BIOLOGICAL ASSESSMENT 

FOR RESTORING FISH PASSAGE 

AT THE PRICE-STUBB DIVERSION DAM 

ON THE COLORADO RIVER 

NEAR PALISADE, COLORADO

Bureau of Reclamation 

Western Colorado Area Office 

Upper Colorado Region 

Grand Junction, Colorado 

June 2003
Price-Stubb Fish Passage Biological Assessment - 1 - 

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232. 3 GVIC Diversion Dam

and Fish Passage

Price-Stubb 

 Diversion Dam

Colorado River Siphon

Grand Valley Project

Diversion Dam

Colorado

River

Plateau Cr.

Ute Water Pump Plant

Interstate 70

Hwy 6

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S Palisade

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Gunnison River

Colorado River

Redlands Diversion Dam

and Fish Ladder

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Price-Stubb Diversion Dam

GVIC Diversion Dam and Fish Passage

Grand Valley Project Diversion Dam

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Price-Stubb Fish Passage Biological Assessment - 2 -

Table of Contents 

 Page

1.1 Purpose 01 

1.2 Recovery Program 02 

2.1 Project Description 03 

2.2 Construction 04 

2.3 Operation, Maintenance and Replacement Measures 04 

3.0 Federally Listed Species 04 

3.1.0 Colorado River Endangered Fishes 05 

3.1.1 Colorado Pikeminnow 05 

3.1.2 Colorado Pikeminnow Distribution-Colorado River 06 

3.1.3 Colorado Pikeminnow Distribution-Gunnison River 08 

3.1.4 Colorado Pikeminnow Augmentation 09 

3.1.5 Colorado Pikeminnow Habitat Use 10 

3.1.6 Colorado Pikeminnow Reproduction 11 

3.2.1 Razorback Sucker 12 

3.2.2 Razorback Sucker Distribution-Colorado River 13 

3.2.3 Razorback Sucker Distribution-Gunnison River 14 

3.2.4 Razorback Sucker Population Augmentation 15 

3.2.5 Razorback Sucker Habitat Use 17 

3.2.6 Razorback Sucker Reproduction 18 

3.3.1 Humpback Chub and Bonytail 19 

3.3.2 Bonytail Population Augmentation 21 

3.4.0 Effects on Colorado River Endangered Fishes 21 

3.5.0 Endangered Fishes Critical Habitat 22 

3.6.0 Bald Eagle 22 

3.6.1 Bald Eagle Habitat Preference 23 

3.6.2 Bald Eagle Distribution and Abundance 23 

3.6.3 Effects on Bald Eagle 23 

3.7.0 Southwestern Willow Flycatcher 24 

3.7.1 Southwestern Willow Flycatcher Habitat Preference 24 

3.7.2 Southwestern Willow Flycatcher Distribution 24 

3.7.3 Effects o Southwestern Willow Flycatcher 25 

4.0 Conclusions 25 

5.0 References 26 
Price-Stubb Fish Passage Biological Assessment - 3 -

List of Figures

Frontispiece Map-Price-Stubb Diversion Dam Vicinity Map 

Figure 1.1-Price Stubb Diversion Dam 01 

Figure 2.1-Price-Stubb Fish Passage Conceptual Drawing 03 

Figure 3.1-Distribution of Colorado pikeminnow in the Colorado and 07 

 Gunnison rivers. 

Figure 3.2-Colorado pikeminnow distribution between GVIC 08 

 and Price-Stubb Diversion Dams. 

Figure 3.3-Gunnison River Colorado Pikeminnow Distribution 10 

Figure 3.4-Potential Colorado Pikeminnow Spawining Sites 13 

 on the Upper Colorado River. 

Figure 3.5-Distribution of Razorback Sucker in the Colorado and 15 

 and Gunnison Rivers. 

Figure 3.6-Larval and Juvenile Razorback Sucker Collections from 16 

 the Colorado and Gunnison Rivers. 

Figure 3.7-Distribution of Humpback Chub and Bonytail in the 20 

 Colorado and Gunnison Rivers. 

List of Tables

Table 3.1-Federally Threatened and Endangered Species that May 05 

 Occur Within the Project Area. 

Table 3.2-Integrated Stocking Plan for Colorado Pikeminnow, 09 

 Third Priority Species. 

Table 3.3-Recovery Program Razorback Sucker Stocked in Gunnison 17 

 and Colorado Rivers, 1996-2001. 

Table 3.4-Integrated Stocking Plan for Razorback Sucker, 18 

 First Priority Species 

Table 3.5-Integrated Stocking Plan for Bonytail, 21 

Second Priority Species
Price-Stubb Fish Passage Biological Assessment - 1 - 

1.1 Purpose

The Price-Stubb Diversion Dam (see Figure 1) constructed in 1911, represents a barrier 

to all upstream fish movement. The Dam was constructed by the Palisade and Mesa 

County Irrigation Districts to provide irrigation water to lands around Palisade, Colorado. 

In 1919, the dam was no longer used following the completion of the Bureau of 

Reclamation’s (Reclamation) Grand Valley Project Diversion Dam and the Government 

Highline Canal. 

Reclamation, on behalf of the Upper Colorado River Endangered Fishes Recovery 

Program, would construct a rock fish passage at the Price-Stubb Diversion Dam to allow 

fish access above the Dam. The purpose of this biological assessment is to evaluate 

affects of the proposed action of restoring fish passage at the Price-Stubb Diversion Dam 

to species listed under the Endangered Species Act of 1973. 

Figure 1.1-Price-Stubb Diversion Dam 

1.2 Recovery Program

The Upper Colorado River Endangered Fish Recovery Program (Recovery Program) was 

established in 1987 to recover four endangered Colorado River fishes: Colorado 

pikeminnow (Ptychocheilus lucius), formerly known as the Colorado squawfish; 

razorback sucker (Xyrauchen texanus); bonytail (Gila elegans); and humpback chub 

(Gila cypha). 
Price-Stubb Fish Passage Biological Assessment - 2 -

The Recovery Program consists of Federal and State agencies, water users and 

environmental interests with a goal of establishing self-sustaining populations of the four 

endangered fish species in the Upper Colorado River Basin while allowing for continued 

use and future development of Colorado River water supplies. The Recovery Program 

has five major elements (USFWS 1987a, 1987b), which are: 

1) provision for instream flows for habitat; 

2) habitat development and maintenance; 

3) native fish stocking; 

4) management of non-native species and sport fishing; and 

5) research, monitoring and data management. 

In the Upper Colorado River Basin, endangered fish access to upstream habitat has been 

blocked by three irrigation diversions dams on the Colorado River (Frontispiece Map). 

These diversion dams are: 

1) the Grand Valley Irrigation Company (GVIC) Diversion Dam, about 3 miles 

downstream of the Price-Stubb Diversion Dam; 

2) the Price-Stubb Diversion Dam (discussed in this biological assessment); and 

3) the Grand Valley Project Diversion Dam, about 5.3 miles upstream of the PriceStubb Diversion Dam. 

In March of 1998, a notch was completed in the GVIC Diversion Dam and a fish 

passageway was constructed below it. The passageway consists of rocks placed in the 

Colorado River channel to form a series of riffles and pools. Restored fish passage at the 

Grand Valley Project Diversion Dam is scheduled for 2003-2004 and Reclamation would 

construct a conventional concrete fish passage through the river left roller bay. Fish 

passage at the Price-Stubb Diversion Dam is discussed in this biological assessment and 

would be completed in 2005. 

