Identification and Evaluation of Scientific Uncertainties 

Related to Fish and Aquatic Resources in the Colorado 

River, Grand Canyon—Summary and Interpretation of 

an Expert-Elicitation Questionnaire

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5027

Identification and Evaluation of Scientific 

Uncertainties Related to Fish and Aquatic 

Resources in the Colorado River, Grand 

Canyon—Summary and Interpretation of an 

Expert-Elicitation Questionnaire

By Theodore A. Kennedy

Scientific Investigations Report 2013–5027

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director 

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Kennedy, T.A., 2013, Identification and evaluation of scientific uncertainties related to fish and aquatic

resources in the Colorado River, Grand Canyon—Summary and interpretation of an expert-elicitation

questionnaire: U.S. Geological Survey Scientific Investigations Report 2013–5027, 34 p.
iii

Contents

Introduction.....................................................................................................................................................1

Methods...........................................................................................................................................................1

Results .............................................................................................................................................................2

True/False Questions............................................................................................................................2

Ordinal Questions................................................................................................................................11

Discussion.....................................................................................................................................................19

Water Temperature ............................................................................................................................19

Nonnatives...........................................................................................................................................20

High-Flow Experiments......................................................................................................................20

Acknowledgments.......................................................................................................................................21

References Cited..........................................................................................................................................21

Appendix 1. Knowledge Assessment Workshop Questionnaire..........................................................23

Appendix 2. Crosswalk between Original Strategic Science Questions (SSQs) and 

This Questionnaire .........................................................................................................................31

Figures

1. Bubble plots showing responses and confidence associated with true/false

questions regarding the impact of four different nonnative taxa on juvenile

humpback chub.............................................................................. 3

2. Bubble plot showing responses and confidence associated with a question

regarding the interaction between fish populations and their food .................. 7

3. Bubble plot showing responses and confidence associated with a question

regarding the influence of water quality on invertebrates ........................... 8

4. Bubble plots showing responses and confidence associated with questions

regarding the effect of temperature and flow fluctuations on spawning and

incubation success for native fish in the mainstem Colorado River .................. 9

5. Bubble plot showing responses and confidence associated with a question

regarding the potential benefits of improving rearing habitat for native fish......... 10

6. Bubble plot showing responses and confidence associated with a question

regarding downstream migration of rainbow trout from Glen Canyon ............... 11

7. Bubble plot showing responses and confidence associated with a question

regarding the effects of turbidity on predation by nonnative species ............... 12

8. Bubble plot showing responses and confidence associated with a question

regarding effects of high-flow experiments on predation by nonnative fish ......... 13

9. Bubble plots showing answers and confidence associated with questions

regarding potential benefits of backwaters and vegetated shorelines to 

native fish .................................................................................... 14

10. Bubble plots showing answers and confidence associated with a question

regarding native-fish response to implementation of a temperature-control

device on Glen Canyon Dam, and the related true/false question asking whether

safeguards are needed before a temperature control device can safely be

operated .................................................................................... 17

11. Bar graphs showing first, second, and third choice actions that respondents

think should be conducted because of their potential to benefit native-fish

populations ................................................................................. 18
iv

Tables

1. Questions in the survey, answers given by respondents, confidence score

associated with the question, rank of the confidence score, and associated

figure number .............................................................................. 4
Identification and Evaluation of Scientific Uncertainties 

Related to Fish and Aquatic Resources in the Colorado 

River, Grand Canyon—Summary and Interpretation of an 

Expert-Elicitation Questionnaire

By Theodore A. Kennedy

Introduction

Identifying areas of scientific uncertainty is a critical 

step in the adaptive management process (Walters, 1986; 

Runge and others, 2011a). To identify key areas of scientific 

uncertainty regarding biological resources of importance to 

the Glen Canyon Dam Adaptive Management Program, the 

Grand Canyon Monitoring and Research Center (GCMRC) 

convened Knowledge Assessment Workshops in May and 

July 2005. One of the products of these workshops was a set 

of strategic science questions that highlighted key areas of 

scientific uncertainty. These questions were intended to frame 

and guide the research and monitoring activities conducted by 

the GCMRC in subsequent years. Questions were developed 

collaboratively by scientists and managers. The questions were 

not all of equal importance or merit—some questions were 

large scale and others were small scale. Nevertheless, these 

questions were adopted and have guided the research and 

monitoring efforts conducted by the GCMRC since 2005.

A new round of Knowledge Assessment Workshops 

was convened by the GCMRC in June and October 2011 

and January 2012 to determine whether the research and 

monitoring activities conducted since 2005 had successfully 

answered some of the strategic science questions. Oral 

presentations by scientists highlighting research findings 

were a centerpiece of all three of the 2011–12 workshops. 

Each presenter was also asked to provide an answer to the 

strategic science questions that were specific to the presenter’s 

research area. One limitation of this approach is that these 

answers represented the views of the handful of scientists 

who developed the presentations, and, as such, they did not 

incorporate other perspectives. Thus, the answers provided 

by presenters at the Knowledge Assessment Workshops may 

not have accurately captured the sentiments of the broader 

group of scientists involved in research and monitoring 

of the Colorado River in Glen and Grand Canyons. Yet a 

fundamental ingredient of resilient decisionmaking and 

problem-solving is the incorporation of a wide range of 

perspectives (Carpenter and others, 2009). To ensure that a 

wide range of scientists had an opportunity to weigh in on the 

strategic science questions, the GCMRC elicited additional 

perspectives through written questionnaires. Independently 

soliciting responses from scientists through questionnaires 

had the added advantage of allowing all scientists to freely 

and openly share their views on complex and controversial 

topics—something which may not have occurred in the group 

setting of the June 2011 Knowledge Assessment Workshop 

because of dominance by one or more scientists. The purpose 

of this report is to document and interpret the questionnaire 

responses. 

Methods

Strategic science questions developed during the 2005 

workshops were reworded so that answers were categorical. 

For each question, respondents also were asked to gauge their 

level of confidence in their answer on a four-point scale: very 

confident, confident, unconfident, and very unconfident. Two 

additional, open-ended questions also were developed to allow 

respondents to weigh in on management actions without the 

constraints inherent in the strategic science questions. 
2 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Questionnaires that included 20 questions were 

distributed to 31 scientists and managers before the October 

2011 workshop (see appendix 1 for a blank questionnaire). 

Questionnaires were provided to scientists who had been 

actively conducting research and monitoring in the Grand 

Canyon since the time of the 2005 workshops, including 

GCMRC scientists and cooperating scientists from Federal 

and State agencies, universities, and consulting firms. 

GCMRC managers who had been involved in scientific 

activities at a programmatic level also were provided the 

questionnaire. A total of 20 completed questionnaire were 

received—a 65-percent response rate. 

Questions where respondents listed both true and false 

as answers on the same question were not coded. Ordinal 

questions where more than one categorical answer was 

checked were coded with the greater of the two scores. Five 

ranking questions were used on the survey, but the wording on 

these was apparently confusing, such that responses could not 

be accurately compiled; based on the notes that were provided 

by respondents, some individuals used a score of 1 for the 

highest ranked item in the list, others used larger numbers (that 

is, 5) to indicate highest ranked items, while still others ranked 

some items as ties. Responses to these ranking questions are 

omitted from this report (questions 2, 5, 7, 13, and 18 of the 

survey; see appendix 1). 

Scoring on the confidence metric was as follows: very 

unconfident was scored as 0, unconfident as 0.33, confident

as 0.67, and very confident as 1. Responses and associated 

confidence are here presented graphically, using bubble plots 

where the x-axis is the response, the y-axis is the associated 

confidence (from very unconfident to very confident), and the 

size of the bubble is proportional to the number of responses 

for a specific answer and confidence score. Questions also 

were ranked based on the basis of the average confidence 

score among all responses. Selected narratives that were 

written by scientists explaining, qualifying, or justifying their 

categorical, and necessarily simple, answers to extremely 

complex questions also are included in this report. Note that 

the narrative responses in this report are presented largely as 

written; minor punctuation was added in a few instances, and 

a few abbreviations or acronyms were defined or explained 

in brackets. Incomplete sentences and run-on sentences were 

retained to reflect the respondent’s thinking. Responses to 

true/false questions are presented first, followed by responses 

to ordinal questions. Responses to one of the open-ended 

questions are presented next. This report concludes with a 

summary and interpretation of the survey responses on three 

key topics: water temperature, nonnative species, and highflow experiments. 

Results

True/False Questions

Question 1A: If rainbow trout populations were large, a 

decrease in their abundance would lead to improvements 

in the recruitment of juvenile humpback chub to the adult 

population. True or False? 

16 of 19 respondents (84 percent) answered True to this 

question, and 3 of 19 (16 percent) answered False

(see fig. 1A and table 1). 

Narratives Associated with True

“This is only one factor potentially influencing 

juvenile [humpback chub] survival.”

 “There are likely other factors that influence 

[humpback chub] recruitment beyond simply 

[rainbow trout] abundance such as spawning and 

rearing habitat availability, carrying capacity/

density-dependence, temperatures, etc. Nevertheless, 

[rainbow trout] abundance is likely a factor in HBC 

[humpback chub] recruitment.”

 “If humpback chub thrive anywhere in the Grand 

Canyon, it is in the Little Colorado River; a river in 

which salmonids are very seldom captured. Virtually 

every other accessible tributary in Grand Canyon, 

including Shinumo and Havasu, contain rainbow 

trout as a common species. Like the [Little Colorado 

River], many of these other systems are warmwater systems, at least during parts of the year. 

