Post-Stocking Dispersal, Habitat Use,

and Behavioral Acclimation of

Juvenile Razorback Suckers (Xyrauchen texanus)

in Two Colorado River Reservoirs

Open File Report 98-301

U.S. Department of the Interior 

U.S. Geological Survey

Prepared in Cooperation with Arizona State University,

Bureau of Reclamation, National Park Service,

and U.S. Fish and Wildlife Service

science 

USGS

fora changing world
U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Post-Stocking Dispersal, Habitat Use, and Behavioral Acclimation of 

Juvenile Razorback Suckers (Xyrauchen texanus) in 

Two Colorado River Reservoirs.

By

Gordon Mueller, U.S. Geological Survey, Midcontinent Ecological Science Center 

2Paul Marsh, Department of Biology, Arizona State University

Open-File Report 98-301

Prepared in cooperation with Arizona State University, National Park Service, 

Bureau of Reclamation, and U.S. Fish and Wildlife Service.

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey 

editorial standards (or with the North American Stratigraphic Code). Any use of trade, product, 

or firm names is for descriptive purposes only and does not imply endorsement by the U.S. 

Government.

'P.O. Box 25007 (D-8220), Denver, Colorado 80225 

Department of Biology, P.O. Box 871501, Tempe, Arizona 85287
TABLE OF CONTENTS 

EXECUTIVE SUMMARY................................................................................... iii

INTRODUCTION................................................................................................ 1

METHODS.......................................................................................................... 2

RESULTS............................................................................................................ 4

DISCUSSION...................................................................................................... 12

RECOMMENDATIONS..................................................................................... 17

LITERATURE CITED........................................................................................ is

APPENDIX A...................................................................................................... 23

TABLES 

Number Page

1 Range (River Miles) and movements of 23 of 28 juvenile 

razorback suckers released into the San Juan Arm of 

Lake Powell, Utah, May-August 1997..................................................... 8

2 Range (River Miles) and movements of 17 of 27 juvenile 

razorback suckers released into Lake Mohave, 

Arizona-Nevada, May-August 1997........................................................ 9

FIGURES

Page

Map of Lake Mohave, Arizona-Nevada, showing numbered 

waypoints 1-71...................................................................................... 5

Time duration that movement could be detected on externally

tagged juvenile razorback suckers released into the San Juan

Arm of Lake Powell, Utah from May through July 1997......................... 6
FIGURES (cont.) 

Number Page

3 Time duration that movement could be detected on externally 

tagged juvenile razorback suckers released into Lake Mohave, 

Arizona-Nevada from May to August 1997......................................... 6

4 Percentage of razorback sucker detected <10, 10 to 50, 

and >50 m from shore in lakes Mohave and Powell, 

May to July 1997.................................................................................. 10

5 Cover use of juvenile razorback suckers released into lakes

Mohave and Powell from May to July 1997......................................... 11

6 A comparison of the detection rate of cove held (3 d) versus juvenile 

razorback suckers simply released into the San Juan Arm of 

Lake Powell, May 3, 1997.................................................................... 14

7 Comparison of the temperature regime used by a juvenile and 

10 adult razorback suckers in Lake Mohave, Arizona-Nevada, 

during 1995-1996 (Mueller et al. 1998)................................................ 14

n
EXECUTIVE SUMMARY

Little information is available regarding the movements and habitat use of early life stages of 

razorback sucker (Xyrauchen texanus). Juveniles are rarely encountered in the wild (Minckley 

1983, Minckley et al. 1991, Gutermuth et al. 1994, Modde 1996, Tyus 1997). Dispersal and 

habitat use of stocked, juvenile razorbacks was studied in lakes Mohave and Powell during the 

summer of 1997. Sonic transmitters (90 day) were externally attached to 55 fish, 27 were 

released into Lake Mohave and 28 into Lake Powell. Half of each lot was held three days in 

blocked coves to test if site acclimation influenced short-term dispersal rates.

