HIGHLIGHTS OF: 

Assessment of Potential Augmentation and 

Management Strategies for Razorback Sucker 

Xyrauchen texanus in Lake Mead and Grand 

Canyon: A 2021 Science Panel Summary

Dr. Phaedra Budy

Utah State University & USGS UCFWRU

Dr. Casey Pennock

Utah State University, Dept. of Watershed Sciences

TWG update

13 Oct 2022
LINK to Panel Summary

• https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1136&c

ontext=eco_pubs

• CITATION:

Pennock, C. A., P. Budy, S. A. Bonar, T. E. Dowling, K. B. Gido, E. I. Gilbert, B. R. Kesner, C. P. Paukert, M. C. 

Quist, J. Stahli, T. F. Turner, and D. L. Ward. 2022. Assessment of potential augmentation and management 

strategies for Razorback Sucker Xyrauchen texanus in Lake Mead and Grand Canyon: A Science Panel 

Summary. UTCFWRU 2022 (3):1-31.
Overarching Question

• Is the current population of Razorback Sucker in Lake Mead and 

Grand Canyon sustainable, and should it be augmented?
Data Presentations
What is the current status of the population(s) in 

Lake Mead and Grand Canyon

• Perception of decline?

• Depends on time series

• Some recruitment is occurring

• Currently sustainable at 200-

500

• BUT, long-term persistence 

questionable

• AND, lack of RZN < 200 mm

• Recruitment Bottleneck
Lake Mead specific Highlights

• Is the current level of 5,800 fish a suitable starting goal towards 

recovery?

• Agreement, 5,800 sexually mature fish is a reasonable starting goal.
Lake Mead specific Highlights (cont.)

• Is the current level of 5,800 fish a suitable starting goal 

towards recovery?

• 5,800 sexually mature fish is a reasonable starting goal.

• What evidence exists for conditions allowing for 

successful recruitment of Razorback Sucker in Lake 

Mead?

• Turbidity at river inflows and lateral washes (e.g., Las Vegas 

Wash) along with submergent and flooded vegetation with 

variation in reservoir water level is predicted to contribute to 

successful recruitment
Lake Mead specific Highlights (cont.)

• Is the current level of 5,800 fish a suitable starting goal 

towards recovery?

• 5,800 sexually mature fish is a reasonable starting goal.

• What evidence exists for conditions allowing for successful 

recruitment of Razorback Sucker in Lake Mead?

• Turbidity at river inflows and lateral washes (e.g., Las Vegas Wash) 

along with submergent and flooded vegetation with variation in reservoir water level is predicted to contribute to successful 

recruitment

• What do you predict are the limiting factors for a larger 

population in Lake Mead?

• This is a critical uncertainty, but most of the ESP thought predation by 

nonnative fishes was limiting the population.
Grand Canyon Specific 

Highlights
What role does the Grand Canyon play in greater 

metapopulation viability and dynamics?

• Populations of Razorback Sucker in Lake Mead and Grand Canyon represent 

core (Lake Mead) and satellite (Grand Canyon) populations rather than a 

metapopulation, because Grand Canyon appears to be reliant on fish in Lake 

Mead moving upstream to recolonize.

• The Grand Canyon population could be contributing to the Lake Mead core 

population (e.g., via larvae drifting downstream), but this contribution is 

likely minimal because the number of adult fish in Grand Canyon appears low 

and all recently tested larvae (n = 14) were hybrids with Flannelmouth Sucker 

Catostomus latipinnis (T. Dowling, unpublished data).
Could Grand Canyon contribute to the greater 

metapopulation viability?

• See above – larval drift.

• The connectivity between Lake Mead and Grand 

Canyon could change if flows were altered in the 

future under different reservoir filling actions 

such as Pearce Ferry Rapid being inundated and 

becoming more passable, or if the rapid becomes 

more passable naturally through erosion or lateral 

movement of the river channel.
What conditions would be needed to establish and 

maintain a population in Grand Canyon?

• Rather speculative.... habitat improvements in the form of creating offchannel rearing habitats in western Grand Canyon to increase the likelihood 

of entraining larvae might improve habitat for early life stages of Razorback 

Sucker prior to any augmentation in the mainstem Colorado River in Grand 

Canyon, if the goal is to establish a naturally recruiting popuation

• Concerns that cold temperatures (depending on water management) in 

mainstem could be limiting
What are critical uncertainties with regard to the 

overarching question and Grand Canyon?