Yet, humpback chub do not thrive in these systems. 

I have always been convinced that if the Little 

Colorado River were more amenable to rainbow 

trout, the humpback chub in Grand Canyon would 

be in very severe trouble.”

Narratives Associated with False

 “We have not shown the linkage yet; [it] appears 

that [humpback chub] are thriving in a period of 

high trout populations.”

“Though [rainbow] trout piscivory is a factor, we 

have not definitively shown that their presence 

vs warmer water is a bigger lever on juvenile 

recruitment.”
Results 3

men13-3094_fig01

Question 1. If (nonnative species X) populations were large, a decrease in their abundance would lead to improvements 

in recruitment of juvenile humpback chub to the adult population. True or false?

A. Rainbow trout B. Brown trout

C. Small-bodied, warm-water nonnatives D. Large-bodied, warm-water nonnatives

Very 

confident

Confident

Confidence

Response

Unconfident

Very 

unconfident

Very 

confident

Confident

Unconfident

Very 

unconfident

False True False True

Figure 1. Responses and confidence associated with true/false questions regarding the impact of four different nonnative taxa on 

juvenile humpback chub (A, rainbow trout; B, brown trout; C, small-bodied, warm-water nonnatives, and D, large-bodied, warm-water 

nonnatives). Area of bubble is proportional to number of responses. Many respondents view brown trout as a threat to humpback 

chub populations relative to the number of respondents who view rainbow trout as a threat. Respondents actually view brown trout 

as a slightly greater threat to humpback chub than large-bodied, warm-water nonnatives, such as channel catfish. Respondents who 

view small-bodied, warm-water nonnatives (that is, red shiner, fathead minnow) as a threat to humpback chub are in the minority. (See 

table 1 for specific numbers.)
4 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Table 1. Questions in the survey, answers given by respondents, confidence score associated with the question, rank of the 

confidence score, and associated figure number.

Question number and question Tally of

answers

Confidence 

score 

(0 to 1)

Confidence 

score 

(rank)

Related

figure

number

1A. If rainbow trout populations were large, a decrease in their 

abundance would lead to improvements in the recruitment of 

juvenile humpback chub to the adult population.

16–True

3–False

0.46 11th 1

1B. If brown trout populations were large, a decrease in their 

abundance would lead to improvements in the recruitment of 

juvenile humpback chub to the adult population. 

19–True

1–False

0.58 6th 1

1C. If populations of small-bodied, warm-water nonnatives (that is, 

fathead minnow, red shiner, etc.) were large, a decrease in their 

abundance would lead to improvements in the recruitment of 

juvenile humpback chub to the adult population. 

6–True

13–False

0.42 13th 1

1D. If populations of large-bodied, warm-water nonnatives (that is, 

channel catfish, common carp, etc.) were large, a decrease in 

their abundance would lead to improvements in the recruitment 

of juvenile humpback chub to the adult population.

16–True

3–False

0.56 8th 1

2. Are trends in the abundance of fish populations or indicators 

from fish such as growth, condition, and body composition (for 

example, lipids) correlated with patterns in invertebrate flux? In 

other words, are fish food limited? 

15–True

2–False

0.64 5th 2

3. Is the amount of invertebrate biomass/production available for 

consumption by fish affected by water quality parameters (for 

example, temperature, nutrient concentrations, turbidity)?

19–True

1–False

0.81 1st 3

4. Do current water temperatures limit spawning and incubation 

success for native fish in the mainstem?

18–True

1–False

0.79 2nd 4

5. Do current flow fluctuations allowed by the Record of Decision 

(that is, MLFF) limit spawning and incubation success for native 

fish in the mainstem?

3–True

14–False

0.57 7th 4

6. Do the potential benefits of improving juvenile native fishrearing habitat in the mainstem (for example, increasing water 

temperatures with a TCD, stabilizing flows, conducting frequent 

HFEs to increase the number of backwater and vegetated 

shorelines) outweigh negative impacts due to increases in 

nonnative fish. 

12–True

3–False

0.46 12th 5

7. To what extent do rainbow trout migrating from Glen Canyon 

support the population of rainbow trout in Marble and eastern 

Grand Canyon?

Choices: ‘Does not support’, ‘Partially Supports’, ‘Largely 

Supports’, and ‘Completely Supports’

2–‘Partially Supports’

18–‘Largely Supports’

0.73 3rd 6

8. To what extent could predation impacts by nonnative fish be 

mitigated by higher turbidities? Higher turbidity would________

impacts by nonnatives.

Choices: ‘Greatly Increase Predation’, ‘Somewhat increase 

predation’, ‘No Impact on Predation’, ‘Somewhat Decrease 

Predation’, ‘Greatly Decrease Predation’ 

3–‘Greatly Decrease Predation’

14–‘Somewhat Decrease Predation’

0.52 10th 7
Results 5

Question 1B: If brown trout populations were large, a decrease 

in their abundance would lead to improvements in the 

recruitment of juvenile humpback chub to the adult population. 

True or False?

19 of 20 respondents (95 percent) answered True, and 

1 of 20 (5 percent) answered False (see fig. 1B; table 1). 

Narratives Associated with True

“This is only one factor potentially influencing 

juvenile [humpback chub] survival.”

“We have data to indicate brown trout are highly 

piscivourous, but whether or not they can cause 

changes in [adult humpback chub] populations is 

unknown, [and] all data from other systems indicate 

that brown trout could have large population level 

effects.”

“Of all the aggregations of humpback chub in Grand 

Canyon, it is most rare to capture a humpback chub 

in the Bright Angel aggregation. This is despite 

some historical information that the species may 

have been very common in this reach of river (type 

locality specimens, and at least one early pre-dam 

photograph of a stringer of large humpback chub 

angled during a leisurely afternoon near Roy’s 

Beach, I believe). Although some may dismiss these 

as anecdotal records, it does suggest that humpback 

chub were occasionally, if not always, a common 

species near Bright Angel Creek.”

“Brown [trout] are very piscivorous...”

Narratives Associated with False

 “Maybe, maybe not. There are a lot of factors 

affecting recruitment of chub to adults, including 

temperature, interactions with nonnatives, 

conditions in the Little Colorado River (likely 

including density dependent survival). Relieving 

one of those pressures would not necessarily lead to 

improvements in recruitment of [humpback chub].”

Question number and question Tally of

answers

Confidence 

score 

(0 to 1)

Confidence 

score 

(rank)

Related

figure

number

9. To what extent could predation impacts by nonnative fish be 

mitigated by dam-controlled high-flow releases? Frequent highflow experiments would_______by nonnatives.

Choices: ‘Greatly Increase Predation’, ‘Somewhat Increase 

Predation’, ‘No Impact on Predation’, ‘Somewhat Decrease 

Predation’, ‘Greatly Decrease Predation’

1–‘Greatly Increase Predation’

6–‘Somewhat Increase Predation

5–‘No Impact on Predation’

5–‘Somewhat Decrease Predation’

0.40 14th 8

10. An increase in the size, distribution, and number of backwaters

would cause a_________in native fish abundance.

Choices: ‘Substantial Decrease’, ‘Decrease’, ‘No 

Change’,‘Increase’, ‘Substantial Increase’ 

1–‘Decrease’

11–‘No Change’

7–‘Increase’

0.36 16th 9

11. An increase in the size, distribution, and number of vegetated\

shorelines would cause a_________in native fish abundance. 

Choices: ‘Substantial Decrease’, ‘Decrease’, ‘No Change’, 

Increase’, ‘Substantial Increase’

11–‘No Change’

7–‘Increase’

0.39 15th 9

12A.What will happen if a temperature control device is 

implemented?

Native fish abundance will_____________. 

Choices: ‘Substantially Decrease’, ‘Decrease’, ‘No Change’, 

‘Increase’, ‘Substantially Increase’

1–‘Substantially Decrease’

13–‘Increase’

4–‘Substantially Increase’

0.53 9th 10

12B.Are safeguards needed before a temperature control device can 

aafely be operated?

13–True

2–False

0.68 4th 10

Table 1. Questions in the survey, answers given by respondents, confidence score associated with the question, rank of the 

confidence score, and associated figure number.—Continued
6 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Question 1C: If populations of small-bodied, warm-water 

nonnatives (that is, fathead minnow, red shiner, etc.) 

were large, a decrease in their abundance would lead to 

improvements in the recruitment of juvenile humpback chub to 

the adult population. True or False?

13 of 19 respondents (68 percent) answered False, and 

6 of 19 (32 percent) answered True (fig. 1C; table 1). 

Narratives Associated with True

“I do not feel that we know very much about these 

species and their interactions with HBC.”

“I am hard pressed to say that any non-native 

occupying similar niches [as humpback chub] would 

not have an effect on juvenile [humpback chub] 

recruitment.” 

Narratives Associated with False

 “I do not think these species compete with 

humpback chub. If anything, I think adult humpback 

chub eat these small-bodied nonnatives.”

“The only small-bodied non-native that I would be 

worried about in high densities is plains killifish, 

as they are highly predatory. They are relatively 

rare, fortunately. I do not think the pressure from 

competition is nearly as important as predation.”

“I really do not believe that small-bodied fishes 

are the limiting factor of humpback chub in the 

Colorado River. If they were, then they should be 

much more abundant in the Little Colorado River 

and near its confluence in the Colorado River.”