Post stocking dispersal was rapid, widespread, and similar to earlier studies in Lake Mohave 

(Mueller et al. 1998). Movement was more pronounced immediately after release and declined 

with time. Maximum daily distance traveled by individuals released in Lake Powell averaged 

>2 km/d (0->7 km/d) and daily movements averaged 347 m/d (3-1,500 m/d) for Lake Mohave 

fish and 480 m/d (3-1,800 m/d) for Lake Powell. After the first week fish were typically found 

backwaters and coves and >50% of the fish detected were found in cover. Prevalent cover types 

in Lake Mohave and Powell included flooded tamarisk (48-86%), emergent vegetation 

(Potamogeton & Najas spp.} (40/0% absent in Lake Powell), and rock cavities (12-14%).

Preliminary data suggests behavioral acclimation may influence short-term dispersal rates. Of 

the 14 Lake Powell fish that remained in the study area for > 30 days, twice as many (64%) 

represented fish held for 3 day than those simply released. The sample size was small and might 

simply reflect normal variability, however, it's doubtful holding fish deter fish from remaining in 

the general area and might encourage it. To few contacts were made in Lake Mohave to draw 

any conclusions.

Sonic transmitters have been used successfully for tracking other fish species (Pelle and Paulson 

1993, Marsh 1997, Mueller et al. 1998), however, they proved less effective on juvenile suckers 

that typically were found using shallow, vegetative backwaters. These habitats greatly reduced 

the effectiveness of sonic equipment. On the basis of our studies, we recommend that stocking 

programs consider the following:

* Expand monitoring programs to sample shallow, flooded habitats (i.e., <2 m depths).

* Stock only fish larger than 30 cm in length.

* Investigate seasonal (autumn-winter) rather than year-round stocking.

* Examine reservoir fluctuation zones and how changes in reservoir elevation influences 

predator population dynamics (i.e. densities, colonization rates).

* Use radio, rather than sonic transmitters for future juvenile telemetry studies.

in
INTRODUCTION

Information pertaining to post-stocking dispersal and habitat use of endangered razorback sucker 

(Xyrauchen texanus) is primarily limited to the adult life stage. Radio or sonic transmitters are 

normally surgically implanted in the fish's abdominal cavity (MeAda and Wydoski 1980, Ulmer 

1987, Tyus 1987, Tyus and Karp 1989, Marsh and Minckley 1989, Creef and Clarkson 1993, 

Ryden and Pfeifer 1995, Burdick and Bonar 1997). Due to transmitter size, this approach is not 

feasible with smaller life stages. Instead of surgery, we externally attached sonic transmitters on 

juvenile razorback suckers which reduced surgically related stress and mortality.

Wild populations consist of old individuals and young fish are rarely encountered (Minckley 

1983, Minckley et al. 1991, Gutermuth et al. 1994, Mueller and Marsh 1995, Modde 1996 and 

1997). Although juvenile or larval razorback suckers have been stocked in relatively large 

numbers (Johnson 1985), efforts to reestablish populations have generally failed (Minckley et al. 

1991, Mueller 1997). Research attempts to determine habitat use and movements of juvenile 

suckers has been plagued by small numbers of wild fish, logistical problems associated with 

sampling remote riverine habitats, and fish disappearance due to dispersal and unknown 

survivorship. To our knowledge, reports of juvenile habitat use is limited to sparse information 

collected on pond-reared fish, stocking dispersal studies, and rare observations of wild fish 

(Brooks 1985, Marsh and Brooks 1989, Minckley et al. 1991, Mueller and Marsh 1993, Modde 

1996, Mueller et al. 1998).

Similar information is lacking regarding the behavioral stress associated with repatriating 

endangered fish into historical or new habitats. Fundamental research has focussed primarily on 

the physiological response of fishes to physical, chemical and handling induced stress. Studies 

have examined the effect of stress on the body, with mortality the usual endpoint and not fixed 

on specific, short-term fish behavior. Factors such as anorexia, tendency toward to downstream 

movement, or abnormal behavior that may increase susceptibility to predation, are difficult, if not 

impossible to measure (Wedemeyer et al. 1990). Nevertheless, these factors undoubtedly 

influence the territorial behavior and repatriation of reintroduced fishes.

