Reclamation Managing Water in the West

Review and Summary of 

Razorback Sucker Habitat 

In the Colorado River System
Cover Photos: 

Top center: Cross Butte at RM 35 of the Green River (R. Valdez, 1986); top left: aerial view of 

riverside floodplain above Brennan at RM 269 on the Green River (USFWS, April 2000); bottom 

left: adult razorback sucker captured in the Upper Colorado River near Grand Junction (R. 

Valdez, June 1980); bottom right: aerial view of Colorado River in Canyonlands National Park 

(R. Valdez, December 1980). 

Disclaimer: 

The opinions and recommendations expressed in this report are those of the authors and do not 

necessarily reflect the views of the U.S. Bureau of Reclamation or any other agency or 

organization. The use or mention of trade names, commercial products, or firms and businesses 

does not constitute endorsements or recommendations for use.

Recommended Citation: 

Valdez, R.A., D.A. House, M.A. McLeod, and S.W. Carothers. 2012. Review and summary of 

razorback sucker habitat in the Colorado River System, Report Number 1. Final Report prepared 

by SWCA, Environmental Consultants for U.S. Bureau of Reclamation, Upper Colorado Region, 

Salt Lake City, Utah. 

i 
Report Number 1 

REVIEW AND SUMMARY OF 

RAZORBACK SUCKER HABITAT 

IN THE COLORADO RIVER SYSTEM

Final Report 

REPORT TO U.S. BUREAU OF RECLAMATION 

UPPER COLORADO REGION 

SALT LAKE CITY, UTAH 

REPORT BY SWCA ENVIRONMENTAL CONSULTANTS 

FLAGSTAFF, ARIZONA 

Richard A. Valdez, Dorothy A. House, 

Mary Anne McLeod, and Steven W. Carothers 

APRIL 1, 2012 

ii 
Preface April 1, 2012

PREFACE 

The U.S. Bureau of Reclamation (Reclamation) has undertaken an investigation to examine the 

potential of habitat for the federally endangered razorback sucker (Xyrauchen texanus) in the 

lower Grand Canyon. Reclamation, in collaboration with the U.S. Fish and Wildlife Service 

(USFWS), may institute an augmentation program for the species in that area, if appropriate. 

This investigation addresses part of a conservation measure of the Final Environmental Impact 

Statement for the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated 

Operations for Lake Powell and Lake Mead. The measure is contained in Concurrences 

(Appendix A) of the 2007 Biological Opinion for that action which states that: "Reclamation 

will, as a conservation measure, undertake an effort to examine the potential of habitat in the 

lower Grand Canyon for the species [razorback sucker], and institute an augmentation program 

in collaboration with FWS, if appropriate."

Reclamation is coordinating this investigation with the U.S. Fish and Wildlife Service, Glen 

Canyon Dam Adaptive Management Program, Lower Colorado River Multi-Species 

Conservation Program, National Park Service, Grand Canyon Monitoring and Research Center, 

Nevada Department of Wildlife, Arizona Game and Fish Department, and the Hualapai Tribe. 

SWCA, Environmental Consultants was retained by Reclamation to assist with the assimilation 

of information for this investigation and to recommend an augmentation strategy for the 

razorback sucker. SWCA and Reclamation established three tasks: (1) assimilate, review, and 

summarize the habitat information for the species, (2) convene a Science Panel of species experts 

for recommended actions, and (3) develop an augmentation strategy. 

This report is the first of three reports produced as part of this investigation that include: 

1. Review and Summary of Razorback Sucker Habitat in the Colorado River System: This

report summarizes habitat used by the razorback sucker throughout its range in the 

Colorado River System, including conditions for spawning and egg incubation; larval 

drift corridors and distances; nurseries used by young; juvenile rearing areas; food 

requirements; movement; and subadult and adult habitat. The information contained in 

this report was used to better gauge the suitability of conditions for the species in the 

lower Grand Canyon and Colorado River inflow. 

2. The Potential of Habitat for the Razorback Sucker in the Lower Grand Canyon and 

Colorado River Inflow to Lake Mead: A Science Panel Report: This report contains the 

views, opinions, and recommendations of a panel of species experts on the suitability of

the lower Grand Canyon and Colorado River inflow for the razorback sucker. It was 

developed from a reconnaissance field trip and meetings of the Panel in September, 2010. 

3. Strategy for Establishing the Razorback Sucker in the Lower Grand Canyon and Lake 

Mead Inflow: This report describes a strategy for establishment of the razorback sucker in 

the lower Grand Canyon, either naturally through expansion of the Lake Mead population 

or possibly through augmentation. 

Razorback Sucker Habitat Final Report 

iii 
Acknowledgments April 1, 2012 

ACKNOWLEDGMENTS 

The U.S. Bureau of Reclamation and SWCA Environmental Consultants appreciate the efforts of 

many individuals that provided support and input into this investigation and the development of 

the three reports (see names and affiliations below). Mark McKinstry, Reclamation’s Contract 

Officer Technical Representative, provided the impetus, support, and guidance for this project. 

We thank the members of the Science Panel (highlighted below) for their critical review, 

evaluation, and input necessary to the development of a scientifically defensible approach for 

evaluating the potential for introducing razorback suckers into the lower Grand Canyon. 

We thank the National Park Service for their collaboration and support of this project, especially 

Brian Healy, Emily Omana Smith, Nate Alvord, and Dave Loeffler of Grand Canyon National 

Park who provided logistical support and rafts for the reconnaissance field trip of September 16–

19, 2010, through the lower Grand Canyon. We thank Greg Squires of Lake Mead National 

Recreation Area for providing a boat to transport the Science Panel in the Lake Mead inflow. 

We thank the participants of the reconnaissance field trip for their valuable time and insight and 

the agencies for supporting members of their staffs to participate in this process. The Bar 10 

Ranch provided aerial and ground transportation from Flagstaff, Arizona to Whitmore Wash. 

Name Affiliation Role

Albrecht, Brandon Bio/West, Inc., Logan, UT Principal Investigator, Lake Mead Razorback 

Sucker Studies

Alvord, Nate National Park Service, Grand Canyon, AZ Staff Assistant, Grand Canyon National Park

Clark, Andy Arizona Game and Fish Department, Kingman, AZ Fisheries Program Manager, AGFD 

Hamill, John U.S. Geological Survey, Flagstaff, AZ Director, Grand Canyon Monitoring and 

Research Center 

Healy, Brian National Park Service, Flagstaff, AZ Fisheries Biologist, Grand Canyon National Park

Herndon, Debora Nevada Department of Wildlife NDOW Representative, Lower Colorado River 

Multi-Species Conservation Program 

House, Dorothy SWCA, Inc., Flagstaff, AZ SWCA Project Assistant 

Loeffler, Dave National Park Service, Grand Canyon, AZ Staff Assistant, Grand Canyon National Park

McAda, Chuck U.S. Fish and Wildlife Service (retired), Grand 

Junction, CO 

Science Panel 

McKinstry, Mark U.S. Bureau of Reclamation, Salt Lake City, UT Contract Officer Technical Representative 

Morgan, Annette The Hualapai Tribe, Peach Springs, AZ Tribal Representative 

Mueller, Gordon U.S. Geological Survey (retired), Denver, CO Science Panel 

Omana Smith, 

Emily 

National Park Service, Flagstaff, AZ Fisheries Biologist, Grand Canyon National Park

Ryden, Dale U.S. Fish and Wildlife Service, Grand Junction, CO Science Panel 

Sponholtz, Pam U.S. Fish and Wildlife Service, Flagstaff, AZ Project Coordinator and Fishery Biologist, 

Arizona Fishery Resources Office 

Stolberg, Jon U.S. Bureau of Reclamation, Boulder City, AZ BOR Representative, Lower Colorado River

Multi-Species Conservation Program 

Trammell, Melissa National Park Service, Salt Lake City Science Panel 

Valdez, Richard SWCA, Inc., Logan, UT Science Panel Chair 

Razorback Sucker Habitat Final Report 

iv 
Table of Contents April 1, 2012 

TABLE OF CONTENTS 

EXECUTIVE SUMMARY .........................................................................................................xiii 

1.0 INTRODUCTION ................................................................................................................. 1 

1.1 Background...................................................................................................................... 1 

1.2 Species Description.......................................................................................................... 1 

1.3 Status................................................................................................................................ 2

1.4 Historical Distribution ..................................................................................................... 2 

1.5 Present Distribution ......................................................................................................... 4 

1.6 General Life History ........................................................................................................ 6 

1.7 Relationship of Life Stages to River Geomorphology..................................................... 8 

2.0 HABITAT CHARACTERISTICS AND MANAGEMENT BY RIVER ........................... 13 

2.1 Green River.................................................................................................................... 13 

2.2 Yampa River.................................................................................................................. 20 

2.3 Upper Colorado River.................................................................................................... 21 

2.4 Gunnison River.............................................................................................................. 25 

2.5 San Juan River ............................................................................................................... 26 

2.6 Lower Colorado River and Reservoirs .......................................................................... 30 

2.7 Gila, Salt, and Verde Rivers .......................................................................................... 34 

3.0 MESOHABITAT USE BY LIFE STAGE .......................................................................... 36 

3.1 Spawning........................................................................................................................ 36 

3.2 Larval Drift and Nursery Habitat................................................................................... 39 

3.3 Subadults and Adults..................................................................................................... 40 

3.4 Synthesis of Mesohabitat Data....................................................................................... 41 

4.0 MICROHABITAT USE BY LIFE STAGE ........................................................................ 43 

4.1 Spawning........................................................................................................................ 43 

4.2 Larval Drift and Nursery Habitat................................................................................... 44 

4.3 Subadults and Adults..................................................................................................... 48 

4.4 Synthesis of Microhabitat Data...................................................................................... 48 

5.0 RAZORBACK SUCKER IN LOWER GRAND CANYON AND LAKE MEAD ............ 54 

5.1 Occurrence of Razorback Sucker in Grand Canyon...................................................... 54 

5.2 Studies of Razorback Sucker in Lower Grand Canyon ................................................. 57 

5.3 Preliminary Evaluation of Razorback Sucker Habitat................................................... 61 

5.4 Status of Razorback Sucker Population in Lake Mead.................................................. 64 

6.0 HABITAT SUITABILITY OF LOWER GRAND CANYON ........................................... 69 

6.1 Overview of Habitat Use ............................................................................................... 69 

6.2 Comparison of Habitat Profiles ..................................................................................... 73 

6.3 Biological Components of Lower Grand Canyon ......................................................... 84 

LITERATURE CITED................................................................................................................. 90 

Appendix A: Razorback Sucker Habitat Suitability Indices from Scientific Reports.............. A-1 

Appendix B: Preliminary Survey of Lower Grand Canyon (Speas and Trammell 2009)........ B-1 

Razorback Sucker Habitat Final Report 

v 
List of Tables April 1, 2012 

LIST OF TABLES 

Table 1. Distribution and status of the razorback sucker in critical habitat by five regions of the 

Colorado River System (USFWS 2002). ....................................................................... 5 

Table 2. Summary of life history strategies and habitat conditions for the razorback sucker in 

five geographic regions of the Colorado River System. ................................................ 7 

Table 3. Channel gradient of various reaches of the five regions of the Colorado River System

and current use by the razorback sucker. Gradients were classified as relatively Low 

(L<5 ft/mi), Moderate (H=5-8 ft/mi), and High (H>8 ft/mi). This table corresponds to 

Figures 4 and 5 which illustrate each reach. .................................................................. 9 

Table 4. Stream characteristics of the three major reaches of the Green River below Flaming 

Gorge Dam. Information from Muth et al. (2000)....................................................... 15 

Table 5. Yampa River reaches from the Green River confluence at Echo Park upstream to the 

Little Snake River confluence at Lily Park, Colorado. Information from Modde et al. 

(1999). .......................................................................................................................... 21 

Table 6. Upper Colorado River strata from Hite Marina at Lake Powell, Utah, upstream to 

Rifle, Colorado. Table adopted from Valdez et al. (1982)........................................... 24 

Table 7. Geomorphic reaches of the San Juan River, Lake Powell to Navajo Dam (from

downstream to upstream). Information from Bliesner and Lamarra (1999) and Dudley 

and Platania (2000). ..................................................................................................... 28 

Table 8. Summary of mesohabitats used by life stage of the razorback sucker as described by 

various investigators. ................................................................................................... 37 

Table 9. Microhabitat data for spawning razorback suckers, Upper and Lower Colorado River 

Basins. .......................................................................................................................... 45 

Table 10. Hatch success rates by temperature in laboratory trials................................................ 46 

Table 11. Microhabitat data for larval and small juvenile razorback suckers. ............................. 47 

Table 12. Microhabitat data for large juvenile and adult razorback suckers................................ 52 

Table 13. Temperature preference and swimming ability data for large juvenile and adult 

razorback suckers from laboratory trials...................................................................... 53 

Table 14. Movement of radio-tagged adult razorback suckers in lower Grand Canyon, June–

October, 1997. Hualapai Aquatic Studies. Unpublished data, SWCA Environmental 

Consultants................................................................................................................... 58 

Table 15. Habitat associations of radio-tagged adult razorback suckers in lower Grand Canyon, 

June–October, 1997; Hualapai Aquatic Studies. Unpublished data, SWCA 

Environmental Consultants. ......................................................................................... 60 

Table 16. Quantitative criteria defining quality of potential razorback sucker habitat in lower 

Grand Canyon (Speas and Trammell 2010)................................................................. 61 

Razorback Sucker Habitat Final Report 

vi 
List of Tables April 1, 2012 

Table 17. A list of citations used as sources for habitat information for the razorback sucker. 

Sources of habitat suitability criteria are highlighted in gray and the criteria provided 

in Appendix A, and summarized for microhabitat in Figures 20–22 and for 

mesohabitat in Figures 33–34. Detailed citations are provided in the Literature Cited 

section of this report..................................................................................................... 70 

Table 18. Profile of habitat used by various life stages of the razorback sucker compared to 

available habitat in lower Grand Canyon..................................................................... 74 

Table 19. Number and percent of fish species caught in the Colorado River from Diamond Creek 

to Pearce Ferry. Data for 1992–1995 from Valdez et al. (1995) and for 2004–2006 

from Ackerman et al. (2006)........................................................................................ 89 

Razorback Sucker Habitat Final Report 

vii 
List of Figures April 1, 2012 

LIST OF FIGURES 

Figure 1. Adult razorback sucker. Illustration by Joseph Tomelleri............................................. 1 

Figure 2. Historical and present distribution of the razorback sucker with designated critical 

habitat in each of five regions of the Colorado River System. Figure adopted from

Maddux et al. (1993) and Schooley and Marsh (2007).................................................. 3 

Figure 3. General riverine life history strategy for the razorback sucker, including Overwinter 

(N-M), Migrate to spawning sites (M-A), Spawn (A-J), and Larvae in Floodplains (MO). The timing of these strategies is linked to flow and temperature and may vary by 

river region. Flow is mean of daily mean values for 64 years of record (10-01-1946 – 

09-30-2010), and temperature is mean of daily mean values for 8 years of record (10-

01-1997 – 09-30-2005), USGS gage near Jensen, Utah. ............................................... 6 

Figure 4. Longitudinal profiles for the Green River, Upper Colorado River, and San Juan River. 

Average channel gradient by reach is indicated (except for reservoirs), and level of use 

by life stage of razorback sucker is shown with color-coded pies. See Table 3 for 

additional information. River profiles and distances from Reclamation (1946) and use 

by life stage in Green and Upper Colorado rivers from LaGory (2003)...................... 11 

Figure 5. Longitudinal profiles for the Lower Colorado River and Gila River. Average channel 

gradient for each river reach is indicated (except for reservoirs), and level of use by 

life stage of razorback sucker for each reach is shown with color-coded pies. See 

Table 3 for additional information. River profiles and distances from Reclamation 

(1946). .......................................................................................................................... 12 

Figure 6. Three reaches of the Green River below Flaming Gorge Dam, Utah. Figure modified 

from Muth et al. (2000)................................................................................................ 13 

Figure 7. Comparison of annual hydrographs for average daily streamflow of the Yampa River 

at Deerlodge Park and the Green River at Greendale and Jensen, Utah (1982–1994). 

Figure from Roehm (2004). ......................................................................................... 14 

Figure 8. A 71-mi reach of the upper Green River in Utah, from Split Mountain Campground 

(RM 199) to Ouray (RM 128) with key life history aspects for the razorback sucker, 

including: spawn on a cobble/gravel bar below Split Mountain Canyon; nursery 

floodplains for drifting larvae at Horseshoe Bend; and floodplains and subadult and 

adult habitat near Leota Bottom, Ouray National Wildlife Refuge. Photos courtesy of 

U.S. Fish and Wildlife Service..................................................................................... 17 

Figure 9. Floodplains of the middle Green River, Utah, managed to entrain drifting razorback 

sucker larvae at (A) Horseshoe Bend connected with the river through a 1,000 ft wide 

levee breach, and (B) Brennan Bottom, with three small levee breaches shown as 

connections between the river channel and the floodplain. Photos courtesy of U.S. Fish 

and Wildlife Service..................................................................................................... 19 

Figure 10. Yampa River reaches from the Green River confluence at Echo Park upstream to the 

Little Snake River confluence at Lily Park, Colorado. Figure from Muth and Nesler 

(1993). .......................................................................................................................... 20 

Razorback Sucker Habitat Final Report 

viii 
List of Figures April 1, 2012 

Figure 11. Upper Colorado River from Lake Powell to Debeque, Colorado. Figure from Valdez 

et al. (1982). ................................................................................................................. 22 

Figure 12. Average daily streamflow of the Colorado River near Cameo (09095550) for the predam period 1934–1949 and for the post-dam period 1950–1998. Figure from Van 

Steeter and Pitlik (1998). ............................................................................................. 22 

Figure 13. Average daily streamflow of the Gunnison River near Grand Junction (09152500) for 

the pred-dam period 1917–1949 and the post-dam period 1950–1998. Figure from Van 

Steeter and Pitlik (1998). ............................................................................................. 26 

Figure 14. San Juan River from Lake Powell, Utah, to Navajo Dam, New Mexico, showing 

reaches 1–8 (downstream to upstream). Figure from Holden (1999). ......................... 27 

Figure 15. Average daily treamflow of the San Juan River at Shiprock, NM; Four Corners, CO; 

and Bluff, UT, for Water Year 1999 (October to October). Figure modified from

Dudley and Platania (2000).......................................................................................... 30 

Figure 16. Lower Colorado River from Lake Mead to the U.S.-Mexico border.......................... 31 

Figure 17. Key life history aspects for the razorback sucker in reservoirs of the Lower Colorado 

River Basin, including spawning on a cobble/gravel shoreline of Lake Mohave; 

capture of larvae; rearing of larvae and juveniles in sanctuary coves of Lake Mohave 

and Lake Havasu, and in sanctuary ponds of the Colorado River; and the result of 

natural reproduction in the Cibola High Levee Pond. Photos from Mueller (2006, 

2007). ........................................................................................................................... 33 

Figure 18. Average daily streamflow of the Gila River near Red Rock, NM, 1930–2005; USGS 

stream gauge 09431500. .............................................................................................. 34 

Figure 19. Mesohabitat used by adult razorback suckers in (A) rivers for all seasons, (B) rivers 

by season, and (C) reservoir/river for all seasons. Data sources are cited in each figure 

and provided in Appendix A. BA=backwater, ED=eddy, GP=gravel pit, PO=pool, 

RI=riffle, RU=run, SC=side channel, SW=slackwater, IM=impoundment, MC=main 

channel. ........................................................................................................................ 42 

Figure 20. Depth used by (A) adult razorback suckers in rivers for all seasons, (B) adults in 

rivers by season, and (C) larvae in the Green River. Data sources are cited in each 

figure and provided in Appendix A. ............................................................................ 49 

Figure 21. Velocity used by (A) adult razorback suckers in rivers for all seasons, (B) adults in 

rivers by season, and (C) larvae in the Green River. Data sources are cited in each 

figure and provided in Appendix A. ............................................................................ 50 

Figure 22. Substrate used by (A) adult razorback suckers in rivers for all seasons, (B) adults in 

rivers by season, and (C) adults in all rivers and seasons. Data sources are cited in 

each figure and provided in Appendix A. SI=silt, SA=sand, GR=gravel, CO=cobble, 

BO=boulder, BE=bedrock. .......................................................................................... 51 

Figure 23. Capture locations of razorback suckers in Grand Canyon and the Lake Mead inflow.

...................................................................................................................................... 55

Figure 24. Photographs of (A) one of the last razorback suckers captured in the Colorado River 

in Grand Canyon near lower Bass Camp (RM 108) by S.W. Carothers and C.O. 

Razorback Sucker Habitat Final Report 

ix 
List of Figures April 1, 2012 

Minckley in April 1984 (Maddux et al. 1987), and (B) a razorback sucker captured by 

Bio/West biologists in April, 2010 in the Colorado River inflow below Iceburg 

Canyon. Photos courtesy of S.W. Carothers and B.A. Albrecht, respectively. ........... 56 

Figure 25. Net movement of 12 radio-tagged adult razorback suckers in lower Grand Canyon and 

Colorado River inflow, June–October, 1997 (see Table 14 for movement data). 

Release locations indicated by black circles; last contacts indicated by black 

rectangles. Map to approximate scale; river miles (RM) 240–290 (shown in boxes) are 

distances downstream from Lees Ferry. ...................................................................... 59 

Figure 26. Complex, less complex, and poor potential habitat of razorback sucker in the 

Colorado River in lower Grand Canyon, RM 179–279. Figure from Speas and 

Trammell (2010). ......................................................................................................... 62 

Figure 27. Water temperature data, RM 179–279, May 2009. Data from Speas and Trammell 

(2010). .......................................................................................................................... 62 

Figure 28. High and low water temperatures at RM 194 (Year 2004), RM 226 (Year 2009), and 

RM 246 (Year 2009) for the months January–September (GCMRC data). Ideal 

spawning temperature for the razorback sucker is 15°C (10–22°C) and ideal hatching 

temperature is 20°C (10–30°C).................................................................................... 63 

Figure 29. Lake Mead and locations of the razorback sucker populations in relationship to the 

Colorado River inflow at right of map. Figure from Albrecht et al. (2010b). ............. 64 

Figure 30. Population estimates (95% confidence intervals, CI) of the razorback sucker in (A) 

Las Vegas Bay, (B) Echo Bay, and (C) Las Vegas Bay + Echo Bay for 1996–2007. 

Data from Albrecht et al. (2008a) for the Chao Mh estimator..................................... 65 

Figure 31. Locations of sonic-tagged razorback suckers, 1997–2007, and larval capture sites, 

2000, 2001, and 2010, in the Colorado River inflow and Gregg Basin area of Lake 

Mead. Figure modified from Albrecht et al. (2008a, 2010a)....................................... 67 

Figure 32. Lake Mead elevation from January 1935 to June 2010 with the number of razorback 

suckers that were hatched each year, based on back-calculated ages as determined 

from fin ray sections. Red bars depict razorback sucker captured at the Colorado River 

inflow area in 2010 and dark bars represent numbers of fish from the cumulative longterm monitoring and aging efforts. Figure from Albrecht et al. (2010a). .................... 68 

Figure 33. Summary of all data for (A) depth, (B) velocity, and (C) substrate used by adult 

razorback suckers in rivers. Data sources are highlighted in Table 17. See Figure 22 

caption for substrate codes........................................................................................... 71 

Figure 34. Mesohabitat use by (A) radio-tagged adult razorback suckers in lower Grand Canyon, 

and (B) adult razorback suckers from all rivers, compared to (C) mesohabitat 

availability in lower Grand Canyon. See Figure 19 caption for mesohabitat codes.... 72 

Figure 35. Photos of cobble/gravel bars at (A) Diamond Creek, and (B) Spencer Canyon in lower 

Grand Canyon. Photo of Diamond Creek courtesy of Hualapai Tribe. Photo of Spencer 

Canyon taken September 18, 2010 by C. McAda when flow of the Colorado River was 

9,200–9,300 cfs. ........................................................................................................... 75 

Razorback Sucker Habitat Final Report 

x 
List of Figures April 1, 2012 

Figure 36. Photos of cobble/gravel bars (A) at Salt Creek in lower Grand Canyon, and (B) 

between Devil’s Cove and North Bay near known spawning area in the Colorado 

River inflow. Flow of the Colorado River was 9,200–9,300 cfs. Photos taken 

September 18–19, 2010 by C. McAda......................................................................... 76 

Figure 37. Comparison of distances from (A) a known spawning bar to nursery floodplains in the 

middle Green River, and (B) three potential spawning bars in lower Grand Canyon to 

known nursery areas in the Colorado River inflow to Lake Mead. Distances on vertical 

bars are approximate distances along the river channel. River miles are shown as 

blocked numbers on each map. .................................................................................... 77 

Figure 38. Photos of (A) sand backwater used by young native suckers, and (B) complex 

shoreline habitat with rocky and vegetated shoreline in lower Grand Canyon. Flow of 

the Colorado River was 9,200–9,300 cfs. Photos taken September 16, 2010 by C. 

McAda.......................................................................................................................... 79 

Figure 39. Photos of (A) eroding sand backs near Pearce Ferry, and (B) exposed Lake Mead 

shoreline and high band of vegetation used by razorback sucker larvae at higher lake 

levels. Flow of the Colorado River was 9,200–9,300 cfs. Photos taken September 19, 

2010 by C. McAda. ...................................................................................................... 80 

Figure 40. Photos of (A) Colorado River near Whitmore Wash, and (B) large rapid about 1 mi

downstream from Pearce Ferry in the Colorado River inflow. Flow of the Colorado 

River was 9,200–9,300 cfs. Photos taken September 19, 2010, courtesy of (A) J. 

Stolberg and (B) C. McAda. ........................................................................................ 82 

Figure 41. Photos of the Colorado River inflow between Devil’s Cove and North Bay showing 

(A) cobble/gravel islands used by razorback suckers, and (B) clusters of quagga 

mussels on rock substrate. Lake Mead at low elevation. Photos taken September 19, 

2010 by C. McAda. ...................................................................................................... 83 

Figure 42. Macroinvertebrate biomass as g AFDM/m2 (ash-free dry mass) and relative taxa 

composition in the three dominant habitat types (cobble, deposits, and talus) at three 

locations on the Colorado River in Grand Canyon: (A) Lees Ferry (RM 0), (B) Little 

Colorado River (RM 62), and (C) Diamond Creek (RM 225) in March 2008. Figure 

from Rosi-Marshall et al. (2010).................................................................................. 84 

Figure 43. Longitudinal cross-section of the lower Grand Canyon from Diamond Creek to Pearce 

Ferry, showing the elevational gradient of the Colorado River, the deltaic sediment 

deposits, and the approximate elevations of Lake Mead during the 1992–95 and 2004–

06 fish surveys. ............................................................................................................ 86 

Figure 44. Aerial views of the lower Grand Canyon taken in June 1992 showing (A) the deltaic 

sediments deposits and growths of riparian vegetation near Emery Fals, and (B) the 

widened river channel at the interface of the Colorado River and Lake Mead in the 

Pearce Ferry Bay. Photos by R. Valdez. ...................................................................... 86 

Figure 45. Percent of total number of fish caught by year from Diamond Creek to Pearce Ferry. 

