U.S. Department of the Interior

U.S. Geological Survey

Context and Comparison: Status of Tailwater 

Fisheries in the Western United States

Kimberly L. Dibble1,2, Charles B. Yackulic1, Theodore Kennedy1, and Phaedra Budy3

1 U.S. Geological Survey, Grand Canyon Monitoring and Research Center, 2255 N. Gemini Drive, Flagstaff, AZ 86001

2 Contact Information: kdibble@usgs.gov; 928-556-7327

3 Utah State University, Utah Cooperative Fish and Wildlife Research Unit, 5290 Old Main Hall, Logan, UT 84322-5290

2014 Annual Reporting Meeting, Phoenix, AZ

January 28, 2014
Lees Ferry Tailwater, 1970s

Photos: Richard Hepworth, 1977

Photo: Colorado River Conservancy
Hypotheses

 Changes in dam operations during the stocking 

era (1990) limit the growth of large rainbow trout

 Hydropeaking may be beneficial to adults

 Created fast-growing, high-quality algal assemblage

 Daily surges in invertebrate drift

 Favored larger invertebrate prey (e.g., Gammarus)

Midges

Black flies

Glen Canyon Dam
Why learn from other tailwaters?

 Would be difficult to evaluate hypotheses 

without changing Glen Canyon dam operations

 Novel flow regimes in other tailwaters to 

enhance trout fishery, benefit native fish

 Flaming Gorge- artificial spring floods, temperature 

modification, summer minimum flows

 Long history of data collection

 Develop broader understanding of linkages 

between dam operations and trout growth
 Western tailwaters 

 AZ, NM, CA, NV, CO, UT, WY, MT, ID, OR

 Data obtained from biologists, databases

 Trout size 

 Discharge

 Reservoir

 Water quality

 Temperature

 Foodbase

 Dam size

 Dam age

 Latitude/elevation

 Stocking

 Whirling disease

 Brown trout density

Data Synthesis
35/56 dams capable of hydroelectric generation

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Ritschard Dam Cheesman Dam

(Wolford Mountain)

Glen Canyon Dam

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Glen Canyon Dam

27,000,000 AF; 710 ft.

Windy Gap Dam

445 AF; 25 ft.

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Response Metric: Length >300mm

>12”

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Response Metric: Catch/mile >300mm

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
August 2011 August 2012

Explanatory Metric: Hydropeaking

Coefficient of Variation 

Ratio of the standard 

deviation to the mean

CV= σ/μ

CV is high when the 

range of discharges 

within a day is large

CV = 488/24,301 

= 0.02

CV = 2815/13,971 

= 0.20

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Hydropeaking Across Years

2011 Equalization

2012

Lagged (2011 

instead of 2012)

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Explanatory Metric: Seasonal Discharge

Summer

Winter

Spring

Lagged (‘11)

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Explanatory Metric: Annual Proportion Q

Lagged (‘11)

Wet Year

Drier Year

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Results: Mean RBT Length >300mm

Fish at higher 

latitudes are larger 

(Libby Dam 48.4°N; 

Navajo Dam 

36.8°N)

Fish that reside 

farther from the 

dam are smaller

Stocked systems 

contain slightly larger 

rainbow trout

Rainbow trout length is 

smaller in systems with 

high densities of small 

brown trout

Rainbow trout length is larger in 

systems with high densities of 

large brown trout

Rainbow trout are larger in 

systems that move the majority 

of their water in summer months

High water years two years prior 

to electrofishing favor the 

growth of larger rainbow trout 

Positive 

Effect

Negative 

Effect

Variables Not in Final Model:

Dam Age

Reservoir Storage Capacity

Proportion of Water in Reservoir

Spring/Winter Flow

Dam Height

Elevation

Mean Discharge/Channel Width

Whirling Disease

Rainbow Trout Density

Systems with large 

variation in subdaily 

discharge have smaller 

rainbow trout

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Results (TL): Discharge metrics

Rainbow trout size declines in systems that hydropeak, but increases in systems 

with high annual and summer discharge relative to other years and seasons 

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite

400

380

360

340

320

300

400

380

360

340

320

300

400

380

360

340

320

300
Results: Catch/mile, RBT >300mm

Catch more large 

fish per mile at 

higher elevations 

(Pine Flat 970ft; 

Taylor Park 9330ft)

Stations farther from the 

dam yield lower catches 

of large fish; size 

structure shifted toward 

smaller individuals

Catch rates of 

fish >300mm 

decline in 

stocked 

systems

Systems with high densities of 

small brown trout have high 

catches of large rainbow trout High water years favor the 

growth of larger rainbow trout 

Positive 

Effect

Negative 

Effect

Variables Not in Final Model:

Dam Age

Reservoir Storage Capacity

Proportion of Water in Reservoir

Spring/Winter Flow

Dam Height

Latitude

Mean Discharge/Channel Width

Whirling Disease

Density of Large Brown Trout

Systems that move 

high proportions 

of water in 

summer exhibit 

reduced catch 

rates of large 

rainbow trout

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite

Catch of large rainbow 

trout declines in systems 

with high variation in 

subdaily discharge 

(hydropeaking)
Results (CPUE): Discharge metrics

Tailwaters that hydropeak may support fewer large fish. 

High flows in summer two years prior to capture increases the size of 

trout in the 300+ length class; however, catch declines

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite

150

55

20

7.5

150

55

20

7.5

150

55

20

7.5
Results: Brown Trout Density

Density, competition, 

and/or predation?

Rainbow trout size declines 

with high densities of small 

brown trout. However, size 

increases with high 

densities of large brown 

trout. Catch of large 

rainbow trout increases in 

systems with brown trout.

150

55

20

7.5

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite
Results: Stocking

Bigger fish, but smaller 

catch of large fish

Preliminary Data; Dibble, Yackulic, Kennedy, and Budy 2014; Do Not Cite

150

55

20

7.5
 Repeat models using other fish metrics 

(condition factor, weight)

 Repeat models using data from other 

salmonids (e.g., brown, cutthroat) and native 

species

 PATH analysis to discern mechanisms behind 

patterns we see in GLMM analysis 

Next Steps
Questions?