• Hybridization with Flannelmouth suckers

• Already occurring 

• Occurred evolutionarily

• Hybrids could swamp

• Lake Mead
What are critical uncertainties with regard to the 

overarching question and Grand Canyon?

• Hybridization with Flannelmouth suckers

• Already occurring 

• Occurred evolutionarily

• Hybrids could swamp

• Lake Mead

• Is spawning success already limited

• Limited numbers of spawning adults

• Larval drift

• Exacerbated by limited low velocity habitat?

• Low survival

• All of above
Connectivity: To what degree is Pearce Ferry Rapid 

a barrier to movement of fish between Lake Mead 

and Grand Canyon?

• 2 way connectivity seems likely to be:

• Limited

• Temporally variable

• Downstream biased
Should augmentation occur in Lake Mead?

• Majority (but not all) agreed augmentation should occur in Lake Mead 

• Where? Multiple locations 

• Spread the risk

• Do site specific features contribute to post-stocking survival?

• How many? What kind? What age/size?

• ~600/year, 300 from Lake Mead and 300 from Lake Mohave

• < 200 mm should be included

• How often?

• ~1 time per year for 3 years while assessed, then re-evaluate
Should augmentation occur in Grand Canyon?

• Near consensus, try experimental augmentation

• Where? Tributaries

• How many? What kind? What age/size?

• Not less than 300/event

• Mixture of Lake Mead and Lake Mohave

• Include juveniles

• How often? 

• ~1 time per year for 3 years while assessed, then re-evaluate
Series of research ideas to address knowledge 

gaps in Grand Canyon with regard to RZB

• Improvement/construction of off channel rearing habitat to increase 

retainment of larvae?

• Inject augmented fish with hormones to promote immediate 

spawning

• Temperature control device on Glen Canyon Dam

• Are food resources abundant enough to support 

a resident population

• Will juvenile fish introduced into Grand Canyon 

become resident or move to Lake Mead
Monitoring and learning are critical!

• Any augmentation should be done in 

an experimental fashion to enhance 

the ability to learn about limiting 

factors

• All fish must be PIT tagged and fin 

clipped (genetics)

• Monitor with PIT tag antennae

• Prioritize management 

actions/augmentation to promote learning

• E.g., limiting factors to early life history 

= top priority

• E.g., choose tributaries that can be 

monitored with PIT antennae
Acknowledgements

We would like to thank all of the researchers who presented data to 

the Expert Science Panel including: Brandon Albrecht and Ron Rogers 

(BIO-WEST, Inc.), Steve Platania (American Southwest Ichthyological 

Researchers, Inc.), Charles Yackulic (Grand Canyon Monitoring and 

Research Center), Dave Rogowski (Arizona Game and Fish Department), 

and Matt Bogaard (Kansas State University). We also thank Emily 

Omana Smith (National Park Service) for providing a thorough 

summary of previous science panels. Matt Bogaard and Nate Cathcart

provided helpful editorial comments. The Science Panel process was 

supported by funding from the Bureau of Reclamation and the U.S. Fish 

& Wildlife Service.
Other management recommendations: 

predators and addressing knowledge gaps

• Localized reduction of non-native fishes at turbid inflows during 

spawning

• System wide nonnative fish eradication

• Fine scale experiments at sites throughout reservoir to test for factors 

potentially limiting to recruitment

• Evaluate predator-free areas:

• Remove predators

• Turbidity curtains

• Series of research ideas to address knowledge gaps
Are current Monitoring efforts adequate in 

Lake Mead and Grand Canyon?

• Lake Mead

• Worth investigating different gear types to target younger age classes in 

Lake Mead

• E.g, smaller benthic trawl

• More data on co-occurring non-natives 

• More standardized and documented PIT tag detection efforts
Are current Monitoring efforts adequate in 

Grand Canyon?

• Grand Canyon

• Current small bodies sampling has not detected larval or juvenile RZB

• Labor-intensive

• Consider larval trigger

• E.g., Do small bodies sampling if RZB are detected that year or year prior