Data for 1992–1995 from Valdez et al. (1995) and for 2004–2006 from Ackerman et

al. (2006). See Table 19 for species codes................................................................... 87 

Razorback Sucker Habitat Final Report 

xi 
List of Figures April 1, 2012 

Figure 46. Percentage of fish composition for Whitmore Wash to Diamond Creek (RM 189–

225), Diamond Creek to Bridge Canyon (RM 225–235), Bridge Canyon to Emery 

Falls (RM 235–275), and Emery Falls to below Pearce Ferry (RM 275–286) during 

1992–1995. See Table 19 for data and species codes. ................................................. 88 

Razorback Sucker Habitat Final Report 

xii 
Executive Summary April 1, 2012

EXECUTIVE SUMMARY 

The U.S. Bureau of Reclamation (Reclamation), in collaboration with the U.S. Fish and Wildlife 

Service (USFWS), is investigating the potential for establishment of the endangered razorback 

sucker (Xyrauchen texanus) in the lower Grand Canyon. This report reviews and summarizes the 

habitat used by the species in the Colorado River System. The information contained in this 

report and two other reports (Science Panel Report and Establishment Strategy) will assist 

Reclamation and the USFWS in the decision to develop an augmentation plan and release 

razorback suckers into the lower Grand Canyon. Reclamation is coordinating this investigation 

with the U.S. Fish and Wildlife Service, Glen Canyon Dam Adaptive Management Program, 

Lower Colorado River Multi-Species Conservation Program, National Park Service, Grand 

Canyon Monitoring and Research Center, Nevada Department of Wildlife, Arizona Game and 

Fish Department, and the Hualapai Tribe. 

The razorback sucker is a highly adaptable fish species capable of using a wide variety of 

habitats. It is endemic to the Colorado River System where it has managed to survive for nearly 2 

million years in perhaps the most variable and rigorous hydrological, chemical, and biological 

environment of any river in North America. This document provides an assimilation of habitat 

information and data for various life stages of the razorback sucker from throughout its range. 

Altogether, 84 scientific reports and publications were used as sources for habitat information 

from five regions of the System, including (1) the Green and Yampa rivers; (2) upper Colorado 

and Gunnison rivers, including Lake Powell; (3) San Juan River; (4) lower Colorado River, 

including the Grand Canyon, Lakes Mead, Mohave, and Havasu; and (5) the Gila, Salt, and 

Verde rivers. 

In the middle Green River, the species spawns on cobble/gravel bars in canyon-confined reaches 

and its larvae drift downstream to nurse and rear in large floodplains that are connected to the 

river by spring runoff. In the upper Colorado River and lower Gunnison River, it also uses main 

channel cobble/gravel bars for spawning, but it may use manmade features such as gravel pits as 

nurseries for young and for resting and rearing. In the San Juan River, it uses complex channel 

areas for spawning and the larvae may use small backwater-like habitats for rearing, as well as 

the inflow to Lake Powell. In the lower Colorado River Basin, razorback suckers were once 

abundant in the expansive floodplains complexes that formed with spring floods, but flood 

control and irrigation projects have disconnected and eliminated most of these floodplains, and 

some razorback suckers survive in reservoirs formed by the mainstem dams. The spring-time 

flows of the historic Colorado River inundated vast bottomlands, particularly in the lower basin, 

that provided rich productive habitats for the species and established large lake-like features as a 

component of the species’ evolutionary environment. Today, the largest remaining numbers of 

wild razorback suckers are found in lakes Mohave, Mead, and Havasu, where adults successfully 

spawn along cobble shorelines and shoals, but where survival of young is low primarily because 

of large numbers of nonnative predaceous fish. In the Salt and Verde rivers, some stocked 

individuals have been able to persist in streams with only a fraction of the water volume of the 

larger riverine habitats. 

Razorback suckers occur and persist in rivers, streams, and reservoirs of the Colorado River 

System as testimony to their adaptability to various habitat conditions. The species has 

Razorback Sucker Habitat Final Report 

xiii 
Executive Summary April 1, 2012

demonstrated an ability to establish self-sustaining populations in reservoirs, despite the presence 

of large numbers of nonnative fish predators. In Lake Mead, where shoreline spawning and 

nursery areas provide vegetation or turbidity as cover from predators, the population is 

successfully recruiting and appears to be sustained at low numbers that altogether ranged from a 

low of 91 adults in 2003–05, to a high of 413 in 2005–07. Spawning by this population occurs 

near inflows of tributaries or washes where turbidity and vegetation are present; i.e., Las Vegas 

Wash, Echo Bay, and Muddy River/Virgin River inflow. Since the year 2000, larvae and adult 

razorback suckers have also been found in the Colorado River inflow at the lower end of the 

Grand Canyon; including sonic-tagged adults moving from one of the three populations. A 

confirmed spawning site was located in 2010 about 10 mi downstream of Pearce Ferry, which is 

the lower end of the Grand Canyon. 

Expansion of the Lake Mead population into the Colorado River inflow could mean that some

razorback suckers are currently using the lower Grand Canyon. However, numerous fisheries 

investigations through the Grand Canyon, starting about the time that Glen Canyon Dam was 

completed in 1963, have yielded few razorback suckers. Since 1944, only 10 razorback suckers 

have been reported from the Grand Canyon, including one from Bright Angel Creek, four from

the mouth of the Paria River, one near Shinumo Creek, and four from the mouth of the Little 

Colorado River. All of these fish were adults, and no razorback suckers have been captured since 

1990. Most fisheries surveys of the Grand Canyon have ended at Diamond Creek, and only one 

survey in the mid-1990s and one in 2005, extended downstream of Diamond Creek to Pearce 

Ferry. These sampling efforts have failed to catch any razorback suckers, but the species could 

be present in such small numbers that the likelihood of catching an individual is low. 

A formal quantitative assessment of habitat for the razorback sucker in the lower Grand Canyon 

has not been conducted. An informal evaluation in 2009 showed that the major mesohabitat 

features used by the species in other river reaches were present, including deep runs, eddies, 

riffles, and backwaters. This suite of mesohabitats was similar to that used by 12 radio-tagged 

adults in the lower Grand Canyon in 1997. An additional visual evaluation of the area in 2010 

also showed that there are at least three large alluvial cobble/gravel bars similar to those used for 

spawning in the Green, upper Colorado, and San Juan rivers. These are located at the mouths of 

Diamond Creek, Spencer Canyon, and Salt Creek. The habitat feature used by the razorback 

sucker that is absent from the lower Grand Canyon is floodplains that are used by larvae as 

nurseries. Large off-channel embayments occur at the mouths of Surprise Canyon, Lost Creek, 

Burnt Spring Canyon, and Ticanebitts Canyon, but these are blocked from the main river channel 

by large sand berms deposited when Lake Mead was at a higher lake level. The lower Grand 

Canyon is a remote region of the Colorado River where it would be impractical to access with 

earth-moving equipment for reconnection of these bays with the main river. 

Larval razorback suckers may use small backwaters as nurseries, as in the San Juan River, but 

most use the larger floodplains. Alternatively, larvae hatched at one of the three cobble/gravel 

bars in the lower Grand Canyon would only have to drift about 32 to 55 mi, or for an estimated 

13 to 22 hr, before reaching the Colorado River inflow to Lake Mead where larvae were found in 

2000, 2001, and 2010. Studies in the Green River have shown that these distances are common 

for larvae drifting from spawning bars to nursery floodplains. 

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This review of razorback sucker habitat indicates that conditions for subadults and adults are 

suitable in the lower Grand Canyon. However, there is an absence of floodplains typically used 

as nurseries by larvae and young, although there are small ephemeral backwaters such as used by 

young in other parts of the basin. Spawning bars similar in appearance to bars used in other 

rivers are present at Diamond Creek, Spencer Canyon, and Salt Creek. Over 20 backwaters may 

be present (depending on river flows) between Lava Falls Rapid (RM 180) and Dry Canyon (RM 

265). These backwaters are presently used by large numbers native flannelmouth suckers 

(Catostomus latipinnis) and could be used by larvae and young of razorback suckers. The 

distances from these potential spawning bars in the lower Grand Canyon to capture sites of 

larvae in the Lake Mead inflow are less than 60 mi, which is similar to drift distances of larvae in 

the middle Green River.

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1.0 INTRODUCTION 

1.1 Background 

This report summarizes the habitat information for the endangered razorback sucker (Xyrauchen 

texanus) throughout its range in the Colorado River System. It describes the physical, chemical, 

and biological attributes used by the species for spawning and egg incubation; larval drift 

corridors and distances; nurseries used by young; juvenile rearing areas; food requirements; 

movement; and subadult and adult habitat. 

The information contained in this report was used to better gauge the suitability of conditions for 

the species in the lower Grand Canyon and the Colorado River inflow to Lake Mead, where the 

U.S. Bureau of Reclamation (Reclamation) has initiated an investigation of the potential to 

improve the status of the razorback sucker. This report and two companion reports (Science 

Panel Report [Valdez et al. 2012a] and Establishment Strategy [Valdez et al. 2012b]) will assist 

Reclamation, in collaboration with the U.S. Fish and Wildlife Service (USFWS), to determine if 

augmentation of the razorback sucker is appropriate and necessary for enabling the species to 

become established in the lower Grand Canyon. 

1.2 Species Description 

The razorback sucker is a large catostomid fish that is endemic to the Colorado River System

(Minckley et al. 1991). Adults attain a maximum size of about 1 m total length (TL) and a weight 

of 5–6 kg (Minckley 1983). The body is fusiform and the ventral sucker-like mouth is designed 

to feed on a variety of insects, crustaceans, and detrital matter. The body is dark, greenish-gray 

above and the belly and underside are yellowish-white. A cartilaginous ridge forms along the 

back of adults that gives the species its characteristic appearance and name (Figure 1). 

Figure 1. Adult razorback sucker. Illustration by Joseph Tomelleri. 

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1.0 Introduction April 1, 2012 

1.3 Status 

The razorback sucker is currently designated as “endangered” under the Endangered Species Act 

of 1973, as amended (ESA; 16 U.S.C. 1531 et. seq.), under a final rule published on October 23, 

1991 (56 FR 54957). A recovery plan was approved on December 23, 1998 (USFWS 1998), and 

Recovery Goals were approved on August 1, 2002 (USFWS 2002). The final rule for 

determination of critical habitat was published on March 21, 1994 (59 FR 13374), and final 

designation became effective on April 20, 1994 (see Figure 2). 

1.4 Historical Distribution 

Detailed descriptions of the historical distribution of the razorback sucker are provided by 

Minckley (1983), Bestgen (1990), and Minckley et al. (1991). The razorback sucker was once 

widely distributed at elevations of up to about 5,500 ft in rivers and major tributaries of the 

Colorado River System from Wyoming to northwestern Mexico (Figure 2). It was typically 

found in calm flat-water reaches and was historically uncommon in swift and turbulent canyon 

reaches. The species was once abundant downstream of present-day Lake Mead, particularly 

near Yuma, Arizona (Gilbert and Scofield 1898), and it was common in the Salton Sea 

(Minckley 1983). River impoundment, flow depletion, and increasing water salinity led to the 

extirpation of the species in this portion of the lower basin (Everman 1916; Coleman 1929). 

The historical distribution of the species has been reduced by about 80% primarily by the 

construction of major dams along the Colorado River (e.g., Hoover Dam in 1935, Parker Dam in 

1938, Davis Dam in 1951, and Glen Canyon Dam in 1963) and the Green River (Flaming Gorge 

Dam in 1962). These dams have fragmented the historical range of the razorback sucker and 

altered the river environment by reducing temperature, turbidity, and seasonal flow fluctuations. 

Dams of the Aspinall Unit (built in 1966–1976) on the Gunnison River are upstream of historical 

range but these further altered flow conditions in occupied reaches of the Gunnison and upper 

Colorado rivers, as did Navajo Dam (completed in 1963) on the San Juan River. 

Riverine habitat of the razorback sucker was further altered by channelization, diversion of water 

for agriculture, and the construction of dikes and levees that reduced connectivity between 

floodplain habitats and the main channel. Disconnection of floodplains reduced nutrient loads to 

the river (Junk et al. 1989) and severed access to larval nursery habitats (Tyus 1987). The biotic 

environment was affected by changes in ecosystem processes that affected food supplies and by 

the proliferation of nonnative fish predators (Miller 1961; Mueller and Marsh 2002). 

By the 1960s, the distribution, abundance, and recruitment of the razorback suckers were already 

markedly reduced in both the upper and lower Colorado River basins (Minckley et al. 1991). The 

largest river population remained in the middle Green River, Utah, and sizeable reservoir 

populations were in Lakes Mohave, Mead, and Havasu. By the end of the 1990s, populations in 

the Green River and Lake Mohave had continued to decline, and it had become necessary to 

augment these populations with fish raised in hatcheries and other artificial rearing facilities. 

More complete summaries of distributions of the razorback sucker are presented by Bestgen 

(1990), Minckley et al. (1991), and the USFWS (2002). 

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1.0 Introduction April 1, 2012 

Figure 2. Historical and present distribution of the razorback sucker with designated critical habitat in each 

of five regions of the Colorado River System. Figure adopted from Maddux et al. (1993) and Schooley and 

Marsh (2007). 

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1.0 Introduction April 1, 2012 

1.5 Present Distribution 

For the purpose of this report, the Colorado River System is divided into five geographic regions 

that are presently occupied by the razorback sucker (Figure 2). These regions are (1) the Green 

and Yampa rivers; (2) upper Colorado and Gunnison rivers, including Lake Powell; (3) San Juan

River; (4) lower Colorado River, including the Grand Canyon, Lakes Mead, Mohave, and 

Havasu; and (5) the Gila, Salt, and Verde rivers. Each of these regions has unique habitat 

features that are formed by channel geomorphology and affected by more recent water 

management systems, especially dams and reservoirs. 

There are 1,724 mi (2,776 km) of critical habitat designated for the razorback sucker in the 

Colorado River System (Figure 2; 50 CFR 13374). A description of each area of critical habitat 

within the five regions is provided in Table 1. Most areas designated as critical habitat are 

presently occupied by the razorback sucker, and in some cases, the species is found outside of 

critical habitat. The numbers of wild fish in these areas are low or non-existent and hatchery fish 

have been used to reintroduce the species to historical habitat. 

In the Green River, a few wild fish remain between the Yampa River confluence and the 

Colorado River confluence, but most are either stocked fish or progeny of stocked and/or wild 

fish. Wild fish are gone from the Yampa River and a few fish from the Green River access the 

lower reaches. Small numbers of fish may be found in the White and Duchesne rivers as 

individuals moving from the Green River. 

Wild fish are extirpated from the upper Colorado and Gunnison rivers, and hatchery fish have 

been stocked in these rivers for over two decades. Fish passage structures have been retrofitted 

onto three diversion dams of the upper Colorado River and one on the lower Gunnison River 

allowing access by the species to historical habitat. Small numbers of larvae are found annually 

in these rivers indicating some reproductive success. 

The wild population is extirpated from the San Juan River, and hatchery fish stocked since 1990 

are surviving to adults and have produced larvae annually since 1997. Several diversion 

structures have been removed or modified to allow passage as far upstream as Farmington, New 

Mexico. The upstream distribution of the species is limited by cold-water releases from Navajo 

Dam, and the downstream distribution is the inflow to Lake Powell, where some razorback 

suckers have been found in recent years. 

The razorback sucker in the Lower Colorado River Basin is found primarily in reservoirs, with a 

few individuals in short intervening reaches of river. The largest self-sustaining population of the 

species is in Lake Mead and repatriated fish inhabit Lakes Mohave and Havasu. These reservoirs 

are periodically stocked with hatchery-reared fish. Stocked fish from Lake Havasu have 

populated the river between the reservoir and Davis Dam, and the fish have spawned and 

produced larvae in this area starting in the year 2000. 

The wild razorback sucker has been extirpated from the Gila and Salt rivers. Small numbers 

remain in the Verde River, where they are stocked and occupy small reservoirs and intervening 

river reaches. 

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1.0 Introduction April 1, 2012 

Table 1. Distribution and status of the razorback sucker in critical habitat by five regions of the Colorado 

River System (USFWS 2002). 

Region Critical Habitat (total river miles) Distribution and Status 

Green River: Yampa River 

confluence to Colorado River 

confluence (345 mi) 

Largest concentration in upper basin, mainly from Split Mountain 

to Colorado River confluence; population augmented by hatchery 

fish. 

Yampa River: Cross Mountain

Canyon to Green River confluence 

(56 mi) 

Last reported in 1980s, although 1 fish caught at Lily Park in

2008; some fish access suspected spawning site in lowest reach 

from Green River. 

White River: Uintah/Ouray Indian 

Reservation to Green River

confluence (18 mi) 

Found in low numbers; upstream distribution blocked by Taylor

Draw Dam.

Green and 

Yampa Rivers 

(421.5 mi) 

Duchesne River: near Green River 

confluence (2.5 mi) 

Found as small aggregations at mouth during spring runoff. 

Upper Colorado River: Rifle, 

Colorado to Lake Powell inflow near 

North Wash (280 mi) 

Wild population extirpated; fish stocked to reestablish population; 

passage at Grand Valley, Price-Stubb, and Government Highline 

dams completed; Lake Powell inflow is downstream distribution.

Upper Colorado

and Gunnison 

Rivers (330 mi)

Gunnison River: Uncompahgre 

River confluence to Colorado River 

confluence (50 mi) 

Wild fish last found in 1970s; fish stocked in lower 34 mi to

reestablish population; Redlands Fishway allows passage since 

1996; upstream distribution limited by Hartland Diversion Dam 

and possibly cold-water releases from Aspinall Unit dams; a few 

larvae found as evidence of reproduction. 

San Juan River 

(156 mi) 

San Juan River: Hogback Diversion 

to Lake Powell inflow at Neskahai 

Canyon (156 mi) 

Wild population extirpated; fish stocked since 1990 are surviving

to adults and have produced larvae annually since 1997; diversion 

structures are being removed or modified to allow passage; Lake 

Powell inflow is downstream distribution; upstream distribution 

cold-water releases from Navajo Dam. 

Paria River confluence to Hoover 

Dam including Lake Mead at full pool 

(320 mi) 

None reported in Grand Canyon in 20 years; reproducing 

population in Lake Mead at Las Vegas Bay, Echo Bay, and the 

Muddy River/Virgin River and Colorado River inflows. 

Hoover Dam to Davis Dam

including Lake Mohave at full pool 

(52 mi) 

Stocked fish from Lake Havasu have populated the river between 

the reservoir and Davis Dam; fish spawned and produced larvae 

beginning in 2000. 

Lower Colorado

River (432 mi) 

Parker Dam to Imperial Dam

including Imperial Reservoir at full 

pool (60 mi) 

Small numbers reported. 

Gila River: AZ/NM border to

Colorado River confluence (300 mi) 

None reported in 10 years. 

Salt River: U.S. Highway 60 to

Roosevelt Diversion Dam (50 mi) 

None stocked since 1996; none reported since 1997. 

Gila, Salt, and

Verde Rivers

(385 mi) 

Verde River: U.S. Forest Service 

boundary to Horseshoe Dam 

including Horseshoe Reservoir at full 

pool (35 mi) 

Small numbers from ongoing stocking. 

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1.0 Introduction April 1, 2012 

1.6 General Life History 

The razorback sucker is the only species of the genus Xyrauchen, but it is related to the lake 

suckers of the genera Deltistes and Chasmistes, such as the Lost River sucker (D. luxatus), June 

sucker (C. liorus), cui-ui (C. cujus), and shortnose sucker (C. brevirostris) found in inland lakes 

of western North America (Miller and Smith 1981; Minckley et al. 1986). The razorback sucker 

was historically found in main-channel riverine habitats and riverside floodplains, but its 

apparent evolutionary predisposition to lake environments has enabled it to survive and 

reproduce in artificial reservoirs created by dams in the last 75 years (Mueller and Marsh 2002). 

The life history of the razorback sucker is closely linked to the highly variable conditions of the 

Colorado River System, especially streamflow and channel geomorphology that differ by river 

region and have been further modified by human intervention (Figure 3; Bestgen 1990; Muth et 

al. 2000). In the Green and upper Colorado regions, where some aspects of natural streamflow 

remain in undammed reaches, adults overwinter in deep pools and migrate to canyons to spawn 

over clean cobble bars during spring runoff (Table 2). Spawning occurs in May through June, 

and the eggs incubate 6–7 days in the spaces between cobble/gravel substrate. The larvae emerge 

and become transported downstream and entrained in floodplains that become inundated during 

spring runoff and connected to the main river channel. These floodplains are rich, productive 

nursery habitats where the young feed on plankton, insects, crustaceans, and detritus. 

Figure 3. General riverine life history strategy for the razorback sucker, including Overwinter (N-M), Migrate 

to spawning sites (M-A), Spawn (A-J), and Larvae in Floodplains (M-O). The timing of these strategies is

linked to flow and temperature and may vary by river region. Flow is mean of daily mean values for 64 years 

of record (10-01-1946 – 09-30-2010), and temperature is mean of daily mean values for 8 years of record (10-

01-1997 – 09-30-2005), USGS gage near Jensen, Utah. 

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1.0 Introduction April 1, 2012 

The timing and chronology of zooplankton development in nursery habitats is vital to the 

survival of early life stages (Modde et al. 1996). The young return to the main channel with 

receding river flows or they may become stranded in floodplains until the following year when 

these are reconnected by the flooding river. The loss or reduction of spring flow peaks together 

with channelization of the river corridor have reduced the extent of these floodplain nurseries 

and greatly reduced successful reproduction and recruitment (Muth et al. 2000). 

In reservoir environments, adults congregate and spawn in shallow gravel shorelines and 

emerging young find food and shelter from predators in complex rocky shorelines and vegetation 

(Kegerries et al. 2009). The numbers of fish predators in these reservoirs is high and in some

locations larvae are captured and raised in aquaria and isolated ponds for release back to the 

reservoir at a larger size (Marsh et al. 2005). 

Table 2. Summary of life history strategies and habitat conditions for the razorback sucker in five 

geographic regions of the Colorado River System. 

Region Spawning Nursing and Rearing Juvenile Habitat Adult Habitat 

Green and 

Yampa rivers

Broadcast eggs on

mid-channel 

cobble/gravel bars 

near spring runoff in 

early June. 

Larvae drift into newly 

inundated food-rich 

floodplains where 

they remain one to 

several months. 

Young remain in

floodplains or occupy 

main channel 

backwaters, runs, 

pools, eddies. 

Main channel runs, 

pools, eddies; may 

aggregate in

connected floodplains

or tributary mouths; 

migrate to spawning

bars in spring.

Upper Colorado 

and Gunnison 

rivers, including 

Lake Powell

Broadcast eggs on

mid-channel 

cobble/gravel bars 

near spring runoff in 

early June. 

Larvae drift into newly 

inundated food-rich 

floodplains and gravel

pits where they

remain one to several 

months. 

Young remain in

floodplains or occupy 

main channel 

backwaters, runs, 

pools, eddies. 

Main channel runs, 

pools, eddies; may 

aggregate in

connected floodplains

or gravel pits. 

San Juan River Broadcast eggs on

mid-channel complex 

cobble/ gravel islands 

near spring runoff in 

early June. 

Larvae drift into main 

channel small 

backwaters and 

embayments; some

drift into Lake Powell. 

Main channel 

backwaters, runs, 

pools, eddies. 

Main channel runs, 

pools, eddies. 

Lower Colorado 

River, including 

Grand Canyon,

Lakes Mead, 

Mohave, and

Havasu

Broadcast eggs on

rocky lake shores 

from February to 

April. 

Larvae emerge and 

remain along 

shorelines where 

subject to predation; 

larvae may be 

captured and raised 

in aquaria and ponds. 

Use variety of 

reservoir habitats; few 

wild juveniles survive

because of large 

predators. 

Use variety of 

reservoir habitats; 

found mostly in and 

near bays and 

inflows. 

Gila, Salt, and 

Verde rivers 

Little natural 

reproduction in small 

streams. 

Larvae may drift into 

reservoirs where 

subject to predation. 

Pools, runs, eddies of

small streams.

Pools, runs, eddies of

small streams.

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1.7 Relationship of Life Stages to River Geomorphology 

The life history and habitat of the razorback sucker in the Colorado River System are closely 

linked to stream flow and river geomorphology. High spring flows annually stimulate instream

production and reshape the channel while cleansing spawning areas of fine sediments. Relatively 

steady summer and winter flows provide stable, productive environments for all life stages. A 

history of variable flows has carved deep canyons and shaped the channel geomorphology that 

provides clean cobble/gravel bars for spawning and productive floodplains for nurseries. 

The most striking feature of the Colorado River is its gradient; i.e., drop in elevation from its 

headwaters in the states of Colorado and Wyoming to its delta in the Gulf of Lower California. 

The Colorado River has the greatest descent of any river in North America with an average drop 

of about 7.5 ft per mi (average gradient of 0.0014; Reclamation 1946). It originates at about 

15,000 ft elevation and has a length of about 1,500 mi. Below about 5,500 ft elevation, the river 

is a warm to temperate stream with a channel that varies from reaches confined by steep canyon 

walls to reaches that are open and meandering. The longitudinal gradient of the river is not 

continuous, but is characterized by intervening reaches with different channel slopes. In general, 

low-gradient reaches have sandy substrates and high-gradient reaches have gravel, cobble, and 

boulder substrates (Schmidt 1996). High to moderate-gradient reaches provide rocky substrate 

used by the razorback sucker for spawning, while low-gradient reaches often have riverside 

floodplains used as nurseries during spring runoff. The longitudinal gradient of the river, 

combined with temperature and productivity, greatly influenced the historical distribution of the 

razorback sucker in the Colorado River System, but the river continuum has been disrupted by 

especially the dams and reservoirs of the last 100 years. 

The average channel gradient for each reach of the five occupied river regions below about 6,000 

ft elevation is presented in Table 3 and illustrated in Figures 4 and 5 (Reclamation 1946). 

Information is also presented on use by various life stages of the razorback sucker in each reach. 