“Fatheads and red shiners currently pose no real 

numerical threat in my opinion.”

“...juvenile and adult humpback chub likely prey 

on fatheads.”

Question 1D: If populations of large-bodied, warm-water 

nonnatives (that is, channel catfish, common carp etc.) 

were large, a decrease in their abundance would lead to 

improvements in the recruitment of juvenile humpback chub to 

the adult population. True or False?

16 of 19 respondents (84 percent) answered True, and 

3 of 19 (16 percent) answered False (fig. 1D; table 1). 

Narratives Associated with True

“This is a good question with terrible examples. 

Carp and catfish have been present in the Colorado 

River for 75+ years, and these large-bodied warm 

water species are likely not the ones to worry about 

the most. Piscivorous warm-water species like 

smallmouth bass, flathead catfish, and striped bass 

are more worrisome.”

“It depends on the species, channel catfish are longlived piscivores that would likely impact recruitment 

of juvenile HBC.”

“Catfish are big time predators...”

 Narratives Associated with False

“I think a decrease in abundance of channel catfish 

in the [Little Colorado River] would lead to 

improvements in juvenile humpback chub survival 

in the [Little Colorado River], but whether that 

would lead to increased recruitment to adults is 

unknown. Again, [we] do not know where the 

bottleneck is...”

“It is hard to say with much confidence how carp 

or catfish influence [humpback chub] recruitment 

since they may be also somewhat limited by cold 

temperatures presently.”

Question 2: Trends in the abundance of fish populations or 

indicators from fish, such as growth, condition, and body 

composition (for example, lipids), are correlated with patterns 

in invertebrate flux—in other words, fish are food limited. 

True or False?

15 of 17 respondents (88 percent) answered True, and 

2 of 17 (12 percent) answered False (fig. 2; table 1). Several 

respondents felt this was a poorly worded question because 

there were actually two questions being asked. In general, 

respondents believed there is strong evidence that rainbow 

trout populations are food limited. Several respondents also 

described observations from their field efforts indicating that 

humpback chub in the Little Colorado River were, at times, 

food limited. 

Narratives Associated with True

“If you look at the [rainbow] trout, then yes they 

are food limited. If you look at the adult humpback 

chub, they seem quite robust and do not seem 

food-limited.” 
Results 7

“...if you are talking about rainbow trout at Lee’s 

Ferry, Korman’s research demonstrates that higher 

food abundances = higher trout abundance (for 

example, after experimental floods). So they are 

experiencing some food limitation. Are brown trout 

near Phantom Ranch food-limited? I do not think 

so; lots of fish to eat, both native and nonnative. 

Are rainbow trout below the Little Colorado River 

food-limited? At least some of the time, based on 

poor conditions we observed in trout [in 2011]. 

Humpback chub do not seem to be food-limited 

based on observed condition, but that is a data-

[poor] area.”

“Downstream fish demand [for invertebrates] is 

close to invertebrate production...”

“Good empirical evidence of this for rainbow trout 

in Lees Ferry and Marble Canyon...”

Narratives Associated with False

“Fish may be food-limited in the Little Colorado 

River, but likely not in the mainstem.”

“Unknown, but if native fish were truly food-limited 

in the mainstem under current operating regimes, 

would not we expect to at least occasionally see 

strikingly poor condition factors en masse in native 

fish, which we do not. On the other hand, I have 

witnessed strikingly poor condition factors of age-1 

humpback chub in the Little Colorado River (skinny 

with ribs poking through their sides) during the 

early 1990s. This suggests to me that while the Little 

Colorado River can be food-limited, the mainstem 

is not.”

Question 2: Are trends in the abundance of fish populations or indicators from fish such 

as growth, condition, and body composition (for example, lipids), correlated with 

patterns in invertebrate flux? In other words, are fish food-limited?

Very 

confident

Confident

Confidence

Response

Unconfident

Very 

unconfident

False True

Figure 2. Responses and confidence associated with a question regarding the interaction between fish 

populations and their food. Invertebrate flux is a term used to represent both the quantity and concentration 

of invertebrate available as food in the drift. Area of bubble is proportional to number of responses. Some 

respondents noted that this was a poorly worded question because there were actually two questions being 

asked. Nevertheless, a large number of respondents feel there is sufficient evidence to conclude that fish in the 

Colorado River are food-limited.
8 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Question 3: The amount of invertebrate biomass/production 

available for consumption by fish is affected by waterquality parameters (for example, temperature, nutrient 

concentrations, turbidity: True or False?

19 of 20 respondents (95 percent) answered True, and 

1 of 20 (5 percent) answered False (fig. 3; table 1). 

Narratives Associated with True

“Bug production 101. But I note that it is not water 

quality per se, but rather the supply or organic 

carbon which is related to nutrients, turbidity, 

hydrology, etc.”

“Based on data collected in rivers around the world, 

we are very certain that these factors influence 

invertebrate production.”

Question 4: Current water temperatures limit spawning and 

incubation success for native fish in the mainstem: True or False?

18 of 19 respondents (95 percent) answered True, and 

1 of 19 (5 percent) answered False (fig. 4A; table 1). 

Narratives Associated with True

“Read the literature. Witness the situation.”

 “Yes for some species and in some locations.”

 “This is supported by miscellaneous research 

publications by Roger Hamman, and others.”

Narratives Associated with False

“I do think that rearing of larvae and juveniles is 

impacted by the cold water.”

Question 3: Is the amount of invertebrate biomass/production available for consumption 

by fish affected by water-quality parameters (for example, temperature, nutrient 

concentrations, turbidity)?

Very 

confident

Confident

Confidence

Response

Unconfident

Very 

unconfident

False True

Figure 3. Responses and confidence associated with a question regarding the influence of water quality on 

invertebrates. Area of the bubble is proportional to the number of responses. This question had the highest 

confidence score in the survey. 
Results 9

Question 5: Do current flow fluctuations allowed by the 

Record of Decision (that is, Modified Low Fluctuating Flows) 

limit spawning and incubation success for native fish in the 

mainstem. True or False?

3 of 14 respondents (21 percent) answered True, and 

11 of 14 (79 percent) answered False (fig. 4B; table 1). 

Narratives Associated with True

“There is likely an interactive effect of flows, 

temperatures, and nonnative fish abundance upon 

native fish recruitment.” 

“Yes, when coupled with cold mainstem water 

temperatures. If not, then I do not think it much 

Question 4. Do current water temperatures limit 

spawning and incubation success for native 

fish in the mainstem?

A B

Very 

confident

Confident

Confidence

Response

Unconfident

Very 

unconfident

False True False True

Question 5. Do current flow fluctuations allowed by 

the Record of Decision (that is, MLFF) limit spawning 

and incubation success for native fish in the mainstem?

Figure 4. Responses and confidence associated with questions regarding the effect of temperature (A) and flow fluctuations (B) on 

spawning and incubation success for native fish in the mainstem Colorado River. Area of the bubble is proportional to the number of 

responses. There is wide agreement among respondents that water temperatures limit spawning and incubation success for native 

fish in the mainstem (A). In contrast, more respondents surveyed believe that flow fluctuations do not limit spawning and incubation 

success for native fish in the mainstem (B). 

matters. Chub spawn and recruit from year to year 

in the Little Colorado River under varying flow 

conditions.”

Narratives Associated with False

“The small fluctuations in flow are not the principal 

problem.”

“The flows currently have little effect on 

temperature and temperature is the overriding factor 

for spawning and incubation success.”

“Maybe to a degree, but I believe water temperature 

is the most limiting factor. The effects of daily 

fluctuations in discharge become more reduced at 

farther downriver distances from the dam.”
10 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Question 6: The potential benefits of improving juvenile 

native fish rearing habitat in the mainstem (for example, 

increasing water temperatures with a [temperature-control 

device], stabilizing flows, conducting frequent HFEs (highflow experiments) to increase the number of backwater and 

vegetated shorelines) outweigh negative impacts due to 

increases in nonnative fish. True or False?

12 of 15 respondents (80 percent) answered True, and 3 

of 15 (20 percent) answered False (fig. 5; table 1). 

Narratives Associated with True

“ One would assume so, but some level of predator 

control may still be necessary. Nonnative fish are 

still a primary threat.”

“Some actions like warming the water, I am 

confident, will have a positive impact on native fish; 

others like [high flow experiments] and backwaters, 

I am less convinced, will have a positive impact.”

“I think we have to assume this to be true.”

Narratives Associated with False

“It is likely that these actions will fail, but not 

absolutely certain. We can find this out with some 

adaptive management experimentation, but the risks 

are high. I am not sure it is worth it since the current 

humpback chub population is stable or increasing, 

and it almost certainly would not be if the river 

warmed up and nonnative predators proliferated.”

“Using the Upper Basin as a case study, which has 

more natural flow and temperature regimes but 

an abundance of warm-water nonnatives and low 

recruitment for some natives, it is likely some form 

of nonnative fish control would be necessary along 

with improvements to native fish habitat to result in 

a benefit to native fish over the long term.”

Very 

confident

Confident

Confidence

Response

Unconfident

Very 

unconfident

False True

Question 6: Do the potential benefits of improving juvenile native fish-rearing habitat in 

the mainstem (for example, increasing water temperatures with a TCD, stabilizing flows, 

conducting frequent HFEs to increase the number of backwaters and vegetated 

shorelines, increasing food availability) outweigh negative impacts due to 

increases in nonnative fish?