We intended to test if behavioral acclimation would influence short-term dispersal rates of young 

razorback suckers. If initial stocking behavior can be influenced, it could improve our ability to 

maintain fish in specific river reaches and improve survival by reducing predation exposure.
METHODS

Sources of Fish

Lake Powell Approximately 300 razorback suckers were transported from Ouray National Fish 

Hatchery, Utah, to golf course ponds in Page, Arizona, on May 16, 1996. Fish originated from 

"Green River" stock in 1993 and were designated "surplus" production from the upper basin 

stocking augmentation program. Fish were held in golf course ponds to determine the ponds 

suitability as grow-out facilities (Mueller and Wick 1997). Fish were scheduled to be released 

into critical habitat areas of Lake Powell (USDOI 1996a & 1996b).

Thirty fish averaging 358 mm in length (335-402 mm) were captured from the golf course ponds 

on May 3, 1997 (Appendix A). Fish were treated with stress reducing chemicals (salt, MS-222, 

stress coat, and furacin) and transported by boat to Castle Creek Canyon, River Kilometer (RK) 

72 on the San Juan Arm of Lake Powell.

Lake Mohave Lake Mohave were supplied by the Willow Beach National Fish Hatchery. Fish 

were smaller, averaging 241 mm (201-290 mm, Appendix A). Fish were hauled in a tank treated 

with stress reducing chemicals. In addition to sonic transmitters, the fish were also PIT (passive 

integrated transponder) tagged.

Telemetry Equipment and Survey Techniques

Ultrasonic transmitters were chosen over radio transmitters for their ability to be detectable 

regardless of depth, which in Lake Powell could exceed 100 m. Transmitters have been 

successfully used on both small razorbacks suckers and bonytail (Gila elegans) in Lake Mohave 

(Marsh et al. 1996, Mueller et al. 1998). Transmitters (Sonotronics, model MT-95-2) used for 

this study measured 9x36 mm, weighed 3 g in water, and had an estimated battery life of 90 

days. Normal detection range was 500 m.

Previous attempts to surgically implant sonic transmitters in juvenile razorback suckers led to 

high transmitter shedding and possibly mortality (Ryden 1997b, Mueller et al. 1998). We 

wanted to test external attachment techniques that might reduce stress, increase survival, and 

would eventually be shed. A literature review revealed various methods of attaching 

transmitters. Saddle-mounted transmitters were tested on several surrogate species (white 

suckers [Catostomus commersoni] and largemouth bass [Micropterus salmoides]) without much 

success (Winter et al. 1978) due to severe fungal and bacterial infections at the point of contact. 

Various combinations of metal wire harnesses were tested to determine if galvanistic corrosion 

could be used as a release mechanism. Combinations of steel, aluminum, and copper proved 

unreliable.
Razorbacks possess a dorsal keel, which is pronounced in adults and less developed in young. 

The keel of preserved speciemens loaned from the Arizona State University was examined as a 

potential attachment site. Dissection indicated the keel was composed of a cartilagineous ridge 

and a thin, poorly ossified bony plate. No major arteries, veins, or musculature were noted 

suggesting external attachment to the fish's keel might be an alternative that might prove less 

intrusive than surgical implants.

External sonic transmitters were attached to five razorback juveniles (32-35 cm TL) in Lake 

Mohave during 1994. The attachment technique is similar to those used for Carlin tags, where 

two sutures and a plastic backing plate held the transmitter in place (Stasko and Pincock 1977, 

Winter et al. 1978, Matthews et al. 1990). We remained in contact with 4 fish, all successfully 

carried the tags for the 45-day study.

