Brown trout in Glen Canyo

Insights from two expert elicitation surveys Jeff Muehlbauer & Lucas Bair GCMRC 

U.S. Department of the Interior U.S. Geological Survey 
Why a survey?

 Lots of talk about brown trout  Little data  Identify broad patterns of consensus? Inform management priorities?  Actually 2 surveys: 

 Initial questions, then 

focused follow-up

Kennedy 2013
Who took the survey? 

 Can’t say for sure (totally anonymous)  Invited list included scientists and man

included in brown trout email threads afish cooperators meeting 

 Survey 1: 14 respondents Survey 2: 13 respondents

Unpublished data, subject 
Survey 1 Themes 

1: Are brown trout a problem? 2: How did they become a problem? 3: What can we do about it? Goal is to look for some expert con
U.S. Department of the Interior

U.S. Geological Survey

Definitely Yes 

Definitely No 

Maybe 

Representative comments:• “Although rainbow and brown trout are both piscivorous, if populations of both specie

numbers, I would expect brown trout to have the most detrimental effect on chub popubehavior in other systems.” 

• “Warmwater centrarchids and other large bodied non natives comprise the biggest thre

Rainbow trout are less of a threat, although brown trout, because of their high level of pworse.” 

• “Rainbow in the Little Colorado area are a threat, but should not be much of one in the 

Brown trout are going to eat other fish wherever they are and could quickly replace the 

• “I think brown trout are a far greater threat to native fishes than rainbow trout or green 

Unpublished data, subject 
1: Are brown trout a problem?

Resounding Yes. • Definitely more than RBT or green su• A little less of a concern than smallmo

bass 

Unpublished data, subject 
U.S. Department of the Interior

U.S. Geological Survey

Definitely Yes 

Definitely No 

Maybe 

Representative comments: • “All of these factors, or many of them, likely contribute to the recent increases. We must all rem

one true answer...it is the interaction of many factors.” 

• “I don't think that anyone really knows why a particular NNF can exist at low levels in a particul

period, and then increase dramatically in numbers. It happens pretty regularly. Maybe conditiontogether to support the NNF.” 

• “The only plausible explanations I've heard for recent recruitment increases at Lees Ferry are th

HFEs and warmer water temperatures.” 

• “ I think it might be a combination of frequent high flow experiments in the fall, timed with a dec

particularly the spawners that were part 2008 and 2011 cohorts. ” Unpublished data, subject 
U.S. Department of the Interior

U.S. Geological Survey

Most important 

Neutra l 

Not important at all 

Representative comments: • “I think the list of potential influences is a good one.” • “The only two plausible answers in my opinion are seasonal timing of HFEs and warm water temp

inevitable (i.e., there is no root cause that we can target for mitigation) is more plausible than thesopinion.” 

• “There is no one important driver, it is a combination of factors that has resulted in an increased 

Trout.” 

Unpublished data, subject 
2: How did BNT become a prob

• Many comments highlighting conflue

factors (warm water, lots of fall HFEs, numbers...) 

• No consensus on a “silver bullet”, sin

issue 

Unpublished data, subject 
U.S. Department of the Interior

U.S. Geological Survey

Definitely Yes 

Definitely No 

Maybe 

Representative comments: • “Trout management flows may have an effect via stranding, but I think more research would nee

assess this potential management alternative.” 

• “While not really confident with any of this, I think that if we can create an environment that fav

spring high flows to increase recruitment) and minimize brown trout reproduction (fall trout mamechanical removal?) we might be able to continue to keep brown trout at bay.” 

• “Would have to be a very large and focused mechanical removal effort targeting spawners and • “A temp control device to cool the water might impact brown trout negatively.” • “I think chemical treatment of the entire Lees Ferry reach is capable of reducing brown trout po

answered NO to this question because the collateral damage to the rainbow trout fishery would likely unacceptable” 

Unpublished data, subject 
U.S. Department of the Interior

U.S. Geological Survey

Most effective 

Not effective at all 

Neutral 

Representative comments: • “The range of choices seems to cover potential options well, but only mechanical removal is imm

us.” 

• “I think its worth considering temperature.” • “I think we need to consider mechanical removal by disrupting redds in the fall.” • “I don't think there is an effective management action for Brown Trout in Lees Ferry.” • “There are few removal efforts in similar systems that have produced the desired results, althou

that they wouldn't have the desired effect, but more likely points to the inefficiency of removal efwestern complex rivers.” 

• “Increased turbidity would likely be a very efficient method for controlling site predators like Bro

Sunfish. It seems ridiculous to have a surplus of sediment on one side of the concrete border another.” Unpublished data, subject 
3: What can we do about it?

• High uncertainty surrounding TCDs, T

and other new actions, but cautious interest. 

• Mechanical removal has interest, but 

many caveats. (very intensive effort, targeted toward reds, possibly in concert with flow op

• Few “outside the box” solutions prop

Unpublished data, subject 
Survey 2 Theme 

What management actions woueffective? Have we moved toward consenafter intensive discussions? 

Unpublished data, subject 
Survey 2 respondents 

 11 research scientists/fisheries biologi 2 resource managers  75% took Survey 1 as well (3 newcome “Have your opinions changed?” 

 Most said “no” 

Unpublished data, subject 
Most effective 

Uncertain 

Not effective at all 

Representative comments: • “A multi-pronged approach is likely the only way to have some effect on brown trout abundance.” • “Even with all of those combined methods it seems like you could expect limited success.” • “Electrofishing has not been successful in other programs and is very expensive. It may just cause a co

and more problems later.” 

• “It is naive to think that a single year effort will alter the population trajectory. And even if the action had 

would be short lived without a long-term commitment in maintaining the BNT population at desired targe

Unpublished data, subject 
Most effective 

Not effective at all 

Uncertain 

Representative comments:  “Flow related management tools in combination with other methods may be more effective than non-f “This remains uncertain and therefore requires long-term planning and experimentation.” 

Unpublished data, subject 
Fully sustainable 

Neutral 

Unsustainable 

Unpublished data, subject 

Representative comments:  Changes to the physical environment (flow, temperature) to control brown trout populations is likely to 

long-term solution to brown trout removal than other mechanical options. 

 “Spring high flow and trout management flows seem the most likely to limit food and spawning succe

populations in the long run.” 

 “Who knows without doing it.” 
Survey 2 summary 

 Skepticism that mechanical removal w

effective, especially without flows. 

 Consensus that some flows (alone or i

combination) are best option. 

 Any action needs study, planning, and  Need to be prepared for the long-term.