Figure 5. Responses and confidence associated with a question regarding the potential benefits of improving 

rearing habitat for native fish. Area of the bubble is proportional to the number of responses. Most respondents 

believe that improving the quality of juvenile native fish rearing habitat outweighs potential negative impacts of 

such habitat improvements due to increase in nonnatives. 
Results 11

Ordinal Questions

Question 7: To what extent do rainbow trout migrating from 

Glen Canyon support the population of rainbow trout in Marble 

and eastern Grand Canyons? Migration from Glen Canyon 

__________ populations in Marble and Grand Canyon. 

Choices: Does not support, Partially Supports, Largely 

Supports, Completely Supports. 

18 of 20 respondents (90 percent) answered Largely 

Supports, and 2 of 20 (10 percent) answered Partially 

Supports (fig. 6; table 1). 

Narratives

“It depends. During periods of high trout density in 

Glen Canyon, I assume that downstream movement 

supports rbt [rainbow trout] between the Paria and 

LCR, assuming turbidity is not a big issue limiting 

their growth and survival. During periods of low 

density in Glen Canyon, they likely do not support 

rbt populations between the Paria and LCR. During 

the late 1980s and early 1990s when the Glen 

Canyon fishery was supported by stocking (little 

to no natural recruitment), all hatchery stocked 

fingerlings were marked with coded wire tags. 

[There was] no evidence of movement of those fish, 

granted sampling was more limited downstream.”

“Lees Ferry is a density-dependent food-limited 

system, and thus fish probably migrate downstream 

over time. The age and timing of migrants is unclear. 

There are likely other suitable spawning locations 

for rainbows downstream, and this should not be 

completely overlooked.” 

Very 

confident

Confident

Confidence

Unconfident

Does not

support

Partially

supports

Largely

supports

Completley

supports

Very 

unconfident

Question 7: To what extent do rainbow trout migrating from Glen Canyon support the 

population of rainbow trout in Marble and eastern Grand Canyon?

Migration from Glen Canyon ___________ populations in Marble and Grand Canyon.

Figure 6. Responses and confidence associated with a question regarding downstream migration of rainbow 

trout from Glen Canyon. Area of bubble is proportional to number of responses. A majority of respondents 

believe there is sufficient evidence to conclude that migration of rainbow trout from Glen Canyon largely 

supports the rainbow trout populations present in Marble and eastern Grand Canyon. 
12 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Question 8: To what extent could predation impacts by 

nonnative fish be mitigated by higher turbidities? Higher 

turbidity would___________impacts by nonnatives.

Choices: Greatly Increase Predation, Somewhat Increase 

Predation, No Impact on Predation, Somewhat Decrease 

Predation, Greatly Decrease Predation.

14 of 17 respondents (82 percent) answered Somewhat 

Decrease Predation, and 3 of 17 (18 percent) answered 

Greatly Decrease Predation (fig. 7; table 1). 

Narratives

“If higher turbidity persisted for long enough...there 

is a temporal and seasonal element here.”

“Depends on the nonnative. If they are a visual 

predator like rainbow trout, then the predation 

impacts could likely be mitigated.”

“There are gobs of peer-reviewed publications 

affiliated with this topic. Overall, this depends on 

the non-visual capabilities of the predators versus 

those of native fishes. For example, channel catfish 

function much better under high turbidities than 

rainbow trout.”

“Many of the predators in the canyon are sightfeeders, so I suspect predation overall would go 

down. However, certain species (channel catfish, 

possibly walleye in the future) are well adapted to 

low-light conditions, so predation by these species 

may remain stable or increase.”

Figure 7. Responses and confidence associated with a question regarding the effects of turbidity on predation 

by nonnative species. Area of bubble is proportional to the number of responses. Most respondents believe that 

higher turbidity would Somewhat Decrease Predation of native fishes.

Question 8: To what extent could predation impacts by nonnative fish be mitigated by 

higher turbidities?

Higher turbidity would ___________ impacts by nonnatives.

Very 

confident

Confident

Confidence

Unconfident

Very 

unconfident

Greatly

decreases

predation

Somewhat

increases

predation

Somewhat

decreases

predation

Greatly

increases

predation

No impact

on predation
Results 13

Question 9: To what extent could predation impacts by 

nonnative fish be mitigated by dam-controlled high-flow 

releases? Frequent high-flow experiments would_________by 

nonnatives. 

Choices: Greatly Increase Predation, Somewhat Increase 

Predation, No Impact on Predation, Somewhat Decrease 

Predation, Greatly Decrease Predation. 

No single answer received a majority of responses (fig. 8; 

table 1); 6 of 17 respondents (35 percent) answered Somewhat 

Increase Predation; 5 of 17 respondents (29 percent) answered 

No Impact on Predation; and 5 of 17 answered Somewhat 

Decrease Predation. 

Narratives

“I assume that this question is geared toward 

[rainbow trout]? If so then the timing of the floods 

would have to be critical as to not increase trout 

recruitment. Would have to be done in conjunction 

with low flows.”

“If the high flow releases were large enough to 

disproportionately displace nonnative fish (which 

they usually are not), then predation would be 

reduced.”

“It is my expectation that HFEs would [cleanse] 

salmonid spawning redd habitat, and contribute to 

higher production of rainbow trout. I do not think 

that this increase in salmonid abundance (and 

presumably emigration rates downriver) would be 

offset by any potential positive aspects of creation of 

backwaters, particularly if ensuing fluctuating flows 

render backwaters of limited utility and duration.”

“The answer to this question appears to be 

dependent on the timing of flows, the magnitude, 

etc. Flows could be designed to maintain lower 

densities of RBT by discouraging recruitment 

possibly, however high flows could also result in 

dramatic increases in RBT recruitment....”

Figure 8. Responses and confidence associated with a question regarding effects of high-flow experiments 

on predation by nonnative fish. Area of the bubble is proportional to the number of responses. Respondents do 

not believe that high-flow releases are a useful tool for decreasing predation of native fishes.

Very 

confident

Confident

Confidence

Unconfident

Very 

unconfident

Greatly

decreases

predation

Somewhat

increases

predation

Somewhat

decreases

predation

Greatly

increases

predation

No impact

on predation

Question 9: To what extent could predation impacts by nonnative fish be mitigated by 

dam-controlled high-flow releases?

Frequent high-flow experiments would ___________ by nonnatives.
14 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Question 10: An increase in the size, distribution, and 

number of backwaters would cause a________ in native fish 

abundance.

Choices: Substantial Decrease, Decrease, No Change, 

Increase, Substantial Increase.

Most respondents (11 of 19, or 58 percent) answered 

No Change in native fish abundance as the most likely 

outcome of an increase in backwaters (fig. 9A; table 1). 

Narratives

“Hard to answer this without knowing what 

‘increase’ means. Unless [backwaters] became 

a substantial part of the mainstem habitat, an 

‘increase’ would do little.”

“I see no reason that native fish would respond 

better than nonnative fish due to increased backwater 

availability. The abundance of warm-water fish will 

increase system-wide, regardless of species. Also, I 

think persistence of backwaters is just as important 

as these other factors, both on diel and seasonal 

scales. We need a high flow event followed by a 

steady flow event if you want to create and maintain 

backwaters long enough to have an effect on warmwater fish.”

“[If backwater does not persist], even the best 

scenario for backwaters is of likely of limited use as 

significant thermal refugia. With stable flows, many 

backwaters should be expected to provide some 

opportunities for increased growth for a fraction 

of the small size classes of native fishes in the 

Figure 9. Answers and confidence associated with questions regarding potential benefits of backwaters (A) and vegetated shorelines 

(B) to native fish. Area of bubble is proportional to number of responses. These two questions had the lowest confidence scores in 

the survey. Respondents who view creation of backwaters as a potentially useful tool for benefitting native-fish populations are in the 

minority. 

Confidence

Very 

confident

Confident

Unconfident

Very 

unconfident

Substantial

decrease

Substantial

increase

Decrease No change Increase Substantial

decrease

Substantial

increase

Decrease No change Increase

A B

Question 10: An increase in the size, distribution, 

and number of backwaters would cause 

a ___________ in native fish abundance.

Question 11: An increase in the size, distribution, 

and number of vegetated shorelines would cause 

a ___________ in native fish abundance.
Results 15

mainstem. Whether that is enough to be measured in 

terms of abundance increase over several years time 

is unknown, but seems to be an expensive approach 

(in terms of power revenue) to achieve a tenuous 

goal.”

“The idea that Colorado River native fishes 

commonly utilize and benefit from backwaters 

comes from the upper [Colorado River] basin 

where many backwaters are numerous acres in size. 

In contrast, Grand Canyon backwaters are more 

limited in size. Furthermore, the humpback chub 

populations in the upper basin continue to drastically 

decline despite the presence of large backwaters. 

The warmer temperatures in Grand Canyon 

backwaters are definitely a positive attribute, while 

the lack of cover is a negative attribute.”

“We have no data to indicate backwaters by 

themselves are beneficial to native fish. If the 

backwater provides increased water temperatures or 

increased food or increased cover then they would 

likely be beneficial to native fish, but as of yet we 

have been unable to show that they provide these 

things.”