The attachment technique was modified to a single suture and no backing plate to allow eventual 

transmitter shedding and speed healing. Prior to attachment, a mono filament line about 30 cm in 

length was positioned and glued to the center of each transmitter. The transmitter, line, and 

needles were sanitized in a solution of alcohol and 10% betadine prior to attachment. Each 

transmitter was activated and tested prior to attachment. Fish were weighed and measured and 

then wrapped in a wet towel and placed in shallow plastic tub filled with water. The needle was 

inserted about 6-8 mm below the fishes' dorsal keel. The ends of the lines were tightened over 

the keel and tied with three square knots, and the fish was placed in a holding tank for transport 

and release.

Twenty eight of the thirty Lake Powell transmitters functioned properly, one produced a weak 

signal, and another had no signal at all. Fish processing and transmitter attachment was rapid, 

typically taking less than a minute per fish. Groups of five fish were place within the blocked 

coves (held) and on the lake side (free) of the blocking nets. Fifteen fish were held three days 

and 13 were immediately released. The entire process took approximately 1.5 hours. Fish 

exhibited no obvious stress nor was their swimming skill impaired. Water visibility was less 

than 25 cm.

Blocking nets were removed 72 hours later and 5 suckers were found entangled in the net. Fish 

were securely held and the mesh was cut to minimize stressing the fish. Fish were examined and 

all sutures were still secure and wounds had not enlarged. One fish was released prior to 

checking its transmitter code, the remaining fish were # 238, 436, 446, and 447.

Lake Mohave Smaller meshed blocking nets were used to reduce the chance of entanglement. A 

group of 10 fish (5 held/5 released) was stocked at Owl Cove (RK45), 10 (5 held/5 released) at 

Tequila Cove (RK32), and 7 at Mesa Cove (RK 29). We only tagged 7 at Mesa Cove because 

we didn't want to use fish smaller than 21 cm. None of these fish were held for the acclimation 

test. On May 23, the holding nets were removed. Only one fish remained in the Owl Point 

holding cell and 2 in Tequila Cove, the other fish had already escaped.
Surveys were conducted each week by boat using a directional hydrophone. The San Juan Arm 

of Lake Powell is narrow and surveyors stopped at 500-800 m intervals along the channel and in 

every cove and side canyon to check for signals. Stream sections were monitored while floating 

downstream.

A GPS grid pattern was designed for Lake Mohave to accommodate its 5 km width. Waypoints 

or "listening stations" (71) were spaced 1,600 m apart to standardize monitoring locations and 

effort (Figure 1). After the second week we increased the number of stops to over 125 

locations, and bimonthly, we visited each cove and intensified (100 m intervals) our monitoring 

of flooded, shoreline vegetation.

When a fish was located the following information was recorded: date, time of day, location 

determined using GPS and/or maps, relative depth, distance from the shoreline, vegetation, cover 

type, and hydraulic characteristics (flowing versus slack). Location was recorded in latitude and 

longitude, river mile, and marked on a map. Water depth was determined visually or by using a 

fathometer, shoreline distance was estimated (<10 m, 10-50 m, >50 m). Surveys continued for 

100 days.

We attempted to recapture fish 80 days into the study to assess the attachment technique and to 

remove the transmitters. Trammel nets were set on fish found in shallow, calm habitats.

RESULTS 

Tracking

Lake Powell Surveys at both study locations began the morning following release. Initially 

Lake Powell surveys were conducted between RK 51 to RK 85, a distance of roughly 34 km. At 

the time of release, fish access upstream of RK 85 was physically blocked by a 3 m high water 

fall.

It was impossible to discern individual signal codes when fish were first released due to garbled 

signals. No cove held fish were detected outside of the enclosures during their period of 

captivity. All fish had left their release sites after 5 days but many remained in the Castle Creek 

Canyon complex. Initial contact was made with 23 of the 28 fish (Figure 2). Fish gradually 

dispersed, with all but three moving upstream. By June 10, the reservoir had risen to a point 

where the falls was inundated and could be negotiated safely by boat. Rising waters also 

inundated hundreds of hectares of flooded tamarisk which was impossible to monitor effectively. 