This presentation illustrates the importance of channel gradient and substrate to the various life

stages of the species in a riverine setting. Generally, spawning takes place in moderate to steep 

channel gradients, such as in canyon reaches, where cobble/gravel bars are kept relatively clean 

of fine particles that otherwise may suffocate eggs and embryos. Examples of this spawning 

activity in higher gradients are spawning bars at the lower end of Split Mountain Canyon and in 

Desolation Canyon of the Green River; below Palisade on the upper Colorado River; and the 

middle reach of the San Juan River. Larvae and young nurse and rear in quiet productive 

floodplains in low-gradient reaches including Jensen to Sand Wash of the Middle Green River; 

and below Palisade of the upper Colorado River. An exception to this relationship is the use and 

apparent survival by young razorback suckers in moderate-gradients of the San Juan River. 

In the lower Colorado River, where the main channel and tributaries have been fragmented by 

dams and reservoirs, the razorback sucker is found primarily in lake environments. Wild fish 

have persisted for about 40 years in major reservoirs of the lower basin, which is equal to about 

the longevity of the species in the wild. These reservoirs appear to simulate large floodplains 

used historically by the species, but reproduction and recruitment are dampened by a large suite 

of predators. Spawning in these reservoirs occurs along open windswept shores over rocky 

substrates, but emerging larvae and developing young are highly susceptible to predation. 

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Table 3. Channel gradient of various reaches of the five regions of the Colorado River System and current 

use by the razorback sucker. Gradients were classified as relatively Low (L<5 ft/mi), Moderate (H=5-8 ft/mi), 

and High (H>8 ft/mi). This table corresponds to Figures 4 and 5 which illustrate each reach.

River Region Reach Gradient1 Current Use 

Flaming Gorge Dam 

to Split Mountain 

M-H: 5.2–20.1 ft/mi 

(0.0010–0.0038) 

Little use of lower end and intervening lowgradient parks for residence and over-winter.

Split Mountain to 

Sand Wash 

L-M: 1.1–4.8 ft/mi 

(0.0002–0.0009) 

High use by all life stages: spawn on

cobble/gravel bars, larval drift throughout, 

entrainment and nursery in productive riverside 

floodplains that flood in spring.

Desolation Canyon

(Sand Wash to

Green River) 

H: 9.8 ft/mi 

(0.0018) 

Little use by adults, subadults; suspected 

spawning on cobble/gravel bars. 

Green River2

Green River to

Colorado River 

confluence 

L: 1.1–2.1 ft/mi 

(0.0002–0.0004) 

Little use by adults, subadults; high use by 

larvae and age-0; suspected spawning on

cobble/gravel bars; little access to riverside 

floodplains isolated by high berms and channel 

incising. 

Rifle to Palisade M: 7.7 ft/mi 

(0.0015) 

Moderate use by adults; access from 

downstream recently restored by fish passage

over dams; channel with oxbows and flooded 

gravel pits as potential nursery areas. 

Palisade to Moab M: 5.1 ft/mi 

(0.0010) 

High use by adults and larvae in upper areas; 

suspected spawning on cobble/gravel bars; 

numerous flooded gravel pits for nurseries; 

recently augmented with stocked fish. 

Moab to Green 

River confluence 

L: 2.3 ft/mi 

(0.0004) 

Low use by adults; low-gradient sand channel 

with riverside floodplains isolated by high berms 

Cataract Canyon H: 10 ft/mi 

(0.0019) 

No use by any life stage reported. 

Upper Colorado 

River3

Lake Powell

-- 

Low use by adults, subadults, young, especially 

in San Juan and Colorado River inflows; deep

reservoir with steep cliff shorelines reduces 

potential for spawning as in Lakes Mead, 

Mohave. 

Navajo Dam to 

Animas River 

H: 9.2 ft/mi 

(0.0017) 

No use by any life stage reported. 

Animas River to 

Bluff 

M: 7.4 ft/mi 

(0.0014) 

Moderate-gradient rock channel with some

complex reaches used by juveniles and adults 

year-around and for spawning; population

augmented through stocking.

San Juan River4

Bluff to Clay Hills 

(Lake Powell inflow) 

H: 8.3 ft/mi 

(0.0016) 

High-gradient confined rock channel; drifting

larvae use backwaters and embayments; some 

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River Region Reach Gradient1 Current Use 

drift into Lake Powell inflow. 

Grand Canyon

(Glen Canyon Dam 

to Lake Mead 

inflow) 

H: 15.4 ft/mi 

(0.0029) 

High-gradient rocky canyon; few floodplains,

some large backwaters; small numbers of 

adults found. 

Lake Mead

-- 

Only self-sustaining population left; spawn on 

cobble shores in bays and inflows; larvae use 

vegetation to escape predation. 

Lake Mohave

-- 

Few wild fish remain; program to rehabilitate

larvae has helped but number of wild adults 

continues to decline. 

Lake Havasu

-- 

Fish stocked in Lake Havasu successfully 

spawn in river between Davis Dam and Lake

Havasu. 

Lower Colorado 

River3

Below Parker Dam 

-- 

Fish stocked below Parker Dam; large numbers 

of oxbows and floodplains; some restoration;

river above delta intermittent.

AZ/NM Line to San 

Carlos Lake 

H: 12.4 ft/mi 

(0.0023) 

Fish reported historically; no current use by any 

life stage reported. 

Coolidge Dam to 

Salt River 

H: 8.7 ft/mi 

(0.0016) 

Fish reported historically; no current use by any 

life stage reported; river intermittent at times.

Salt River to 

Colorado River 

confluence 

L: 3.5 ft/mi (0.0007) Fish reported historically; no current use by any 

life stage reported; river intermittent at times.

Salt River -- Low survival of stocked fish; few fish remain.

Gila River3

Verde River -- Fish stocked annually with some survival in 

reservoirs. 

1 Channel gradient is measured as the length of the river center in its meander divided by the drop in elevation 

2Muth et al. (2000) 

3Reclamation (1946) 

4 Brandenburg and Farrington (2009) 

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Figure 4. Longitudinal profiles for the Green River, Upper Colorado River, and San Juan River. Average 

channel gradient by reach is indicated (except for reservoirs), and level of use by life stage of razorback 

sucker is shown with color-coded pies. See Table 3 for additional information. River profiles and distances 

from Reclamation (1946) and use by life stage in Green and Upper Colorado rivers from LaGory (2003). 

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1.0 Introduction April 1, 2012 

Figure 5. Longitudinal profiles for the Lower Colorado River and Gila River. Average channel gradient for 

each river reach is indicated (except for reservoirs), and level of use by life stage of razorback sucker for 

each reach is shown with color-coded pies. See Table 3 for additional information. River profiles and 

distances from Reclamation (1946). 

Razorback Sucker Habitat Final Report 

12 
2.0 Habitat Characteristics and Management by River April 1, 2012

2.0 HABITAT CHARACTERISTICS AND 

MANAGEMENT BY RIVER 

2.1 Green River 

The Green River is the largest tributary of the Colorado River. It originates in western Wyoming 

and flows south 730 mi to its confluence with the Colorado River in southeastern Utah (Figure 

6). The Green River is impounded by Flaming Gorge Dam, about 410 mi upstream from the 

confluence, and by Fontenelle Dam further upstream. Flaming Gorge Dam strongly affects river 

flow patterns, sediment load, and water temperature of the Green River. These effects are 

somewhat moderated by the seasonally variable, sediment-laden, warm waters of the unregulated 

Yampa River about 65 mi downstream from the dam (Muth et al. 2000). 

Figure 6. Three reaches of the Green River below Flaming Gorge Dam, Utah. Figure modified from Muth et 

al. (2000). 

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2.0 Habitat Characteristics and Management by River April 1, 2012

The annual hydrographs of the Green River (Figure 7) above the confluence (at Greendale, Utah, 

in red) and below the confluence (at Jensen, Utah, in purple) are compared with the hydrograph 

from the Yampa (at Deerlodge Park, Colorado, in blue) and a composite hydrograph combining 

flows from Greendale and Deerlodge Park (in turquoise). This composite of hydrographs shows 

that the flow at Jensen, on average, approximates the sum of the flows at Greendale and 

Deerlodge. The hydrographs also demonstrate the differences between the highly regulated 

Green River and the unregulated Yampa River. Tributaries further downstream, such as the 

White, Duchesne, Price, and San Rafael rivers, also help to mitigate the effects of Flaming Gorge 

Dam. This pattern influences the occurrence of the razorback sucker, which is largely restricted 

to the portion of the Green River downstream of the Yampa River confluence. 

Figure 7. Comparison of annual hydrographs for average daily streamflow of the Yampa River at Deerlodge 

Park and the Green River at Greendale and Jensen, Utah (1982–1994). Figure from Roehm (2004). 

Stream flow characteristics of the Green River below Flaming Gorge Dam were described by 

Muth et al. (2000) for three major reaches delimited by large tributaries (Figure 6, Table 4). The 

reach between the dam and the Yampa River has a regulated flow pattern with significant withinday variation, cold water temperatures (4–13oC) and low sediment load. The middle Green River 

between the Yampa River and the White River has a more natural flow and sediment regime

because of inputs from the Yampa River. The reach includes two canyon segments with a steep 

gradient, cobble/gravel substrate, and numerous rapids and debris fan-eddy complexes, as well as 

open parks and a long gentler meandering segment. The lower Green River consists primarily of 

a low-gradient channel with numerous sandbars and a canyon-bound segment with abundant 

gravel bars and banks composed of coarse debris-flow material or talus. 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Table 4. Stream characteristics of the three major reaches of the Green River below Flaming Gorge Dam. 

Information from Muth et al. (2000).

Reach Extent Description

1. Upper 

Green 

River 

Flaming Gorge Dam to 

Yampa River confluence (65 

mi) 

Straight to meandering channel. Except for Browns Park, channel 

confined by adjacent steep-walled canyons. Except for minor

contributions from tributary streams, flow pattern regulated by 

Flaming Gorge Dam, with significant within-day variation. Cold water 

temperatures (4–13oC) and low sediment load. 

Yampa River confluence to 

White River confluence (99 

mi) 

More natural flow and sediment regime than Reach 1 because of 

inputs from the Yampa River, which contributes about 2,000 cfs 

discharge and 1.9 million tons of sediment. This reach includes four 

segments: 

Whirlpool Canyon 

(11 mi) 

Canyon-bound with channel slope of about 0.002. Numerous rapids

and debris fan-eddy complexes. Gravel/cobble substrates. 

Island, Rainbow, and 

Little Rainbow Parks 

(7 mi) 

Open, with multiple channels and vegetated islands common. 

Relatively low channel gradient (about 0.0009). Sand substrate.

Split Mountain Canyon 

(7 mi) 

Canyon-bound with steeper river gradient (about 0.0038). 

Boulder/cobble/gravel substrates. 

2. Middle 

Green 

River 

Segments 

Uinta Basin (71 mi) Predominantly restricted meanders. Gradient from 0.0009 below Split 

Mountain Canyon to about 0.0003 downstream. Bed materials 

primarily sand with cobble alluvial fans. Vegetated and unvegetated 

islands common. Contains inundated floodplains. 

White River confluence to

Colorado River (245 mi)

The White and Duchesne rivers join the Green River in the Uinta 

Basin and add about 1,095 cfs discharge and about 4.9 million tons

of sediment per year to the mainstem. This reach includes four 

segments: 

Uinta Basin (21 mi) Low gradient (about 0.0002). Numerous sandbars at low flow and 

prominent low-elevation floodplain areas. 

Gray and Desolation 

Canyons (94 mi) 

Abundant gravel bars and banks composed of coarse debris-flow 

material or talus. Prevalent recirculating eddies and regions of 

stagnant flows. Average channel gradient canyons about 0.001, and

bed material ranges from sand in the upper portion and in the 

recirculating eddies to cobbles and boulders in the riffles and rapids 

formed by debris fans. The Price River is the largest tributary. 

Broad Valley (39 mi) Primarily restricted meanders, with some straight channels. Gradient 

is about 0.0004. Bed material ranges from sand to gravel and cobble. 

The San Rafael River is the largest tributary.

3. Lower 

Green 

River 

Segments 

Labyrinth and 

Stillwater Canyons 

(92 mi) 

Sinuous river channel with a relatively mild gradient of about 0.0002.

Bed material predominantly sand, with numerous emergent sand

bars at low flow. 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Fish sampling of the Green River began in the late 1960s, and from that period through the 1990s 

adult razorback suckers were found distributed throughout flat-water sections from the mouth of 

the Yampa River downstream to the Colorado River, with greatest concentrations generally 

between the Yampa and Duchesne rivers (e.g., McAda and Wydoski 1980; Tyus 1987; Modde 

and Wick 1997). This portion of the Green River provides a full complement of suitable riverine 

habitat, including spawning bars and downstream nurseries in the form of inundated floodplains 

to support all life stages of the razorback sucker. However, little or no evidence of successful 

reproduction and recruitment was found, and it was determined that principal causes were 

disconnection of floodplains from the main channel during all but the highest flows and the 

presence of large numbers of fish predators in these floodplains. 

In 1989, the middle Green River population of adult razorback suckers was estimated at 948 

adults (95% confidence interval: 758–1,138; Lanigan and Tyus 1989). Less than 10 years later, 

Modde et al. (1996) estimated this population at 524 adults, and characterized it as being stable 

or declining slowly with some evidence of recruitment. They attributed this suspected 

recruitment to unusually high spring flows during 1983–1986 that inundated portions of the 

floodplain used as nurseries by young fish. By the year 2000, Bestgen et al. (2002) estimated that 

the population of wild adult razorback sucker in the middle Green River was only about 100. 

Between 1993 and 1999, the abundance of the razorback sucker in the middle Green River 

dropped to a level comparable to that in the lower Green River (Bestgen and Haines 2010), 

where only a few larvae and juveniles were captured, indicating probable spawning in the 

vicinity of the San Rafael River confluence (Gutermuth et al. 1994; Chart et al. 1999; Muth et al. 

2000). In the last two decades, augmentation has helped to rebuild population numbers 

throughout the Green River and stocked fish are being found in spawning areas with wild fish, 

indicating an incorporation of hatchery fish into the remaining wild stock.

The life history of the razorback sucker in the middle Green River is closely linked to river flow 

and geomorphology, as is illustrated in Figure 8. Adults migrate in spring to spawn at a 

cobble/gravel bar below Split Mountain Canyon. The broadcast eggs incubate 6–7 days and 

emerge as tiny larvae about 0.7 in. long. Following emergence, the larvae are transported 

downstream by river currents during high flows and become entrained in floodplains (Hedrick et 

al. 2009). These inundated floodplains are important nursery habitats for larvae and juveniles 

(Wydoski and Wick 1998; Valdez and Nelson 2004). 

Ideally, juvenile razorback suckers would be able to mature in the floodplains for 12 to 24 

months before returning to the main channel during high flows (Valdez and Nelson 2004). 

However, despite the presence of wild larvae in floodplains, few appear to survive to be 

juveniles and recruitment to the adult population remains low or nonexistent (Modde 1997; Muth 

et al. 2000; Modde and Fuller 2002; Hedrick et al. 2009). Low survival in these floodplains is 

attributed to large numbers of nonnative fish that prey upon these larvae (Christopherson et al. 

2004). Bestgen et al. (2002) also suggested that negligible recruitment of razorback suckers in 

the Green River is related to reduced availability of warm, productive floodplain habitat in 

spring, a mismatch in timing of availability of larvae and inundated floodplains, and the presence 

of large numbers of nonnative species that prey on the early life stages of the razorback sucker. 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Spawn on Cobble/Gravel Bar 

(below Split Mtn. Canyon) 

Nursery Floodplains for Drifting Larvae 

(Horseshoe Bend) 

Floodplains, Subadult and Adult Habitat 

(Leota Bottom—Ouray NWR)

Figure 8. A 71-mi reach of the upper Green River in Utah, from Split Mountain Campground (RM 199) to 

Ouray (RM 128) with key life history aspects for the razorback sucker, including: spawn on a cobble/gravel 

bar below Split Mountain Canyon; nursery floodplains for drifting larvae at Horseshoe Bend; and floodplains 

and subadult and adult habitat near Leota Bottom, Ouray National Wildlife Refuge. Photos courtesy of U.S. 

Fish and Wildlife Service. 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Management efforts on the Green River beginning in 1997 have included breaching levees 

between the main channel and floodplains to allow entrainment of razorback sucker larvae 

during high flows (Figure 9; Crowl et al. 2002; Hedrick et al. 2009). Management strategies also 

involve the draining of some floodplains every few years to kill all nonnative fish and to “reset” 

floodplain productivity (Valdez and Nelson 2004; Modde and Haines 2005). This strategy 

appears to be effective as densities of nonnative fish were much lower in reset floodplains than in 

floodplains with residual fish populations (Modde and Haines 2005). Larval razorback suckers 

stocked into floodplains that had not been reset had little or no survival (Birchell and 

Christopherson 2004), but enclosure experiments showed that larvae stocked at densities ranging 

from 400 to over 4 million per acre could survive and grow at nonnative fish densities found 

under reset conditions (Christopherson et al. 2004; Brunson and Christopherson 2005).

Another important aspect of allowing floodplains to dry and reset is the large amount of 

productivity that takes place in these habitats as a principal food source for the larvae. Newly 

inundated floodplains surge with populations of zooplankton that undergo a chronology of taxa 

and sizes synchronous with the arrival of developing larvae. Larvae arriving at floodplains have 

a small terminal mouth that increases in size with growth and eventually becomes subterminal. 

Zooplankton populations in newly inundated floodplains undergo a chronology of development 

from small forms such as rotifers, to medium-size copepods, and finally to large cladocerans and 

bottom-dwelling immature insects. The arrival of drifting larvae and development of their mouth 

parts must coincide with the development of this zooplankton and benthic community or the 

young fish will starve (Papoulias and Minckley 1990). 

Given the importance of inundated and connected floodplains as nurseries for drifting razorback 

sucker larvae, the upper Colorado River Endangered Fish Recovery Program has an ongoing 

agreement with Reclamation to provide a spring-runoff research flow request. A request is made 

annually for timing and magnitude of releases from Flaming Gorge Dam on the Green River to 

correspond with high flows from the Yampa River (about 65 mi downstream) in order to 

maximize flow stage and floodplain inundation. This management action emphasizes the 

importance of floodplains as nurseries in the Green River. 

Adult razorback suckers are known to migrate long distances (>50 mi) to spawn in spring, but 

they may remain within a localized river reach for the remainder of the year (Tyus and Karp 

1990; Modde and Wick 1997). In spring, fish from the lower and middle Green rivers may move 

upstream for nearly 100 mi to a spawning bar located at the base of Split Mountain Canyon. It 

appears that hatchery fish are exhibiting movement patterns of wild fish; for example, a hatchery 

fish stocked in 2004 near the town of Green River, Utah, was captured about 285 mi upstream in 

the Yampa River near Lily Park in April 2008 (Upper Colorado River Endangered Fish 

Recovery Program 2009). 

Conversely, adult razorback suckers overwintering in the Green River are mostly sedentary, 

remaining within a 1- to 3-mi reach of river with small, local movements between mesohabitats, 

each of which may be occupied for several hours at a time (Valdez and Masslich 1989). Flow 

fluctuations cause razorback suckers to move between habitats, and flow recommendations for 

Flaming Gorge Dam call for low, steady winter flows to minimize stress to razorback suckers 

(Muth et al. 2000). 

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2.0 Habitat Characteristics and Management by River April 1, 2012

B

A 

Figure 9. Floodplains of the middle Green River, Utah, managed to entrain drifting razorback sucker larvae 

at (A) Horseshoe Bend connected with the river through a 1,000 ft wide levee breach, and (B) Brennan 

Bottom, with three small levee breaches shown as connections between the river channel and the floodplain. 

Photos courtesy of U.S. Fish and Wildlife Service. 

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2.0 Habitat Characteristics and Management by River April 1, 2012

2.2 Yampa River 

The Yampa River is the largest tributary of the Green River. It originates in northwestern 

Colorado and flows approximately 200 mi in a westerly direction to join the Green River in 

northeastern Utah. Because the Yampa River has not been substantially altered by waterdevelopment projects, it still experiences spring peak flows from melting snowpack (see 

Figure 5), undergoes seasonal temperature patterns, and carries sediment concentrations that 

resemble historical loads. Spring runoff typically begins as early as mid-March and declines no 

later than mid-July, with peak flows occurring between April and June (Roehm 2004). 

The Yampa River below 6,000 ft elevation comprises both relatively high-gradient canyon 

reaches dominated by boulder, cobble, and gravel substrates and lower-gradient reaches of 

meandering canyons and open valleys dominated by finer substrates (Tyus and Karp 1989). 

Modde et al. (1999) divided the Yampa River between Craig, Colorado, and the confluence with 

the Green River into eight reaches. The lowest three reaches, from the Little Snake River 

confluence at Lily Park to the Green River at Echo Park are shown in Figure 10 and briefly 

described in Table 5. Significant amounts of sediment (2.5 million tons on average) are carried 

by the river through lower Yampa Canyon each year (O’Brien 1987). 

Figure 10. Yampa River reaches from the Green River confluence at Echo Park upstream to the Little Snake 

River confluence at Lily Park, Colorado. Figure from Muth and Nesler (1993). 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Table 5. Yampa River reaches from the Green River confluence at Echo Park upstream to the Little Snake 

River confluence at Lily Park, Colorado. Information from Modde et al. (1999).

Reach River Mile Extent Description

1 0.0–20.0

Harding Hole to Green River 

Confluence at Echo Park (20 mi) 

A medium-gradient canyon-bound reach, consisting

of run, riffle, and pool habitat, with boulder, gravel, 

and sand substrate. 

2 20.0–45.0

Deerlodge Park to Harding Hole

(25 mi) 

A high-gradient canyon-bound reach, consisting of

run, riffle and pool habitat, with boulder and gravel

substrate. 

3 45.0–51.0 Little Snake River confluence at 

Lily Park to Deerlodge Park (6 mi) 

A low-gradient open-valley reach, consisting of run 

and riffle habitat, with gravel and sand substrate. 

One razorback sucker spawning bar was historically identified about 0.25 mi upstream from the 

mouth of the Yampa River and another about 1.35 mi further upstream (Seethaler et al. 1979; 

McAda and Wydoski 1980; Tyus and Karp 1990). The principal spawning bars used today are on 

the Green River at the southern boundary of Dinosaur National Monument upstream of Jensen, 

Utah (Tyus and Karp 1990; Hedrick et al. 2009) and upstream of Ouray, Utah (Tyus 1987). 

In the Green River, spawning is triggered by a sharply ascending hydrograph and, to a lesser 

degree, by rising water temperatures (Modde and Wick 1997; Muth et al. 1998). The response of 

razorback suckers to the rising hydrograph may serve to synchronize spawning activity with 

floodplain development and food availability (see description of zooplankton and benthic 

community chronology in section 2.1). 

To facilitate spawning activity, flow recommendations for Flaming Gorge Dam call for timing 

peak releases from the dam to coincide with peak flows from the Yampa River to maximize the 

spring peak, mimic the natural hydrograph, and inundate riverside nursery floodplains (Muth et 

al. 2000). Larval razorback sucker are caught annually in the Green River between Jensen and 

Ouray as evidence of successful reproduction under these flows. 

2.3 Upper Colorado River 

The upper Colorado River originates in the Rocky Mountains of central Colorado (Figure 11). Its 

principal tributaries are the Gunnison River and the Dolores River, which originate in San Juan 

Mountains of southern Colorado. Discharge, streamflow pattern, temperature, and turbidity of 

these rivers are affected by numerous diversions and dams. The larger storage dams are located 

some distance upstream from habitat occupied by the razorback sucker and the effect to the 

hydrograph is primarily a reduction in high spring runoff flows. As with the Green River, this 

reduction in spring flow has disconnected nursery floodplains from the main river channel. In 

reaches occupied by the razorback sucker, the annual hydrographs of these rivers are dominated 

by snowmelt runoff with high flows that usually begin in late April, reach a peak in late May or 

early June, and wane through July (Pitlick et al. 1999; Figure 12). 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Figure 11. Upper Colorado River from Lake Powell to Debeque, Colorado. Figure from Valdez et al. (1982). 

Figure 12. Average daily streamflow of the Colorado River near Cameo (09095550) for the pre-dam period 

1934–1949 and for the post-dam period 1950–1998. Figure from Van Steeter and Pitlik (1998). 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Formal sampling for razorback suckers in the upper Colorado and Gunnison rivers began in the 

1960s (Minckley et al. 1991). Since that time, razorback suckers have been captured in at least 7 

of the 11 strata described in Table 6 (Taba et al. 1965; Holden 1973; Valdez et al. 1982; Modde 

et al. 1995; Osmundson 2001), although the majority of razorback suckers have been captured in 

the Grand Valley area (Stratum I) (McAda and Wydoski 1980; Valdez et al. 1982; Osmundson 

and Kaeding 1989a; Osmundson and Seal 2009). This stratum is generally divided into the “15-

Mile Reach,” which extends upstream from the Gunnison River confluence, and the “18-Mile 

Reach,” which extends downstream from the confluence. An inventory of bottomland 

(floodplain) habitats along the upper Colorado River showed that the best quality bottomlands 

were located in the 15-Mile and 18-Mile reaches, as well as near Debeque, Colorado (Irving and 

Burdick 1995). The 15-Mile and 18-Mile reaches also contain numerous off-channel gravel pits 

that fill with water during high flows and are often connected to the river. 

The numbers of razorback suckers captured in the upper Colorado River decreased dramatically 

after about 1975. During a 3-year period (1979–1981), Valdez et al. (1982) captured only 52 

individuals, all old adults, in a 289-mi reach of the Colorado River from Hite Marina, Utah, to 

Rifle, Colorado. Between 1984 and 1990, only 12 individuals, including some in reproductive 

condition, were captured in the Grand Valley, and none were reported anywhere in the upper 

Colorado River from the mid-1960s to about 1990 (Osmundson and Kaeding 1991). 

The last putative wild razorback sucker recorded from the upper Colorado River was captured in 

1998 in the 18-Mile Reach (Osmundson and Seal 2009). All razorback suckers captured since 

then have been stocked fish or (presumably) originated from larvae of stocked fish. While 

reproduction occurs, no evidence of recruitment in the Upper Colorado River Subbasin has been 

identified since the 1960s (Burdick 1992; McAda 2003). As in the Green River, the lack of 

recruitment is thought to be the result of reduced availability of productive, warm-water 

floodplain habitats and the presence of large numbers of piscivorous nonnative fishes (Burdick 

1992). 