“Until backwaters provide a large component of 

the available habitat for fish, I would say that the 

effects of backwaters to overall population levels is 

negligible. However, based on the question, if sizes 

of backwater habitat and the number of backwaters 

substantially changes then there may be an effect.”

“It is difficult to say if fluctuating flows continue. 

The benefits of backwaters may be a stable, warmer 

environment for native fish rearing; however, 

fluctuating flows during the summer minimize the 

potential benefits. In addition, limited research into 

the use of backwaters, relative to other habitats, by 

native fish has been conducted.”

Question 11: An increase in the size, distribution, and number 

of vegetated shorelines would cause a________ in native fish 

abundance.

Choices: Substantial Decrease, Decrease, No Change, 

Increase, Substantial Increase.

The distribution of responses to this question was similar 

to the related question on backwaters (fig. 9B; table 1), 

with most respondents (11 of 18, or 61 percent) answering 

No Change as the most likely outcome of an increase in 

vegetated shorelines. 

Narratives 

“Young humpback chub in the [Little Colorado 

River] commonly utilize [vegetation] for cover. 

In the mainstem humpback chub do seem to be 

often captured along vegetated shorelines in the 

mainstem. I am not sure that enhancement of 

vegetated shoreline in the mainstem would increase 

the abundance of native fish in the mainstem, but 

it should be expected to provide some cover and 

perhaps some food.”

“Vegetated shorelines do provide cover for small 

fish and reduce predation vulnerability.”

“...there is much more vegetated shoreline habitat 

than backwaters, and because of this [an increase 

in] vegetated shorelines would have a greater effect 

[than an increase in backwaters].”

“The vegetative shorelines will provide an increase 

in terrestrial invertebrates for food, and high cover 

if the vegetation extends into the water column. 

However, juvenile native fish still need to grow to 

become less susceptible to piscivory.”

“Hard to answer this without knowing what increase 

means.”
16 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Question 12A: What will happen if a temperaturecontrol device is implemented? Native fish abundance 

will___________

Choices: Substantially Decrease, Decrease, Not Change, 

Increase, Substantially Increase.

Most respondents (13 of 18, or 72 percent) answered an 

Increase in native fish abundance as the most likely outcome 

should a temperature control device be implemented on 

Glen Canyon Dam (fig. 10A; table 1). 4 of 18 respondents 

(22 percent) answered Substantial Increase, and 1 of 18 

respondents (6 percent) answered Substantial Decrease, as the 

most likely outcome. 

Narratives

“This is a tough question because I fear that 

nonnative fish will expand rapidly as well and 

they may have negative impacts on native fish. If 

nonnatives do not increase in abundance, then some 

improvement in native fish populations [is likely].”

 “Given increasing [humpback chub] status, does not 

seem worth the risk!”

“As long as it is operated in a fashion to prevent the 

establishement and expansion of other warm-water 

nonnative fishes.”

“Depends on nonnative fish population response and 

new species of invaders.”

“Only so long as nonnatives do not increase more 

and wipe out the natives. Uncertainty lies there. 

If no nonnatives, then native fish would be much 

happier with a warmer river (in summer)”

“In the absence of any other treatment action, we 

will lose the native species in Grand Canyon. I am 

confident that there will be a large initial increase in 

native fish populations, especially if temperatures 

are warmed enough to kill off large numbers of 

trout. However, once the warmwater predators 

become established, the subsequent die-off of native 

fish will far surpass the boost provided by initial 

warming and will likely lead to their extirpation.”

Question 12B: Are safeguards needed before a temperature 

control device can safely be operated?

13 of 15 respondents answered True (87 percent) while 2 

of 15 (13 percent) answered False.

Narratives

“Lots of safeguards are needed.”

“[There is a] need to not just have warm water, 

but warm and cold water both. The river is not just 

colder, but has lost the annual variability.”

“I do not think that you can operate a temperature 

control device in a way that will benefit warmwater 

native species, yet not benefit warmwater nonnative 

species. The only option that I can see to even 

experiment with is to keep the mainstem cold during 

spawning and rearing season (spring and summer), 

when young humpback chub drift out of the LCR 

and into the mainstem. That is the only way you are 

going to keep nonnative warmwater piscivores from 

reproducing and taking over.” 

“Ability and willingness to [have] both hot and cold 

water years.”

“Fish monitoring, followed by remedial actions if 

need be. A [temperature control device] should allow 

managers to quickly revert back to colder releases if 

need be.”
Results 17

“Monitor for establishment of warm-water 

nonnative fish and develop action plan in the event 

this occurs.”

“The biggest safeguard needed in my estimation is 

that we need the ability to control the TCD at least to 

the ability to run dam release temperatures between 

10 and 16 [degrees Celsius]. Other safeguards 

would be a [fish] monitoring regime, probably 

at near existing levels. Provided that managers 

do not increase water temperatures beyond that 

already experienced (about 16 [degrees Celsius]), or 

increase the duration of warmer water longer than 

already experienced, the invasion of other warm 

water predators may not be of great concern.”

Figure 10. Answers and confidence associated with a question regarding native-fish response to implementation of a temperaturecontrol device on Glen Canyon Dam (A), and the related true/false question asking whether safeguards are needed before a 

temperature control device can safely be operated (B). Area of bubble is proportional to the number of responses. Most respondents 

believe that implementation of a temperature-control device will lead to an increase in native-fish populations; however, note that this 

question had a low confidence score (0.53, or about halfway between unconfident and confident). Furthermore, most respondents 

believe that safeguards (for example, effective nonnative control, a willingness to not use the temperature-control device in some years; 

see narratives) are needed before a temperature-control device can safely be implemented. 

Confidence

Very 

confident

Confident

Unconfident

Very 

unconfident

Substantially

decrease

Substantially

increase

Decrease No change Increase

A B

Question 12A: What will happen if a temperature 

control device is implemented?

Native fish abundance will ___________.

Question 12B: Are safeguards needed before a 

temperature control device can safely be operated?

Response

False True
18 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

12

10

8

6

4

2

0

12

10

8

6

4

2

0

Number of responses

Temperature

control device

Nonnative

control

Translocate Flow

Temperature

control device

Non-native

control

Translocate Flow

Temperature

control device

Nonnative

control

Translocate Flow

1st choice

3rd choice

2nd choice

List up to 3 actions that you think should be taken because of their potential to benefit native fish populations.

Translocate includes:

1) Translocation of eggs or ripe adults to tribs (n=2)

2) Translocation of juveniles to downstream mainstem 

 locations (n=1)

3) Translocation of juveniles to tributaries (n=1)

Nonnative control includes:

1) Nonnative control in general (n=6)

2) Brown trout control (n=5)

3) Rainbow trout supression flows (n=5)

4) Annual high-flow experiment to disadvantage 

 nonnatives (n=1)

Flow includes:

1) Natural flow regime including HFEs (n=5)

2) Stable summer to warm (n=2)

Figure 11. First, second, and third choice actions that respondents think should be conducted because of their potential to benefit 

native-fish populations. Installation of a temperature control device was listed as the first choice by 10 respondents and a total of 

16 respondents included a temperature-control device somewhere on their list. Nonnative control in various forms was another 

common type of action listed by most respondents (17 of 20, or 85 percent). Translocation of humpback chub was listed as the first 

choice by one respondent, a total of four respondents listed translocations somewhere on their list. Seven respondents listed various 

types of flow-regime change as a management action that they think would benefit native fish. 

Question 13: List up to three actions that you think should 

be taken because of their potential to benefit native-fish 

populations. 

Nonnative control (17 of 20 respondents, or 85 percent) 

and installation of a temperature-control device (16 of 20 

respondents, or 80 percent) were the most common actions 

recommended by respondents (fig. 11). Respondents also 

listed various types of humpback chub translocations (4 of 20 

respondents, or 20 percent) and experimental flow regimes 

(7 of 20 respondents, or 35 percent) as actions that might be 

considered for benefiting native fish. 
Discussion 19

Discussion

Expert elicitation (the process of soliciting information 

from highly skilled and knowledgeable scientists) is 

increasingly being used as a tool to help managers make 

informed decisions when actual data on the system being 

managed are scarce, incomplete, or unavailable (Runge and 

others, 2011a). Formal expert elicitation involves asking 

experts independently to provide input on hypotheses or 

parameters of interest regarding the system being managed. 

Expert responses are then collated and presented to the whole 

group, along with the basis and rationale for each expert’s 

decision. Experts are then given the opportunity to revise their 

answers on the basis of the insights from others in the group. 

These revised answers are then used as a tool to evaluate the 

various policy options being considered (Runge and others, 

2011a). 

The questionnaire results presented in this report do 

not represent a complete expert elicitation process. The 

strategic science questions presented here were discussed 

by all respondents several months before distribution of the 

questionnaire during the June 2011 Knowledge Assessment 

Workshop. These earlier discussions may have influenced 

or biased the answers that were given in the questionnaire. 