2.1 Project Description

The proposed fish passage at the Price-Stubb Diversion Dam was designed based on the 

behavior of the endangered fish, their swimming abilities, dam design and maintenance 

needs, and the need to limit impacts associated with upstream uses (i.e. Ute Water’s 

Pumping Plant, Landslide Areas, Colorado River Siphon, Palisade and Mesa County 

Irrigation Districts Water Rights, and Union Pacific Railroad and Interstate 70 

foundations). 

The fish passage would be built along the left1

 riverbank below the Price-Stubb Diversion 

Dam (Figure 2). An 800-ft. riprap lined channel along the riverbank would comprise the 

fish passage channel. A notch would be made in the dam to allow the first 100 cfs of the 

river to pass through the fish passage channel. An 800-ft. berm sloping downstream 

would be constructed to keep flows in the channel at a slope of 2.0 percent. Boulders 

 

1

 Refers to the left side of the river when facing downstream. 
Price-Stubb Fish Passage Biological Assessment - 3 -

would be placed in the fish passage channel as needed to maintain the desired fish 

passage velocities and create low flow resting areas. The remaining portion of the dam 

face would also be riprapped at a slope of 4.0 percent for a length of 400 ft. The riprap 

would provide stability to the passage channel and address safety issues with recreational 

boating. Reclamation is also incorporating a boat passage in its designs. The boat 

passage would be constructed with non-federal funds during fish passage construction if 

are available. 

Figure 2.1-Price-Stubb Fish Passage Conceptual Drawing 

#

Top of Berm

Bottom of Fish 

Passage Channel

Riprap Fill

Rock Ramp

Interstate 70

Flow

N

Fish Passage Entrance

Railroad

Riprap Fill

Fish Passage Exit

<

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400 '

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800'

 As river flows increase, the length of the fish passage channel would decrease. Flows 

greater than 100 cfs would begin to spill over the remaining portion of the dam. 

The fish passage at the Price-Stubb Diversion Dam would allow unrestricted fish 

movement upstream of the Diversion Dam. A selective passage device (fish trap) is 

incorporated in the designs for the Grand Valley Project Diversion Dam and would 

prevent non-native fish movement upstream of the Grand Valley Project Diversion Dam. 

The Biology Committee requested that Reclamation evaluate the feasibility of installing 

selective fish passage using the rock ramp design at the Price-Stubb Diversion Dam to 

prevent non-native species from entering the 4.4 miles of critical habitat between the 

Price-Stubb Diversion Dam and the Grand Valley Project Diversion Dam. To provide 

access to the fish trap, about 0.3 miles of road along the Colorado River would need to be 
Price-Stubb Fish Passage Biological Assessment - 4 -

built at a cost of about $1,500,000. The cost of including selective fish passage was 

determined to be prohibitive. 

The fish passage would be a run of the river type passage and require minimal operation 

and maintenance activities. The fish passage would operate year-round. 

The proposed Jacobson Hydro No. 1 Project (FERC, 2001) with modifications would not 

impact the fish passage structure. Modifications would require that the Hydro Project 

pipe its return flows under the river and return them to the fish passage entrance. 

Because the Jacobson Hydro No. 1 Project license has been terminated, no additional 

discussion of this project is provided (FERC, 2002). 

2.2 Construction

The fish passage would be completed under construction contract. The Dam owners 

(Palisade and Mesa County Irrigation Districts) would participate in the design process. 

Temporary construction easements and permits would also be acquired from all affected 

landowners prior to construction. Following construction, any damaged areas would be 

restored, as near as possible, to its original condition. 

The project area would be accessed from an existing railroad service road under Interstate 

70. Construction staging and material storage would be on the right riverbank. A 

cofferdam would likely be necessary to divert river flows while the 640 cfs notch was cut 

in the Dam. Reclamation would request Clean Water Act, Section 404 authorization 

under Regional General Permit No. 057 for projects that benefit the recovery of 

endangered fish. If discharging water for dewatering the construction site is needed, the 

contractor would obtain a Section 402 permit. 

Construction would begin during low water during the fall of 2004 with completion prior 

to the spring of 2005. Total project costs are estimated at $3,100,000. 

2.3 Operations, Maintenance and Replacement Measures

The fish passage would operate year-round. Because the fish passage is designed as a 

“run-of-the-river” type passage, no manual operation activities are necessary. Fish 

passage maintenance would be limited to removing large debris and sediment from the 

fish passage channel and “fine tuning” boulder placements in the fish passage channel. 

This is expected to be infrequent and would be conducted on an “as needed” basis and at 

low river flows. 

3.0 Federally Listed Species 

The U.S. Fish and Wildlife Service identified six federally listed threatened or 

endangered species that could potentially occur within the project area. These species are 

listed in Table 1. The know distribution and status of these species in the project area are 

discussed individually. 
Price-Stubb Fish Passage Biological Assessment - 5 -

Inventories conducted by Reclamation biologists as part of the present investigation were 

performed in 2001 and 2002. Inventories included visual surveys for bald eagle nesting 

and Southwestern willow flycatcher habitats. Literature searches were conducted for the 

four endangered Colorado River fishes. 

Table 3.1-Federally Threatened and Endangered Species That May Occur Within the Project Area. 

Species Status Project Effect 

Colorado Pikeminnow Endangered May affect, not likely to 

adversely affect (Beneficial)

Razorback Sucker Endangered May affect, not likely to 

adversely affect (Beneficial)

Bonytail Endangered May affect, not likely to 

adversely affect (Beneficial)

Humpback Chub Endangered No effect 

Southwestern Willow 

Flycatcher 

Threatened No effect 

Bald Eagle Threatened No effect 

3.1 Colorado River Endangered Fishes

3.1.1 Colorado Pikeminnow

Colorado pikeminnow (formerly known as Colorado squawfish) is a large piscivorus 

cyprinid endemic to the Colorado River Basin (Minckley 1973) and is one of four large 

cyprinids of the genus Ptychocheilus native to the western United States (Robins et al., 

1991). 

Colorado pikeminnow is the largest of the four and reportedly reached lengths 

approaching 1.8 m and weights of 45 kg (Minckley, 1973) during European settlement of 

the west. The largest Colorado pikeminnow captured in recent years was 960 mm long 

and exceeded 5-kg (McAda, 2000). In 2002, an adult female Colorado pikeminnow 940 

mm long and 7.6 kg was captured at the Redlands fish passageway. 

Colorado pikeminnow was once widespread in the large river of the Colorado River 

Basin, but it was eliminated from the basin downstream of Lake Powell by the late 1960s 

(Minckley, 1973). Although it still exists in the upper basin, its range has been reduced 

by construction of large reservoirs that eliminated habitat and changed downstream water 

quality (e.g. Vanicek et al. 1970) and construction of instream barriers that blocked 

access to historic range (Burdick and Kaeding, 1990). The reduced habitat and declining 

number of fish occupying the remaining habitat prompted the species to be included as 

endangered when a list of endangered species was published in 1967 (USFWS, 1967). 
Price-Stubb Fish Passage Biological Assessment - 6 -

3.1.2 Colorado Pikeminnow Distribution-Colorado River 

Colorado pikeminnow are distributed throughout the Colorado River from Price Stubb 

Dam, an impassible barrier at the upper end of the Grand Valley (RM 188.3), 

downstream to Lake Powell (Figure 3.1, Osmundson and Burnham 1988). Construction 

of fish passageways at the Price Stubb Diversion Dam in 2005 and the Grand Valley 

Project Diversion Dam in 2004 will remove barriers and will allow Colorado 

pikeminnow access to about 50 miles of critical habitat upstream to Rifle, Colorado. 

Burdick (1999), conducted intensive inventories in 1998 and 1999 to evaluate restored 

fish passage at the Grand Valley Irrigation Company Diversion Dam. Colorado 

pikeminnow captures are shown in Figure 3.2. 