Submerged vegetation absorbed the sonic signal significantly reducing the signal range in some 

cases <50 m. During this period the water falls was also inundated and surveys were extended 

upstream (20 km) to Slickhorn Rapids (RK106) and during the week of August 12, two boat 

crews searched the entire 106 km reach between the confluence of the San Juan and Colorado 

rivers (RK 0) to Slickhorn Rapids (RK 106). Although the search effort was extensive, no 

additional fish were found.
Waypoint 1

Davis Dam

MAP OF LAKE MOHAVE 7

~ Zone 5: Black Canyon

N

21 frf - Zone 3: Castle Cliff Basin

22

* Zone 4: Interface Zone

Zone 1: Reservoir Canyons

0 5km

Figure 1. Map of Lake Mohave, Arizona and Nevada, showing numbered waypoints 1-71 and reservoir zones 1-5.
! Movement Stationary

80 100

Monitoring Days

Figure 2. Time duration and movement for externally tagged juvenile razorback suckers released 

into the San Juan Arm of Lake Powell, Utah, May through July 1997.

Movement Stationary

20 40 60 80 100

Monitoring Days

Figure 3. Time duration and movement for externally tagged juvenile razorback suckers released 

into Lake Mohave, Arizona-Nevada, May into August 1997.
Over time, the distance fish traveled declined and some fish appeared to take up residency in the 

shallow coves that typically had abundant cover. In several cases we were unable to detect any 

movement and suspected some fish had lost their tags. Into the fourth week of the study, we 

attempted to disturb several fish to determine if they would actually move and some moved 

distances greater than 100 m, only to return to their original location. Possibly juveniles had 

found cavities or "preferred" niches. During this period, reservoir elevations rose 10m and it 

became increasingly difficult to detect fish movement. While it was quite possible that fish 

simply were not moving, we felt it equally likely that transmitters had been shed. For purposes 

of analysis, we only present location data that we are certain represents fish movement (Table 1).

Several transmitters were not detected in the search area, which prompted us to expand the 

weekly search area further downstream. During the week of August 12, two boat crews 

searched the entire 106 km reach between the confluence of the San Juan and Colorado rivers 

(RK 0) to Slickrock Rapids (RK 106). The search was not expanded any further upstream due to 

safety and power craft restrictions. Although the search effort was extensive, no additional fish 

were found.

Over time, the distance fish traveled declined and some fish appeared to take up residency in 

selected spots. These areas usually were at the back of coves or in areas that had abundant cover. 

In several cases we were unable to detect any movement and suspected some fish had lost their 

tags or had died. Into the fourth week of the study, we attempted to disturb and move several 

fish to determine their status. Some fish moved distances greater than 100 m, only to return to 

their original location. Possibly juveniles had found cavities or "preferred" niches. During this 

period, reservoir elevations rose 10 m and it became increasingly difficult to detect fish 

movement. While it was quite possible that fish simply were not moving, we felt it equally 

likely that transmitters had been shed. For purposes of analysis, we only present location data 

that we are certain represents fish movement (Table 1).

Lake Mohave The entire length (106 km) of Lake Mohave was surveyed, which normally took 

2 days. We detected 17 of the initial 27 fish released but remained in contact with only 7 after 

the second week of the study. Of the 17, we detected 2 moving uplake, the rest moved down 

reservoir (Table 2, Figure 3).

Habitat Use

Habitat use was strikingly similar for both reservoirs. Fish were typically found within 10 m 

from 62% of the time in Lake Mohave compared to 65% in Lake Powell (Figure 4). Fish found 

at distances greater than 50 m from shore only represented 15 to 20% of the sightings.
Table 1. Range (River Kilometers) and movements of 23 of 28 juvenile razorback suckers 

released into the San Juan Arm of Lake Powell, Utah, May-August 1997.