Furthermore, although questionnaire responses were 

collated and presented to the group during the October 2011 

Knowledge Assessment Workshop, respondents were never 

given an opportunity to revise their answers. If respondents 

had been given an opportunity to revise their answers on the 

basis of insights from others in the group, some respondents 

would likely have changed some of their answers. For 

example, the two questions that had the highest confidence 

assessments also received nearly unanimous answers (see 

fig. 3 [Is the amount of invertebrate biomass/production 

available for consumption by fish affected by water-quality 

parameters such as temperature, nutrient concentrations, 

turbidity?] and fig. 4A [Do current water temperatures 

limit spawning and incubation success for native fish in the 

mainstem?]). In the case of the invertebrate question, studies 

throughout the world have documented a strong and clear 

link between invertebrate biomass/production and the waterquality parameters listed (see Huryn and Wallace, 2000, 

for a review). In the case of the temperature-fish spawning 

question, laboratory studies clearly demonstrate that current 

water temperatures limit spawning in the mainstem Colorado 

River (see Hamman, 1982). Responses to these two questions 

highlight the shortcomings of both the expert elicitation 

process in general (even ”experts” sometimes get the answer 

wrong initially), and the abbreviated expert-elicitation exercise 

presented here (Responses presented here represent an initial 

assessment of complex issues from 20 scientists and have 

not been refined and revised on the basis of insights from 

others in the group). With this qualifier in mind, what follows 

is a discussion of questionnaire responses regarding three 

issues that are of continuing interest to the Glen Canyon Dam 

Adaptive Management Program: effects of water temperature 

on native fish, effects of nonnative trout on native fish, and use 

of high-flow experiments as a tool for managing native-fish 

populations. 

Water Temperature

There is strong consensus among respondents that cold 

water temperatures are playing a role in limiting native-fish 

populations in Grand Canyon (see figs. 4, 10, 11). On an openended question (fig. 11), 10 of 20 respondents (50 percent) 

listed implementation of a temperature-control device as 

the first management action they would conduct because of 

potential benefits to native fish. The question with the second 

highest confidence score in the survey (fig. 4) was temperature 

related: Do current water temperatures limit spawning and 

incubation success for native fish in the mainstem? 18 of 20 

respondents (90 percent) answered True to this question, and 

the certainty score—0.76—places it between confident and 

very confident. But when asked the question of how nativefish populations would actually respond to implementation of 

a temperature-control device in an ordinal question (fig. 10A), 

respondents expressed concerns over potential increases in 

warm-water nonnative species in basically every narrative, 

leading to a low confidence score on this question (0.53, or 

approximately halfway between unconfident and confident). 

Most respondents listed an Increase in native fish populations 

as the likely outcome, should a temperature-control device 

be implemented (13 of 18, or 72 percent), and 4 of 18 

respondents (22 percent) listed a Substantial Increase in 

native-fish populations as the likely outcome. One respondent 

listed a Substantial Decrease in native-fish populations as the 

most likely outcome, with an associated assessment of Very 

Confident. Most respondents—13 out of 15 (87 percent)—

believe that safeguards, especially programs for monitoring 

and controlling nonnative species, are needed before a 

temperature-control device can safely be implemented 

(fig. 10B). 

Water temperature is clearly a double-edged sword for 

native fish in Grand Canyon. Implementation of a temperaturecontrol device on Glen Canyon Dam could greatly benefit 

native-fish populations by increasing growth and survival 

rates (Petersen and Paukert, 2005) and providing water 

temperatures conducive to mainstem spawning. However, 

warmer water temperatures might also allow warm-water 

nonnative species (for example, smallmouth bass, northern 

pike, channel catfish) to become established in Grand Canyon 

(currently, populations of these warm-water nonnatives are 

extremely low or nonexistent). Predation by warm-water 
20 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

nonnative species is a primary factor driving native-fish 

decreases in the upper Colorado River basin (see Bestgen and 

others, 2007). If warm-water nonnatives become established 

at high densities in Grand Canyon because of implementation 

of a temperature-control device, negative impacts of predation 

on native species would likely far outweigh any intended 

benefits to native fish (for example, improvements in growth 

and spawning). If managers are interested in more detailed 

predictions regarding native and nonnative-fish response to 

implementation of a temperature-control device, a full and 

interative expert elicitation process is a logical next step. 

Nonnatives

Most respondents (16 of 19, or 84 percent) believe there 

is sufficient evidence to conclude that when populations of 

nonnative rainbow trout are large, they limit abundance of 

adult humpback chub populations (fig. 1A). Interestingly, a 

larger number of respondents (19 of 20, or 95 percent) believe 

there is sufficient evidence to conclude that when brown 

trout populations are large they limit the abundance of adult 

humpback chub (fig. 1B). The confidence score for the brown 

trout question (6th) also was ranked higher than the rainbow 

trout question (11th). Note, however, that both confidence 

scores are low, falling between unconfident and confident. 

Respondents answers and the confidence on these trout 

questions were qualitatively similar to those of the answers 

provided as part of a nonnative-fish-control structureddecisionmaking process (Runge and others, 2011b). 

Respondents’ answers to these questions about the 

relative threat of these two nonnative salmonids were likely 

informed by the findings of Yard and others (2011), who 

documented that brown trout in Grand Canyon are extremely 

piscivorous (5–70 percent of brown trout stomachs analyzed 

contained fish remains, depending on season and location), 

whereas rainbow trout were less piscivorous (0.5–3.3 percent 

of rainbow trout stomachs analyzed contained fish remains). 

Rainbow trout were 50 times more abundant in the study area 

of Yard and others (2011) relative to brown trout, leading these 

investigators to conclude that rainbow trout piscivory was 

actually a greater source of mortality for native fish relative 

to piscivory by brown trout. Although predation by both 

rainbow trout and brown trout was a large source of mortality 

to native fish in general and humpback chub specifically (for 

example, during 2003–04, rainbow trout preyed upon more 

than 2,500 individual humpback chub per year and brown 

trout preyed upon more than 1,500 individual humpback chub 

per year), Yard and others (2011) cautioned that their study 

did not provide proof that rainbow or brown trout piscivory 

was having a population-level effect on humpback chub. 

Thus, Yard and others (2011) demonstrated that individual 

humpback chub were vulnerable to trout predation, but the 

population as a whole might be constrained by other factors, 

such that the mortality imposed by trout has only a minor 

effect on overall humpback chub population abundance. 

Brown trout control seems like a logical focus for 

nonnative-fish management in Grand Canyon National Park, 

given scientists’ views on the threat that brown trout pose 

to humpback chub populations. Brown trout populations 

are considerably smaller than rainbow trout populations 

(Makinster and others, 2010). Furthermore, most brown trout 

spawning in Grand Canyon is restricted to a single tributary—

Bright Angel Creek—whereas rainbow trout spawning occurs 

throughout the 16-mi Glen Canyon tailwater reach (Makinster 

and others, 2010). Both of these factors make controlling 

brown trout using mechanical removal cheaper and more 

feasible logistically than mechanically removing rainbow 

trout. 

Limiting the abundance of rainbow trout populations near 

the Little Colorado River confluence also is consistent with 

scientists’ views and available data (see Yard and others, 2011) 

on the threat that rainbow trout pose to endangered humpback 

chub populations; however, mechanical removal of rainbow 

trout may be ineffective when rainbow trout populations are 

increasing (Coggins and others, 2011). Alternative rainbow 

trout control strategies involving experimental flows will 

be evaluated as part of ongoing adaptive-management 

experimentation (Bureau of Reclamation, 2011). If these new 

strategies are effective at controlling rainbow trout, have a 

low cost of control, and have minimal or acceptable impacts 

on other resources (for example, aquatic food base), then 

resolving the uncertainty about whether rainbow trout are 

actually having a population-level effect on humpback chub 

may be unnecessary (Runge and others, 2011b). In contrast, 

if these new strategies for controlling rainbow trout are 

ineffective and excessively costly, result in negative impacts to 

other resources, and become unacceptable to managers, then 

resolving the uncertainty regarding population-level effects of 

rainbow trout on humpback chub may be necessary (Runge 

and others, 2011b). 

High-Flow Experiments

Most respondents do not view high-flow experiments as 

a useful tool for managing native-fish populations (see figs. 8; 

9A). It has been hypothesized that high-flow experiments 

could benefit native fish by displacing nonnative species (U.S. 

Department of the Interior, 1995). Nonnative species are more 

likely to be displaced during extreme flood events, whereas 

native species exhibit various behavioral adaptations that make 

them less susceptible to displacement (Ward and others, 2003); 

however, long-term monitoring failed to document substantial 

declines in nonnative fish abundance after high-flow 

experiments in 2004 and 2008 (Makinster and others, 2010). 

Recent observations that the 2008 high-flow experiment 

actually led to significant increases in nonnative rainbow trout 

populations (Cross and others, 2011; Korman and others, 

2011) also call into question the validity of this hypothesis. 

These recent results likely influenced scientists’ responses 

to a question regarding the effect of high-flow experiments 
References Cited 21

on nonnative predation (fig. 8). This question had a low 

confidence score (rank of 14 out of 16) and no single answer 

received a majority of responses. Five respondents believe 

that frequent high-flow experiments will Somewhat Increase 

Predation by nonnatives, and five respondents believe that 

there will be No Change in predation by nonnatives if frequent 

high-flow experiments occur (fig. 8). Thus, there is little 

support from the questionnaire respondents or from available 

data to suggest that high-flow experiments of the magnitude, 

duration, or frequency previously evaluated actually benefited 

native fish through displacement of nonnatives. 

A second hypothesis regarding effects of high-flow 

experiments on native fish posits that the creation of 

backwaters will benefit juvenile native fish by providing highquality rearing areas (U.S. Department of the Interior, 1995). 