Although pikeminnow use the entire river, there are distinct differences in distribution 

among age classes. In general, most adults are found in the upper reaches of the river and 

most sub-adults, juveniles, and young-of-year (YOY) are found in the lower reaches 

(McAda, 2000; Valdez et al. 1982b; Archer et al. 1985; McAda and Kaeding 1991; 

Osmundson et al. 1997). Osmundson and Burnham (1998) conducted an intensive riverwide study using mark recapture to estimate the population size of sub adult (250-500 

mm long) and adult Colorado pikeminnow (>500 mm long) in the Colorado River. The 

river was divided into two sub reaches —Westwater Canyon upstream to Price Stubb 

Diversion Dam (RM 125-188) and confluence with the Green River upstream to 

Westwater Canyon (RM 0-113). They estimated that the average population size in 

1991—1994 was 253 (95% CI, 161-440) for the upper reach and 334 (95% CI, 196-604) 

for the lower reach. 

Although most adults were captured from the upper river, they were not distributed 

equally throughout the reach. Catch rates in two segments of the upper reach—known as 

the 18-mile reach (RM 154-171) and the 15-mile reach (RM171-185)—where five to six 

times higher than in the lower third of the reach (McAda, 2000). 

Density and distribution of YOY Colorado pikeminnow have been monitored in the 

Colorado River since 1982 (McAda and Ryel, 1999). Density has been highly variable 

over that period, but YOY have been captured every year since monitoring began 

(McAda, 2000). YOY Colorado pikeminnow were found throughout the Colorado River 

downstream from the confluence with the Gunnison River, but were most abundant in the 

65 miles between Moab, Utah and the mouth of the Green River (McAda, 2000). McAda 

et al. (1998) attributed this to recruitment of a large group of individuals from 1985-1987 

year-classes recruiting to young adulthood and moving into the upper reach. The strong 

year-classes of young adults corresponded to high density of YOY Colorado pikeminnow 

in 1985-1986. An increasing population in the Colorado River during the mid 1990s was 

also implied by a constant increase in catch per unit effort during spring Interagency 

Standardized Monitoring Program (ISMP) electrofishing (McAda et al. 1998). 
Price-Stubb Fish Passage Biological Assessment - 7 -

Figure 3. 1- Distribution of Colorado Pikeminnow in the Colorado and Gunnison Rivers. 

Osmundson (2002) investigated population dynamics of the Colorado River population of 

Colorado pikeminnow. Two multi-year data collection efforts were made: 1991 to 1994, 

and 1998 to 2000. Annual estimates of whole-river population size (all fish > 250 mm 

TL) averaged 582 during the early study period and 742 during the more recent study 

period, a 27 % increase. Annual estimates of adults (> 500 mm TL) averaged 362 during 

the early study period and 490 during the recent study period, representing a 35% 

increase in adults. Backwater-netting catch rates supported this trend with an increase in 

rates between 1994 and 1998. 

In both 1999 and 2000, males comprised 51% of the population: females, 49% 

(Osmundson, 2002). Average body condition for almost all length-classes of 

pikeminnow significantly declined between the early and recent study periods 

(Osmundson, 2002). 
Price-Stubb Fish Passage Biological Assessment - 8 -

Figure 3.2- Colorado Pikeminnow Distribution Between GVIC and Price-Stubb Diversion Dams. 

3.1.3 Colorado Pikeminnow Distribution-Gunnison River 

Although isolated from the Colorado River population by construction of the Redlands 

Diversion Dam in 1917, a small, remnant population of Colorado pikeminnow persisted 

upstream of the dam (Figure 3.1). Burdick (1995) captured five adult Colorado 

pikeminnow (ranging from 497-847 mm total length) in the Gunnison River upstream 

from the dam during an intensive study from 1992-1994. Four fish were positively 

identified while electrofishing but were not captured. Two of the captured fish were ripe 

males found together in a large eddy at RM 33.7 on July 14, 1993. Of the remaining 

pikeminnows, one was captured at RM 33.5, one in the flooded mouth of Kannah Creek 

(RM 18.2) on May 5, 1993 and another at RM 16.7 on the same day. Fish that were 

observed, but not captured were seen at RM 7.7, 30.8 and 32.9 in 1992 and at RM 48.4 in 

October of 1993 (Figure 3.3). In earlier investigations, Valdez et al. (1982a) captured 

four adult Colorado pikeminnow between RM 26.7 and RM 33 and observed, but did not 

collect, four more between RM 22.1 and 31.4 (Figure 3.3). The upstream limit of 

Colorado pikeminnow in the Gunnison River is Hartland Diversion Dam, an impassible 

barrier at RM 59.9, about 57 miles upstream from Redlands Diversion Dam (Burdick, 

1995). 
Price-Stubb Fish Passage Biological Assessment - 9 -

In addition, 51 Colorado pikeminnow used the Redlands Fish Passageway from 1996 to 

2000 (Burdick, 2001a). Eight additional Colorado pikeminnow ascended the passageway 

in 2001 and 2002. All pikeminnow used the passageway in July and August. There is 

some movement back and forth between the Colorado and Gunnison Rivers: two 

pikeminnow that ascended the passageway in 1997, were recaptured in 1998. In addition, 

one other Colorado pikeminnow that ascended the passageway in 1997 was recaptured in 

1998 from the Colorado River upstream of its confluence with the Gunnison River 

(Burdick, 2000). It is not know when these fish moved back downstream over the 

Redlands Diversion Dam or how many other fish have returned to the Colorado River 

and not have been recaptured. 

Colorado pikeminnow movements in the Gunnison River were monitored during 1993 

and 1994 (Burdick, 1995). Seven adult Colorado pikeminnow were implanted with radio 

transmitters. The radio-tagged fish used most of the Gunnison River between Redlands 

and Hartland Diversion Dams and one pikeminnow moved back downstream of the 

Redlands Diversion Dam after 78 days. Forty-eight percent of the radio contacts were 

made between RM 30—40.9, and thirty-two percent were made between RM 15—29. 

Colorado pikeminnow congregated in a short reach between RM 30—33 during the 

estimated spawning period in 1993, with four fish between RM 32—33. The reach 

contained numerous riffles with cobble and gravel substrates similar to reaches in other 

rivers identified as Colorado pikeminnow spawning areas (Lamarra et al., 1985; Harvey 

et al., 1993; Miller and Ptacek, 2000). Occurrence of a congregation at the same location 

for 2 consecutive years during the estimated spawning period suggests that Colorado 

pikeminnow were spawning there (McAda, 2000). 

Larval Colorado pikeminnow have also been collected from the Gunnison River in 1995 

and 1996(Anderson, 1999), but downstream locations do not help locate specific 

spawning sites because the larvae may have drifted downstream for an unknown distance. 

3.1.4 Colorado Pikeminnow Augmentation 

The Recovery Program has identified Colorado Pikeminnow augmentation as a third 

priority behind razorback sucker and bonytail (Nesler et al., 2003). The integrated 

stocking plan for the Colorado River is presented in Table 3.2 (Nesler et al., 2003). 

Table 3.2. Integrated stocking plan for Colorado pikeminnow, third priority species. 

Priority by State and 

River Reaches 

Fish age and 

Size (mm 

TL) 

Season Stocked1

Numbers of fish 

stocked per year 

Number of 

years 

stocked 

Colorado: 

Colorado River: 

Rifle to DeBeque Canyon 

Age 3+ 

150 

1o Fall 

2o

 Spring-Summer

1,1252 6 

Gunnison River: 

Hartland to Redlands dams 

Age 3+ 

150 

1o Fall 

2o

 Spring-Summer 

1,1252 6 

1

 1o refers to the primary season; 2o refers to secondary season to cull fish and allow 

smaller individuals to achieve stocking size by the next fall. 

