AZGFD Lees Ferry Monitoring 

• Project Elements 

Project H: Salmonid Research and Monitoring 

Project I: Warmwater Native and Nonnative Fish Research and Monitoring 

Project J: Socioeconomic Research in the Colorado River Ecosystem 

• Project Objectives 

-Long term monitoring of trout population 

-Assess angler use of fishery 

-Detect warmwater nonative species 

• Funding Source: GCDAMP supplemented with DJ funds 

• Cooperators: USGS, NPS 

• Products: Annual Reports, presentations, publications 
AZGFD Lees Ferry Monitoring 

• Standardized Electrofishing 

-Spring, summer, and fall 

• Angler Surveys (creel) 

-6 days/month 

• Citizen Science 

• Game Camera 
 

Lees Ferry 2023 Sampling Sites 

• Stratified Random Sampling 

-Spring 

-Summer 

-Fall 

• Fixed Nonnative Sites 

-Dam, Slough, and other sites 

-Unable to sample slough in October 
Electrofishing – catch 2023 
Green Sunfish by river mile 2023 • Most Green Sunfish between RM -10 an

the dam

• 70 (29%) of Green Sunfish were ripe

-54 males

-16 females

d
 

 

• Fewer Smallmouth Bass than 

Green Sunfish 

• Most Smallmouth Bass captured 

between RM -10 and the dam 

• All juveniles <150mm 
 

 

• Rainbow Trout CPUE 

remained very low in 

2023 

• Below management 

goal of 1 fish/min 

Rainbow Trout CPUE 

Fish/m 

in 
Fish/m 

in 

Brown Trout CPUE 
• Condition of large 

Brown Trout increases 

with small Rainbow 

trout CPUE 

Fish/m 

in 
Angler Surveys (creel) 

2023 Data: 

• Walk-in Area (n=151) 

• Boat Ramp (n=717) 

Fish/m 

in 

Brown Trout CPUE 

Management Goal 

Mitigation Threshold 
Year 

2014 

Anglers 

10 

Caught 

14 

Harvested 

2 

% Harvested 

14 

2015 20 23 3 13 

2016 5 6 1 17 

2017 26 30 8 27 

2018 47 96 14 15 

2019 95 165 37 22 

2020 114 301 34 11 

2021 

2022 

64 

153 

111 

420 

35 

126 

Fish/m

in

31 

30 

2023 125 326 257 79 

Angler surveys – Brown Trout 
Summary

• Rainbow Trout relative abundance is the lowest ever recorded 

Recruitment has been declining since 2017 

• Brown Trout relative abundance is similar to last year (increasing recruitment?) 

• More warmwater fishes observed in 2023 (FMS and GSF) 

• Lees Ferry Rainbow Trout fishery is not meeting AZGFD management goals: 

-CPUE electrofishing was less than 1 fish/min 

-Angler catch rates < 1 fish/hour 
 

 

Rainbow and Brown Trout Population Dynamics in 

Glen Canyon

Trout Recruitment and Growth Dynamics (TRGD) Project (H.2) 

GCD AMP Annual Reporting Meeting, January 2024 

Josh Korman (Ecometric Research)

James Crossman (Cross Ecology)

Molly Webb (USFWS, Bozeman)

Mariah Giardina, Charles Yackulic (U.S. Geological Survey, Southwest Biological Science

Center, Grand Canyon Monitoring and Research Center) 

Photo Credit. David Herasimtschuk, ©Freshwaters Illustrated 13 
Rainbow Trout Abundance 

Survival 

of Adults 

New 

Recruits 

Spawning 

(maturation, 

frequency, 

fecundity) 

Growth 

Phosphorus Flow Oxygen / 

Temperature 

Brown Trout 

Abundance/ 

Condition 

Competition 

Prey (inverts) 

2006 

2014 

2012-

2016 2008 

2008 

2011 2018-

2023 

14 
Mark-Recapture Provides Direct Observations of 

Growth in Length and Weight over Time 

15 
 

 

 

 

 

 

 

Mean Monthly Growth Rates (@ 300 g) 

Rainbow Trout 

Brown Trout: 

Growth was poor in 2022 and even worse 

in 2023, leading to rapid decline in 

condition. Note poor growth in 

spring intervals when DO/Temperature 

was OK (likely indicating prey supply / 

competition limitation). 

Rainbow Trout: 

Late fall and winter growth has been good, 

allowing recovery in condition following 

poor growth summer- fall period (even 

following poor growth in summer 

and early fall of 2019 and 2020). 

16 

Brown Trout 
 

 

~-14 - -12 mile 

Take: 37 302 90 

Low DO/High temperature in summer & Take: 195 574 383 

fall did not result in population collapse ~-4 - -3 mile 

 

 

Abundance Trends 

2023 spring HFE and steady and high balancing flows Brown Trout recruitment peaked in 2020- 2021.

did not increase rainbow recruitment as occurred in Population has stabilized owing to lower recruitment. 2008 and 2011 

17 
 

 

 

 

 

 

 

 

Summary 

• 2023 spring HFE and high and steady balancing flows did not result in higher recruitment of Rainbow 

Trout as occurred in 2008 and 2011 (LTEMP). Low oxygen, high water temperature, and more 

abundant Brown Trout likely limited the recruitment response. 