Radiotelemetry studies in 1986–1988 showed that most razorback suckers in the Grand Valley 

stratum spent much of the year in the 18-Mile Reach but moved into the 15-Mile Reach in the 

spring to spawn (Osmundson and Kaeding 1989a). During high spring flows native fish used 

inundated, off-channel gravel pits, presumably to rest, feed, and stage for reproduction, and 

spawn. Eighty percent of razorback suckers captured in two gravel pits (Walter Walker Wildlife 

Area gravel pit in the 18-Mile Reach and Clifton Ponds in the 15-Mile Reach) displayed late 

stages of sexual maturity, although the predominately silt substrate in the pits did not appear to 

provide suitable spawning habitat (Valdez et al. 1982). 

Razorback suckers and other native fish likely use gravel pits as surrogate habitats for the natural 

floodplains that were once much more common along the upper Colorado River. However, the 

predator load in gravel pits is heavy, with nonnative fish occupying the pits year-round, while 

native fish move in and out of the pits seasonally (Valdez et al. 1982; Burdick et al. 1997; 

Burdick 2002). Resident populations of nonnative fish in these gravel pits become sources of 

predators and competitors for mainstem habitats otherwise used by the native fishes. 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Table 6. Upper Colorado River strata from Hite Marina at Lake Powell, Utah, upstream to Rifle, Colorado. 

Table adopted from Valdez et al. (1982).

Stratum Extent Stream Characteristics

A Hite Marina – Rapid 27 (32 mi) Lake Powell: Canyon-bound with slow current. 

B 

Rapid 27– Spanish Bottom (13 

mi) 

Cataract Canyon: Steep canyon walls and talus slopes. Habitat deep, 

swift runs; many rapids and large eddies; some deep pools and 

backwaters. 

C 

Spanish Bottom – Potash (50 

mi) 

Meandering channel with wide floodplain. Habitat mostly shallow runs 

with many backwaters. Substrate mostly sand and sand-silt. Banks 

overgrown with tamarisk. Green River confluence in this reach. 

D Potash – Big Bend (24 mi) Open valley near Moab. Habitat mainly runs; eddies and backwaters 

common. Substrate mostly sand-silt. Banks overgrown with tamarisk. 

E 

Big Bend – Onion Creek (15 

mi) 

Steep canyon walls with intermittent open valleys. Habitat mostly 

deep, slow-flowing runs and pools over sand-rock substrate. Few 

eddies and backwaters. 

F 

Onion Creek – Agate Wash (25 

mi) 

Meandering, slow runs and eddies; few backwaters. Substrate mostly 

rock and sand or rock and sand-silt. Dolores River confluence in this 

reach. 

G Agate Wash – Westwater (14 

mi) 

Westwater Canyon: Confined channel; deep runs, eddies and pools. 

Numerous rapids. 

H 

Westwater – Loma (29 mi) Ruby and Horsethief Canyons: Meandering channel through 

alternating high walls and open parks. Habitat generally runs, some

eddies and pools, few backwaters. Substrate generally gravel and 

rubble with sand-silt deposits. In the Black Rocks segment, channel 

narrow and deep, with deep eddies, pools and runs, few backwaters. 

I 

Loma – Palisade (31 mi) 18-Mile Reach and 15-Mile Reach: Meandering channel through 

Grand Valley, alternating between singlet and multiple channels. 

Average gradients of 15-Mile and 18-Mile reaches are 0.00175 are 

0.0013, respectively. Substrate predominately cobble- and gravel, 

banks and floodplain mostly fine sand and silt with dense vegetation. 

Some banks artificially modified by levees and riprap. Numerous

vegetated gravel islands and inundated commercial gravel pits. 

Habitat mostly runs and riffles with some eddies, backwaters, and 

side channels. 

J 

Palisade – Debeque (25 mi) Debeque Canyon: Includes Price-Stubbs Dam, Government Highline

Dam (recently fitted with fish passage) Banks rip-rapped with boulders 

in many places. Habitat mostly swift runs with small pools and eddies, 

few backwaters. Substrate mostly gravel, rubble, and boulders. 

X 

Debeque – Rifle(31 mi) Meandering channel through open valleys and foothills. Habitat 

shallow- to moderate-depth runs and riffles with numerous pools and 

eddies. Backwaters uncommon. Substrate mostly gravels, rubble, 

boulders with some sand-silt deposits. 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Management actions and recommendations along the upper Colorado River include restoring 

floodplain habitats by breaching levees that separate floodplains from the main channel and 

recontouring off-channel, gravel-pit ponds to promote complete draining during low water and 

elimination of nonnative fishes (Burdick et al. 1997; Burdick 2002; Valdez and Nelson 2006). In 

addition to habitat restoration, management actions include augmentation of late summer/fall 

base flows; spring peak enhancement; fish passage through diversion dams; nonnative fish 

removal; and propagation and stocking of endangered fishes (USFWS 1999). Between 1999 and 

2007, a total of 78,723 juvenile, sub-adult, and adult razorback suckers were stocked in the upper 

Colorado River, primarily in the 15-Mile and 18-Mile reaches (Osmundson and Seal 2009). Until 

recently, the Price-Stubb Diversion Dam (11 mi upstream of Palisade, Utah) blocked upstream

movement of fish, and the Grand Valley Diversion Dam (8 mi upstream of Palisade) blocked 

upstream movement of fish seasonally (Osmundson et al. 1995). Both dams have now been 

equipped with fish passage structures—Grand Valley Diversion Dam in 2005 and Price-Stubb 

Diversion Dam in 2009—and the species has regained access to historical habitat. 

2.4 Gunnison River 

The Gunnison River flows approximately 180 mi in a northwesterly direction through Colorado 

from its headwaters in the San Juan and Elk Mountains to its confluence with the Colorado River 

at the City of Grand Junction in western Colorado (see Figure 11). Milhous (1995) characterized 

the lower Gunnison River (below Delta, Colorado, at RM 56) as being a cobble and gravel river, 

with considerable sand and fine sediment on and amongst the cobbles and gravel. Since 1918, 

the Redlands Diversion Dam (2.3 mi upstream from the mouth of the river) had blocked 

upstream movement of fish in the Gunnison River, and in 1996, a fish passageway was installed 

that allows upstream movement of selected species. Below the Redlands Diversion Dam, the 

habitat is composed mostly of long, laminar runs, with few side channels and deep pools 

(Burdick 1997). The average gradient in this reach is about 7 ft/mi. Streamflow of the Gunnison 

River is affected by upstream dams and diversions, such that spring peak flows have been 

reduced and summer and winter base flows have been increased (Figure 13). 

Above Redlands Diversion Dam to Whitewater (RM 14), the Gunnison River features a wide 

floodplain with gravel pits; from Whitewater to Bridgeport (RM 29) the river runs through 

canyon habitat; and from Bridgeport to Delta, the river is braided and bounded by floodplains 

(Reclamation 2008). Irving and Burdick (1995) identified 48 bottomland sites along the 

Gunnison River with a total potential area of 3,227 acres. Bottomlands included terraces, 

depressions, gravel pits, oxbows, side channels, and canyon mouths. The majority of such habitat 

occurs between Delta and the confluence with Roubideau Creek (RM 50), with the greatest 

potential for flooded habitat at the Escalante State Wildlife Area (RM 50–52). 

In the Gunnison River, razorback suckers were historically abundant near Delta, Colorado. The 

last two putative wild adults were recorded in 1981 (Holden et al. 1981; Burdick 1992). In an 

attempt to re-establish the population, approximately 3,000 juveniles and adults were stocked 

annually in the Gunnison River between 1994 and 2003 (Burdick 2003). Based on captures of 

larval fish, stocked razorback suckers are reproducing between the Redlands Diversion Dam and 

Delta, although the spawning location has not been identified (Osmundson and McAda 2007). 

Razorback Sucker Habitat Final Report 

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2.0 H

Razo

abitat Characteristics and Management by River April 1, 2012

rback Sucker Habitat Final Report 

26 

Figure 13. Average daily streamflow of the Gunnison River near Grand Junction (09152500) for the pred-dam 

period 1917–1949 and the post-dam period 1950–1998. Figure from Van Steeter and Pitlik (1998).

2.5 San Juan River 

The San Juan River originates in the San Juan Mountain of southern Colorado. For the 224 mi

from Navajo Dam to Lake Powell (Figure 14), mean gradient of the river channel is about 10.1 

ft/mi, but it can be as high as 21.2 ft/mi (Brandenburg and Farrington 2009). The San Juan River 

is narrower, steeper, and shallower than the Green and upper Colorado rivers and lacks the 

extensive backwaters or flooded bottomlands (Ryden 2000) used in those rivers as nurseries by 

young razorback suckers. Table 7 provides a brief description of eight geomorphic reaches of the 

San Juan River between Lake Powell and Navajo Dam (from downstream to upstream) as

identified by Holden (1999).

Information on the historical presence of razorback suckers in the San Juan River is limited to a 

report based on local accounts of razorback suckers ascending the Animas River in spring, 

presumably to spawn (Jordan 1891) and the testimony of a local fisherman who reported 

occasionally catching a species, whose description suggests that the fish were razorback suckers,

in the San Juan River above Farmington, New Mexico (Koster 1960).

Razorback suckers were not found in 1962 when 100 mi of the San Juan River around the

proposed Navajo Dam site was treated with the fish toxicant rotenone (Olson 1962). The only 

confirmed historical report of the razorback sucker in the San Juan River Basin is two adults

seined from a pond near Bluff, Utah, in 1976 (Minckley et al. 1991).
2.0 H

Razo 27

abitat Characteristics and Management by River 

rback Sucker Habitat 

Figure 14. San Juan River from Lake Powell, Utah, to Navajo Dam, New Mexico, showing reaches 1–8 (downstream to upstream(1999).
2.0 Habitat Characteristics and Management by River April 1, 2012

Razorback Sucker Habitat Final Report 

 28 

Table 7. Geomorphic reaches of the San Juan River, Lake Powell to Navajo Dam (from downstream to 

upstream). Information from Bliesner and Lamarra (1999) and Dudley and Platania (2000). 

Reach Extent Stream Characteristics

1 

Lake Powell – near 

Slickhorn Canyon (16 mi) 

Canyon-bound with an active sand bottom. Abundance of ephemeral lowvelocity habitat present at certain flows, but greatly influenced by fluctuating

Lake Powell levels. Sand and silt deposited to a depth of about 12 m in the 

lowest end of reach. Lowest-gradient reach in the river. 

2 

Near Slickhorn Canyon – 

Chinle Creek confluence 

(50 mi) 

Canyon-bound but upstream of Lake Powell influence. Channel primarily 

bedrock confined and influenced by debris fans at ephemeral tributary 

mouths. Riffle habitat dominates, with major rapids. Backwater abundance 

low, usually in association with debris fans. 

3 

Chinle Creek to Aneth,

Utah (37 mi) 

Sinuous channel. Broad floodplain, multiple channels and islands, high

percentage of sand substrate. Number of backwater habitats extremely 

vulnerable to change during storm events. Debris piles common following 

spring runoff. Low gradient. 

4 

Aneth, Utah, to below “the 

Mixer” (123 mi) 

Transitional zone between the upper cobble substrate-dominated reaches

and the lower sand substrate-dominated reaches. Moderate sinuosity and

gradient with some islands. Few backwater habitats. 

5 

The Mixer to just below

Hogback Diversion (23 

mi) 

Predominantly multi-channeled with the largest total wetted area and 

greatest secondary channel area of any of the reaches. Cobble and gravel 

are more common in channel banks than sand. Cudei diversion dam in this

reach. 

6 

Below Hogback Diversion 

to confluence with the 

Animas River (125 mi) 

Predominately single channel. Cobble and gravel dominant substrate with

abundant cobble bars containing clean interstitial spaces. Backwater 

habitat abundance low. Channel altered by dike construction in several 

areas. Four diversion dams that may impede fish passage in this reach. 

7 

Animas River confluence 

to between Blanco and 

Archuleta, New Mexico

(32 mi) 

River channel very stable, primarily embedded cobble substrate as a result

of Navajo Dam upstream. Much of the bank stabilized and/or diked. Water

temperature influenced by hypolimnetic releases from Navajo Dam. 

8 

Between Blanco and 

Archuleta and Navajo

Dam (11 mi) 

Tailwaters of Navajo Dam. Primarily single channel, with 4–8 secondary 

channels. Cobble dominant substrate. Cool, clear water conditions. 
2.0 Habitat Characteristics and Management by River April 1, 2012

River-wide electrofishing surveys of the San Juan River in 1987–1989 from Farmington to Lake 

Powell yielded only one ripe male razorback sucker near Bluff, Utah, and 16 ripe adults at Piute 

Farms in the San Juan arm of Lake Powell (Platania et al. 1991). Subsequent surveys in 1991–

1997 failed to yield any wild razorback suckers of any life stage from the main channel of the 

San Juan River (Ryden 2000). 

Hatchery-raised razorback suckers were stocked into the San Juan River beginning in 1994, and 

the population in the river is currently maintained by stocking hatchery fish. Spawning activity 

by razorback suckers was detected in the San Juan River in 1997, and an intensive monitoring 

program for larvae was initiated in 1998, when two larval razorback suckers were collected 

(Ryden 2000). Annual monitoring for small-bodied and larval fish from 1998 to 2008 has 

resulted in the capture each year of larval razorback suckers (Brandenburg and Farrington 2009). 

Although young-of-year were not detected during fall sampling, individual age-1 razorback 

suckers were collected in 2004 and 2006 (Paroz et al. 2009). The lower San Juan River provides 

little nursery habitat, and razorback sucker larvae that drift downstream into Lake Powell may 

not survive because of predation by large numbers of nonnative fish (Marsh and Minckley 1989; 

Minckley et al. 1991; Mueller et al. 2001). 

Notably, because of its steep gradient, the San Juan River lacks the large riverside floodplains 

used as nurseries by young razorback suckers in the middle Green River and the upper Colorado 

River. Nevertheless, the San Juan River channel is complex is some locations and small-bodied 

fishes use backwaters and embayments along shorelines as nursery habitats. Research in the San 

Juan River continues to determine if larval razorback suckers can survive and recruit by using 

alternative nursery areas, other than inundated floodplains (SJRIP 2009). 

Management actions identified in a Long-Range Plan (SJRIP 2009) are designed to benefit the 

razorback sucker and other native fish in the San Juan River, and include operation of Navajo 

Dam in a manner that mimics the natural hydrograph, restoration of backwater and side channel 

habitats, construction of fish passages and screens at diversion structures, nonnative fish 

removal, off-site propagation, augmentation, and monitoring. A total of 58,916 razorback 

suckers were stocked into the San Juan River in the period 1994–2008, with 46,073 (78%) of 

these stocked from 2006 to 2008 (Furr and Davis 2009; see also Valdez et al. 2012). 

Beginning in 1992, Navajo Dam has been operated to mimic a natural San Juan River 

hydrograph (Holden 1999), with the magnitude of the high spring release linked to the amount of 

precipitation recorded during the preceding winter (Dudley and Platania 2000). As an example, 

Figure 15 shows the hydrograph for the San Juan River at three gauging stations in Water Year 

1999. 

Razorback Sucker Habitat Final Report 

 29 
2.0 Habitat Characteristics and Management by River April 1, 2012

Figure 15. Average daily treamflow of the San Juan River at Shiprock, NM; Four Corners, CO; and Bluff, UT, 

for Water Year 1999 (October to October). Figure modified from Dudley and Platania (2000). 

2.6 Lower Colorado River and Reservoirs 

The lower Colorado River, as defined here, extends approximately 800 mi from Glen Canyon 

Dam to the river’s outflow in the Gulf of Lower California (Figure 16). It is a highly regulated 

river with three large water storage reservoirs (Lakes Mead, Mohave, and Havasu) and several 

smaller reservoirs and water diversion structures. Portions of the river not impounded by dams

have been heavily dredged, channelized, and confined by levees, and river banks are often riprapped. Major habitat types in the lower Colorado River include reservoirs, inter-reservoir river 

segments, and natural and modified backwaters. Backwater types include oxbow lakes, 

abandoned river channel pools, off-channel ponds and lakes, secondary river channel pools, and 

hydrologically isolated coves on reservoirs (Saiki et al. 1980; LCRMSCP 2004). 

Hoover Dam, Davis Dam, and Parker Dam impound the waters of the lower Colorado River in 

Lake Mead, Lake Mohave, and Lake Havasu, respectively. Lake Mead, as the oldest reservoir 

(1935), is a mesotrophic lake (i.e., intermediate in nutrient levels and productivity); Lake 

Mohave, as the youngest reservoir (1951), is clear but highly productive; and Lake Havasu 

(1938) is a relatively shallow, mesoeutrophic (i.e., tending toward high nutrient levels and high 

primary productivity), warm-water lake (LCRMSCP 2004). 

Razorback Sucker Habitat Final Report 

 30 
2.0 Habitat Characteristics and Management by River April 1, 2012

Figure 16. Lower Colorado River from Lake Mead to the U.S.-Mexico border. 

All three reservoirs feature complex and irregular shorelines with numerous coves formed by 

topographic relief. All have shallow, warm littoral zones with shoals of cobble, gravel, and sand 

(Minckley 1983; Bozek et al. 1991; LCRMSCP 2004; Wydoski and Mueller 2006). Shorelines 

and littoral habitat vary with reservoir water levels that fluctuate on an annual basis as dam

operations respond to inflow volumes and downstream water demands. 

Since 1999, drought conditions in the Southwest have resulted in a major drawdown of Lake 

Mead and major changes in shoreline morphology as the water level recedes. Water in the 

reservoirs is generally clear, but at shallow inflow areas, sediment-laden rivers (e.g., Colorado, 

Muddy, and Virgin rivers) generate turbidity plumes. The low-angle shoreline topography of 

these reservoirs is quite in contrast to the high-angle, canyon-bound shoreline of Lake Powell, 

which is formed within the largely confined vertical cliffs of Glen Canyon; these vertical cliffs 

minimize opportunities for shoreline spawning fish. 

Razorback Sucker Habitat Final Report 

 31 
2.0 Habitat Characteristics and Management by River April 1, 2012

Razorback suckers occur in small numbers in all major habitat types along the lower Colorado 

River (reservoirs, inter-reservoir mainstream segments, and natural and artificial backwaters). 

Through 2004, approximately 2.4 million razorback suckers were repatriated into the lower 

Colorado River mainstem; 507,123 into Lake Havasu; 121,668 into Lake Mohave; and 146 into 

Lake Mead (Albrecht et al. 2009). Repatriation is the process whereby recently hatched larvae 

are captured and raised in artificial environments, then held in sheltered coves before releasing 

them back to the reservoir after they are sufficiently large to avoid most predators. The program 

has had some success, but survival of stocked razorback suckers has been low, most likely due to 

predation by large nonnative species, such as striped bass (Minckley et al. 2003; Mueller 2006). 

Nevertheless, this repatriation program has helped to extend the life of the population in 

especially Lake Mohave (Marsh et al. 2003). 

The razorback sucker’s unusual ability to spawn in both flowing and standing water (Mueller 

2006) is demonstrated in the lower Colorado River corridor, where spawning has been 

documented in Lakes Mead and Mohave; in the mainstem river between Davis Dam and Lake 

Havasu; in Senator Wash Reservoir; and in Cibola High Levee Pond, an off-channel pond below 

Parker Dam (Wydoski and Mueller 2006; Mueller 2007; Albrecht et al. 2008b). Recruitment is 

limited but has been documented in the lower Colorado River corridor in Lake Mead (Las Vegas 

Bay, Echo Bay, and the Muddy River/Virgin River and Colorado River inflow areas); Lake 

Mohave (Yuma and Davis Coves); and in Cibola High Levee Pond in the Cibola National 

Wildlife Refuge below Parker Dam (Mueller 2007, Albrecht et al. 2008b). Yuma and Davis 

Coves and Cibola High Levee Pond are semi-natural areas managed as off-channel “sanctuaries” 

for native fish (Mueller 2006). Recruitment also occurred outside the lower Colorado River 

valley in a population of razorback suckers stocked into Rock Tank, an isolated stock tank in 

Buenos Aires National Wildlife Refuge in southeastern Arizona. The fish were removed in 1997 

after being observed gasping for oxygen at the surface of the tank (Bonar et al. 2002).

The life history of the razorback sucker in reservoirs of the lower Colorado River is similar to 

that seen in riverine environments, but is manifest differently because of available habitats, an 

earlier seasonal warming pattern with the more southern location of the lower basin, and 

management actions that help the young fish survive. Reservoirs in the lower basin warm earlier 

than rivers of the upper basin, and razorback suckers spawn in February-April on shorelines with 

cobble and large gravels. Because of the large numbers of fish predators in these reservoirs, 

larvae are captured at emergence and raised in small aquaria then placed in isolated coves or 

ponds that serve as sanctuaries from predators. Such isolated coves include Yuma Cove on the 

shoreline of Lake Mohave and Office Cove on the shoreline of Lake Havasu (Figure 17). The 

fish are generally held in these sanctuaries until they reach 300–400 mm TL, which is a size no 

longer susceptible to predators. The fish are then released back into the reservoir. This strategy 

of repatriation is described more fully in Marsh et al. (2005) and Mueller (2006, 2007). 

Razorback Sucker Habitat Final Report 

 32 
2.0 Habitat Characteristics and Management by River April 1, 2012

Figure 17. Key life history aspects for the razorback sucker in reservoirs of the Lower Colorado River Basin, 

including spawning on a cobble/gravel shoreline of Lake Mohave; capture of larvae; rearing of larvae and 

juveniles in sanctuary coves of Lake Mohave and Lake Havasu, and in sanctuary ponds of the Colorado 

River; and the result of natural reproduction in the Cibola High Levee Pond. Photos from Mueller (2006, 

2007). 

Isolated Shoreline Sanctuary 

(Yuma Cove-Shoreline of Lake Mohave) 

Spawning on Cobble/Gravel Shoreline Capture of Larvae with Dip Net 

(Shoreline of Lake Mohave) (Lake Mohave) 

Isolated Shoreline Sanctuary 

(Office Cove-Shoreline of Lake Havasu) 

Natural Reproduction in Sanctuary 

(Cibola High Levee Pond-Colorado River) 

Razorback Sucker Habitat Final Report 

 33 
2.0 Habitat Characteristics and Management by River April 1, 2012

2.7 Gila, Salt, and Verde Rivers 

The Gila River is the major tributary of the lower Colorado River (Figure 16). It originates in the 

mountains of western New Mexico and flows in a westerly direction into Arizona. The major 

tributaries of the Gila River are the Salt, Verde, and Aqua Fria rivers, which originate in northcentral Arizona. The Gila River has a highly variable flow, as indicated by the stream gauge near 

Red Rock, New Mexico (Figure 18). Through regions of the Gila River, historic flows may have 

exceeded 10,000 cfs—or the channel may have dried at times. Water diversions and dams have 

moderated, but also exacerbated this flow variability and the lower portions of the Gila River 

often dry in summer. 

The razorback sucker was once abundant and widely distributed throughout the Gila River Basin 

in Arizona, including all major tributaries except the Santa Cruz River; however, wild razorback 

suckers are now extirpated from the drainage (Desert Fishes Team 2003, 2006). In a massive 

effort to re-establish the species, more than 12 million razorback suckers were stocked in the 

Gila, Salt, and Verde rivers and several tributaries between 1981 and 1991 (Hendrickson 1993). 

This effort was considered largely unsuccessful, primarily because of predation by nonnative, 

fish such as flathead catfish (Pylodictus olivaris; Marsh and Brooks 1989). The fish were 

variously stocked throughout the system and 14 adults were later reported from Fossil Creek, a 

small tributary of the Verde River. 

Figure 18. Average daily streamflow of the Gila River near Red Rock, NM, 1930–2005; USGS stream gauge 

09431500. 

Razorback Sucker Habitat Final Report 

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2.0 Habitat Characteristics and Management by River April 1, 2012

Beginning in 1991 and extending through 2003, close to 23,000 larger razorback suckers (>300 

mm TL) were stocked into the Verde River, and in 1996 approximately 2,000 were stocked into 

the Salt River (Hyatt 2004). Razorback suckers continue to be stocked in the Verde River, but 

none have been stocked in the Salt River since 1996. Despite intensive monitoring, none have 

been recaptured since a single fish was caught in 1997. Both rivers appear to provide suitable 

habitat for the species, including heterogeneous streams with both canyon-bound and open 

reaches, stretches of fast and slow current, and areas of coarse (gravel/cobble) and fine (silt/sand) 

sediment substrates. Nonetheless, few stocked fish are known to have survived longer than a few 

months after repatriation, and there is no evidence of recruitment. Most razorback suckers 

captured were at or near stocking sites (Hyatt 2004). 

The Arizona Game and Fish Department (AGFD) stocks razorback suckers in the Verde River as 

mitigation for the operation of Bartlett and Horseshoe reservoirs. A Habitat Conservation Plan 

(HCP) in 2010 includes provisions for expanding the Page Springs Bubbling Pond Fish 

Hatchery, the only warm water hatchery in Arizona. The hatchery currently raises about 12,000 

endangered razorback suckers annually for replenishment in the Colorado River, and will expand 

the facility to release more fish into the Verde River. As part of the HCP, the Salt River Project 

(SRP) has agreed to construct a fish barrier at Lime Creek to prevent nonnative fish from

traveling upstream and threatening the native species.

Razorback Sucker Habitat Final Report 

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3.0 Mesohabitat Use by Life Stage April 1, 2012

3.0 MESOHABITAT USE BY LIFE STAGE

Sections 1.0 and 2.0 of this report have described the historical and present distribution of the 

razorback sucker, and the habitat characteristics by each of the major regions and rivers. These 

sections have provided the setting for the historical and present conditions used by the species in 

the Colorado River Basin. The following Sections 3.0 and 4.0 describe the more localized 

mesohabitat and microhabitat used by various life stages of the species. 

The term mesohabitat is used in this report to describe major local physical features used by the 

razorback sucker. In rivers, mesohabitats include pools, eddies, runs, cobble and gravel bars, 

backwaters, inundated floodplains, oxbows, and gravel pits. In reservoirs, mesohabitats include 

shallow cobble and gravel shoals, shorelines, coves, turbid inflow areas, and deep pelagic zones. 

Razorback suckers are also known to occupy small streams, irrigation canals, ponds, and stock 

tanks (Ulmer et al. 1985; Marsh and Minckley 1989; Bonar et al. 2002). A summary of 

mesohabitats used by various life stages is provided in Table 8, and the following sections 

describe habitat use in detail. 

3.1 Spawning 

The razorback sucker is a broadcast spawner that releases and fertilizes its semi-adhesive eggs 

near the river bottom so that incubation can take place in protected interstitial spaces of cobble 

and gravel substrates. In the Upper Colorado River Basin, razorback suckers spawn in rivers 

during spring runoff (mostly April–June) in association with the ascending and peak hydrograph 

(Tyus and Karp 1989, 1990, 1991; Bestgen 1990; Osmundson and Kaeding 1991). Muth et al. 