2

 Represents one population in the Upper Colorado and Gunnison rivers. 
Price-Stubb Fish Passage Biological Assessment - 10 -

Figure 3. 3 - Gunnison River Colorado Pikeminnow Distribution 

3.1.5 Colorado Pikeminnow Habitat Use 

Adult and Sub-Adults—Adult Colorado pikeminnow use a variety of habitats, but 

exhibit preferences for specific habitats during different periods of the year (Tyus and 

McAda, 1984; Osmundson et al., 1995). In the Colorado River near Grand Junction, 

pools and slow runs (<2.0 ft/sec) accounted for 77 to 95% of all habitats used by 

Colorado pikeminnow from November through February (Osmundson et al., 1995). 

More than 74% of all observations during this period had mid-column velocities <1.0 

ft/sec. Eddies and backwaters were the only other habitats used by Colorado pikeminnow 

in the winter. 

During April—June, river discharge and velocities increased and Colorado pikeminnow 

sought off-channel habitats with reduced water velocities and warmer water temperatures 

than the main river channel (Osmundson et al., 1995). In the Colorado River, 

Osmundson et al. (1995) found that backwaters and flooded gravel pits (combined) 

comprised 45% of radio tagged Colorado pikeminnow locations in April, 49% in May, 

and 47% in June. These quiet, warm water areas allow Colorado pikeminnow to 

minimize energy expenditures and begin somatic growth or gonad maturation sooner than 

would be possible if they were unable to escape swift, cold water of the main river 

channel (Valdez and Wick, 1983). Other habitats such as eddies and shorelines were also 

used to a lesser degree (Osmundson et al., 1995). Use of main-channel habitats increased 

at summer base flows with slow and fast runs accounting for 49 to 52% of habitats 
Price-Stubb Fish Passage Biological Assessment - 11 -

selected during July—September (Osmundson et al., 1995). Eddies were used 9 to 16%, 

pools 13 to 16%, and riffles 3 to 10% of the time. 

Osmundson and Kaeding (1991) determined that radio-tagged Colorado pikeminnow 

preferred river segments with complex channels (i.e. areas with islands, backwaters, and 

side channels) over simple channels with no side channels or islands. These braided 

areas provide a greater diversity of habitats for Colorado pikeminnow to exploit for 

resting or foraging and were preferred during all seasons. 

Young-of-Year and Yearlings—Small Colorado pikeminnow are highly dependent 

upon backwaters or shallow embayments for nursery habitat (Tyus and Haines 1991; 

Trammel and Chart, 1999a,b). Archer et al. (1985) concentrated sampling efforts on 

backwaters in the Colorado River. More than 98% of the small Colorado pikeminnow 

collected were found in backwaters. Although backwaters are preferred habitat, young 

Colorado pikeminnow move between backwaters and the main channel in response to 

environmental variables, including changes in water temperatures (McAda and Tyus, 

1984; Tyus 1991). Trammel and Chart (1999b) divided backwaters into six categories, 

but two backwater types were found in greatest abundance in the lower Colorado River—

scour channels and migrating sand waves. Scour channels are formed by the erosion of 

small channels behind large sandbars during spring runoff and are revealed by receding 

water levels and typically deep and permanent. Migrating sand wave backwaters are 

formed by the movement of migrating sand waves adjacent to sandbars and are relatively 

shallow and ephemeral. Density of Colorado pikeminnow was highest in scour channels 

and Colorado pikeminnow exhibited a significant preference for scour channels 

(Trammel and Chart, 1991a,b). Winter habitat use by YOY Colorado pikeminnow has 

not been studied. 

3.1.6 Colorado Pikeminnow Reproduction

Colorado pikeminnow spawn as spring flows decrease and water temperatures increase 

(Haynes et al., 1984; Nesler et al., 1988; Tyus 1990, 1991; McAda and Kaeding, 1991; 

Bestgen et al. 1998; Anderson, 1999; Trammel and Chart, 1999a,b). In the Colorado 

River, Colorado pikeminnow do not migrate to the extent that they do in the Green River, 

but migration occurs with movement beginning in response to declining runoff and 

increasing water temperature (McAda and Kaeding, 1991). Although some spawning 

may occur at cooler temperatures, most spawning in the Colorado, Green and Yampa 

rivers occurs at water temperatures between 18—22 o

C (McAda and Kaeding, 1991; 

Tyus, 1991, Bestgen et al., 1998; Anderson, 1999, Trammel and Chart, 1999a,b). 

Specific spawning sites in the Colorado River are not as well documented as those in the 

Green River sub-basin, although successful spawning occurs every year (Anderson, 1999; 

McAda and Ryel, 1999; Trammel and Chart, 1999a). McAda and Kaeding (1991) 

concluded that spawning in the Gunnison River is generally done by smaller groups and 

in more locations than the Green River sub-basin. McAda and Kaeding (1991) reported a 

presumed spawning aggregation of radio-tagged Colorado pikeminnow upstream from 

the mouth of the Gunnison River, but the aggregation was not repeated in subsequent 
Price-Stubb Fish Passage Biological Assessment - 12 -

years. Recent efforts have identified five more possible spawning sites based on 

aggregation of Colorado pikeminnow during the presumed spawning season (Figure 3.4) 

(McAda, 2000). 

Aggregations of pikeminnow at one of the sites downstream of the mouth of the 

Gunnison River were documented in 3 different years. A total of 18 fish were collected 

from a pool-rifle complex in 1994 during the spawning period (D. Osmundson, 

unpublished data). Ten of these fish were ripe males and five others appeared to be 

females, but no eggs were emitted (sex of three other could not be determined). The area 

was sampled again during the presumed spawning period in 1998 and 12 fish were 

collected, including 7 ripe males and 4 apparent females (D. Osmundson, unpublished 

data). About 25 additional Colorado pikeminnow were observed during electrofishing, 

but could not be captured by the sampling crew. In 1999, nine Colorado pikeminnow 

were captured at this site, including five ripe males and one ripe female (gentle pressure 

extruded eggs when the fish was captured and it was spawned in the hatchery later that 

day without hormone injections [McAda, 2000]). 

Colorado pikeminnow are broadcast spawners that deposit their eggs on cobble substrates 

in riffles and runs (Tyus, 1991). Lamarra et al. (1985) described a known spawning site 

on the Yampa River as being composed of cobble substrate with large interstitial spaces. 

Hamman (1981) documented that Colorado pikeminnow embryos adhered to clean 

cobble substrate in hatchery raceways, so it is likely that a similar process occurs in 

rivers. After deposition and fertilization, the embryos incubate in the cobble for 4-7 days 

depending on water temperature (Hamman, 1981; Marsh, 1985; Bestgen and Williams, 

1994). The larvae remain in the gravel for another 6-7 days after hatching before 

emerging from the substrate and becoming entrained in the river current (Bestgen et al., 

1998). Colorado pikeminnow larvae may drift downstream for many miles before 

settling in low-gradient reaches with abundant backwaters and other quiet-water habitats 

(Tyus and Haines, 1991, Bestgen et al., 1998; Anderson, 1999; Trammell and Chart, 

1999a). 