Backwaters have been viewed as high-quality rearing areas for 

juvenile native fish because of the warm-water temperatures 

that can sometimes occur. Recent research indicates that 

increases in backwater area and number following high-flow 

experiments are extremely transitory and short-lived when 

discharge fluctuates owing to hydropeaking (that is, increases 

in backwater area due to the 2008 high-flow experiment lasted 

less than 6 months; Grams and others, 2010). Furthermore, 

daily fluctuations in river stage associated with hydropeaking 

causes frequent flushing of backwaters (Behn and others, 

2010), which limits the amount of warming that can occur in 

these areas. These recent findings likely informed respondents’ 

answers to an ordinal question regarding potential nativefish response to an increase in backwaters (see fig. 9)—11 

of 19 respondents (58 percent) answered that No Change

in native-fish abundance was the most likely outcome of an 

increase in backwaters. Several of the narratives associated 

with this question noted that fluctuating flows quickly erode 

backwaters and limit the amount of warming that can occur 

during the summer. Other narratives noted that backwaters are 

a small proportion of shoreline habitat in Grand Canyon, even 

immediately following a high-flow experiment. Thus, there is 

little support from questionnaire respondents or from available 

data to suggest high-flow experiments benefit native fish 

through backwater creation, particularly if daily fluctuations in 

discharge associated with hydropeaking immediately follow a 

high-flow experiment. 

Acknowledgments

I thank the 20 scientists and managers who responded 

to this questionnaire, particularly for their thoughtful and 

insightful narratives. I thank David Ward and Jack Schmidt 

for providing informative and helpful feedback on a draft of 

the questionnaire, and Charles Yackulic for discussions and 

advice regarding the graphical and statistical presentation of 

these data. David Ward, Brian Healy, Dennis Stone, Scott 

Vanderkooi, Jeff Lovich, Charles Yackulic, Ted Melis, and 

Jack Schmidt provided constructive criticism in their reviews 

of the draft manuscript of this report. 

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resources in backwaters of the Colorado River below 

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of/2010/1075/of2010-1075.pdf.

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response to altered flow and temperature regimes, and 

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fish control in the Colorado River in Grand Canyon, 

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management—Food web response to a controlled flood on 

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response of eddy-deposited sandbars and associated aquatic 

backwater habitats along the Colorado River in Grand 

Canyon National Park: U.S. Geological Survey Open-File 

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pubs.usgs.gov/of/2010/1032/.
22 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

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water temperature changes in the Grand Canyon, Colorado 

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http://pubs.usgs.gov/of/2011/1012/.

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Canyon Dam—Final environmental impact statement, 

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resources: New York, MacMillan Publishing Company, 

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in swimming ability and behavior in response to high 

water velocities among native and nonnative fishes: 

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and Korman, J., 2011, Trout piscivory in the Colorado 

River, Grand Canyon—Effects of turbidity, temperature, 

and fish prey availability: Transactions of the American 

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10.1080/00028487.2011.572011, accessed on April 19, 

2011, at http://www.tandfonline.com/doi/abs/10.1080/00028

487.2011.572011.
Appendix 1 23

Appendix 1. Knowledge Assessment Workshop Questionnaire

Blank questionnaire that was distributed to scientists. 

Knowledge Assessment Workshop Questionnaire

Questionnaire completed by:_______________________________________

Background information: As part of a knowledge assessment workshop being convened by 

the Grand Canyon Monitoring and Research Center (GCMRC) October 18-19, 2011, GCMRC 

is summarizing the state of our understanding of the aquatic ecosystem of the Colorado River 

downstream from Glen Canyon Dam, including our present understanding of the biotic and abiotic 

factors most likely affecting populations of native and nonnative fishes. 

During the previous round of knowledge assessment workshops, in 2007, a set of strategic science 

questions was developed as a framework for focusing the research and monitoring activities 

conducted by GCMRC. These questions were originally developed as a collaboration of scientists 

and managers. As such, the questions that originated 5 years ago are not necessarily similar to those 

that might be developed in a proposal to the National Science Foundation. Also, all the questions 

are not necessarily of equal importance or merit – some questions are large-scale and others are 

of small-scale. Nevertheless, these questions were adopted and partly drive the mission of the 

GCMRC research program.

This questionnaire summarizes all of the major strategic science questions that have formed the 

basis for research and monitoring projects conducted since that 2007 workshop. These science 

questions have been reworded to make them more categorical, and hopefully easier to compile 

as we strive to summarize the state of scientific understanding. We have also included a section 

for you to score the level of confidence you have in your answer. A crosswalk that shows the 

original strategic science question and the associated, but reworded, questions in this questionnaire 

is included as an appendix 2. Several strategic science questions are not addressed in this 

questionnaire—these are also noted in appendix 2, including the basis for their omission. 

As a scientist that has been involved in Colorado River research and monitoring, your answers to 

this questionnaire are of great interest to GCMRC. Your answers will be compiled in anonymous 

summary statistics to identify areas where there is consensus among the science community, and 

where there is still uncertainty and disagreement. Your name will be reported in a list of science 

experts that were surveyed. 

We have provided a ‘Notes’ section at the end of each question. Please feel free to use this space to 

comment on any questions that you think are inherently intractable, and/or to qualify your answer 

or describe any assumptions you made in arriving at your answer. Please also feel free to leave any 

questions blank if you do not feel qualified to answer. 
24 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

Questionnaire

1. Why are the humpback chub not thriving, and what can we do about it?

List in order of importance three factors that you think presently limit humpback chub adult abundance, and then briefly 

describe an action that could be taken to mitigate this.

1.

2.

3.

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

2. To what extent are adult populations of native fish controlled by (rank from 1 to 4 in order of importance, 1 being of 

greatest importance): 

____Production of young fish from tributaries

____Spawning and incubation in the mainstem

____Survival of young-of-year (YOY) and juvenile stages in the mainstem

____Changes in growth and maturation in the adult population as influenced by mainstem conditions

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

 

A) If rainbow trout populations were large, a decrease in their abundance would lead to improvements in recruitment of 

juvenile humpback chub to the adult population_______(true or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:
Appendix 1 25

B) If brown trout populations were large, a decrease in their abundance would lead to improvements in recruitment of 

juvenile humpback chub to the adult population_______(true or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

C) If populations of small-bodied warm water non-natives (i.e., fathead minnow, red shiner, etc.) were large, a 

decrease in their abundance would lead to improvements in recruitment of juvenile humpback chub to the adult 

population_______(true or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

D) If populations of large-bodied warm water non-natives (i.e., channel catfish, common carp, etc.) were large, a 

decrease in their abundance would lead to improvements in recruitment of juvenile humpback chub to the adult 

population_________(true or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

4. To what extent do rainbow trout migrating from Glen Canyon support the population of rainbow trout in Marble and 

eastern Grand Canyon? (select one)

______Migration from Glen Canyon does not support populations in Marble and Grand Canyon

______Migration from Glen Canyon partially supports populations in Marble and Grand Canyon

______Migration from Glen Canyon largely supports populations in Marble and Grand Canyon

______Migration from Glen Canyon completely supports populations in Marble and Grand Canyon

 

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:
26 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

5. What are the important pathways that link lower trophic levels with fish?

(Rank from 1 to 6 in order of importance, 1 being of greatest importance)

______Algae-> invertebrates->fish

______Detritus->invertebrates->fish

______Terrestrial invertebrates->fish

______Prey fish->predatory fish

______algae->fish

______detritus->fish

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

6. Are trends in the abundance of fish populations or indicators from fish such as growth, condition, and body 

composition (for example, lipids), correlated with patterns in invertebrate flux? In other words, are fish food 

limited?________(true or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

7. Which mainstem habitats are most important to native fishes? (rank from 1 to 5 in order of importance, 1 being of 

greatest importance)

Habitat types

_______Talus

_______Backwaters

_______Cliff

_______Cobble

_______Vegetated shoreline

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:
Appendix 1 27

8. To what extent could predation impacts by nonnative fish be mitigated by higher turbidities? (select one)

____Higher turbidity would greatly increase predation impacts by nonnatives

____Higher turbidity would somewhat increase predation impacts by nonnatives

____Higher turbidity would have no impact on predation by nonnatives

____Higher turbidities would somewhat reduce predation impacts by nonnatives

____Higher turbidities would greatly reduce predation impacts by nonnatives

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

9. To what extent could predation impacts by nonnative fish be mitigated by dam-controlled high-flow releases? (select 

one)

____Frequent artificial floods would greatly increase predation by nonnatives

____ Frequent artificial floods would somewhat increase predation by nonnatives

____ Frequent artificial floods would have no impact on predation by nonnatives

____ Frequent artificial floods would somewhat reduce predation by nonnatives

____ Frequent artificial floods would greatly reduce predation by nonnatives

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

10. Is the amount of invertebrate biomass/production available for consumption by fish affected by water quality 

parameters (e.g., temperature, nutrient concentrations, turbidity)?_____(True or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:
28 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

11. An increase in the size, distribution, and number of backwaters would cause (select one):

_________A substantial decrease in native fish abundance

_________A decrease in native fish abundance

_________No change in native fish abundance

_________An increase in native fish abundance

_________A substantial increase in native fish abundance

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

12. An increase in the size, distribution, and number of vegetated shorelines would cause (select one):

_________A substantial decrease in native fish abundance

_________A decrease in native fish abundance

_________No change in native fish abundance

_________An increase in native fish abundance

_________A substantial increase in native fish abundance

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes:

13. What are the most important aspects of high-quality juvenile native fish rearing habitat? (rank from 1 to 4, 1 being of 

greatest importance)