(1998) reported that spawning activity spanned 4–6 weeks each year, with the exact timing 

varying annually with changing flow conditions. During spawning, adults congregated in runs, 

backwaters (flooded bottomlands and gravel pits), and impounded tributary mouths near 

spawning sites (Holden and Crist 1981; Valdez and Wick 1983; Tyus 1987; Osmundson and 

Kaeding 1989a; Tyus and Karp 1990; Osmundson et al. 1995; Modde and Wick 1997; Modde 

and Irving 1998). In the Green and Yampa rivers, these spawning sites included bars of cobble, 

gravel, and sand in the main channel and alluvial deposits at confluences (McAda and Wydoski 

1980; Tyus 1987; Tyus and Karp 1990). 

Spawning has also been documented or suspected in off-channel habitats. In the upper Colorado 

River near Grand Junction in the 1930s and 1940s, large congregations of presumably spawning 

razorback suckers were reported in inundated floodplains (Osmundson and Kaeding 1989a). In 

the 1970s, several hundred spawning adults were found in a zero-velocity riverside pool near 

Debeque, Colorado, and eggs were found in the substrate (Osmundson 2001). Razorback suckers 

in spawning condition were also captured in gravel-pit ponds in the Grand Junction area, but it 

was unclear if the fish were spawning in the ponds or using the warm, low-velocity habitat to 

stage for or recover from spawning (McAda and Wydoski 1980; Valdez et al. 1982; Osmundson 

and Kaeding 1991). Juveniles and adults were captured in Old Charley Wash, a floodplain 

wetland along the middle Green River, but it was unclear if reproduction had occurred in the 

wetland or if the juveniles had entered the wetland from the main channel (Modde 1996). 

Razorback Sucker Habitat Final Report 

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3.0 Mesohabitat Use by Life Stage April 1, 2012

Table 8. Summary of mesohabitats used by life stage of the razorback sucker as described by various 

investigators.

Life 

Stage Summary of Mesohabitats Used Citation 

Spawn on river bars of cobble/gravel mix in Green, 

Yampa, Upper Colorado, Gunnison, San Juan, and 

Lower Colorado Rivers. 

McAda and Seethaler 1975; McAda and

Wydoski 1980; Tyus 1987; Mueller 1989; Tyus

and Karp 1990; Modee and Irving 1998; Chart 

et al. 1999; Ryden 2000; Wydoski and Mueller 

2006 

May spawn in gravel pit ponds and floodplain wetlands. McAda and Wydoski 1980; Valdez et al. 1982;

Osmundson and Kaeding 1991; Modde 1996 

Spawning 

Habitat 

In reservoirs spawn along sloping, wave-sorted gravel or 

cobble shorelines, often in bays, coves, and tributary 

inflows. 

Douglas 1952; Jonez and Sumner 1954; 

Mueller et al. 1982, 1985, 1998, 2000; Minckley

1983; Medel-Ulmer 1983; Bestgen 1990; Bozek 

et al. 1991 

In rivers, drift along quiet shorelines in main channels and 

become entrained in the quiet, warm, shallow waters of 

floodplain wetlands, backwaters, and tributary mouths, 

which serve as nursery habitats. 

Valdez et al. 1985; Tyus 1987; Mueller 1989; 

Marsh and Minckley 1989; Bestgen 1990; 

Gutermuth et al. 1994; Modde 1996; Muth et al. 

1998; Wydoski and Wick 1998; Bestgen and 

Haines 2010 

Drift and 

Nursery 

Habitat 

In reservoirs, emerge along cobble shoals and move

toward shorelines, where they rear in warm, shallow 

backwaters, coves, or tributary inflows. 

Minckley 1983; Bozek et al. 1984; Marsh and 

Papoulias 1989; Pacey and Marsh 1998

Subadults 

and 

Adults 

In rivers, subadults and adults occupy a variety of 

generally low-velocity habitats, including runs, eddies, 

pools, shorelines, mouths of tributaries, backwaters, 

floodplain wetlands, and gravel pits. They may prefer 

turbid conditions and soft substrates. In reservoirs, use 

variety of deep habitats and eddies and pools in 

intervening river.

Simon 1951; Vanicek 1967; Holden and 

Stalnaker 1975; McAda and Seethaler 1975; 

Kidd 1977; Valdez et al. 1982; Tyus 1987; Tyus 

and Karp 1990; Bradford and Vlach 1995; 

Burdick and Bonar 1997; Modde and Wick 

1997; Modde et al. 1999; Pacey and Marsh 

1998; Gurtin and Bradford 2000; Burdick 2002, 

2003 

Spring 

(high flow) 

Low-velocity runs and eddies, backwaters 

and areas of Inundated vegetation. 

Tyus 1987; Osmundson and Kaeding 1989a; 

Valdez et al. 1982; Miller et al. 1982; Holden

and Masslich 1997; Ryden 2000 

Summer 

(baseflow) 

Runs near shorelines, Mid-channel bars. In 

the San Juan River, fast water runs. 

Valdez et al. 1982; Tyus 1987; Ferriole 1988; 

Osmundson and Kaeding 1989a; Tyus and 

Karp 1989; Holden and Masslich 1997; Ryden

2000 

Fall Pool use increased, use of runs decreased. Osmundson and Kaeding 1989a; Valdez and

Masslich 1989 

Seasonal 

Use of 

Rivers by 

Adults 

Winter Low-velocity runs and eddies, pools and 

slackwaters. In the San Juan River, pool

edges. 

Osmundson and Kaeding 1989a; Valdez and

Masslich 1989; Ryden 2000

Razorback Sucker Habitat Final Report 

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3.0 Mesohabitat Use by Life Stage April 1, 2012

In the San Juan River, hatchery-raised, ripe, male razorback suckers were collected over midchannel cobble riffles or run/riffles or over cobble shoal/runs at the river’s edge along with 

aggregations of ripe flannelmouth suckers (Catostomus latipinnis; Ryden 2000). These captures 

occurred in May during the ascending limb of the hydrograph, and indicate that razorback 

suckers in the San Juan River were spawning during increasing spring flows, as they do in the 

Green River (Muth et al. 1998). Larval razorback suckers have been caught every year in the San 

Juan River since 1998, indicating that successful reproduction is occurring in that river system

(Ryden 2009). 

In the Lower Colorado River Basin, razorback sucker spawning has been documented in rivers, 

reservoirs, and artificial ponds and backwaters (Pacey and Marsh 1998). In the mainstem

Colorado River, spawning was documented below Hoover Dam over scoured sand, gravel, and 

cobbles deposited in the river channel at the mouth of a dry wash (Mueller 1989). Several 

hundred adults were also found spawning in the river between Davis Dam and Lake Havasu, just 

upstream of Needles, California (Wydoski and Mueller 2006). As in other areas, spawning was 

taking place over predominately coarse substrate deposited at the mouth of a wash. 

In reservoirs, razorback suckers begin moving in late fall or early winter from relatively deep 

pelagic waters (≤18.3 m) to congregate and spawn in shallow, littoral zones (0.6–6.1 m) (Jonez 

and Sumner 1954; Minckley 1983; Mueller and Marsh 1998; Albrecht et al. 2008a). Spawning in 

lower basin reservoirs can occur as early as late November and extend into May. In Lake 

Mohave, razorback suckers spawned over cobble shoals from January through April (Mueller 

and Marsh 1998) and November through May (Bozek et al. 1991). In Lake Mead, spawning 

occurs in February through April over spawning sites with rocky substrate and vegetation, 

although the fish may shift locations with changes in reservoir elevation (Kegerries et al. 2009). 

In Senator Wash Reservoir, south of Lake Mohave, spawning began in late November and 

continued through early May, with peak activity in December through March (Kretschmann and 

Leslie 2006). In Cibola Levee Pond, spawning occurred along the southern portion of the river 

levee over gravel and cobbles substrate that was cleansed of silt by the movements of spawning 

fish (Mueller 2006). 

Razorback suckers in reservoirs of the Lower Colorado River Basin typically spawn on gentle 

sloping shorelines with wave-sorted gravel or cobble, often in bays or coves and over debris fans 

at mouths of ephemeral washes and inflowing rivers (Jonez and Sumner 1954; Minckley 1983; 

Medel-Ulmer 1983; Bestgen 1990, Bozek et al. 1991). Douglas (1952) observed spawning 

activity in Lake Havasu in a shallow bay with substrate described as silt over sand intermixed 

with boulders and gravel. In Lake Mohave, it has been hypothesized that the gravel terraces and 

shoals along shorelines used for spawning are generated and maintained by wave action, 

fluctuating water levels, and deposition of new coarse material from flashfloods down tributary 

washes (Mueller et al. 1982; Bozek et al. 1991). 

Notably, spawning has not been documented or suspected in Lake Powell where the shoreline is 

predominantly steep, vertical canyon walls, and in contrast to Lakes Mead, Mohave, and Havasu, 

which occur in open basins with low-angle terraces or shoals that are suitable spawning and 

nursery habitat. 

Razorback Sucker Habitat Final Report 

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3.0 Mesohabitat Use by Life Stage April 1, 2012

3.2 Larval Drift and Nursery Habitat 

Razorback sucker eggs hatch in approximately 6–7 days and the larvae swim up in 10–14 days 

(Snyder and Muth 1990; Bestgen and Haines 2010). In reservoirs (Bozek et al. 1990) and rivers 

(Bestgen 1990), the larvae spent daylight hours in interstitial spaces of the substrate and emerged 

at night to feed. In reservoirs and ponds, larvae and post-larvae have been collected in quiet 

shoreline habitats, where they remained for a few weeks before moving to deeper water 

(Langhorst and Marsh 1986; Minckley et al. 1991). In reservoirs, nursery habitat for juveniles 

most likely occurs in warm, shallow backwaters, embayments, and tributary mouths (Pacey and 

Marsh 1998). 

In rivers, once larvae emerge they become vulnerable to downstream drift, the nature of which 

depends on current velocity, channel morphology, and the size/age of larvae (Bestgen 1990). 

Razorback sucker larvae drift along channel margins and colonize quiet, nearshore areas quite 

rapidly (Bestgen and Haines 2010). Larvae have been collected from low- or zero-velocity 

habitats such as shallow shoreline eddies, backwaters, gravel pits, and floodplain wetlands in the 

Green River (Tyus 1987; Gutermuth et al. 1994; Modde 1996; Muth et al. 1998; Bestgen and 

Haines 2010), upper Colorado River (Valdez et al. 1985), Gunnison River (Burdick 2003), San 

Juan River (Brandenburg and Farrington 2009), and Gila River (Bestgen et al. 1987). 

In studies of larval drift in the Green River, razorback sucker larvae and near-neutrally buoyant 

artificial beads were released simultaneously to evaluate downstream drift and entrained in 

floodplain wetlands (Hedrick et al. 2009; Bestgen and Haines 2010). Entrainment occurred to the 

greatest degree in wetlands nearest to and on the same side of the river as the point of release; 

however, some beads were detected 53 mi downstream. Hedrick et al. (2009) found that 

entrainment in floodplain wetlands was most effective when the levee had multiple breaches 

(flow-through wetlands), allowing water to enter the site on both the ascending and descending 

limbs of the hydrograph. In contrast, larval razorback suckers in the San Juan River, where large 

floodplains are absent, are typically found in backwaters and small embayments. 

For razorback sucker larvae and young juveniles to survive and grow, they require conditions 

most likely to be found in floodplain wetlands that include: 

• an ample food supply (e.g., algae, phytoplankton, zooplankton, larval chironomids), 

• warm water temperatures that allow rapid growth, and 

• cover from potential predators (Bestgen 1990; Wydoski and Wick 1998; Muth et al. 

1998). 

Larval razorback suckers need to feed within 8–19 days of hatching (Papoulias and Minckley 

1990, 1992), and main channel habitats typically do not provide sufficient nutrients (Modde 

1996, 1997; Mabey and Shiozawa 1993); thus, it is critical for drifting larvae to reach suitable 

nursery habitat 1–2 days after swim-up (Valdez and Nelson 2004). Historically, floodplains 

inundated and connected to the main channel by spring runoff likely provided the most important 

nursery habitat for razorback suckers in the Colorado River System (Modde 1996; Wydoski and 

Wick 1998), although all juvenile razorback suckers collected in the upper basin by 1997 had 

come from backwaters (Modde 1997), suggesting that these habitats provide important habitat 

Razorback Sucker Habitat Final Report 

 39 
3.0 Mesohabitat Use by Life Stage April 1, 2012

for the older fish. While much floodplain and backwater habitat has been lost as a result of 

channelization, levees, and flow regulation, razorback suckers have come to use gravel pits and 

other artificial, off-channel ponds as a partial substitute (USFWS 2002). 

Floodplains, backwaters, and other sheltered habitats are also used by many species of nonnative 

fish, and predation by these fish has been widely implicated as one of the causes of recruitment 

failure among larval razorback suckers (e.g., McAda and Wydoski 1980; Marsh and Langhorst 

1988; Mueller et al. 2001; Modde and Haines 2005). Juvenile nonnative fish may be the most 

common predators of larval razorback suckers in nursery areas (Modde and Haines 2005), but 

adult nonnative fish and other aquatic species (e.g., dragonfly nymphs, crayfish and bullfrogs) 

also prey on these small fish (Karp and Tyus 1990; Muth 1990; Johnson et al. 1993; Horn et al. 

1994; Modde and Wick 1997; Mueller et al. 2006; Carpenter and Mueller 2008). Predation on 

juvenile razorback suckers by nonnative species is widely thought to be the primary reason that 

millions of small razorback suckers stocked by agencies have failed to survive (Marsh and 

Brooks 1989; Pacey and Marsh 1998; Minckley et al. 2003; Mueller 2006). 

3.3 Subadults and Adults 

Adult and subadult razorback suckers are the most adaptable life stage of the species (Minckley 

et al. 1991; Modde et al. 1995). In riverine systems, adults use both main channel and backwater 

habitats (e.g., Valdez et al. 1982; Osmundson and Kaeding 1989a; Tyus and Karp 1990; 

Minckley et al. 1991; Clarkson et al. 1993; Modde 1996) but generally avoid steep, canyon 

reaches (Tyus 1987). Low-velocity habitats predominate (Holden and Stalnaker 1975; Tyus 

1987; Tyus and Karp 1990; Bestgen 1990; Minckley et al. 1991; Mueller and Marsh 2002), but 

adults have also been documented in fast runs (Ryden 2000). Adult razorback suckers appear to 

be relatively sedentary, occupying localized reaches except during spawning season (McAda and 

Wydoski 1980; Osmundson and Kaeding 1989a). Mueller (2006) has emphasized the importance 

of backwater habitats to adult razorback suckers, particularly large off-channel backwaters that 

are generally warmer than the main channel, support more food organisms, and offer a lowvelocity refuge for fish to recover after spawning. 

Adult razorback suckers in rivers use different habitats seasonally, selecting low-velocity 

habitats adjacent to shorelines more often in spring than in other seasons (Valdez et al. 1987; 

Tyus 1987). Historical accounts and more recent surveys indicate that during periods of high 

flow in spring, adults congregate in eddies and backwaters (including inundated floodplains and 

gravel pits) removed from main channel currents, and occupy backwaters until those areas are 

dewatered in summer (Minckley 1983; Valdez et al. 1982; Osmundson and Kaeding 1989a; Tyus 

and Karp 1989, 1991; Bradford and Vlach 1995). The fish typically move to main channel runs, 

pools, and eddies (Osmundson and Kaeding 1989a; Burdick and Bonar 1997). Mid-channel 

habitats associated with submerged sandbars and pools behind boulders and logs are used more 

often in summer than in other seasons (Tyus 1987; Bestgen 1990; Minckley et al. 1991). Modde 

and Wick (1997) found most adult razorback suckers in runs, eddies, and eddy fences during 

both spring and summer. During winter, adult razorback suckers in the Green River occupied a 

1- to 3-mi reach of river and used slow runs, slackwaters, and eddies (Valdez and Masslich 

1989). In the upper Colorado River, they used pools and low-velocity eddies, also in localized 

reaches (Osmundson and Kaeding 1989a). 

Razorback Sucker Habitat Final Report 

 40 
3.0 Mesohabitat Use by Life Stage April 1, 2012

In the San Juan River, stocked, radio-tagged adult razorback suckers during winter and spring 

selected areas with greater habitat richness, including low-velocity habitats such as edge pools, 

eddies, pools, and backwaters (Ryden 2000). During summer and fall, when overall flow 

velocity was low, razorback suckers selected areas with less complex habitats and higher 

velocity, including runs. Razorback suckers selected inundated vegetation when it was available 

in June, and likely used this area for feeding and as a refuge from high flows; they also used deep 

water as cover when turbidity was low (Ryden 2000). In the Verde River, stocked radio-tagged 

adults tended to move downstream after release and were often found in pools or runs over silt 

substrates (Clarkson et al. 1993). 

Little has been reported regarding habitat use by adult razorback suckers in reservoirs outside of 

the spawning period; however, in Lake Mead, adults occupy both pelagic and littoral zones, 

seeking deeper waters (≤18.3 m) in bays during summer and fall, and shallower waters (≤6.1 m)

along gravelly or vegetated shorelines and turbid inflows during winter and spring (Albrecht et 

al. 2008a). In Lake Mohave, Mueller et al. (2000) found that adults used some areas of the 

reservoir year-round, but used other areas only for spawning or only in the hotter summer 

months. In general, the monitored fish occupied broad, shallow shoreline habitats but were 

located closer to the surface in spring and autumn and in deeper water in summer. Mueller et al. 

(1998) reported that five sonic-tagged juveniles in Lake Mohave moved throughout the pelagic 

zones for the first week after release but then tended to occupy vegetated areas near the shore. 

In Cibola Levee Pond, adult razorback suckers occupied the lower portion of the water column in 

July, mostly around or under dense vegetation (Mueller et al. 2005). The pond was warm (12–

34°C) and offered abundant and diverse cover in the form of submerged vegetation and large riprap, natural bank cavities, and beaver dens. 

3.4 Synthesis of Mesohabitat Data 

A synthesis of mesohabitat use shows that adult razorback suckers in a riverine environment 

favor the deeper areas of the channel with low to moderate velocity, such as deep runs, eddies, 

and pools, but use gravel pits, slackwaters, and backwaters when available (Figure 19). Adults in 

a reservoir/riverine environment use large backwaters (i.e., oxbows, floodplains) as well as side 

channels, or features that tend to provide depth, low velocity, shelter, and food. 

The various investigators may use different criteria to define a mesohabitat type, and 

comparisons of these datasets may not be concise but offer a good insight into the types of 

mesohabitats used by the species in different settings. It is reasonable to surmise that adult 

razorback suckers favor deep, quiet areas in the river channel as well as off-channel areas, when 

available. This species clearly does not favor moderate or high-velocity mesohabitats, such as 

riffles used by other sucker species of the Colorado River System including the bluehead sucker 

(Catostomus discobolus) (Bezzerides and Bestgen 2002). 

Razorback Sucker Habitat Final Report 

 41 
3.0 Mesohabitat Use by Life Stage April 1, 2012

Adult River Mesohabitat Use (all seasons)

0

20

40

60

80

100

BA ED GP PO RI RU SC SH SW

Mesohabitat

Perc

e

nt

Green R (20) - Valdez et al. (1987)

Green R (17) - Valdez & Masslich (1989)

Colo. R (24) - Osmundson & Kaeding (1989)

Green R (19) - Modde & Wick (1997)

A

Adult Seasonal River Mesohabitat Use - Colorado River

1986-1988 (Osmundson & Kaeding 1989)

0

20

40

60

80

100

BA ED GP PO RI RU SC SH SW

Mesohabitat

Perc

e

nt

Spring (6)

Summer (7)

Fall (5)

Winter (6)

B

Adult Reservoir/River Mesohabitat Use - Imperial Div. LCR (n = 74)

1995-1997 (Bradford & Gurtin 2000)

0

20

40

60

80

100

BA ED GP PO RI RU SC SH SW IM MC

Mesohabitat

P

ercent

Spring

Summer

Fall

Winter

C

Figure 19. Mesohabitat used by adult razorback suckers in (A) rivers for all seasons, (B) rivers by season, 

and (C) reservoir/river for all seasons. Data sources are cited in each figure and provided in Appendix A. 

BA=backwater, ED=eddy, GP=gravel pit, PO=pool, RI=riffle, RU=run, SC=side channel, SW=slackwater, 

IM=impoundment, MC=main channel.

Razorback Sucker Habitat Final Report 

 42 
4.0 Microhabitat Use by Life Stage April 1, 2012

4.0 MICROHABITAT USE BY LIFE STAGE 

The term microhabitat is used in this report to describe the quantifiable physical attributes of

mesohabitats used by razorback sucker. These include depth, velocity, substrate, and water 

temperature. A summary of microhabitats used by various life stages of the razorback sucker is 

provided in Table 9. Microhabitat and mesohabitat used by various life stages of the razorback 

sucker are summarized in Section 5.0 and compared with mesohabitat availability in lower 

Grand Canyon. 

Cover is an important habitat variable in addition to temperature, depth, velocity, and substrate; 

however, the scientific literature has rarely included quantitative data for cover conditions. For 

this reason, information related to cover is not included in the following tables. Nonetheless, 

cover is an important component of razorback sucker habitat, particularly for larvae and 

juveniles which have been observed seeking cover in submerged vegetation, woody material, or 

debris (Muth and Wick 1997; Mueller 2003). Mueller and Marsh (1998) reported that juveniles 

were concealed in vegetation during daylight hours and emerged at night, presumably to feed. 

They have also been collected in turbid conditions in the shelter of large boulders (Gutermuth et 

al. 1994), presumably using low water clarity as cover from predators. Adult razorback suckers 

have showed similar behavior, seeking vegetative and rocky cover during the day (Mueller et al. 

2003). 

Cover provided by turbidity likely increases survival rates of young fishes by reducing the 

feeding efficiency of sight-based predators (Dill 1944; Johnson and Hines 1999; Albrecht et al. 

2008a). Turbid conditions at the inflows of Las Vegas Wash and the Muddy River/Virgin and 

Colorado rivers are believed to be a beneficial factor in recent recruitment of razorback suckers 

in Lake Mead, particularly when the reservoir elevation is low and receding, as in recent years 

(Albrecht et al. 2008a, 2010; Kegerries et al. 2009). As the lake recedes, formerly submerged 

fine sediment deposits are increasingly exposed to erosion and suspension by river currents and 

wave action, resulting in increased turbidity levels at the inflow. 

4.1 Spawning 

Razorback suckers spawn in rivers of the Upper Colorado River Basin from early April through 

early June on the ascending limb of hydrograph, with highest activity in mid through late May 

(Table 9). Spawning takes place at a wide range of water temperatures (6–21°C), at shallow 

depths (<1.0 m), in low current velocities (<1.0 m/s), and on substrates of small-to-large cobbles, 

gravel, or cobble/gravel mix. 

In the Lower Colorado River Basin, spawning in rivers and reservoirs occurs somewhat earlier 

(most commonly from late January/early February to mid-March) and at somewhat higher 

temperatures (6.6–25.5°C). Spawning in the lower basin takes place at shallow depths, in 

currents of low or zero velocity, and on gravel and gravel/cobble substrates. In both riverine and 

lacustrine environments, spawning substrate consists of loose, rocky material relatively free of 

silt, which is cleared away by hydrologic processes (river currents, wave action) and by the 

Razorback Sucker Habitat Final Report 

 43 
4.0 Mic

Razo

 44

rohabitat Use by Life Stage April 1, 2012

rback Sucker Habitat Final Report 

 

agitation of spawning fish. Clean substrates with deep interstitial voids are needed to prevent 

eggs and larvae from suffocating (Tyus and Karp 1989; Severson et al. 1990).

Although evidence of spawning activity (e.g., congregations of ripe fish) has been documented in 

the field over a wide temperature range (6–25.5°C), laboratory tests suggest that successful 

hatching of razorback sucker eggs, and therefore successful reproduction, occurs most often 

within a narrow range. As shown in Table 10, hatching rates were highest at 20–23.5°C, survival 

of eggs was poor at 10–12°C and most or all eggs died at 5–10°C and 30°C. Moreover, Marsh 

(1985) found a significantly lower incidence of deformed larvae at 20°C than at either 15°C or 

25°C, and Bozek et al. (1984) found that hatching and development times were significantly 

lower at 20°C than at 10°C. While the available data suggest that the optimal temperature for 

reproductive success is near 20°C (Osmundson 2001) or 20–22°C (Hamman 1985; Bozek et al. 

1990), lower water temperatures (>10°C) apparently do not preclude successful spawning

(Bozek et al. 1990).

4.2 Larval Drift and Nursery Habitat 

Larval razorback suckers in the Green River have been collected at water temperatures ranging

from 11.0°C to 24.4°C, at varying but mostly shallow depths, in low- or zero-velocity current, 

and over silt substrate (Table 11). Larvae survived and grew in Old Charley Wash, a managed 

floodplain wetland adjacent to the Green River, at temperatures ranging from about 11°C to

29°C, and water depths of 0.4 m to 2.3 m (Modde 1997).

In The Stirrup, another managed floodplain wetland, larvae were reared in warm (19–28°C),

shallow water (1.0 m) (Christopherson et al. 2004). In Lake Mead, larvae are generally found 

along shorelines with inundated terrestrial vegetation and high levels of turbidity that provide 

littoral nursery cover for larval and juveniles, allowing them to avoid predation (Albrecht et al.

2010b).

Juvenile razorback suckers have been collected in very warm water temperature (21.7–34.0°C),

at shallow depth (0.1–0.2 m), in zero-velocity current, over silt substrate (see Table 11). Juvenile 

razorback suckers stocked in June into Humphrey Pond, a gravel-pit pond adjacent to the lower 

Colorado River, survived and grew in water temperatures that ranged from 26°C down to ~3°C

the following January (Osmundson and Kaeding 1989b).

As expected for a warm-water species, young razorback suckers generally fare better in warm

temperatures than in cool temperatures. The lengths, weights, and growth rates of larvae and 

young juveniles in the laboratory were significantly higher at 20°C than at 10°C and 14°C

(Clarkson and Childs 2000).
4.0 Microhabitat Use by Life Stage 

Table 9. Microhabitat data for spawning razorback suckers, Upper and Lower Colorado River Basins. 