3.2.1 Razorback Sucker 

The razorback sucker is a large catostomid, endemic to the Colorado River Basin of the 

western United States (Minckley, 1973). The species belongs to a monotypic genus that 

is distinguished by a prominent dorsal keel that rises immediately posterior to the occiput 

(Minckley, 1973). Large individuals may reach a meter in length and weights of 5 or 6 

kg (Minckley, 1973), but most individuals captured in the upper basin are less than 650 

mm long and weigh less than 3 kg (McAda and Wydoski, 1980; Tyus, 1987; Tyus and 

Karp, 1990). It is long-lived and individuals may exceed 40 years of age (McCarthy and 

Minckley, 1987). The historic distribution of razorback sucker has been reduced by 75% 

(Minckley et al., 1991) and its extremely low abundance within remaining habitat caused 

it to be listed as endangered under the Endangered Species Act of 1973, as amended 

(USFWS 1991). 
Price-Stubb Fish Passage Biological Assessment - 13 -

Figure 3. 4 - Potential Colorado Pikeminnow Spawning Sites on the Upper Colorado River 

3.2.2 Razorback Sucker Distribution-Colorado River

In the Colorado River upstream of Lake Powell, most razorback suckers have been 

captured in the Grand Valley (Loma to Palisade) near the confluence of the Gunnison and 

Colorado rivers (Figure 3.5). However, their abundance has decreased to the point that 

they were only infrequently captured there. During intensive efforts that were 

specifically targeted at known concentration areas of razorback sucker, Kidd (1977) and 

McAda and Wydoski (1980) captured a combined total of 54 razorback suckers in 1974 

and 204 in 1975 from two gravel-pit ponds connected to the Colorado River near Grand 

Junction. These numbers reflect the combined total of independent collections, but 

probably include some recaptures of the same fish since sampling was done in the same 

area and Kidd (1977) did not mark fish before release. All of these fish exhibited signs of 

old age (i.e. large size, missing eyes, heavy scarring) (McAda, 2000). The high numbers 

of razorback suckers captured in 1975 were not repeated in subsequent years 

(summarized by Osmundson and Kaeding, 1991). The highest number captured in later 

years was 30 fish that were collected in 1982 from the same gravel-pit pond sampled by 

Kidd (1977) and McAda and Wydoski (1980). Only 11 razorback suckers have been 

collected from the Grand Valley since 1990 despite intensive sampling in some years 

(Osmundson and Kaeding, 1991; McAda, 2000). All of these fish have been removed 
Price-Stubb Fish Passage Biological Assessment - 14 -

from the river to support propagation activities for the Recovery Program (McAda, 

2000). 

Although most razorbacks have been collected from the Grand Valley, they have also 

been collected both up and downstream of the area. Kidd (1997) reported 22 razorbacks 

from the Colorado River near DeBeque (RM 209.7) in 1974-1975. No razorbacks have 

been collected from that reach since then (Valdez et al., 1982; Burdick, 1992). Burdick 

(1992) captured one razorback sucker from a gravel-pit pond along the river at RM 243.8 

and discovered a small population in another gravel-pit pond at RM 204.5. About 75 

razorback suckers were captured from the second pond, but DNA analysis revealed that 

they were siblings. They were probably offspring from two or three razorback suckers 

trapped in the pond during the high water year of 1983 or 1984. Three razorbacks were 

incorporated into the propagation program, but their close relationship precluded 

extensive use in the brood stock program. Forty-five razorback suckers stocked in the 

Gunnison River as part of an experimental stocking; six of those fish were confirmed 

alive at the end of the 2-year study (Burdick and Bonar 1997). 

Few razorback suckers have been captured downstream from the Grand Valley, between 

Loma and Lake Powell. Taba et al. (1965) captured eight juveniles in backwaters of the 

Colorado River downstream of Moab, Utah. One adult was captured near Salt Wash 

(RM 144.2 in 1988 (McAda et al. 1994). Further downstream, Valdez et al. (1982) 

captured two razorback suckers within 2 miles of the confluence with the Green River, 

and Valdez (1990) captured one more in the same area. 

3.2.2 Razorback Sucker Distribution-Gunnison River

Anecdotal accounts indicate that razorback sucker were common in the Gunnison River 

near Delta in the early and middle portions of the 20th Century (Kidd, 1997; Quartrone, 

1993). 

Razorback suckers in the Gunnison River recorded from knowledgeable collectors are 

rare. Two specimens from the 1940s are in the University of Michigan Museum of 

Zoology (reported by Wiltzius, 1978). Wiltzius (1978) captured one razorback sucker 

near Delta in 1975 and Holden et al. (1981) captured three razorbacks in the same general 

area in 1981 (Figure 3.5). 

Extensive sampling by Valdez et al. (1982a) and Burdick (1995) failed to capture any 

razorback suckers from the Gunnison River. Sampling efforts in 2002 collected the first 

larval razorback suckers at two locations on the Gunnison River at a site near Roubideau 

Creek and a site near Whitewater (Figure 3.6) (C. McAda, unpublished data). These 

were the first collection of larval razorback suckers from the Colorado or Gunnison 

rivers. In addition, Taba et al. (1965) collected the only record of juvenile razorback 

sucker from the Colorado or Gunnison rivers. 
Price-Stubb Fish Passage Biological Assessment - 15 -

Figure 3. 5-Distribution of razorback sucker in the Colorado and Gunnison rivers. 

In 2001 and 2002, six razorback suckers ascended the Redlands fish passageway (B. 

Burdick, unpublished data). The fish passageway was constructed in 1996; however, 

razorback suckers did not begin using the passageway until 2001. 

3.2.3 Razorback Sucker Population Augmentation

Although razorback sucker populations have dramatically declined in abundance in 

recent years, the Recovery Program considers the Colorado and Gunnison rivers to be 

suitable habitat for razorback suckers and has begun a reintroduction program to restore 

populations in the two rivers (Burdick, 1992). The Recovery Program developed a 

broodstock to supplement razorback sucker populations in the Colorado and Gunnison 

Rivers. The Recovery Program in 1996 initiated a five-year stocking program with the 

stocking of 7,700 young razorback suckers into the Gunnison River near Delta, Colorado 

(Burdick, 1999). The stocking program has continued with the fish stocking of 18,423 

juvenile, sub-adult, and adult razorback sucker in the Gunnison River and 31,531 

juvenile, sub-adult, and adult razorback sucker in the Upper Colorado River between 

April 1994 and October 2001 (Burdick, 2001b). Table 3.3 presents the sizes, number and 

locations of razorback stocking from 1996—2001 (Burdick, 2001b). The goal of the 
Price-Stubb Fish Passage Biological Assessment - 16 -

stocking plan is to establish a self-sustaining population of 600 individuals in the 57 

miles of usable habitat between Harland and Redlands diversion dams. 

 

Figure 3.6-Larval and Junvenile Razorback Sucker Collections from 

the Colorado and Gunnison Rivers. 

The Recovery Program also approved a stocking plan by the Colorado Division of 

Wildlife (CDOW) (Nesler, 1998) for the Colorado and Gunnison rivers that includes and 

expands on Burdick’s (1992) plan. The goal of CDOW’s plan is to establish populations 

of 475 razorbacks per mile in suitable habitat within Colorado. An equivalent plan has 

been developed for the Colorado River within Utah (Hudson et al., 1999) which 

recommends a population of about 3,190 or an average of about 30 fish per mile in the 

section of river razorback suckers are expected to inhabit. An integrated stocking plan 

for Colorado and Utah was developed in 2002 to address inconsistencies between the 

states stocking plans (Nesler et al., 2003). Table 3.4 on the following page presents 

priority by State and river reaches as well as fish size, seasons to stock, number of fish 

per year, and number of years to stock razorback sucker. 
Price-Stubb Fish Passage Biological Assessment - 17 -

Table 3.3. Recovery Program Razorback Sucker Stocked in 

the Gunnison and Colorado Rivers 1996—2001.