_______Water temperatures

_______Cover

_______Low energy/slow water velocities

_______Food availability

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes: 
Appendix 1 29

14. What will happen if a temperature control device is implemented? (select one)

______Native fish abundance will substantially decrease 

______Native fish abundance will decrease

______Native fish abundance will not change

______Native fish abundance will increase

______Native fish abundance will substantially increase

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes: 

15. Are safeguards needed before a temperature control device can safely be operated? _______(True or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

If above is true, list potential safeguards______________________________________________

Notes: 

16. Do current water temperatures limit spawning and incubation success for native fish in the mainstem?_________

(True or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes: 
30 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

17. Do current flow fluctuations allowed by the Record of Decision (i.e., MLFF) limit spawning and incubation success for 

native fish in the mainstem?_____________(True or false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes: 

18. What is the relative importance of increased water temperatures, shoreline stability, and food availability on 

the survival and growth of YoY and juvenile native fish? (Score each: 1 = unimportant, 2 = somewhat important, 3 = 

important, 4 = very important)

________Water temperatures

________Shoreline stability

________Food availability

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes: 

19. Do the potential benefits of improving juvenile native fish rearing habitat in the mainstem (e.g., increasing water 

temperatures with a TCD, stabilizing flows, conducting frequent HFEs to increase the number of backwaters and 

vegetated shorelines, increasing food availability) outweigh negative impacts due to increases in nonnative fish 

abundance?__________(true/false)

Confidence in your answer:

______Very Unconfident 

______Unconfident

______Confident

______Very Confident

Notes: 

20. List up to 3 actions that you think should be taken because of their potential to benefit native fish populations.

__________________________________________________________________________

__________________________________________________________________________

__________________________________________________________________________
Appendix 2 31

Appendix 2. Crosswalk between Original Strategic Science Questions (SSQs) and This Questionnaire

AMWG Priority 1: Why are the humpback chub not thriving, and what can we do about it? How many humpback chub are there and how are 

they doing? (GCDAMP Goal 2)

Original questions Associated questions in this questionnaire

AMWG Priority Question: Why are the humpback chub not 

thriving, and what can we do about it?

1. Why are humpback chub not thriving, and what can we do about 

it?

 List in order of importance three factors that you think presently 

limit humpback chub adult abundance, and then briefly describe 

an action that could be taken to mitigate this.

SSQ1. To what extent are adult populations of native fish 

controlled by production of young fish from tributaries, 

spawning and incubation in the mainstem, survival of young-ofyear (YOY) and juvenile stages in the mainstem, or by changes 

in growth and maturation in the adult population as influenced 

by mainstem conditions? (FY2006-2011)

2. To what extent are adult populations of native fish controlled 

by (rank from 1 to 4 in order of importance, 1 being of greatest 

importance): 

SSQ 2. Does a decrease in the abundance of rainbow trout and 

other cold- and warm water nonnatives in Marble and eastern 

Grand Canyons results in an improvement in the recruitment rate 

of juvenile humpback chub to the adult population? (FY2006-

2011)

3A) If rainbow trout populations were large, a decrease in their 

abundance would lead to improvements in recruitment of juvenile 

humpback chub to the adult population_______(true or false)

 Etc.

SSQ 3. Do RBT immigrate from Glen to Marble and eastern Grand 

Canyons, and, if so, during what life stages? To what extent do 

Glen Canyon immigrants support the population in Marble and 

eastern Grand Canyons? (FY2007-2011)

4. To what extent do rainbow trout migrating from Glen Canyon 

support the population of rainbow trout in Marble and eastern 

Grand Canyon? (select one)

SSQ 5. What are the important pathways, and the rate of flux 

among them, that link lower trophic levels with fish and how 

will they link to dam operations? (FY2006-2009)

5. What are the important pathways that link lower trophic levels 

with fish?

SSQ 6. Are trends in the abundance of fish populations or 

indicators from fish such as growth, condition, and body 

composition (for example, lipids), correlated with patterns in 

invertebrate flux? (fy2006-2009)

6. Are trends in the abundance of fish populations or indicators 

from fish such as growth, condition, and body composition (for 

example, lipids), correlated with patterns in invertebrate flux? In 

other words, are fish food limited?________(true or false)

SSQ 7. Which tributary and mainstem habitats are most important 

to native fishes and how can these habitats best be made useable 

and maintained? (FY2008-2009)

7. Which mainstem habitats are most important to native fishes? 

(rank from 1 to 5 in order of importance, 1 being of greatest 

importance)

AMWG Priority 3: What is the best flow regime?

SSQ 2. To what extent could predation impacts by nonnative fish 

be mitigated by higher turbidities or dam-controlled high-flow 

releases? (FY2007-2008)

8.To what extent could predation impacts by nonnative fish be 

mitigated by higher turbidities? (select one)

9. To what extent could predation impacts by nonnative fish be 

mitigated by dam-controlled high-flow releases? (select one)

SSQ 5. How is invertebrate flux affected by water quality (for 

example, temperature, nutrient concentrations, turbidity) and 

dam operations? (FY2006-2008)

10. Is the amount of invertebrate biomass/production available for 

consumption by fish affected by water quality parameters (e.g., 

temperature, nutrient concentrations, turbidity)?_____(True or 

false)
32 Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources in the Colorado River

AMWG Priority 4: What is the impact of sediment loss and what should we do about it? (GCDAMP goal 8)

Original questions Associated questions in this questionnaire

SSQ 2. How important are backwater and vegetated shoreline 

habitats to the overall growth and survival of YoY and juvenile 

native fish? Does the long-term benefit of increasing these 

habitats outweigh short-term potential costs (displacement and 

possibly mortality of young humpback chub) associated with 

high flows? (FY2007-2011)

11. An increase in the size, distribution, and number of backwaters 

would cause (select one):

12. An increase in the size, distribution, and number of vegetated 

shorelines would cause (select one):

13. What are the most important aspects of high-quality juvenile 

native fish rearing habitat? (rank from 1 to 5, 1 being of greatest 

importance)

AMWG priority 5: What will happen when we test or implement the temperature control device (TCD)? How should it be operated? Are 

safeguards needed for management? (GCDAMP goals 1-4 and 7-10)

AMWG Priority 5. What will happen when we test or implement 

the temperature control device (TCD)?

14. What will happen if a temperature control device is 

implemented? (select one)

Are safeguards needed for management? 15. Are safeguards needed before a temperature control device can 

safely be operated?

SSQ 3. To what extent do temperature and fluctuations in flow limit 

spawning and incubation success for native fish? (FY2003-2008)

16. Do water temperatures limit spawning and incubation success 

for native fish in the mainstem?_________(True or false)

17. Do flow fluctuations limit spawning and incubation success for 

native fish in the mainstem?_____________(True or false)

SSQ 4. What is the relative importance of increased water 

temperatures, shoreline stability, and food availability on the 

survival and growth of YoY and juvenile native fish? (FY2003-

2008)

18. What is the relative importance of increased water temperatures, 

shoreline stability, and food availability on the survival and 

growth of YoY and juvenile native fish? (Score each: 1 = 

unimportant, 2 = somewhat important, 3 = important, 4 = very 

important)

SSQ 6. Do the potential benefits of improved rearing habitat 

(warmer, more stable, more backwater and vegetated shorelines, 

more food) outweigh negative impacts due to increases in 

nonnative fish abundance? (FY2007-2011)

19. Do the potential benefits of improving juvenile native 

fish rearing habitat in the mainstem (e.g., increasing water 

temperatures with a TCD, stabilizing flows, conducting 

frequent HFEs to increase the number of backwaters 

and vegetated shorelines, increasing food availability) 

outweigh negative impacts due to increases in nonnative fish 

abundance?__________(true/false)
Appendix 2 33

SSQs that do not have an associated question in this questionnaire:

AMWG Priority 1, SSQ 4. Can long-term decreases in abundance of RBT in Marble and eastern Grand Canyons be sustained with a reduced 

level of effort of mechanical removal or will recolonization from tributaries and from downstream and upstream of the removal reach 

require that mechanical removal be an ongoing management action? This question also applies to future removal programs targeting other 

nonnative species. (FY2007-2011)

Reason not included: question is too open-ended and leading. A target abundance for rainbow trout is not specified, which makes it 

impossible to answer the question. The question assumes RBT abundance at the LCR needs to be minimized—this issue of RBT impacts is 

the subject of numerous other SSQs. 

AMWG Priority 1, SSQ 8. How can native and nonnative fish best be monitored while minimizing impacts from capture and handling or 

sampling? (FY2007-2011)

Reason not included: This was addressed by the 2009 PEP.

AMWG Priority 5, SSQ 2. How is invertebrate flux affected by water quality (for example, temperature, nutrient concentrations, turbidity) 

and dam operations? (FY2006-2008)

Reason not included: This question is redundant with earlier questions. 

AMWG Priority 5, SSQ 5. Will increased water temperatures increase the incidence of Asian tapeworm in humpback chub or the magnitude 

of infestations, and if so, what is the impact on survival and growth rates? (FY2003-2008)

Reason not included: There are no data available on the impact of tapeworm loads on survival and growth of HBC.
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Kennedy—Identification and Evaluation of Scientific Uncertainties Related to Fish and Aquatic Resources, Colorado River, Grand Canyon—Scientific Investigations Report 2013–5027