Location Timing Temperature Depth Velocity1 Substrate C

Upper Colorado River Basin Middle GreenRiver 

Mid-Apr to late Jun; (mostly mid-May to late May; ascending limb of hydrograph) 

8.0–19.5°C 0.2–1.0 m 0.1–1.4 m/s Coarse sand/ 

gravel/cobbles

Vanicek 1967; Tyus Tyus and Karp 1990Bestgen and Haines 

Lower Green River 

Early Apr to early Jun 6.0–21.0°C - - - Muth et al. 1998; Be

Green River Hatching 

Late Apr to early Jun (mean 26 May)

12.0–16.0°C (mean 14.3°C) 

- - - Bestgen and Haines 

Yampa River Late Apr to late May 

(Ascending limb of hydrograph) 

6.0–16.0°C 0.7–1.0 m 0.64–1.0 m/s Small to large 

cobbles 

McAda and Seethal1979; McAda and WKarp 1989; Tyus an

Upper Colorado River 

Late Apr to late May 12.4–19.0°C 0.6–1.0 m 0.9 m/s Cobbles, 

gravel 

Wick et al. 1982; Mc1975; Osmundson a

Gunnison River Mid-Apr to late May 11.4–12.3°C - - - Osmundson and SeSan Juan River Apr to May - <1.0 m - Cobbles Ryden 2000, 2001Lower Colorado River Basin Lower Colorado River mainstem 

Early Feb to mid-Mar - 0.75–1.0 m 0.0–0.37 m/s Sand, gravel, 

cobbles 

Mueller 1989; Wydo

Lake Mead Early Feb to mid-Mar 12.0–18.0°C 0.6–5.0 m - Gravel Jonez and Sumner Lake Mohave Nov to May (Peak Jan to 

Mar) 

9.5–22.0°C <2.75–5.0 m - Coarse, wavewashed 

cobble andgravel 

Minckley 1983; MueBozek et al. 1984, 1Minckley et al. 1991 

Lake Havasu March 14.4–18.3°C 0.25–1.8 m - Silt over sand

and gravel 

Douglas 1952

Razorback Sucker Habitat  45
4.0 Microhabitat Use by Life Stage 

Location Timing Temperature Depth Velocity1 Substrate C

Senator WashReservoir 

Late Nov to early May, with peak Dec to Mar 

6.6–25.5°C 0.6–5.5 m - Mixed

medium- sizecobble andgravel, with slopes of 30–45%

Medel-Ulmer 1983; 2006 

Cibola LeveePond 

- - >1.5 m - Gravel/cobble Mueller et al. 2005

1 Velocity usually measured at surface or mid-column and is likely greater than at the level occupied by the fish (Osmundson and Kaeding 1989a; BraTable 10. Hatch success rates by temperature in laboratory trials. 

Temperature Citation

95% hatch success at 14.4–17.2°C; Poor success at 11.6°C Toney 1974Spawning: 10.0–15.0°C; Hatching: 17°C (10–20% egg survival at 14.0-16.0°C); Clean gravel 0.6–10.2 cm diameter 

Inslee 1981 

46% hatch success at 20.0–23.5°C Loudermilk 1981 Hatch at 20.0–22.00°C Hamman 1985 High success at 20.0°C (35%) and 25.0°C (29%); Lower: 15.0°C (19%); Egg mortality: 5.0°C, 10.0°C, and 30.0°C 

Marsh 1985; Marsh and Pisano 1

High success: 20.0°C (34–65%); Lowest: 10.0°C 9; Egg mortality: 8.0°C Bozek et al. 1990 75% hatch success at 20.0°C Severson et al. 1990 48% hatch success at 12°C and 67% at 20°C Haines 1995 

Razorback Sucker Habitat  46
4.0 Microhabitat Use by Life Stage 

Razo 47

rback Sucker Habitat 

Location Timing Temperature Depth Velocity Substrate 

Larvae Green River - 0.3 m 0.06 m/s Silt Holden 197

Old Charley Wash 

Spring–summer 

11–29°C ~0.4–2.3 m - - Modde 199

The Stirrup Mar to 

Aug 

19–28°C 1.0 m - - Christophe

Late March 

Lower Colorado 11.4°C–17.4°C - - - Schooley eRiver 

Mid-June 21.1–24.4°C on shoreline 

while mainstem 15.5°C mean 

<1.0 m - - Sigler and 

Lower Basin - 12.0–20.0°C - - - Pacey and Lake Mohave Late Jan 

to early May 

11.0–15.0°C Most at ~1 m, many at 2.8 

m, some at 4.9 m and 6.1 m 

- Mostly

gravel/sand 

Bozek et a

Juveniles Location Timing Temperature Depth Velocity Substrate CitationLower Green River 30 July 34.0°C 0.1–0.2 m 0.0 m/s Silt Guterrmuth Lower Colorado River (Humphrey Pond) 

Yearround 26.0°C(Jun); ~3°C (Jan) 1.4–2.0 – – Osmundso

Lower Colorado River 

- 21.7–24.4°C - - - Sigler and 

Table 11. Microhabitat data for larval and small juvenile razorback suckers. 
4.0 Microhabitat Use by Life Stage April 1, 2012

4.3 Subadults and Adults 

Adult razorback suckers in the wild appear to tolerate a wide range of water temperatures (0–

27°C) (Table 12). Laboratory studies indicate preferred temperatures of 22.0–24.8°C for both 

adults and subadults, with lower avoidance temperatures at 8.0–14.7°C, and upper avoidance 

temperatures at 27.4–31.6°C (Table 13). Swimming ability of adults was optimal at 20–26°C and 

poor at 14°C (Bulkley et al. 1981). 

In riverine environments, adults are generally found in deep water, but can be found in a range of 

depths (0.18–3.4 m), with no consistent seasonal pattern across studies. Depths occupied in 

summer in the San Juan River were similar to those occupied in winter in the upper Colorado 

River. There was, however, a strong relationship between season and depth in Lake Mead, where 

fish used deeper water in the hot summer months (9.1–18.3 m) than in cool winter months (1.5–

6.1 m). Reported current velocities were uniformly low (<1.0 m/s) and substrates consisted 

predominately of sand and silt. 

4.4 Synthesis of Microhabitat Data 

Data on water depth, velocity, and substrate used by the razorback sucker were assimilated from

various investigations and are provided in Figures 20–22. Depths used by adults ranged from

shallow water to about 11.5 ft, but the majority of fish were found at depths that ranged from

about 2 to 4.5 ft (Figure 20). Seasonal data were based on four radio-tagged adults, which 

tended to use deeper water ranging from 3 to 7 ft, with deeper water being used in fall and 

winter. As expected, larvae used water that was 1 ft or less, but were found in water as deep as 5 

ft where vegetative cover was present. 

Water velocity used by most adult razorback suckers ranged from 0 to about 2 ft/sec (Figure 21). 

Water velocity recorded was either at the fish location in the water column, or at 0.6 of the water 

depth which may not reflect the velocity at the actual fish location. These different methods for 

measuring water velocity may explain the range of values seen in Figure 21. Nevertheless, these 

datasets indicate that the species favors low velocity areas, not necessarily absent of water 

velocity. As expected, all larvae were found at water velocities at or near 0 ft/sec. 

Substrate used by adult razorback suckers in all seasons showed a strong selection for silt and 

sand, with less use of gravel and cobble (Figure 22). These substrate types are consistent with 

mesohabitat selection of slow deep habitats and low to moderate water velocities, which help to 

shape the types of substrates in the channel. It should be noted that despite their apparent yeararound use of finer substrates (i.e., silt and sand), razorback suckers are known to spawn only on 

rocky substrates consisting of cobble and gravel (in rivers) or imbricated rock talus (in 

reservoirs). Also, investigators consistently report selection by larvae for vegetative cover, which 

was not sufficiently quantified to provide in this report, as was done for depth, velocity, and 

substrate. 

Razorback Sucker Habitat Final Report 

 48 
4.0 Microhabitat Use by Life Stage April 1, 2012

Adult River Depth Use (all seasons)

0

10

20

30

40

50

0.01.02.03.04.05.06.07.08.09.0

10.011.0

Depth (ft)

P

ercent

Colo. R (52) - Valdez et al. (1982)

Green R (18) - Valdez et al. (1987)

Green R (17) - Valdez & Masslich (1989)

Green R (18) - Modde & Wick (1997)

A

Adult Seasonal River Depth Use - Colorado River

1986-1988 (Osmundson & Kaeding 1989)

0

10

20

30

40

50

0.01.02.03.04.05.06.07.08.09.0

10.011.0

Depth (ft)

Perc

e

nt

Spring (6)

Summer (7)

Fall (5)

Winter (6)

B

Larval River Depth Use - Green River (n = 1,498)

Valdez et al. (1987)

0

10

20

30

40

50

0.

0

1.

0

2.

0

3.

0

4.

0

5.

0

6.

0

7.

0

8.

0

9.

0

10.011.0

Depth (ft)

Perc

e

nt C

Figure 20. Depth used by (A) adult razorback suckers in rivers for all seasons, (B) adults in rivers by season, 

and (C) larvae in the Green River. Data sources are cited in each figure and provided in Appendix A. 

Razorback Sucker Habitat Final Report 

 49 
4.0 Microhabitat Use by Life Stage April 1, 2012

Adult River Velocity Use (all seasons)

0

20

40

60

80

100

0.000.501.001.502.002.503.00

Velocity (fps)

P

ercent

Colo. R (52) - Valdez et al. (1982)

Green R (18) - Valdez et al. (1987)

Green R (17) - Valdez & Masslich (1989)

A

Adult Seasonal River Velocity Use

0

20

40

60

80

100

0.000.501.001.502.002.503.00

Velocity (fps)

P

ercent

Spring (11) - Green R (Valdez et al. 1987)

Summer (18) - Green R (Valdez et al. 1987)

Winter (17) - Green R (Valdez & Masslich 1989)

B

Larval River Velocity Use - Green River (n = 1,521)

Valdez et al. (1987)

0

20

40

60

80

100

0.000.501.001.502.002.503.00

Velocity (fps)

P

ercent C

Figure 21. Velocity used by (A) adult razorback suckers in rivers for all seasons, (B) adults in rivers by 

season, and (C) larvae in the Green River. Data sources are cited in each figure and provided in Appendix A. 

Razorback Sucker Habitat Final Report 

 50 
4.0 Mic

Razo

 51

rohabitat Use by Life Stage April 1, 2012

rback Sucker Habitat Final Report 

Adult River Substrate Use (all seasons)

0

20

40

60

80

100

SI

SA

GRCOBO

BE

Substrate

Perc

e

nt

Colo. R (52) - Valdez et al. (1982)

Green R (32) - Valdez et al. (1987)

Green R (17) - Valdez & Masslich (1989)

Green R (13) - Modde & Wick (1997)

A

Figure 22. Substrate used by (A) adult razorback suckers in rivers for all seasons, (B) adults in rivers by

season, and (C) adults in all rivers and seasons. Data sources are cited in each figure and provided in

Appendix A. SI=silt, SA=sand, GR=gravel, CO=cobble, BO=boulder, BE=bedrock.

Adult Seasonal River Substrate Use

100

0

20

40

60

80

SI

SA

GRCOBO

BE

Substrate

Perc

e

nt

Spring (32) - Green R (Valdez et al. 1987)

Summer (32) - Green R (Valdez et al. 1987)

Winter (17) - Green R (Valdez & Masslich 1989)

B

Adult River Substrate Use

0

10

20

30

40

50

SI

SA

GRCOBO

BE

Substrate

P

ercent C

 
4.0 Microhabitat Use by Life Stage 

Table 12. Microhabitat data for large juvenile and adult razorback suckers. 

Reach Timing Temperature Depth Velocity1 Substrate 

Apr to Nov - 0.18–3.0 m 0.0–0.7 m/s Sand, silt, sand/silt mixed; 

some gravel; mud/cobble ingravel pit; boulders in Split Mountain Canyon 

Tyus et 1987; M

Green River 

Nov to Mar 0.0-10.5°C 0.4–1.8 m Primarily 0.0–

0.4 m/s 

Sand, silt; some cobble Valdez a

Yampa - - 0.6–3.4 m - Sand, silt Tyus an

Mid-March through Late October 

7.8–27.0°C 0.8–2.0 m

(common); 1.0–1.7 m (peak use) 

90% in 0.0 m/s; 19% in 0.03–0.61m/s 

Silt dominant Valdez e

Spring - 0.9–2.3 m <0.3 m/s Mostly silt/sand; some

cobble 

Valdez eand Kae

Summer/fall 11.5–12.5°C 0.6–3.0 m 0.34–0.52

m/s 

Mostly silt and sand; some gravel/rubble; mud/cobble inshallowest area of gravel pit 

McAda Valdez eand Kae

Upper Colorado River 

Winter - 1.86–2.19 m - Mostly silt and sand Osmund

Mar to May 10.9–14.8°C 

(mean) 

0.7–0.8 m (mean) 0.3–0.5 m/s 

(mean) 

- 

Jun to Aug 15.0–23.7°C 

(mean) 

1.2–1.9 m (mean) 0.5–0.6 m/s 

(mean) 

- 

Oct and Nov 5.3–11.5°C 

(mean) 

1.2 m (mean) 0.5 m/s 

(mean) 

- 

San Juan River 

Dec to Feb 1.3–4.3°C (mean) 0.8–1.1 m (mean) 0.2–0.5 m/s 

(mean) 

- 

Ryden 2

Verde River - - 0.60–1.19 m <0.1 m/s Mostly silt/sand; some

gravel/cobble 

Clarkso

Razorback Sucker Habitat  52
4.0 Microhabitat Use by Life Stage 

Razo 53

rback Sucker Habitat 

Reach Timing Temperature Depth Velocity1 Substrate 

Gila River - - <0.4 m 0.1–0.2 m/s 65% sand, 20% gravel, 

5% silt, 5% cobble 

Marsh a

Lake Mead Fall and summer - 9.1–18.3 m - - 

Winter and spawning season

- 1.5–6.1 m - -

Albrech

1 Velocity usually measured at surface or mid-column and is likely greater than at the level occupied by the fish (Osmundson and Kaeding 1989a). Table 13. Temperature preference and swimming ability data for large juvenile and adult razorback suckers from laboratory tria

Study Parameter Study Finding Citation 

Subadults (150–300 mm) preferred 22.0–23.0°C 

Valentine 1981

Subadults (150–300 mm) preferred 23.0–24.0°C 

Bulkley et al. 1981

Adults preferred 22.9–24.8°CUpper avoidance: 27.4–31.6°C Lower avoidance: 8.0–14.7°C

Bulkley and Pimentel 1983 

Temperature Preference 

Adults preferred 23–24°C Black and Bulkley 1985 

Swimming Performance Optimal swimming ability: 20.0–26.0°C 

Poorer swimming performance at 14.0°C 

Bulkley et al. 1981
5.0 R

Razo

 54

azorback Sucker in Lower Grand Canyon April 1, 2012

rback Sucker Habitat Final Report 

5.0 RAZORBACK SUCKER IN LOWER GRAND

CANYON AND LAKE MEAD

5.1 Occurrence of Razorback Sucker in Grand Canyon 

Ten documented records exist for the razorback sucker between Glen Canyon Dam and the upper 

extent of the Lake Mead inflow (Valdez 1996; Valdez and Carothers 1998; Figure 23):

• one adult caught by an angler in Bright Angel Creek in 1944 (Minckley and Carothers 

1979);

• one captured by the AGFD at the mouth of the Paria River just after closure of Glen 

Canyon Dam in 1963 (Minckley and Carothers 1979);

• three adults, including a gravid female, from the mouth of the Paria River in June 1978 

(Minckley and Carothers 1979);

• one adult from near lower Bass Camp (RM 108) in April 1984 (Maddux et al. 1987); 

• one female (555 mm TL, 1,860 gm) from the Little Colorado River (LCR) inflow in May

1989 (C.O. Minckley, USFWS, pers. comm., as cited in Valdez and Carothers 1998); and

• three adults from the LCR inflow in April 1990, including two males (475 mm TL, 1,211 

gm; 476 mm TL, 1,219 gm) and one female (588 mm TL, 2,035 gm) (W. Persons,

AGFD, pers. comm., as cited in Valdez and Carothers 1998).

All confirmed razorback suckers captured in were adults, suggesting that either the reach is not 

used as rearing habitat or reproduction and recruitment do not occur in this region of the 

Colorado River (Valdez and Carothers 1998). More than a decade ago, Valdez (1996) surmised

that fewer than 100 razorback suckers probably remained in Grand Canyon, and the species was 

nearing extirpation from this reach. Douglas and Marsh (1996) conjectured that razorback 

suckers were never abundant in Grand Canyon, occupying the area as transients rather than 

residents, moving between more desirable habitats upstream and downstream.

Numerous morphologic intergrades or apparent hybrids between the razorback sucker and the

more common flannelmouth sucker have been reported from the Grand Canyon (Suttkus et al. 

1976; Maddux et al. 1987; Valdez and Ryel 1995), as well as from various parts of the Colorado 

River System (Minckley et al. 1991). Larval suckers collected at the mouths of the LCR and 

Havasu Creek in the late 1990’s were either razorback suckers or hybrids of razorback sucker

and flannelmouth sucker (Douglas and Douglas 2000).

One of the last razorback suckers documented in the Grand Canyon was an adult captured in the

Colorado River near lower Bass Camp (RM 108) by S.W. Carothers and C.O. Minckley in April 

1984 (Maddux et al. 1987). Adult razorback suckers have been caught recently in the Colorado 

River inflow (Figure 24). These fish moved from the Lake Mead populations in Echo Bay and 

Las Vegas Wash, and the presence of larvae in 2000, 2001, and 2010, as well as ripe and gravid 

fish in 2010 indicates that a cobble/gravel island between Devil’s Cove and North Bay is being 

used for spawning (Kegerries et al. 2009; Albrecht et al. 2010a, 2010b).

 
azorback Sucker in Lower Grand Canyon 

Razorback Sucker Habitat  55Figure 23. Capture locations of razorback suckers in Grand Canyon and the Lake Mead inflow.5.0 R
5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

A 

B 

Figure 24. Photographs of (A) one of the last razorback suckers captured in the Colorado River in Grand 

Canyon near lower Bass Camp (RM 108) by S.W. Carothers and C.O. Minckley in April 1984 (Maddux et al. 

1987), and (B) a razorback sucker captured by Bio/West biologists in April, 2010 in the Colorado River inflow 

below Iceburg Canyon. Photos courtesy of S.W. Carothers and B.A. Albrecht, respectively. 

Razorback Sucker Habitat Final Report 

 56 
5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

5.2 Studies of Razorback Sucker in Lower Grand Canyon 

5.2.1 Fisheries Surveys 

The razorback sucker has been absent from all fisheries surveys of the lower Grand Canyon (i.e., 

Lava Falls rapid to Lake Mead inflow; see section 6.3.2). Fisheries investigations during the 

1970s failed to capture or observe the species in this region of the Colorado River (Carothers and 

Minckley 1981; McCall 1980; Bookstein 1985). Intensive sampling from Diamond Creek to 

Pearce Ferry from June 1992 through January 1994 also did not report razorback suckers (Valdez 

1994; Valdez et al. 1995), nor did more contemporary surveys during 2004–2006 (Ackerman et 

al. 2006; Ackerman 2007), and 2005 (Rogers et al. 2007). 

Razorback suckers, however, have been caught annually in Lake Mead since 1990, although 

none were caught in the Colorado River inflow until 2000; the first individuals caught were 

larvae and not adults. Altogether, 33 larvae were found in the inflow in 2000 (11) and 2001 (22), 

but no adults were detected despite considerable netting efforts (Albrecht et al. 2008a) until 2008 

when the AGFD captured a large adult during annual gill netting in Gregg Basin. In 2010, two 

sonic-tagged adults, originally stocked into the Muddy River/Virgin River inflow area (one fish, 

code 3354) and Las Vegas Bay (one fish, code 465), were contacted in Gregg Basin near the 

Colorado River inflow. These findings provide evidence that wild razorback suckers may occur 

in various part of Lake Mead and that lake-wide movement of stocked fish may lead 

investigators to these wild fish. The strategy of translocating wild fish sonic-tagged fish is being 

employed in Lake Mead to reveal aggregations of wild fish and possible spawning locations. In 

May and June of 2010, four fish were sonic-tagged and release in Gregg Basin, and four were 

tagged and released in the Colorado River inflow, but the subsequent contact information from

these fish was not available for this report. 

Prior to about 2000, few razorback suckers were evidently using the Colorado River inflow. 

Changes in lake elevation and movement of fish from the Las Vegas Bay, Echo Bay, and Muddy 

River/Virgin River populations may have lead to fish moving to the inflow. The first suspected 

spawning site in the Colorado River inflow was identified in upper Gregg Basin in 2010, and 

larvae were captured near the site in 2000, 2001, and 2010. Given the size and continuous flow 

of the Colorado River through lower Grand Canyon, it is not unreasonable to expect that 

razorback suckers could use the entire inflow area—including the river in lower Grand Canyon. 

5.2.2 Studies of Movement and Habitat Use 

One study in 1997 attempted to evaluate potential habitat use and movement of the species in the 

region. On June 24, 1997, the Hualapai Tribe with assistance from SWCA and Reclamation 

released 15 radio-tagged adult razorback suckers into the Colorado River in lower Grand Canyon 

(Unpublished data, SWCA Environmental Consultants, Flagstaff, AZ). Five fish were released at 

each of three sites: Spencer Canyon (RM 246), Quartermaster Canyon (260.1), and Separation 

Canyon (239.6). 

Over 15 weeks, 12 of the fish were detected a total of 48 times. The net distance traveled from

each release site ranged from 0 to 26.7 mi, with 4 of the 12 fish last detected at or upstream of 

Razorback Sucker Habitat Final Report 

 57 
5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

the release site and 8 last detected downstream (Table 14; Figure 25). Of the seven fish tracked 

over the longest period (≥69 days), five traveled relatively long distances (23.0–26.7 mi), two 

traveled moderate distances (6.4–11.1 mi), and one traveled only 2.3 mi in 104 days. 

Six of the 12 tagged fish remained or moved into a region downstream of Quartermaster Canyon 

(RM 260), which in 1997 was a slow-flowing, semi-turbid lake environment, well below the 

interface of the Colorado River and Lake Mead (i.e., 1,203.7 ft, about RM 241, below Separation 

Canyon). Their movement into and use of this area is not explained, but the fish moved from

portions of the river channel that had been filled with sediment into a more diverse area with 

vegetated shorelines. In contrast, subsequent fisheries surveys in 2009 were conducted at a lower 

lake elevation when the river/lake interface was about 20 mi downstream (i.e., 1,099.1 ft, about 

RM 261, below Quartermaster Canyon) and the river had carved a channel into the sediment 

exposing the original diverse river bottom and shoreline features. Because of these extensive 

geomorphic changes to the lower Grand Canyon, the 1997 radio-telemetry study of razorback 

suckers may not be representative of what the fish might do in the contemporary river setting. 

Table 14. Movement of radio-tagged adult razorback suckers in lower Grand Canyon, June–October, 1997.

Hualapai Aquatic Studies. Unpublished data, SWCA Environmental Consultants. 

Fish Tag 

Frequency 

Release Site

(RM) 

Last Observation 

(RM) 

Days since 

Release 

Net Movement

(River Miles) 

Direction of 

Movement 

40.011 239.6 266.3 83 26.7 Downstream 

40.021 239.6 240.5 1 0.9 Downstream 

40.031 239.6 265.0 83 25.4 Downstream 

40.051 239.6 238.0 7 1.6 Upstream 

40.120 239.6 246.0 103 6.4 Downstream 

40.061 246.0 271.0 104 25.0 Downstream 

40.081 246.0 248.3 104 2.3 Downstream 

40.141 246.0 246.0 1 0 No Movement 

40.150 246.0 242.5 8 3.5 Upstream 

40.091 260.2 260.2 8 0 No Movement 

40.101 260.2 285.0 69 24.8 Downstream 

40.131 260.2 271.3 83 11.1 Downstream 

The radio-telemetry study also provided some information on habitat use. The radiotagged fish were contacted primarily in eddies (38%), and in pools, slackwaters, and 

“lake” habitat (31%; Table 15). Vegetated banks were the most common shoreline type 

used and about 18% of the fish were detected in submerged vegetation. This association 

with vegetation indicates that in 1997 the fish relocated in the area below Quartermaster 

Canyon where habitat was more diverse and vegetative cover was more available. 

Razorback Sucker Habitat Final Report 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

Figure 25. Net movement of 12 radio-tagged adult razorback suckers in lower Grand Canyon and Colorado 

River inflow, June–October, 1997 (see Table 14 for movement data). Release locations indicated by black 

circles; last contacts indicated by black rectangles. Map to approximate scale; river miles (RM) 240–290

(shown in boxes) are distances downstream from Lees Ferry. 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

Table 15. Habitat associations of radio-tagged adult razorback suckers in lower Grand Canyon, June–

October, 1997; Hualapai Aquatic Studies. Unpublished data, SWCA Environmental Consultants. 

Fish Habitat Shoreline Type Temp (C) Substrate Turbidity Shade RM Location Comments 

0.041 ED SA,VG SA 246.0 Above Mouth of Spencer 

0.081 ED 245.9

0.061 ED 246.2

0.141 ED SA,VG SA 246.0 Above Mouth of Spencer 

0.150 ED SA,VG SA 246.0 Above Mouth of Spencer 

0.011 ED 239.6

0.021 ED 239.6

0.120 TS L H 240.0

0.141 ED Rock face 245.8 Above Spencer Drift Site 

0.910 RU VG 260.1

0.121 TS 240.0

0.051 SW 238.0

0.081 PO VG (1.5 m) 19 GR L. H 248.3 Mouth of Surprise Canyon

0.031 SC 237.0

0.031 SW

0.151 VG 242.5

0.081 PO VG L H 248.3 Mouth of Surprise Canyon 

0.141 SW H 246.0 500 yards above Spencer 

0.121 ED VG L L 244.0

0.031 ED L L 245.5

0.011 ED L L 239.5 1\4 mi below Separation 

0.031 H L 243.5

0.121 H L 243.5

0.131 SW VG 16 H L 271.0 flooded vg

0.061 SW VG 16 H L 269.0 flooded vg

0.081 PO VG H L 248.3 Mouth of Surprise Canyon

0.121 ED 15.5 L H 246.0 Above Mouth of Spencer 

0.121 RU BE 15.5 H H 247.0

0.061 VG VG H H 269.0

0.031 RU VG 16 L H 265.0

0.101 LK CO (2 m) 19.5 GR H L 280.0 Pearce Ferry

0.081 PO VG 19 GR H L 248.3

0.131 VG VG L H 272.0

0.011 VG VG L H 266.3

0.101 LK CO 24 GR L L 285.0 God's Pocket 

0.031 VG VG 15 L H 264.5

0.011 VG VG 15 H H 266.3

0.131 VG VG 15 H H 271.3

0.081 PO VG 22.5 L L 248.3 Mouth of Surprise Canyon

0.121 ED 20 L H 246.0 Mouth of Spencer Canyon

0.081 PO VG 16.5 L L 248.3 Mouth of Surprise Canyon 

0.121 ED L H 246.0 Mouth of Spencer Canyon

0.121 ED Alluvial fan (2-5 m) GR,SI H H 246.0 Mouth of Spencer Canyon

0.081 PO VG L H 248.3 Mouth of Surprise Canyon

0.061 VG VG H H 269.0

1Source: Unpublished data on-file at SWCA Environmental Consultants 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

5.3 Preliminary Evaluation of Razorback Sucker Habitat 

In May 2009, Dave Speas (Reclamation) and Melissa Trammell (National Park Service) 

conducted a preliminary evaluation of potential razorback sucker habitat in lower Grand Canyon 

(Speas and Trammell 2009; see Appendix B).1

 They surveyed the habitat of the Colorado River 

by boat from Lava Falls (RM 179) to Lake Mead (RM 279). For each river mile in that reach, 

they recorded: (1) number and location of backwaters; (2) number of islands and side channels; 

(3) major habitat types as riffles, runs, eddies, spawning cobble, low-velocity habitat; (4) 

presence of cover (vegetation, turbidity); (5) water temperature; and (6) larval seine samples 

(collected opportunistically). Based on 1–4 above, they determined habitat complexity (i.e., the 

ability of the habitat to support multiple life stages of the razorback sucker) for each river mile. 