Burdick (2001b) reported that 235 razorback suckers stocked in the Gunnison and 

Colorado river were either captured (226) from sampling or were found dead (9) during 

other research sampling efforts. This represented about 0.5% of all razorback suckers 

stocked prior to 2002 (50,254). Additional 93-razorback suckers were found dead on the 

trash grates at the Redlands fish passageway in 1999 and 2001 (Burdick, 2001b). 

7.2.5 Razorback Sucker Habitat Use

Adults and Sub-adult—Because few razorback suckers remain in the Colorado River, 

little habitat use data are available. Early collections by Kidd (1977) and McAda and 

Wydoski (1980) concentrated in gravel-pit ponds connected to the river. The most 

heavily used pond was in Walker State Wildlife Area (near Grand Junction, Colorado) 

where razorback sucker were collected year-round even though there was access to the 

Colorado River at all times. This site was highly altered by high spring run-off in 1983 

and 1984, and razorback sucker use was reduced. 

Osmundson and Kaeding (1989) monitored radio telemetered razorback sucker in the 

Colorado River and found that the river main channel, pools and slow runs were the most 

commonly used habitats on a year-round basis, with highest use occurring from early 

autumn through late winter. Backwaters were also used year round, but were most 

heavily used during spring runoff when use of flooded gravel-pit ponds was also high. 

The greatest variety of habitats were used in summer when eddies, riffles, fast runs, and 

shorelines were occupied; however, slow runs were still the most heavily used habitats 

during that period. Burdick and Bonar (1997) also monitored radio-tagged razorback 

sucker habitat use by fish stocked into the Colorado and Gunnison rivers after rearing in 

Year Stocking Location Mean Size of Fish 

Actual Number of Fish 

Stocked 

Prior to 1996 Gunnison River 

Colorado River 

18”-21” 

18”-21” 

25 

20 

1996 Gunnison River near Delta 8” 316 

1997 Gunnison River near Delta 8” 

12” 

3,732 

282 

1998 Gunnison River near Delta 12” 608 

1999 Gunnison River near Delta 8” 

12” 

2,742 

30 

1999 Colorado River near Parachute 8” 3,498 

2000 Gunnison River near Delta 8” 6,587 

2000 Colorado River near Parachute and 

Price Stubb Diversion Dam to the 

confluence with the Gunnison 

River 

8” 25,859 

2001 Gunnison River near Delta 8” 4,101 

2001 Colorado River near Parachute and 

Price Stubb Diversion Dam to the 

confluence with the Gunnison 

River 

8” 2,154 
Price-Stubb Fish Passage Biological Assessment - 18 -

riverside gravel-pit ponds. These fish primarily used the main river channel (47%), 

backwaters (23%), and eddy/pools (16%). Fish movements were monitored from 

March—October, however the data was not partitioned by season. 

Table 3.4 Integrated Stocking Plan for Razorback Sucker, First Priority Species. 

Priority by State and 

River Reaches 

Fish age and 

Size (mm 

TL) 

Season Stocked1

Numbers of fish 

stocked per year 

Number of 

years 

stocked 

Colorado 

1C: Colorado River: 

Rifle to DeBeque Canyon 

Age 2+ 

300 

1o Fall 

2o

 Spring-Summer

3,3102 6 

2C: Gunnison River: 

Hartland to Redlands Dams 

Age 2+ 

300 

1o Fall 

2o

 Spring-Summer 

3,3102

 6 

3C: Colorado River: 

Palisade to Stateline 

Age 2+ 

300 

1o Fall 

2o Spring-Summer 

3,3102 6 

Utah 

1U: Middle Green River: 

(RM 302-249) 

Age 2+ 

300 

1o Fall 

2o

 Spring-Summer 

9,930 6 

2U: Lower Green River: 

(RM 120-249) 

Age 2+ 

300 

1o Fall 

2o Spring-Summer 

9,9303 6 

1

 1o refers to the primary season; 2o refers to secondary season to cull fish and allow 

smaller individuals to achieve stocking size by the next fall. 

2

 Represents one population in the Upper Colorado and Gunnison rivers. 

3

 Represents an additional population in case of catastrophic event. 

Larvae and Juveniles—Prior to 2002, no razorback sucker larvae had been collected 

from the Colorado or Gunnison rivers. In 2002, razorback sucker larvae were collect 

from the Gunnison River. Larval razorback sucker were collect downstream of the 

mouth of Roubideau Creek and downstream of Whitewater, Colorado providing evidence 

that stocked razorback sucker have successfully spawned in the Gunnison River. 

Habitats were consistent with those reported by Muth et al. (1998) from the middle Green 

River where 95% of razorback sucker larvae were collected from the flooded mouths of 

tributaries or other floodplain-type habitats. It is presumed that swim up larvae emerge 

from the gravel and are carried by the rising river into floodplain habitats where they 

remain during the runoff period (McAda, 2000). 

The only juvenile razorback suckers reported from the Colorado River were captured by 

Taba et al. (1965), who found eight juveniles (90-115 mm TL) in a “quiet backwater 

area” of the river between Moab and Dead Horse Point. This observation was consistent 

with juvenile razorback sucker collected from backwater habitats on the Green River 

(Modde, 1996). 

3.2.6 Razorback Sucker Reproduction 

Because of the limited number of razorback suckers found in the upper Colorado River, 

most information comes from other parts of the basin. Ripe female razorback sucker 

have been found in Lake Mohave from December through early June (Minckley et al. 

1991), but most spawning occurs in January—April (Minckley, 1983; Langhorst and 

Marsh, 1986; Mueller, 1989). Based upon capture of ripe fish and subsequent capture of 

larvae, riverine razorback suckers in the upper basin spawn in spring during increasing 
Price-Stubb Fish Passage Biological Assessment - 19 -

and peak snow-melt flows (McAda and Wydoski, 1980; Tyus, 1987; Tyus and Karp, 

1990; Muth et al., 1998; Modde and Irving, 1998). 

Osmundson and Kaeding (1991) summarized data collected from the Colorado River 

near Grand Junction and reported that 42 of 157 razorback suckers captured were in 

spawning condition when handled. Of the 42 ripe fish, 40 (95%) were captured between 

May 24 and June 17. 

Riverine razorback suckers spawn in riffles or shallow runs over gravel or cobble bars 

(McAda and Wydoski, 1980; Tyus, 1987; Tyus and Karp, 1990). Water depths and water 

velocities vary, but are generally relatively shallow (<1 m) and swift (>1 ft/s). In the 

upper Colorado River basin, most ripe fish have been captured from main-channel 

habitats, but a few were found in floodplain habitats (Tyus and Karp, 1990.). In most 

cases, floodplain habitats were near known spawning bars and the fish were probably 

staging in preparation for spawning (Tyus and Karp, 1990). McAda and Wydoski (1980) 

captured two ripe females with a single trammel net along a shoreline with gravel and 

cobble substrate at Walter Walker State Wildlife Area. Also, 38 of the 42 razorbacks 

sucker in spawning condition collected in the Grand Valley during 1974—1991 were 

found in flooded gravel pits (Osmundson and Kaeding, 1991). 

No specific spawning sites have been identified in the Colorado, but the presence of ripe 

adults and presence of mid-channel cobble bars similar to those used in the Yampa and 

middle Green rivers suggests that most spawning in the Colorado River occurs near 

Grand Junction, Colorado (McAda, 2000). The collection of razorback sucker larvae at 

two locations on the Gunnison River (C. McAda, unpublished data), confirms that 

suitable spawning habitat occurs in the Gunnison River, however, no spawning locations 

have been identified. 