Fish#

225

227

229

236

238

335

336

337

338

339

345

346

347

348

435

436

437

438

439

446

447

448

449

Days 

Tracked

3

11

25

6

5

4

32

33

38

34

4

58

1

34

33

6

34

34

52

34

33

40

34

# 

Contacts

5

8

9

6

2

1

7

13

10

6

5

15

2

9

7

8

11

13

14

11

6

7

7

Range (RK)

73.2

73.2 - 78.8

68.9 - 78.4

73.2 - 74.8

72.7 - 74.0

73.2

73.2 - 80.1

73.2 - 78.8

73.2 - 78.8

73.4

73.2

73.2 - 81.3

73.2 - 73.5

73.2 - 76.7

73.2 - 77.6

73.2 - 74.8

73.2 - 75.1

73.2 - 78.8

73.2 - 79.0

73.2 - 73.4

73.2 - 78.8

72.7 - 75.5

73.2 - 80.6

Tot. Dis. 

Travel(m)

1,800

8,700

18,700

5,400

2,600

100

14,800

17,000

7,600

100

1,200

6,700

1,800

4,750

14,700

6,100

9,300

22,900

10,090

4,400

16,700

8,250

16,150

Max.* 

m/day

900

2,100

2,400

2,600

1,000

_

2,700

3,800

2,900

-

700

2,000

1,800

400

4,800

2,500

1,200

5,000

1,200

1,000

2,000

1,600

1,200

Avg. 

m/day

600

791

748

900

520

25

462

515

200

3

300

115

1,800

140

445

1,016

274

674

194

129

506

206

475

* Within 24 hours (consecutive days).
Table 2. Range (River Kilometers) and movements of 17 of 27 juvenile razorback suckers 

released into Lake Mohave, Arizona-Nevada, May-August 1997.

Fish#

225

226

227

228

236

238

335

337

338

345

437

438

439

445

446

448

449

Days 

Tracked

5

5

2

2

40

12

2

5

5

12

19

3

5

2

8

8

3

# 

Contacts

3

4

1

1

15

10

1

3

3

5

2

2

2

2

2

3

2

Range (RK)

33.8

33.0 - 33.8

33.0 - 33.8

33.0 - 33.8

28.2

32.2 - 65.2

23.7

12.2 - 23.7

23.7

23.7

32.2 - 33.8

33.8

33.0 - 33.8

45.4

43.4 - 45.4

44.2 - 45.4

44.2 - 45.4

Tot. Dis. 

Travel(m)

15

700

1,200

2,100

200

84,700

7,500

200

300

1100

20

1,150

300

3,300

1,800

1,900

Max.* 

m/day

15

300

-

-

-

20,500

7,100

200

200

-

-

-

300

-

-

-

Avg. 

m/day

3

140

600

1,050

5

7,050

1,500

40

150

60

10

230

150

410

225

635

*Within 24 hours (consecutive days).

It was impossible to discern individual signal codes when fish were first released due to garbled 

signals. No cove held fish were detected outside of the enclosures during their period of 

captivity. All fish had left their release sites after 5 days but many remained in the Castle Creek 

Canyon complex. Initial contact was made with 23 of the 28 fish (Figure 2). Fish gradually 

dispersed, with all but three moving upstream. By June 10, the reservoir had risen to a point 

where the falls was inundated and could be negotiated safely by boat. Rising waters also
Lake Mohave

(N=60)

Lake Powell

(N=159)

Figure 4. Percentage of razorback sucker detection less than 10, 10 to 50, and greater than 

50 m from shore in lakes Mohave and Powell, May through July 1997.

inundated hundreds of hectares of flooded tamarisk which was impossible to monitor effectively. 

Submerged vegetation absorbed the sonic signal significantly reducing the signal range in some 

cases <50 m. During this period the water falls was also inundated and surveys were extended 

upstream (20 km) to Slickhorn Rapids (RK106) and during the week of August 12, two boat 

crews searched the entire 106 km reach between the confluence of the San Juan and Colorado 

rivers (RK 0) to Slickhorn Rapids (RK 106). Although the search effort was extensive, no 

additional fish were found.

Cover was an important habitat component and represented >50% of our observations. It 

appears cover was being used for concealment and the type used varied, dependent upon its 

availability. Fish utilized three types in Lake Mohave; submerged tamarisk (Tamarix 

pentandra), large rocks and ledges, and submergent vegetation (No/as or Potamogeton spp.). 