• Current condition of Rainbow Trout is surprisingly good given recent low oxygen/high water 

temperatures. High growth rates in late fall and winter allow seasonal recovery in condition. 

• Very Surprising that sustained low oxygen in summer/fall 2023 did not result in population collapse 

(regardless of condition). 

• Recruitment of young Rainbow Trout has been poor since 2019, so current population is largely 

composed of older/larger fish. Brown Trout predation a likely possible cause for this pattern (more 

study needed). 

• Abundance of Brown Trout appears to have stabilized. Growth rates in 2022 and especially 2023 

much lower than in previous years, perhaps due to a combination of low prey supply (fewer small 

Rainbow Trout) and higher competition (more Brown Trout), and perhaps other factors (e.g., 

Gammarus?). 

18 
Population Reproductive Potential 

Describe the reproductive 

dynamics that influence 

population abundance of 

trout 

19 
 

 

 

Reproductive Objectives 

• Understand the proportion of spawning capable fish

Successful reproduction directly influences population 

abundance 

• Describe how this differs between Rainbow Trout and 

Brown Trout 

Dynamics which influence reproductive success in fishes are

important to understand 

• Develop an approach for data collection that can be 

integrated into native fish research and monitoring 

Limited number of studies of the effects of reproductive

condition on population regulation in fishes (lots in captivity,

less in the wild) 

20 
Methods 

• Used histology to validate noninvasive ultrasonography (2018-

2022) 

• Developed approach to apply 

ultrasonography to population 

assessments (2022-2024) 

Female brown trout 

Rainbow Trout Brown Trout 

Nov 2018* 

Jan 2019* 

Apr 2019* 

Nov 2019+ 

Jan 2020+ 

Nov 2020+ 

Jan 2021+ 

Apr 2021+ 

Nov 2021* Nov 2021* 

Jan 2022* Jan 2022* 

Apr 2022* Apr 2022* 

Nov 2022 Nov 2022 

Feb 2023 Feb 2023 

Nov 2023 Nov 2023 

Jan 2024 Jan 2024 
 

 

Trout Reproductive Cycle 

• Fish will enter the reproductive cycle and progress through these 

phases annually, unless conditions are suboptimal 

• Fish can fail to spawn 3 different ways during the cycle 

–

–

–

-

-

-

Immature 

Developing 

(March September) 

Regressing 

(October March) 

Regenerating 

Mature 

Post ovulatory 

Post 

spermiation 

Mass 

follicular 

atresia 

Partial follicular 

atresia 

(10 30% fecundity 

regulation) 

Spawning Capable 

(October March) 
 

 

 

Results 

• Proportion of Brown and Rainbow Trout in 3 different reproductive 

phases 

Brown Trout Rainbow Trout 

Month Developing 

Spawning 

Capable Atretic Developing 

Spawning 

Capable Atretic 

Nov-21 0.00 0.95 0.05 0.40 0.47 0.09 

Jan-22 0.00 0.05 0.07 0.17 0.65 0.12 

Apr-22 0.17 0.17 0.12 0.00 0.36 0.19 

Nov-22 0.03 0.90 0.06 0.87 0.06 0.07 

Jan-23 0.03 0.84 0.12 0.34 0.64 0.01 

Apr-23 Data being processed 

Nov-23 0.07 0.93 0.00 0.80 0.11 0.08 

Jan-24 

• High spawning capability in Brown Trout compared to Rainbow Trout 

• Increased proportions of female Rainbow Trout in developing phases 

indicates skip spawning 
–

–

–

-

-

-

Immature 

Developing 

(March September) 

Regressing 

(October March) 

Regenerating 

Mature 

Rainbow Trout 

Spawning Capable 

(October March) 

Partial follicular 

atresia 

(10 30% fecundity 

regulation) 

Post ovulatory 

Post 

spermiation 

Mass 

follicular 

atresia 

Trout Reproductive Cycle 

• Rainbow Trout in Glen Canyon appear to be skip spawning, with 

higher proportions of fish remaining in developing phases 
Rainbow andBrown Growth Rates 

26 
 

 

 

1) High abundance from 3) Good recruitment in 2017/2018 

high and steady 2011 results in recovery 4) Owing to poor recruitment since 2018, equalization flows & 2) 2015 population collapses due current population dominated by older/ high SRP by high densities, low prey, and larger fish high water temperatures 

2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 

Rainbow Trout Population Trend and Causes for Change 

over the Last Decade 
Good growth in late fall and winter has allowed condition factor to recover in 

spite of high temperatures and low dissolved oxygen in 2022 and 2023