In rivers, razorback sucker larvae emerge from the gravel after swim up and are entrained 

in the current, which carries many of the young fish into floodplains, backwaters, flooded 

tributary mouths or other quiet-water habitats for rearing (Tyus and Karp, 1990). Timing 

of spawning (at or approaching the peak of runoff) ensures that these habitats are 

available to the larvae when they emerge from the substrate. Floodplains, backwaters, 

and other quiet-water areas are the most productive habitats of the river (Wydoski and 

Wick, 1998) and provide important nursery habitat for young razorback suckers during 

the first few months of their lives (Tyus, 1987; Tyus and Karp, 1980; Modde, 1996, 

1997;Wydoski and Wick, 1998; Muth et al., 1998). These habitats are temporary and, 

with the exception of main channel backwaters, usually do not last through a fish 

growing season. Reduced spring flows caused by water development, and construction 

of dikes and levees reduced the availability of flooded bottomlands (McAda, 2000). 

 

3.3.1 Humpback Chub and Bonytail

The humpback chub and bonytail are mid-sized cyprinid endemic to the Colorado River 

Basin (Minckley 1973). Both species are closely related to the roundtail chub (Gila 

robusta). 
Price-Stubb Fish Passage Biological Assessment - 20 -

Humpback chub are currently found in discrete populations, within canyon-bound 

reaches or other areas of similar habitat (Valdez and Clemmer, 1982). Bonytail is the 

most imperiled of the four endangered fishes (Maddux et al., 1993) and its distribution in 

recent years is limited to scattered individuals. Most recently collected individuals were 

from reservoirs in the lower basin where remnant populations remain (Figure 3.7). One 

individual humpback chub was found during an intensive survey of the Gunnison River 

from Delta, Colorado to its mouth (Burdick, 1995). It was captured in a deep eddy-pool 

complex within a canyon-bound reach at RM 22.0 and is the only record of a humpback 

chub from the Gunnison River. The Black Canyon of the Gunnison contains habitat 

typical of other canyon-bound areas where humpback chubs are currently found. It is 

possible that they were eliminated from the Black Canyon after water temperature was 

reduced by Blue Mesa Reservoir, but the only Gila spp. reported during preimpoundment surveys were roundtail chub (summarized by Wiltzius, 1978). The 

humpback chub and bonytail, except for the one humpback chub record as noted, do not 

occur within the Gunnison River and are not discussed in further detail in this BA. 

Because all four of the endangered fish evolved together in the Colorado River 

ecosystem, flow recommendations are based on habitat requirements of the more 

common species. Basic river restoration principals (sensu Stanford et al., 1996) 

Figure 3. 7 - Distribution of Humpback Chub and Bonytail in the Colorado and Gunnison Rivers. 
Price-Stubb Fish Passage Biological Assessment - 21 -

should also benefit humpback chub and bonytail (McAda, 2000). The Recovery Program 

has plans to stock bonytail in the Colorado River from Palisade to Loma including the its 

confluence with the Gunnison River as presented in the next section. 

3.3.2 Bonytail Population Augmentation

Because of its extreme rarity, the Recovery Program began a reintroduction program in 

1997 and has stocked about 35,000 bonytail into the Colorado River near Moab to 

reestablish populations (McAda, 2000). Nesler et al. (2003) in the Colorado/Utah 

integrated stocking plan, identified bonytail stocking in the Colorado River between 

Palisade and Loma as a secondary priority species behind razorback sucker. The 

integrated stocking plan for the Colorado River is as follows in Table 3.5 (Nesler et al., 

2003). 

Table 3.5. Integrated Stocking Plan for Bonytail, Second Priority Species. 

Priority by State and 

River Reaches 

Fish age and 

Size (mm 

TL) 

Season Stocked1

Numbers of fish 

stocked per year 

Number of 

years 

stocked 

Colorado: 

Colorado River: 

Palisade to Loma 

Age 2+ 

200 

1o Fall 

2o

 Spring-Summer

2,6652 6 

Utah 

Colorado River: 

(RM 110.5) 

Age 2+ 

200 

1o Fall 

2o Spring-Summer 

2.6652 6 

1

 1o refers to the primary season; 2o refers to secondary season to cull fish and allow 

smaller individuals to achieve stocking size by the next fall. 

2

 Represents one population in the Upper Colorado River. 

3.4 Effect on Colorado River Endangered Fishes

The proposed project may affect, but is not likely to adversely affect (beneficial), 

Colorado pikeminnow, razorback sucker, and bonytail. Restoring fish passage at PriceStubb Diversion Dam in conjunction with restored passage at Grand Valley Project 

Diversion Dam would allow endangered fish access to upstream habitats including 50+ 

miles of designated critical habitat. 

As described in the Section 3.1, Colorado pikeminnow occupy habitats downstream of 

the Price-Stubb Diversion Dam and 31,531 razorback suckers have been stocked in the 

Colorado River both upstream and downstream of the dam between 1994 and 2001. 

Colorado’s stocking plan as previously described includes additional stockings of 

Colorado pikeminnow, razorback sucker and bonytail at sites upstream and downstream 

of the Price-Stubb Diversion Dam. It is anticipated that some of these stocked fish will 

use the fish passage. Fish stocked in the Gunnison River may also travel downstream, 

enter the Colorado River and move upstream to occupy suitable habitats. 
Price-Stubb Fish Passage Biological Assessment - 22 -

The proposed project is predicted to have no effect on humpback chub. Humpback chub 

have not been documented in the Colorado River upstream of Westwater Canyon and the 

state does not plan to stock humpback chub. 

Unrestricted fish passage at the Price-Stubb Diversion Dam could allow non-native fish 

species access to about 3 miles of designated critical habitat between Price-Stubb and 

Grand Valley Project Diversion Dams, which has been blocked since 1911. Non-natives, 

primarily channel catfish and largemouth bass, are of concern because they predate and 

compete with adult Colorado pikeminnow and razorback sucker. Non-native fish 

movements upstream would be controlled with selective passage at the Grand Valley 

Project Diversion Dam. 

The proposed action is not likely to result in incidental take of Colorado pikeminnow, 

razorback sucker or bonytail. The Price-Stubb fish passage would be constructed during 

the late-fall/winter months at low river flows when endangered fish movements are 

minimal. Because there is no selective fish passage (fish trap) proposed at the PriceStubb Diversion Dam and the fish passage would have the run of the river, it is unlikely 

that incidental take would occur at the fish passage. 

3.5 Endangered Fishes Critical Habitat

The Colorado River and its 100-year flood plain within the project area are designated as 

critical habitat for the Colorado pikeminnow and razorback sucker (USFWS, 1994). The 

Price-Stubb Diversion Dam is within designated critical habitat and restored fish passage 

will allow endangered fish access to 50+ miles of critical habitat upstream. The proposed 

project would not adversely modify critical habitat designated for Colorado pikeminnow 

and razorback sucker. The proposed project is not within designed critical habitat for the 

humpback chub and bonytail. 

3.6 Bald Eagle 

The bald eagle (Haliaeetus leucocephalus) was classified as endangered in 43 of the 48 

contiguous states on February 14, 1978. The species was reclassified as threatened by the 

U.S. Fish and Wildlife Service August 11, 1995 (USFWS, 1995b). 

 

The bald eagle is distinctive by it white head, white tail plumage, dark brown to charcoal 

black wing and body plumage, and massive yellow bill. The bald eagle ranges from 30-

43 inches (75-108 cm) in height and has a wingspan between 7-8 ft. Males often appear 

darker than females. Females are larger than males. Immature bald eagles (6 months to 2 

years old) have a dusky head and tail plumage (Peterson, 1990; USBR, 1994). 