The quantitative criteria they used to define three habitat categories (complex, less complex, and 

poor) are shown in Table 16. 

Table 16. Quantitative criteria defining quality of potential razorback sucker habitat in lower Grand Canyon

(Speas and Trammell 2010).

Habitat Category Backwaters / mi Islands / mi No. Habitat Types 

Present (mean) 

Percent 

Vegetation Cover 

Complex Habitat 0.50 0.62 2.2 0.29

Less complex 

Habitat 0.46 0.05 1.44 0.12

Poor habitat 0.19 0.08 1.00 0.04

Speas and Trammell (2010) designated the following reaches of the Colorado River in the lower 

Grand Canyon according to habitat complexity (Figure 26): 

• Complex: RM 179–208, 220–223. 

• Less complex: RM 209–219, 224–253. 

• Poor habitat: RM 253–279. 

The reach from RM 179–208 extends from Lava Falls rapid to just upstream of Granite Park. 

This 29-mi reach of river contains numerous side canyons, debris fans, eddy complexes, as well 

as a complexity of backwaters, islands, sand bars, and vegetation that could be suitable for 

different life stages of the razorback sucker. This complex habitat also occurs in a 3-mi reach 

from RM 220–223. Less complex habitat occurs in RM 209–219 and RM 224–253, where the 

channel is more canyon-bound with fewer debris fans and eddy complexes. The poorest habitat 

reported by Speas and Trammell (2009) occurs in RM 253–279, where the channel is lined by 

eroding sand banks that remain from deltaic deposits when Lake Mead was at a higher elevation. 

It should be noted that this reach also has a large cobble/gravel bar at the mouth of Salt Creek 

which is considered a potential spawning site. 

 

1 We wish to thank Dave Speas and Melissa Trammel for providing the information regarding their 2009 survey as

presented in this section. The results shown here are preliminary and should be understood as such. 

Razorback Sucker Habitat Final Report 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

Figure 26. Complex, less complex, and poor potential habitat of razorback sucker in the Colorado River in 

lower Grand Canyon, RM 179–279. Figure from Speas and Trammell (2010). 

Speas and Trammell (2009) also collected water temperature data during the May 2009 survey. 

Temperature ranged from a low of about 15.5°C at RM 179 to 18.5°C at RM 279 (Figure 27). 

Figure 27. Water temperature data, RM 179–279, May 2009. Data from Speas and Trammell (2010). 

Razorback Sucker Habitat Final Report 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

Additional water temperature data gathered at GCMRC gauges are presented below (GCMRC 

data online at http://www.gcmrc.gov/products/otherdata/gcmrc.aspx). Three gauges are located 

within the lower Grand Canyon: RM 194 (194 Mile Canyon), RM 226 (Diamond Creek 

confluence), and RM 246 (Spencer Canyon confluence). Figure 28 shows the highest and lowest 

temperatures recorded at each gauge during January through September for the last full year of 

record: 2004 for RM 194 and 2009 for RM 226 and RM 246. Ideal spawning temperature for the 

razorback sucker is 15°C (range of 10–22°C) and ideal hatching temperature is 20°C (range of 

10–30°C) (USFWS 2002) as displayed on each hydrograph. These figures show that ideal 

spawning temperature is reached about April, but a suitable range of hatching temperatures is not 

reached until May; temperatures shown are main channel temperatures and do not account for 

nearshore or sheltered habitats with warmer temperatures. 

Figure 28. High and low water temperatures at RM 194 (Year 2004), RM 226 (Year 2009), and RM 246 (Year 

2009) for the months January–September (GCMRC data). Ideal spawning temperature for the razorback 

sucker is 15°C (10–22°C) and ideal hatching temperature is 20°C (10–30°C). 

Razorback Sucker Habitat Final Report 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

5.4 Status of Razorback Sucker Population in Lake Mead 

The largest populations of the razorback sucker are currently found in Lake Mohave and Lake 

Mead of the Lower Colorado River Basin (USFWS 2002). The Lake Mead population appears to 

be the only population with continued and sustained recruitment (Albrecht et al. 2010b). 

Between 1996 and 2008, a total of 517 individual adult and subadult razorback suckers were 

captured in Lake Mead, including 218 at Las Vegas Bay, 248 at Echo Bay, and 51 near the 

Muddy/Virgin River inflow areas (Figure 29). 

Figure 29. Lake Mead and locations of the razorback sucker populations in relationship to the Colorado River 

inflow at right of map. Figure from Albrecht et al. (2010b). 

Mark-recapture population estimates of the razorback sucker were computed for Las Vegas Bay 

and Echo Bay for 1996–2007 using the Chao Mh estimator (Albrecht et al. 2008a; Figure 30). 

The population in Las Vegas Bay has ranged from a low of 52 individuals (95% CI = 18–272) 

for the period 2003–05, to a high of 310 (95% CI = 108–1,104) for the period 2002–04. The 

latest estimate is 271 (95% CI = 113–793) for the period 2005–07. The population in Echo Bay 

has ranged from a low of 39 individuals (95% CI = 25–89) for the period 2003–05, to a high of 

142 (95% CI = 97–242) for the latest period, 2005–07. The sum of estimates for the two bays for 

each of the 11 periods range from a low of 91 individuals for 2003–05, to a high of 413 for the 

latest period, 2005–07. 

Razorback Sucker Habitat Final Report 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

Figure 30. Population estimates (95% confidence intervals, CI) of the razorback sucker in (A) Las Vegas Bay, 

(B) Echo Bay, and (C) Las Vegas Bay + Echo Bay for 1996–2007. Data from Albrecht et al. (2008a) for the 

Chao Mh estimator. 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

From 1997 to 2007, a total of 12,607 larval razorback suckers were captured in Lake Mead, 

including 2,410 in Las Vegas Bay; 10,113 in Echo Bay; 47 in the Muddy River/Virgin River 

inflow area; 33 in the Colorado River inflow area (sampled from 1998 to 2004); and 4 in other 

locations (Albrecht et al. 2008a). The dates that larvae were first found in each of the four areas 

spanned from early February to late April, including February 5 to April 5 in Las Vegas Bay; 

February 22 to April 20 in Echo Bay; March 2 to April 12 in the Muddy River/Virgin River 

inflow; and April 29 for the Colorado River inflow. 

The 33 larvae found in the Colorado River inflow area were caught on April 29 each in 2000 (11 

larvae) and 2001 (22 larvae). These newly-hatched fish were captured between Iceberg Canyon 

and Grand Wash Bay, about 8 mi downstream from Pearce Ferry (Albrecht et al. 2008a; Figure 

31). During the 2002 and 2003 spawning periods, no larval razorback suckers were captured in 

this area. This spawning site was either not used in 2002–2003, or spawning took place outside 

of the sampling area. Physical and chemical changes in spawning sites resulting from lake 

elevation changes may be responsible for the apparent inconsistent use of these sites in the 

Colorado River inflow region, as in other sites on Lake Mead described above. 

In spring of 2010, seven larval razorback suckers were captured in the Gregg Basin region of the 

Colorado River inflow (Figure 31), as well as one larval flannelmouth sucker and four larval fish 

thought to be either flannelmouth sucker or hybrid flannelmouth x razorback sucker (Albrecht et 

al. 2010a). All larvae were captured April 13–14, 2010 at water temperatures of 14–16°C. 

Although catch rate was low, the identification of larval razorback suckers in the Colorado River 

inflow, as well as concurrent locations of radio-tagged fish and adults in spawning condition, 

provided compelling evidence of successful spawning in 2010. Spawning is believed to have 

occurred on rock and gravel points between North Bay and Devil’s Cove, in the lake interface 

about 10 mi downstream of Pearce Ferry. 

Albrecht et al. (2010a) reported that trammel netting in the inflow area on April 20, 2010, 

yielded three male razorback suckers expressing milt, which helped confirm spawning activities. 

Two of these individuals were 6 years old and one was 11 years old. Altogether, four razorback x 

flannelmouth sucker hybrids, and 52 flannelmouth suckers were captured with trammel nets in 

2010 in the Colorado River inflow. Sonic-tagged razorback sucker released near the Colorado 

River inflow in 2010 used the riverine habitat and inflow region as far upstream as the mouth of 

Devil’s Cove, about 8 mi downstream of Pearce Ferry. Individual sonic-tagged fish have been 

tracked as far upstream as the base of the newly formed “Pearce Ferry rapid” (about 1 mi

downstream of Pearce Ferry; see Figure 31), but the fish have not ascended this rapid, suggesting 

that it is an impediment to upstream fish movement. Razorback suckers have not been caught 

recently upstream of Pearce Ferry or in the lower Grand Canyon. 

Ongoing studies of the Lake Mead razorback sucker population suggest that changes in lake 

elevation are responsible for the apparent and sudden recruitment in the late 1970s (Albrecht et 

al. 2010b). The population in Lake Mead is believed to have originated from resident or transient 

individuals that became trapped in the reservoir as it was filling from the 1930s to about 1963. 

The lake was drawn down approximately 100 ft in the mid-1960s as Lake Powell filled, but from

about 1964 to 1987, Lake Mead filled slowly with small annual fluctuations that reflected 

seasonal inflow and releases to satisfy downstream water demand and delivery (Figure 32). 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

Figure 31. Locations of sonic-tagged razorback suckers, 1997–2007, and larval capture sites, 2000, 2001, and 

2010, in the Colorado River inflow and Gregg Basin area of Lake Mead. Figure modified from Albrecht et al. 

(2008a, 2010a). 

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5.0 Razorback Sucker in Lower Grand Canyon April 1, 2012

Figure 32. Lake Mead elevation from January 1935 to June 2010 with the number of razorback suckers that 

were hatched each year, based on back-calculated ages as determined from fin ray sections. Red bars depict 

razorback sucker captured at the Colorado River inflow area in 2010 and dark bars represent numbers of fish 

from the cumulative long-term monitoring and aging efforts. Figure from Albrecht et al. (2010a). 

Expansive deltaic deposits formed at the inflows during high lake elevations, and these became 

populated with dense stands of tamarisk, willows, cottonwoods, and other riparian plants that got 

regularly watered with the fluctuating reservoir levels. A drawdown in the early 1990s allowed 

further downslope encroachment of vegetation along the lake shorelines, and much of the 

riparian vegetation at higher elevations became desiccated and died. The low-lying vegetation 

was inundated as the lake rose in the late 1990s, providing cover in coves and other littoral 

habitats for young razorback suckers. It is hypothesized that the reinundation of this low-lying 

vegetation provided the cover and nutrients that allowed the young suckers to escape predators 

and provided an abundance of food. 

The level of Lake Mead has continued to drop since about 2000 because of continuing regional 

drought, but it appears that sufficient vegetation remains to provide cover for the young suckers. 

Investigators are finding that both turbidity and vegetation are substantially more abundant in 

Las Vegas Bay and Echo Bay than in other coves, suggesting that both cover factors play a role 

in recruitment (Albrecht et al. 2010b). Recent aging of razorback suckers from Lake Mead shows 

that recruitment pulses have occurred when shoreline vegetative cover was available—but 

recruitment has also occurred at low lake conditions when vegetative cover was limited but 

turbidity was high. These findings suggest that the best chances for successful reproduction and 

recruitment by the razorback sucker is in areas that provide vegetative cover and turbidity, such 

as the large river inflows including the Colorado River. 

Razorback Sucker Habitat Final Report 

 68 
6.0 Habitat Suitability of Lower Grand Canyon April 1, 2012 

6.0 HABITAT SUITABILITY OF LOWER GRAND 

CANYON 

6.1 Overview of Habitat Use 

This document provides an assimilation of habitat information and data for various life stages of 

the razorback sucker from throughout its range in the Colorado River System. Altogether, 84 

scientific reports and publications were used as sources for this habitat information (Table 17). 

Information gleaned from these sources is presented in sections 2.0, 3.0, and 4.0 of this report. 

The information gleaned from these reports and publications is used in this section to help 

evaluate the suitability of habitat for the razorback sucker in the lower Grand Canyon. This 

evaluation begins with a comparative analysis of system-wide quantitative information and the 

limited information available for the lower Grand Canyon. Quantitative data on depth, velocity, 

substrate, and mesohabitat were available from seven sources highlighted in Table 17. These are 

provided in Appendix A in their original forms as “habitat suitability criteria” and data were 

extracted from each to derive a summary of frequency information for depth, velocity, and 

substrate (i.e., microhabitat) used by adult razorback suckers system-wide (Figure 33).

Microhabitat data were not available for the lower Grand Canyon and a comparison with existing 

habitat was not possible. However, mesohabitat data were available for comparisons among 

radio-tagged adult razorback suckers in lower Grand Canyon (SWCA unpublished data), adults 

from all rivers (see highlighted citations in Table 17), and mesohabitat availability (Speas and 

Trammell 2010) (Figure 34). A direct comparison among these three datasets is not entirely 

possible because of different criteria used to classify mesohabitat types and an apparent 

inconsistent use of terminology for habitat types. 

Visual examination of these three datasets shows that radio-tagged adult razorback suckers in the 

lower Grand Canyon used eddies, pools, runs, slackwaters, and vegetated shorelines, which is a 

similar suites of mesohabitats used throughout the species range. Speas and Trammell (2009) 

found that the most common primary mesohabitats available in lower Grand Canyon were runs, 

riffles, eddies, and rapids; whereas backwaters were less common. 

A Chi2

 association test was not possible for these datasets because of the large numbers of zeros 

in mesohabitat categories. A Kolmogorov-Smirnov test was run to determine if the three 

samples had the same distribution. Two-tailed tests revealed that comparisons among all three 

distributions (radiotelemetry, all rivers, and availability) were significantly different (p < 0.05). 

In other words, despite apparent similarities among distributions, the degree of similarity was 

significantly different. Given the paucity of habitat data for the lower Grand Canyon, these data 

and analysis are considered preliminary and inconclusive. 

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6.0 Habitat Suitability of Lower Grand Canyon April 1, 2012 

Table 17. A list of citations used as sources for habitat information for the razorback sucker. Sources of 

habitat suitability criteria are highlighted in gray and the criteria provided in Appendix A, and summarized for 

microhabitat in Figures 20–22 and for mesohabitat in Figures 33–34. Detailed citations are provided in the 

Literature Cited section of this report. 

Number Citation Number Citation

1 Albrecht et al. 2008a 43 McAda and Seethaler 1975

2 Albrecht et al. 2008b 44 McAda and Wydoski 1980 

3 Albrecht et al. 2009 45 Medel-Ulmer 1983

4 Albrecht et al. 2010a 46 Miller et al. 1982

5 Albrecht et al. 2010b 47 Minckley 1983 

6 Bestgen 1990 48 Minckley et al. 1991 

7 Bestgen and Haines 2010 49 Modde 1996

8 Bestgen et al. 2002 50 Modde 1997

9 Bezzerides et al. 2002 51 Modde and Wick 1997

10 Black and Bulkley 1985 52 Modde and Irving 1998 

11 Bozek et al. 1984 53 Modde et al. 1999

12 Bozek et al. 1990 54 Mueller 1989

13 Bozek et al. 1991 55 Mueller et al. 1982

14 Bradford and Vlach 1995 56 Mueller et al. 1985

15 Bradford and Gurtin 2000 57 Mueller et al. 2005

16 Bulkley and Pimentel 1983 58 Muth et al. 1998

17 Bulkley et al. 1981 59 Osmundson and Kaeding 1989a 

18 Burdick 2002 60 Osmundson and Kaeding 1991

19 Burdick 2003 61 Osmundson and Seal 2009 

20 Burdick and Bonar 1997 62 Pacey and Marsh 1998

21 Chart et al. 1999 63 Ryden 2000

22 Christopherson et al. 2004 64 Ryden 2001

23 Clarkson et al. 1993 65 Schooley et al. 2008 

24 Douglas 1952 66 Seethaler et al. 1979 

25 Ferriole 1988 67 Severson et al. 1990 

26 Guterrmuth et al. 1994 68 Sigler and Miller 1963

27 Gurtin and Bradford 2000 69 Simon 1951 

28 Haines 1995 70 Toney 1974

29 Hamman 1985 71 Tyus 1987

30 Holden 1977 72 Tyus and Karp 1989 

31 Holden and Masslich 1997 73 Tyus and Karp 1990 

32 Holden and Stalnaker 1975 74 Tyus et al. 1981

33 Inslee 1981 75 Tyus et al. 1982

34 Jonez and Sumner 1954 76 Valdez and Masslich 1989 

35 Kegerries et al. 2009 77 Valdez et al. 1982

36 Kidd 1977 78 Valdez et al. 1985

37 Kretschmann and Leslie 2006 79 Valdez et al. 1987

38 Loudermilk 1981 80 Valentine 1981

39 Marsh 1985 81 Vanicek 1967

40 Marsh and Minckley 1989 82 Wick et al. 1982

41 Marsh and Papoulias 1989 83 Wydoski and Mueller 2006

42 Marsh and Pisano 1985 84 Wydoski and Wick 1998

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Figure 33. Summary of all data for (A) depth, (B) velocity, and (C) substrate used by adult razorback suckers 

in rivers. Data sources are highlighted in Table 17. See Figure 22 caption for substrate codes. 

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Figure 34. Mesohabitat use by (A) radio-tagged adult razorback suckers in lower Grand Canyon, and (B) 

adult razorback suckers from all rivers, compared to (C) mesohabitat availability in lower Grand Canyon. See 

Figure 19 caption for mesohabitat codes. 

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6.2 Comparison of Habitat Profiles 

This section uses the information assimilated on habitat use by the razorback sucker to develop a 

profile of habitat for the species and draws a qualitative comparison between habitat used and 

available habitat in the lower Grand Canyon. To clarify, the lower Grand Canyon is considered 

to be the Colorado River from the base of Lava Falls rapid (RM 180) to Pearce Ferry (RM 280). 

This comparison cannot be done without including an assessment of the potential role of Lake 

Mead and the Colorado River inflow below Pearce Ferry. 

6.2.1 Spawning and Larval Drift 

Table 18 provides a profile of habitat used by various life stages of the razorback sucker and 

qualitatively compares habitat attributes with available habitat in lower Grand Canyon and the 

Colorado River inflow to Lake Mead. The razorback sucker in a riverine setting consistently uses 

cobble/gravel bars for spawning. These bars may be located at the base of canyons, such as Split 

Mountain Canyon or Desolation Canyon on the Green River, or they may be located in complex 

channel areas such as “The Mixer” on the San Juan River. In a reservoir setting, razorback 

suckers use rocky shorelines and shoals for spawning, such as the shorelines of Lakes Mohave 

and Mead. 

Large cobble/gravel bars similar in appearance to those used for river spawning are present at 

tributary inflows and canyon mouths in lower Grand Canyon, including Diamond Creek (RM 

226), Spencer Canyon (RM 246), and Surprise Canyon (RM 248.3) (Figures 35 and 36). Rocky 

shorelines are also present in the Colorado River inflow, where razorback suckers are believed to 

have spawned in 2010. 

Razorback suckers broadcast and fertilize their eggs over cobble/gravel bars, whereupon the eggs 

become semi-adhesive and adhere to the rocks in crevices and interstitial spaces. The eggs 

incubate for 6–7 days and the embryos emerge as tiny larvae (about 0.7 in long) without fins or a 

functional mouth. Newly emerged larvae are typically swept downstream by river currents or 

washed by wave action in reservoirs, but they must quickly find sheltered productive nursery 

areas for feeding and shelter from predators. The larvae rely on a small yolk sac for nourishment, 

but it is quickly absorbed and they must feed within 8–19 days of hatching or they will starve. 

Unimpeded and secure drift corridors are essential to larval survival. Many larvae drift at night 

or under the cover of turbidity to escape predation. Because the larvae lack well-developed fins, 

they are reliant on river currents to become carried into a productive nursery area. Hence, the 

location of nursery areas a short distance downstream from spawning sites is vital to the species. 

Although there are no floodplains in the lower Grand Canyon, there are numerous backwaters 

that are used by other native Colorado River suckers, and are similar to backwaters used by 

razorback sucker larvae in the San Juan River. Speas and Trammell (2009) counted 22 

backwaters between RM 181 and RM 265 that could provide potential nursery habitat for larval 

razorback suckers. Additionally, the Colorado River inflow could provide substantial nursery 

habitat, depending on lake elevation. 

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Table 18. Profile of habitat used by various life stages of the razorback sucker compared to available habitat 

in lower Grand Canyon. 

Life Stage Habitat Profile Habitat in Lower Grand Canyon 

Spawning and Larval 

Drift 

• In Rivers: Cobble/gravel bars 

• In Reservoirs: Rock shoals 

• In Lower River: Cobble/gravel bars in 

river at canyon mouths (Spencer, Salt) 

• In Lake Mead: Rock shoals in upper 

Gregg Basin 

Larval Nursing, and 

Rearing 

• In Green, Colorado Rivers: Seasonally 

inundated floodplains 

• In San Juan River: backwaters and 

embayments 

• In Reservoirs: Rock shoals with 

vegetative cover and turbidity from river 

inflow 

• In Lower River: No large floodplains in

river, but numerous large backwaters 

used by other native suckers

• In Lake Mead: Rock shoals with 

vegetative cover and turbidity from river 

inflow 

Juvenile and Adult 

Maintenance and 

Movement 

• In Rivers: low velocity eddies, pools, 

runs, backwaters, floodplains 

• In Reservoirs: shorelines with rocky and 

vegetative cover 

• In Lower River: Low velocity eddies, 

pools, runs, backwaters 

• In Lake Mead: shorelines with rocky 

and vegetative cover 

If spawning was to occur at the three large cobble/gravel bars identified in the lower Grand 

Canyon (i.e., Diamond Creek, RM 225.6; Spencer Canyon, RM 246; and Surprise Canyon, RM 

248.3), the distance that larvae would have to drift to reach potential nursery habitat in Pearce 

Ferry Bay (RM 280) would be 54.4, 34, and 31.7 mi, respectively (Figure 37). At an estimated 

average river speed of 2.5 mph, a passively drifting larva could reach Pearce Ferry Bay in about 

21.8, 13.6, and 12.7 hr, respectively, which is presumably sufficient time to prevent starvation. 

As a comparison for larval drift, the distance from a known spawning bar to floodplains used as 

nurseries in the middle Green River ranges from about 6 to 60 mi, and the greatest distance from

the uppermost bar in lower Grand Canyon (Diamond Creek) to the known spawning bar in the 

Colorado River inflow is 64 mi. 

It is noted that of the 33 razorback sucker larvae found in the Colorado River inflow in 2000 and 

2001, one was located in Pearce Ferry Bay. The origin of this fish is unknown, but at the time of 

collection, Pearce Ferry Bay was inundated by Lake Mead and it is possible that this larva was 

transported to that location by winds and water currents. It is unlikely that the fish was hatched 

from a local spawning event because there are no known cobble/gravel bars in the area and the 

river channel in and near Pearce Ferry Bay is part of the large eroding silt/sand delta of the 

Colorado River. It is also possible that this and other larvae originated from one of several bars 

in the lower Grand Canyon. 

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A 

B 

Figure 35. Photos of cobble/gravel bars at (A) Diamond Creek, and (B) Spencer Canyon in lower Grand 

Canyon. Photo of Diamond Creek courtesy of Hualapai Tribe. Photo of Spencer Canyon taken September 18, 

2010 by C. McAda when flow of the Colorado River was 9,200–9,300 cfs. 

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A 

B 

Figure 36. Photos of cobble/gravel bars (A) at Salt Creek in lower Grand Canyon, and (B) between Devil’s 

Cove and North Bay near known spawning area in the Colorado River inflow. Flow of the Colorado River was 

9,200–9,300 cfs. Photos taken September 18–19, 2010 by C. McAda. 

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A B

Figure 37. Comparison of distances from (A) a known spawning bar to nursery floodplains in the middle 

Green River, and (B) three potential spawning bars in lower Grand Canyon to known nursery areas in the 

Colorado River inflow to Lake Mead. Distances on vertical bars are approximate distances along the river 

channel. River miles are shown as blocked numbers on each map. 

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6.2.2 Larval Nursing and Rearing 

Larval razorback suckers in a riverine setting typically use large riverside floodplains as 

nurseries. These floodplains become connected and inundated with high spring flows that 

coincide with spawning events. Floodplains used as nurseries include the areas on the Green 

River between Split Mountain and Desolation Canyon, and in the area of Grand Junction in the 

Colorado River. Where natural floodplains are absent or lacking, the larvae nurse in artificial 

features that function like floodplains, including gravel pits, such as the Colorado River and the 

Gunnison River near Grand Junction. Few larval razorback suckers are found in backwaters of 

these rivers because this habitat feature forms at lower river flows. In steep-gradient rivers where 

floodplains are lacking, such as the San Juan River, larval razorback suckers use backwaters or 

small embayments. It should also be noted that larvae hatched in the San Juan River are also 

found in the Lake Powell inflow, where investigations continue to determine if these fish are 

surviving and recruiting back to the river population. 

In a reservoir setting, emerging larvae are subject to wave action and wind, but may be exposed 

to high levels of predation because of high water clarity, a lack of cover, and large numbers of 

predators. Recent investigations in Lake Mead have found larval razorback suckers along 

vegetated shorelines and in areas with moderate to high turbidity, such as river inflows. These 

findings suggest that cover in the form of vegetation and/or turbidity helps the larvae find shelter 

from predators and enhances their chances of survival. 

