -3 mile 

No spring increase in RBT No population 

despite spring HFE and steady collapse despite low 

and high balancing flows dissolved oxygen/high 

(differs from 2008 & 2011) temperature in summer 

& fall 17 

search, preliminary data, subject to review and change, do not cite. 
 

 

 

 

RBT fishery: 

Poor growth/condition of RBT – but 

we’ve seen this before 

Rainbow Trout growth @ 300g 

Summer-growth/condition is poor 

Winter- good for RBT; allows for recovery 

Courtesy of Josh Korman, Ecometric Research, preliminary data, subject to review and change, do not cite. 
 

RBT fishery: 

Angler catch is low, but above mitigation threshold 

Angler Surveys (creel) 

2023 Data: 

• Walk-in Area (n=151) 

• Boat Ramp (n=717) Management Goal 

Mitigation Threshold 

Courtesy of Dale Fonken, Arizona Department of Fish & Game, preliminary data, subject to review and change, do not cite. 
JCM

-west

JCM-east 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

Humpback Chub: 

Juvenile HBC are high in the 

LCR, JCM-East, and JCM-West

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

JCM-West

JCM-East

LCR
Humpback Chub: 

Large subadult HBC in JCM-East are below 

the trigger in 2023

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

Spring abundances of large subadult HBC in lower LCR remains 

above the trigger

Abundance (N ± 95% CI)

150-199 mm TL

2021-2023

3-year average:

1,418

1,250

Preliminary Information – Data from USFWS, Michael Pillow, Subject to Revision. Not for Citation or 

Distribution.
Humpback Chub:

Adult abundances in the LCR aggregation 

are above the trigger

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

Adult abundance is high above 

Chute Falls

Also – some evidence of reproduction above 

Chute Falls!

Preliminary Information –Data from USFWS, Michael Pillow, Subject to Revision. Not for Citation or Distribution.
Apparent survival of HBC 

Humpback Chub:

Uncertainty about adult survival in 

western Grand Canyon

Apparent survival = probability of survival and not 

emigrating from the study site

Preliminary Information - Subject to Revision. Not for Citation or Distribution.
Map by Tom Gushue

JCM-west

Western GC
Humpback Chub:

Stable/increasing adult abundance in 

western Grand Canyon & JCM-West

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

 Non-native species

 Smallmouth Bass (SMB)

 Low entrainment of adults

 Forecast for 2024: likely colder water temps = less SMB 

pop. growth

 slough = warmwater refugia

 SMB are eating a lot of different food items 

 Brown Trout (BNT)

 Slowest growth/lowest condition seen yet 

 Poor env. conditions & lack of recruitment
Summary (cont’d)

 RBT fishery

 Little production (future pop crash?)

 Adult population stable

 Angling could be better, could be worse

 Humpback Chub

 2023 was a good year for age-0 production 

through Grand Canyon

 Adult abundance is high near LCR & in western 

GC