Fish were most often (48-86%) found in flooded tamarisk (Figure 5). The second most 

prevalent cover type where juvenile suckers were found in Lake Mohave was submergent 

vegetation (40%) and the last cover type used was rock ledges or rubble (12-14%). Similar cover 

types were found in Lake Powell with the exception of emergent vegetation.

Range

Lake Powell We detected 23 of the 28 fish released at Castle Creek Canyon (Table 1). The 

initial movement of some fish was pronounced, and generally uplake (RK >73) and only two 

ventured downstream. The maximum distance fish were detected from the release site was 4.6 

km upstream and 2.7 km downstream.

10
The average maximum distance traveled by 21 fish was more than 2,080 m/d (range 400-5,000 

m/day). One fish (#438) traveled a total distance of 5 km/d. Juvenile fish frequented and moved 

between Castle Creek Canyon and Mike's Canyon (RK 73-79). The average observed range was 

2.2 km (0.1 to 7.4 km). We were unable to determine the actual dispersal range since we lost 

contact with 50% of the study fish.

100

80

u

c 

o

§ 40

20

(Tamarisk O Boulder Pond weed

Lake Mohave 

(N=33)

Lake Powell

(N=77)

Figure 5. Cover used by juvenile razorback suckers released into lakes Mohave and Powell, 

May through July 1997.

Lake Mohave Fish rapidly dispersed and we only maintained contact with one fish (#437) past 

the third week. Fish #337 traveled 7.1 km in one day. On the fourth day we contacted and 

followed fish #238 moving at a rate more than 3 km/hour. It was traveling up the middle of the 

reservoir and by mid-day had moved an astonishing rate of 20.5 km/day. The transmitter 

traveled nearly 63 km, through the pelagic zones in Lake Mohave during the next four days, 

suggesting it might have been eaten by a striped bass.

Equipment Performance and Survey Design

Signal reception was best under calm conditions and when the transmitter was located in open 

water. At times signals could be heard at distances of 1-2 km. Wind, rain, wave action, and 

watercraft traffic interfered with listening and reduced detection range. The disappearance of 

nearly 80% of our transmitters in Lake Mohave caused us to examine if, and to what extent, 

aquatic vegetation might interfere with signal strength. We found if transmitters were placed

11
inside sago pondweed beds or behind dense stands of submerged tamarisk, detection range was 

reduced to <40 m. Unfortunately, as spring run-off increased, rising reservoir elevations flooded 

broad (>200 m) bands of tamarisk. Tests proved submergent vegetation not only interfered with 

signal reception, but also proved impenetrable to watercraft. We were unable to effectively 

survey hundreds of hectares of flooded habitat near Owls Point and Wagon Wheel Cove (Lake 

Mohave) or at Piute Farms (Lake Powell).

Equipment failure is always a consideration when contact is lost with a fish. Initial failure rate 

was 2.5% (2 of 80). It is impossible to determine transmitter failure after fish were released, 

however, based on the longevity of the stationary transmitters, we believe failure was low. 

While we acknowledge that we could not be 100% effective on each survey, we feel that any fish 

that remained active, in either of the survey areas would have been eventually detected. The only 

other explanations for losses are: 1) equipment failure, 2) the removal offish and transmitter 

from the system by terrestrial or avian predator, or 3) fish found, penetrated, and remained in the 

large, impenetrable flooded habitats where they were undetectable by telemetry equipment.

Tank Tests

We conducted tank tests on 2 groups of juvenile suckers to determine the shedding rate of 

externally attached transmitters and the healing process. Transmitters were attached with a 

single suture to the dorsal keel of a group of five fish (x23 cm/21-27 cm). Fish were held in a 

holding tank (2m diameter X 1 m deep) for 8 weeks. Fish were fed daily and examined weekly. 

The sutures gradually worked through the dorsal tissue. The wounds appeared clean, no bacterial 

or fungal infections were noticed. Average transmitter retention was 3.8 weeks (2->.8 weeks) 

and all fish recovered. Suture wounds healed within 2-4 weeks.