Floodplains, such as used in the Green and Colorado rivers as nurseries by larval razorback 

suckers, are absent from the lower Grand Canyon. Large embayments occur at canyon mouths 

that could serve as floodplains if connected to the main channel at locations such as Surprise

Canyon, Lost Creek, Burnt Spring Canyon, and Ticanebitts Canyon. These embayments were 

formed when Lake Mead was at a higher elevation, but the receding lake levels deposited large 

sand/silt berms that blocked the mouths of these canyons. Some of these isolated embayments 

retain water from up-canyon seepage or from subterranean river connection, but reconnecting 

these features is not reasonable because of the remote location and the uncertainty of their value 

as nurseries in this setting. Isolated embayments also exist at Grand Wash Bay and Driftwood 

Cove (below Pearce Ferry), and numerous small, muddy, backwater-like indentations along the 

river’s margins may provide ephermeral rearing habitat. The only features that could reliably 

function as nurseries for larvae in the lower Grand Canyon are small sandy backwaters and 

complex shorelines (Figure 38). Much of the shoreline in the Colorado River inflow is unstable 

sand bars, but past about Iceberg Canyon a more stable rocky habitat is available (Figure 39). 

Based on calculations provided in the previous subsection, potential spawning bars in the lower 

Grand Canyon are a sufficient distance from the Colorado River inflow to be reached by a 

drifting larva before starving. 

Many investigators feel that the most important factor affecting survival of larval razorback 

suckers in nurseries is predation by nonnative fish species, as well as amphibians and insects. 

Predators clearly exist in the lower Grand Canyon and in the Colorado River inflow. No 

management action is available to minimize this predation, although the apparent history of 

razorback sucker recruitment in Lake Mead suggests that turbidity and vegetated shorelines help 

to enhance larval survival and recruitment (Albrecht et al. 2010b). 

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A 

B 

Figure 38. Photos of (A) sand backwater used by young native suckers, and (B) complex shoreline habitat 

with rocky and vegetated shoreline in lower Grand Canyon. Flow of the Colorado River was 9,200–9,300 cfs. 

Photos taken September 16, 2010 by C. McAda. 

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A 

B 

Figure 39. Photos of (A) eroding sand backs near Pearce Ferry, and (B) exposed Lake Mead shoreline and 

high band of vegetation used by razorback sucker larvae at higher lake levels. Flow of the Colorado River 

was 9,200–9,300 cfs. Photos taken September 19, 2010 by C. McAda. 

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6.2.3 Juvenile and Adult Maintenance and Movement

Large juvenile and adult razorback suckers in rivers use a variety of habitats generally 

characterized by low to moderate velocity, moderate to deep water, and a soft silt or sand 

substrate. The only time that adults consistently use swift, shallow water with a rocky substrate is 

during spawning, or during movements to and from spawning sites. Habitats typically used by 

juveniles and adults for maintenance include runs, pools, and eddies where the fish can maintain 

their position and feed on drifting or bottom organisms and detritus with little energy 

expenditure. 

In a reservoir setting juveniles and adults also use a variety of habitats, but tend to stay near 

shorelines with rocky or vegetative cover or in areas with turbidity. These fish may move 

extensively in reservoirs and not necessarily for spawning. 

The Colorado River in the lower Grand Canyon is a canyon-bound reach with a complex of 

habitat types potentially useable by subadult and adult razorback suckers (Figure 40A). There are 

no barriers to movement in this reach of the Colorado River except perhaps for a large rapid that 

formed in 2009 about 1 mi downstream from Pearce Ferry (Figure 40B). Radio-tagged fish from

Lake Mead have been tracked to areas below this rapid, but none have been documented to 

ascend past this point. The water level at the rapid drops about 10 ft, and water velocities appear 

to be quite high. Possibly, this feature is at least a partial barrier to upstream movement of 

razorback suckers, although the single larvae collected in Pearce Ferry Bay indicates that at least 

some fish have been upstream of this rapid. Because the river channel is still eroding the deltaic 

deposits in the Colorado River inflow to Lake Mead, the appearance of this rapid is likely to 

change over time. Hence, although the habitat in the lower Grand Canyon appears suitable for 

large juvenile and adult razorback suckers, movement of fish from the Lake Mead population 

may currently be impeded by this rapid. 

The habitat in the Colorado River inflow downstream of the Pearce Ferry Rapid also appears 

suitable (Figure 41A) and has recently been used by razorback suckers, including fish moving 

into the area from the other populations at Las Vegas Bay, Echo Bay, and the Muddy 

River/Virgin River inflow. The suitability of the habitat in this area evidently varies with lake 

elevation, but the lake level for optimal habitat is not presently known. 

The recent invasion of the nonnative quagga mussel (Dreissena rostriformis bugensis) into Lake 

Mead (Figure 41B) may have adverse consequences on the aquatic ecosystem, especially at the 

primary producer level. The quagga mussel is a filter feeder and its rapid rate of population 

increase can result in large amounts of nutrients being filtered from the water column and a 

collapse of the primary producers, including the phytoplankton and zooplankton communities. 

Because young razorback suckers rely on zooplankton for food, the quagga mussel could have a 

detrimental effect on their food supply in Lake Mead. 

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A 

B 

Figure 40. Photos of (A) Colorado River near Whitmore Wash, and (B) large rapid about 1 mi downstream 

from Pearce Ferry in the Colorado River inflow. Flow of the Colorado River was 9,200–9,300 cfs. Photos 

taken September 19, 2010, courtesy of (A) J. Stolberg and (B) C. McAda. 

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A 

B 

Figure 41. Photos of the Colorado River inflow between Devil’s Cove and North Bay showing (A) 

cobble/gravel islands used by razorback suckers, and (B) clusters of quagga mussels on rock substrate. 

Lake Mead at low elevation. Photos taken September 19, 2010 by C. McAda.

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6.3 Biological Components of Lower Grand Canyon 

6.3.1 Food Base 

The food base of the Colorado River in the lower Grand Canyon has not been described. Recent 

samples from Diamond Creek may reflect the macroinvertebrate biomass and species 

composition for stable substrates, but a large portion of the river channel in the lower Grand 

Canyon continues to erode and create unstable conditions for invertebrate communities. The 

river at the interface of Lake Mead has carved a channel into the deltaic sediment deposits where 

there is a great deal of woody debris that is being washed into the river with the eroding sand 

banks. This woody debris is rich in organic matter and may be supporting a large, but rather 

dynamic biomass of invertebrates in what more closely resembles the historical allochthonous 

productivity system than the autochthonous system found closer to Glen Canyon Dam. 

Samples taken in March 2008 from cobble, deposits, and talus habitats at three sites: (A) Lees 

Ferry (RM 0), (B) the confluence of the Little Colorado River (RM 62), and (C) Diamond Creek 

(RM 225) show that six taxonomic groups were common but varied by reach and habitat type 

(Figure 42; Rosi-Marshall et al. 2010). For the downstream-most site at Diamond Creek, the 

invertebrates were found primarily in cobble and talus. Invertebrates were nearly absent from

silt/sand deposits, which is likely reflective of the invertebrate communities in the lower Grand 

Canyon. These findings highlight the importance of relatively stable features, such as cobble and 

talus as areas of local productivity, but also suggest that there is little local productivity in the 

inflow region where channel erosion continues. 

 

Figure 42. Macroinvertebrate biomass as g AFDM/m2 (ash-free dry mass) and relative taxa composition in 

the three dominant habitat types (cobble, deposits, and talus) at three locations on the Colorado River in 

Grand Canyon: (A) Lees Ferry (RM 0), (B) Little Colorado River (RM 62), and (C) Diamond Creek (RM 225) in 

March 2008. Figure from Rosi-Marshall et al. (2010). 

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6.3.2 Fish Community 

There are reportedly 21 species of fish that occur in the Colorado River between Glen Canyon 

Dam and Pearce Ferry, including 16 introduced and 5 native species; native species include the 

humpback chub (Gila cypha), flannelmouth sucker, bluehead sucker, and speckled dace 

(Rhinichthys osculus) (Valdez and Carothers 1998). The razorback sucker appears to be

extirpated from Grand Canyon, but is found as a small reproducing population downstream from

the canyon in and below the Colorado River inflow in Lake Mead (Albrecht et al. 2008, 2010). 

The largest population of humpback chub in the Colorado River System is found in the Grand 

Canyon upstream of Diamond Creek, but only one individual has been caught in the lower Grand 

Canyon during recent surveys; an adult female (329 mm TL) was caught and released at RM 

253.2, near Maxon Canyon in October 1993 (Valdez 1994). Evidently, all three species of Gila

were present in the lower Grand Canyon prior to the inundation by Lake Mead and the 

subsequent build-up of deltaic deposits. In the 1940's, five humpback chub (G. cypha) were 

collected from the area of Spencer Canyon (near Lava Cliff rapid, RM 246), along with 16 

bonytail (G. elegans), and six roundtail chub (G. robusta) (Miller 1944; Bookstein et al. 1985). 

Razorback suckers were not reported from these early collections from the lower Grand Canyon. 

Contemporary surveys of the fish community between Diamond Creek and Pearce Ferry were 

conducted during 1992–1995 (Valdez et al. 1995), 2004–2006 (Ackerman et al. 2006), and 2005 

(Rogers et al. 2007). The earliest survey took place when Lake Mead was at a high level, and the 

other two took place at a low reservoir level (Figure 43). Because the lower Grand Canyon is 

part of the inflow region of Lake Mead, there were substantial differences in habitat conditions 

during the two surveys. For the first survey, the river between Separation Canyon (RM 240) and 

Emery Falls was wide and slow-flowing with a flat-bed channel of sand and silt that was lined 

with dense stands of riparian vegetation. Downstream of Emery Falls, there was an expansive 

area of water, as a lake-type habitat, that inundated much of the riparian vegetation and Pearce 

Ferry Bay (Figure 44). 

A standard fish monitoring program has been in effect for several years from Glen Canyon Dam

to Diamond Creek (e.g., Makinster et al. 2007, 2008, 2009), but has not been extended 

downstream on a regular basis. During June 2007 and July 2008, the AGFD, in cooperation with 

GCMRC, launched a pilot project to investigate movement of channel catfish (Ictalurus 

punctatus) from the Lake Mead inflow into the Grand Canyon, since channel catfish are 

considered a principal predator of the humpback chub. A number of gears were deployed and 

evaluated, including angling, electrofishing, and baited hoop nets. Catches of channel catfish 

were variable and the number of individuals does not appear to be stable in the lower Grand 

Canyon—possibly as a consequence of the dynamic nature of the inflow. 

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Figure 43. Longitudinal cross-section of the lower Grand Canyon from Diamond Creek to Pearce Ferry, 

showing the elevational gradient of the Colorado River, the deltaic sediment deposits, and the approximate 

elevations of Lake Mead during the 1992–95 and 2004–06 fish surveys.

A B 

Figure 44. Aerial views of the lower Grand Canyon taken in June 1992 showing (A) the deltaic sediments

deposits and growths of riparian vegetation near Emery Fals, and (B) the widened river channel at the 

interface of the Colorado River and Lake Mead in the Pearce Ferry Bay. Photos by R. Valdez. 

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6.0 Habitat Suitability of Lower Grand Canyon April 1, 2012 

During 1992–1995, seven species made up about 95% of the total fish composition; red shiners 

(Cyprinella lutrensis) were the most abundant, followed by common carp (Cyprinus carpio), 

threadfin shad (Dorosoma petenense), and fathead minnow (Pimephales promelas). Channel 

catfish, mosquitofish (Gambusia affinis), and flannelmouth suckers were less common (Table 

19). The 2004–2006 survey was conducted at a much lower reservoir level when the river was 

carving a channel through the deltaic deposits. The fish community was still dominated by 

nonnative species such as red shiners, common carp, channel catfish, and mosquitofish, but 

native species including the speckled dace and flannelmouth sucker were far more abundant than 

during 1992–1995 (Figure 45). 

0%

10%

20%

30%

40%

50%

60%

1992 1993 1994 1995 2004 2005 2006

P

erc

e

nt C

o

m

p

o

sitio

n

RS

CP

FH

CC

Nonnative Species

72% 91%

0%

5%

10%

15%

20%

25%

1992 1993 1994 1995 2004 2005 2006

P

erc

e

nt C

omp

o

sitio

n

FM

SD

BH

Native Species

Figure 45. Percent of total number of fish caught by year from Diamond Creek to Pearce Ferry. Data for 

1992–1995 from Valdez et al. (1995) and for 2004–2006 from Ackerman et al. (2006). See Table 19 for species 

codes. 

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itability of Lower Grand Canyon April 1, 2012 

rback Sucker Habitat Final Report 

RM 189-225

(Whitmore-Diamond)

SD

57% FM

18%

BH

7%

CP

FH 7%

7%

PK

0.3%

CC 

3%

For the period 1992–1995, the longitudinal distribution of fish species from Whitmore Wash

(RM 189) to below Pearce Ferry (RM 286) was dramatic, largely because the deltaic sediment 

deposits filled the river channel and reduced habitat complexity below about Bridge Canyon 

(RM 235). The interface of the Colorado River with the Lake Mead inflow created a slowflowing environment more conducive to introduced nonnative fishes (Figure 46). The reach from

Whitmore Wash to Diamond Creek was dominated by three native species, the speckled dace, 

flannelmouth sucker, and bluehead sucker, with smaller proportions of nonnative carp, fathead 

minnows, and channel catfish. The reach from Diamond Creek to Bridge Canyon was dominated 

by carp and channel catfish, although speckled dace, flannelmouth suckers, and bluehead suckers

persisted.

The longitudinal transition in the fish community was most dramatic below Bridge Canyon,

where sediment deposits had transformed the historical river channel into a flat uniform channel. 

Dominant species were red shiners, carp, fathead minnows, and channel catfish. Downstream of

Emery Falls, the fish community was more indicative of a lake-like environment, and was 

dominated by threadfin shad, carp, and red shiners. This longitudinal transition in the fish 

community was changed to a more uniform pattern of species as the reservoir dropped and the 

river eroded a new channel into the sediment deposits. Some of the historical habitat, such as 

rock outcrops and bottom rock substrates are becoming exposed and the fish community in the 

lower Grand Canyon is transitioning toward a native fish community, dominated by speckled

dace, flannelmouth suckers, and bluehead suckers.

RM 225- (Diamond-B235 ridge) 

SB 

1%

CC

11%

FH

1%

BH

1%

SD

11%

CP

72%

FM

3%

RM 235-275

(Bridge-Emery)

GA 

3%

SB

CC 1%

4%

PK

0.1%

RS 

72%

FH

4%

CP 

12%

TS

0.3%

GS

0.1%

FM

1%

SD

1%

Figure 46. Percentage of fish composition for Whitmore Wash to Diamond Creek (RM 189–225), Diamond

Creek to Bridge Canyon (RM 225–235), Bridge Canyon to Emery Falls (RM 235–275), and Emery Falls to

below Pearce Ferry (RM 275–286) during 1992–1995. See Table 19 for data and species codes.

RM 275-286

(Emery-Pearce)

BC

0.5%

BG

5%

GS

0.1%

LM

4%

TS

36%

CP 

20%

FH

0.1%

RS 

25%

BB 

0.2%

CC

4%

SB 

GA 2%

4%

 
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itability of Lower Grand Canyon 

rback Sucker Habitat 

1992 1993 1994 1995 2004 2005 

Species Name and Code No. Per. No. Per. No. Per. No. Per. No. Per. No. 

Red shiner - RS 1351 54.9% 913 45.0% 1792 71.8% 937 91.2% 87 17.6% 191 Common carp - CP 315 12.8% 656 32.4% 327 13.1% 48 4.7% 33 6.7% 82 Threadfin shad 310 12.6% 10 0.5% 0 0.0% 0 0.0% 0 0.0% 1 Fathead minnow - FH 174 7.1% 44 2.2% 58 2.3% 16 1.6% 15 3.0% 9 Channel catfish - CC 85 3.5% 171 8.4% 90 3.6% 19 1.9% 76 15.4% 126 Mosquitofish 68 2.8% 109 5.4% 52 2.1% 2 0.2% 80 16.2% 8 Flannelmouth sucker - FM 38 1.5% 25 1.2% 28 1.1% 4 0.4% 82 16.6% 106 Bluegill 37 1.5% 1 0.0% 0 0.0% 0 0.0% 0 0.0% 0 Speckled dace - SD 36 1.5% 18 0.9% 98 3.9% 0 0.0% 118 23.8% 96 Largemouth bass 23 0.9% 12 0.6% 9 0.4% 0 0.0% 0 0.0% 0 Striped bass 14 0.6% 51 2.5% 38 1.5% 0 0.0% 0 0.0% 60 Black crappie 2 0.1% 2 0.1% 0 0.0% 0 0.0% 0 0.0% 0 Black bullhead 2 0.1% 0 0.0% 0 0.0% 0 0.0% 0 0.0% 0 Walleye 2 0.1% 0 0.0% 0 0.0% 0 0.0% 0 0.0% 0 Plains killifish 1 0.0% 4 0.2% 0 0.0% 0 0.0% 0 0.0% 0 Green sunfish 1 0.0% 6 0.3% 0 0.0% 0 0.0% 0 0.0% 0 Bluehead sucker - BH 0 0.0% 1 0.0% 2 0.1% 1 0.1% 3 0.6% 0 Smallmouth bass 0 0.0% 0 0.0% 0 0.0% 0 0.0% 0 0.0% 4 Humpback chub 0 0.0% 1 0.0% 0 0.0% 0 0.0% 0 0.0% 4 Rainbow trout 0 0.0% 3 0.1% 1 0.0% 0 0.0% 1 0.2% 0 Golden shiner 0 0.0% 0 0.0% 1 0.0% 0 0.0% 0 0.0% 0 Total 2459 100% 2027 100% 2496 100% 1027 100% 495 100% 687 

Table 19. Number and percent of fish species caught in the Colorado River from Diamond Creek to Pearce Ferry. Data for 1992(1995) and for 2004–2006 from Ackerman et al. (2006). 
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Appendix A: Habitat Suitability Indices April 1, 2012 

Razorback Sucker Habitat Final Report 

APPENDIX A: RAZORBACK SUCKER HABITAT SUITABILITY 

INDICES FROM SCIENTIFIC REPORTS 

 A-1 
Appendix A: Habitat Suitability Indices April 1, 2012 

Razorback Sucker Habitat Final Report 

Habitat Suitability Indices – Upper Colorado River Basin 

(From Valdez et al. 1987) 

 

Figure A-1. Habitat suitability index (HSI) 

criteria (depth, velocity, substrate) for adult 

razorback suckers observed in the Green River 

May–June. 

Figure A-2. Habitat suitability index (HSI) 

criteria (depth, velocity, substrate) for adult 

razorback suckers observed in the Green River 

July–October.

 A-2 
Appendix A: Habitat Suitability Indices April 1, 2012 

Habitat Suitability Indices – Upper Colorado River, 15-Mile Reach 

(Data collected in Grand Valley, Colorado, during 1986, 1987, and 1988. N = number of 

observations; n = number of different suckers. From Osmundson and Kaeding 1989) 

Figure A-3. Mesohabitat used by four radio-tagged razorback suckers by month. 

Figure A-4. Frequency of depths at locations of radio-tagged razorback suckers by

month. 

Razorback Sucker Habitat Final Report 

 A-3 
Appendix A: Habitat Suitability Indices April 1, 2012 

Habitat Suitability Indices – Upper Colorado River, 15-Mile Reach 

(Osmundson and Kaeding 1989)

Figure A-5. Mean depth at location of four radio-tagged razorback suckers by month. 

Figure A-6. Frequency of mean column velocity (in cubic feet per second) at locations of four radio-tagged 

razorback suckers by month. 

Figure A-7. Frequency of substrate type at locations of four radio-tagged razorback suckers by month. 

Razorback Sucker Habitat Final Report 

 A-4 
Appendix A: Habitat Suitability Indices April 1, 2012 

Habitat Suitability Indices – Upper Colorado River 

(Valdez et al. 1982) 

Figure A-8. Habitat suitability index (HSI) criteria (depth, velocity, substrate) for adult razorback suckers 

captured in the upper Colorado River, 1979–1981. 

Razorback Sucker Habitat Final Report 

 A-5 
Appendix A: Habitat Suitability Indices April 1, 2012 

Habitat Suitability Indices – Green River (winter) 

(Valdez and Masslich 1989) 

 

Figure A-9. Habitat suitability index (HSI) criteria (depth, velocity, substrate) for razorback sucker overwinter 

use from 1987 and 1988 no ice data. 

Razorback Sucker Habitat Final Report 

 A-6 
Appendix A: Habitat Suitability Indices April 1, 2012 

Habitat Suitability Indices –Verde River 

(Clarkson et al. 1993) 

Figure A-10. Frequency distributions for velocity, depth, and substrate (A) available in the Verde River, and 

(B) used by 24 radio-tagged subadult and adult razorback suckers in the Verde River, 1991–92.

Razorback Sucker Habitat Final Report 

 A-7 
Appendix B: 

Razo

 B-1

Preliminary 2009 Field Survey April 1, 2012

rback Sucker Habitat Final Report 

APPENDIX B: PRELIMINARY SURVEY OF LOWER GRAND CANYON 

(SPEAS AND TRAMMELL 2009)

 
Appendix B: Preliminary 2009 Field Survey 

Table B-1. Aquatic habitat characteristics by river mile in lower Grand Canyon; preliminary results of 2009 field survey (Speas Color-coded columns to the left highlight the presence or absence of cobble substrate, gravel substrate, and backwaters. Gray 

channel type break points. We wish to thank Dave Speas and Melissa Trammell for providing the information regarding their 20this report. The results shown here are preliminary and should be understood as such. Results from this field survey should n

without permission of the authors. 

Cobble 

Substrate 

Gravel 

Substrate 

Backwater RM1 Backwaters BW right BW left BW wpt Temp oC Hab 12,3 Hab 22,3 Hab 32,3 # Hab4 Cover5 Islands Complex ?6 

181 1 na 1 269 RU ED BW 3 VG 1 Y B

185 1 na 1 na ED RI RU 3 na 0 N 1 

187 1 1 na 271 RU ED 2 VG 0 N

18S

188 0 na na na RI RU ED 3 na 1 Y

Cw

189 0 na na na ED RU 2 na 0 Y

Swgr

191 2 1 1 272 RI RU 2 na 1 Y

SBB

192 1 1 na 274 RI ED 2 VG 1 Y B

193 1 na 1 275 16 RU ED RI 3 VG 3 Y

TeisshL nola(8

Razorback Sucker Habitat  B-2
Appendix B: Preliminary 2009 Field Survey 

Cobble 

Substrate 

Gravel 

Substrate 

Backwater RM1 Backwaters BW right BW left BW wpt Temp oC Hab 12,3 Hab 22,3 Hab 32,3 # Hab4 Cover5 Islands Complex ?6 

194 0 na na na RI RU 2 VG 1 Y

1 at shsuhe

196 1 1 na 276 RU RI 2 na 1 Y

Cfaw

198 1 1 na 277 RI 1 na 1 Y

PcoR

199 1 na 1 278 RI RU 2 VG 1 Y

Lg 20m

200 0 na na na 16 RI RU 2 na 2 Y

Tealat 

201 1 na 1 279 ED RI 2 na 0 Y

BBha

202 2 2 na 280 16.5 ED RI 2 na 1 Y

Teis

204 2 2 na

281, 

282 ED RI 2 na 1 Y

CTwflo

205 0 na na na RI ED RA 3 na 2 Y C

208 1 na 1 na RU ED RI 3 na 1 Y 

R20

Razorback Sucker Habitat  B-3
Appendix B: Preliminary 2009 Field Survey 

Cobble 

Substrate 

Gravel 

Substrate 

Backwater RM1 Backwaters BW right BW left BW wpt Temp oC Hab 12,3 Hab 22,3 Hab 32,3 # Hab4 Cover5 Islands Complex ?6 

210 0 na na na RU ED 2 na 0 N

Mlebase

214 0 na na na ED RU 2 na 0 N

Oan

216 0 na na na RU ED 2 VG 0 N

Fru

217 0 na na na RU ED RA 3 VG 0 N

Abereraon"p

220 1 na 1 284 17 RI ED 2 VG 1 Y

Frifdeertelavalo

221 0 na na na RU RI 2 VG 0 Y

Vansh

222 0 na na na RU RI RA 3 na 1 Y

Isberuis

Razorback Sucker Habitat  B-4
Appendix B: Preliminary 2009 Field Survey 

Cobble 

Substrate 

Gravel 

Substrate 

Backwater RM1 Backwaters BW right BW left BW wpt Temp oC Hab 12,3 Hab 22,3 Hab 32,3 # Hab4 Cover5 Islands Complex ?6 

223 0 na na na RI RA 2 na 1 Y

Drifbethbe

225 0 na na na RU 1 VG 0 N

Mberu

229 2 2 na 285,286 0 na 0 Y

SG

236 1 na 1 287 ED RA 2 na 0 N S

238 1 1 na 288 ED 1 na 0 N

Mmw1/

239 1 na na 289 ED 1 na 0 N

SB

240 3 na 3 na 17 RU 1 na 0 N

Msata

241 1 1 na 290 RU 1 na 0 N B

242 2 2 na na RU 1 na 0 N

Losm at 

243 1 1 na 293 17.5 RU 1 na 0 N

"Mlase17

244 2 1 1 294,295 RU 1 na 0 N

B24

Razorback Sucker Habitat  B-5
Appendix B: Preliminary 2009 Field Survey 

Cobble 

Substrate 

Gravel 

Substrate 

Backwater RM1 Backwaters BW right BW left BW wpt Temp oC Hab 12,3 Hab 22,3 Hab 32,3 # Hab4 Cover5 Islands Complex ?6 

246 1 1 na 297 RU 1 na 0 N B

247 1 na na 298 RU 1 na 0 N

Bco

249 1 1 na na RU RI 2 na 0 Y

Rcodo20

250 1 na 1

299, 

300 RU 1 na 0 N

N29

253 1 na 1 na RU 1 na 0 N 

Bfo

255 1 na 1 na RU 1 TURB 0 N B

258 1 na na 303 RU 1 TURB 0 N S

259 1 1 na 304 RU 1 TURB 0 N

Rba

263 1 1 na 305 18 RU 1 TURB 0 N B

265 1 1 na na RU 1 TURB 2 N

Snesaon 

1 River miles from Stevens, L. 1983. The Colorado River in Grand Canyon. Red Lake Books, Flagstaff, Arizona. 2 Hab 1=dominant habitat type; Hab 2=secondary habitat type; Hab 3=tertiary habitat type 3 RU=run; RI=riffle; ED=eddy; BW=backwater; RA=rapid 4 # Hab=Number of habitat types present 5 Cover=overhanging or turbidity; VG=terrestrial vegetation; TURB=sediment turbidity 6 Complex=Categorical variable based on presence of habitat for multiple life stages (more than one habitat type present; backwaters, riffles, islands, Razorback Sucker Habitat  B-6