Feeding habitats are eclectic, reflecting the opportunistic behavior of large raptors. Prey 

include fishes, ground dwelling scuirids, waterfowl, ungulate carrion and lagomorphs 

(USBR, 1994). 
Price-Stubb Fish Passage Biological Assessment - 23 -

Age of first breeding is commonly assumed to be coincident with acquisition of definitive 

adult plumage. Breeding commonly occurs between ages 6 and 7 years old. Nest 

building and repair occur every year. Both male and females build stick nests used over 

many years. Nests can be as large as 3 m (10 ft.) high and 2.1 m (7 ft.) wide. Alternate 

nests may be present in the breeding area, but pairs usually use one nest until it either 

falls from the tree or the tree is lost (USBR, 1994). 

Egg laying normally occurs in early February to mid-April depending on elevation. 

Average clutch size is two eggs. Incubation averages 31 to 35 days. Eggs hatch in midMarch to mid-May and the nesting period lasts 11 to 14 weeks. Both genders incubate, 

brood and feed young but the female performs most of the tasks. Fledglings are 

dependent on adults for 6 to 10 weeks and adults will feed juveniles other than their own 

(USBR, 1994). 

3.6.1 Bald Eagle Habitat Preference 

Bald eagles occupy riparian or lacustrine habitats almost exclusively during the breeding 

season, but occasionally exploit upland areas for food and roost sites, especially during 

the winter. Nests sites are mostly commonly distributed around the periphery of lakes 

and reservoirs larger than 80 acres in size. Nesting also occurs linearly along forested 

corridors of major rivers, usually within 1 mile of shore, however cases have been 

reported of birds nesting as far as 9.3 miles from water while exploiting locally abundant 

prey such as prairie dogs (USBR, 1994). 

3.6.2 Bald Eagle Distribution and Abundance 

The bald eagle is the only species of Haliaeetus occurring in and restricted to North 

America. Historic bald eagle distribution included every state (except Hawaii) and 

Canadian province and portions of northern and eastern Mexico (Brown, 1976). 

Populations became depressed in the 1960's from effects of use of the pesticide DDT. 

The Colorado Division of Wildlife considers the Colorado River to be bald eagle winter 

range. Eagles have been observed in concentrations at the mouth of DeBeque Canyon 

and usage observed throughout the riparian corridor. The closest known nest site is 

Westwater (CDOW, 2000). A major roosting site was recorded on the south side of 

Plateau Creek (UTM 750850, 4341250) approximately 14 miles southeast of the project 

site (BLM, 1996). 

3.6.2 Effects on Bald Eagle 

No roosting or nesting habitat was found within the project area, however bald eagles 

may use the area during winter for foraging. One large cottonwood tree is found on river 

right near the Price-Stubb Diversion Dam. Larger stands of cottonwood trees occur 

further north of this site, approximately 2 mile upstream of the Price-Stubb Diversion 

Dam. No cottonwood trees would be removed during construction. 
Price-Stubb Fish Passage Biological Assessment - 24 -

Construction activities during the winter season may result in the birds avoiding the area 

during the construction period, however the project is not expected to affect wintering 

bald eagle habitat. No known wintering concentrations of bald eagle are known within 1 

mile of the project area; therefore, the project is not expected to impact bald eagles. 

3.7 Southwestern Willow Flycatcher 

The southwestern willow flycatcher (Empidonax traillii extimus) was listed by the U.S. 

Fish and Wildlife Service as endangered on February 27, 1995 (USFWS, 1995a). Critical 

habitat was designated on July 22, 1997 (USFWS, 1997).

The southwestern willow flycatcher is a small riparian obligate neotropical migrant, 

approximately 15 cm (5.75 inches) long. It has a grayish green back and wings, whitish 

throat, light gray-olive breast, and pale yellowish belly. Two wingbars are visible; the 

eye ring is faint or absent. The upper mandible is dark, the lower is light. The 

Southwestern willow flycatcher is an insectivore and feeds in dense riparian vegetation 

(USFWS, 1995a). 

The southwestern willow flycatcher normally nests in late May or early June and fledges 

young in early to mid-July. Birds typically arrive onsite in May, build nests in late May 

to June, lay eggs and incubate in June and July, and fledge in late June to early August 

(Sogge et al., 1997). The presence and status is often confused by the presence of 

migrating individuals of the northern subspecies passing through southwestern willow 

flycatcher breeding habitat. The nests are a compact cup of fiber, bark and grass, 

typically rimmed with feathers and lined with layers of grass or other fine, silky material. 

Material dangling from the bottom of the nest is often seen (USFWS, 1995a). 

 

3.7.1 Southwestern Willow Flycatcher Habitat Preference 

The Southwestern willow flycatcher occurs in riparian habitats along water bodies, 

wetlands and streams, where dense vegetation growths of willows (Salix sp.), Baccharis, 

arrowweed (Plucea sp.), buttonbush (Cephalanthus sp.), tamarisk (Tamarix sp.), Russian 

olive (Eleagnus sp.) or other plants are present. Scattered overstory of cottonwood 

(Populus sp.) are often also present Flycatchers use these riparian communities for both 

nesting and foraging (USFWS, 1995a). Nesting habitat is described in detail in Sogge et 

al. (1997). 

3.7.2 Southwestern Willow Flycatcher Distribution 

The breeding range of the Southwestern willow flycatcher includes southern California, 

Arizona, New Mexico, southwestern Colorado, extreme southern portions of Nevada and 

Utah and Western Texas. The Southwestern willow flycatcher is currently known to 

breed in only about 75 sites in riparian habitats in the southwest. The known breeding 

population is estimated between 300 and 500 pairs (Sogge et al., 1997). 
Price-Stubb Fish Passage Biological Assessment - 25 -

Population decline is believed to be contributed primarily from habitat loss and 

modification, however Black-headed cowbird parasitism is also believed to make a 

significant contribution. 

Two territorial males were documented in Plateau Creek approximately 14 miles 

southeast of the project area. These birds were documented in 1995 by WestWater 

Engineering. Both sites were described as a thick, narrow band of willows with one or 

more tall trees or shrubs adjoining with open country on each side of the band (BLM, 

1996). 

3.7.3 Effects on Southwestern Willow Flycatcher 

No habitat described in Sogge et al. (1997) occurs within the proposed fish passage 

project area. The Colorado River is riprapped along both banks to protect Interstate 70 

and the Union Pacific Railroad. The bank is nearly vertical with large boulders. The 

proposed action is predicted to have no effect on southwestern willow flycatcher. 

4.0 Conclusions 

Restored fish passage at the Price-Stubb Diversion Dam would benefit the Colorado 

pikeminnow, razorback sucker and bonytail. The fish passage in conjunction with 

restored passage at the Grand Valley Project Diversion Dam would allow endangered fish 

access to an additional 50+ miles of designated critical habitat. Non-selective passage at 

the Price-Stubb Diversion Dam would allow endangered, native and non-native species 

access to the Colorado River between the two diversion dams. Therefore, the proposed 

fish passage may affect, but is not likely to adversely affect Colorado pikeminnow, 

razorback sucker, and bonytail and would not result in adverse modification of 

designated critical habitat for Colorado pikeminnow and razorback sucker. The proposed 

action would have no effect on humpback chub. Incidental take of Colorado 

pikeminnow, razorback sucker, and bonytail as a result of construction, operation, and 

maintenance is not predicted. 

The proposed project would have no effect on bald eagle or southwestern willow 

flycatcher. 
Price-Stubb Fish Passage Biological Assessment - 26 -

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