Similar tests were conducted with ten larger fish (x=29 cm/27-32 cm) using two sutures. A 

control fish (no transmitter) was also placed in the tank. Five fish, including the control, died of 

unknown causes. Sutures of the study fish did not appear inflamed or infected. The first 

transmitter was lost on week 5 and the remaining 5 fish retained their tags through week 9.

DISCUSSION 

Stocking Dispersal

Individual movements and ranges are quite variable. It appears roughly 50% of stocked suckers 

emigrate out of the 46 km study area during the first month. These movements are similar to 

those reported for juvenile flannelmouth suckers by Chart and Bergensen (1992). They reported 

that juvenile flannelmouths moved more, and had ranges larger than sexually active adults. 

Results were similar to comparisons made between the home ranges of adults and the movements 

of a single juvenile razorback sucker in Lake Mohave (Mueller et al. 1998).

Other than knowing that dispersal is wide spread, the actual range continues to be unknown.

12
Unfortunately, in Lake Powell, ambient noise generated by a water fall and then by high spring 

flows prevented us from effectively monitoring upstream sections of the study area. However, 

reservoir survey conditions were generally ideal. Efforts to locate fish downstream of the release 

site extended over 72 km. Only two fish moved 2.7 km downstream, the furthest 2.7 km. 

Twenty-one of 23 fish (92%) moved uplake whereas 84% moved down lake in Lake Mohave. It 

is unknown whether this might be a behavioral response triggered by handling, current, turbidity, 

or simply a factor of shoreline morphology.

Stocking Acclimation Methods of handling and stocking endangered or threatened fishes are 

generally the same as for trout, bass, catfish, or other game fish (USFWS 1992, 1994). They are 

transported by truck to the release site where they are acclimated to physical conditions, 

normally temperature and rarely pH (Stickney 1983, Wedemeyer et al. 1990). At that point they 

are simply released. The Upper Colorado River Basin Recovery Implementation Program (RIP) 

has establish stocking criteria and guidelines (USFWS 1992, USFWS 1994), however, 

behavioral acclimation is not included. Protocols have been established which mandate that 

stocked fish be "released in quiet-water areas (e.g., backwaters) that communicate with the 

river." Unfortunately, augmentation programs have met with mixed, if not poor results.

For instance, a ten-year reintroduction program in Arizona stocked nearly 12 million razorback 

suckers with no measurable results. The majority were stocked as fmgerlings or fry and 

subsequent studies showed young fish moved en masse downstream and were rapidly eaten by 

channel and flathead catfish (Brooks 1985, Marsh and Brooks 1989, Minckley et al. 1991).

Since then, some success has been reported by stocking larger fish to reduce predation (Mueller 

1995, Marsh 1997, Ryden 1997a). While survival can be improved with larger fish, managers 

often have been unable to stock and retain fish in desired locations. Often stocked fish travel 

great distances downstream. Several scientists speculated that fish reared in hatchery or rearing 

ponds might not have developed adequate muscle tone to cope with flowing habitats (Todd 

Crowl personal communique ). Laboratory investigations that were conducted proved 

inconclusive.

Research on Lake Mohave (Mueller et al. 1998) suggests stocked juveniles travel substantial 

distances, even in lentic environments where hydraulics were not a factor. We believe this 

supports the contention that other factors, such as normal early life migratory behavior, handling 

and transport associated stress, or even habitat conditioning could also be factors.

Recent studies examining the movements and habitat use of bonytail in Lake Mohave found 

quite a difference in response between pond-reared and resident fish (Marsh et al. 1996, Foster 

et al. 1997). Researchers found that pond-reared bonytails roamed more widely and were more 

difficult to detect than resident fish that had distinct territorial ranges. When non-resident 

bonytail were found, they were detected in shallow, vegetated habitats, similar to habitats where 

they were taken from. Fish captured from the reservoir were more pelagic in nature and were 

quite territorial suggesting habitat conditioning might have occurred.

13
Released 5 days 15 days 30 days 

Study Duration

Figure 6. A comparison of the detection of cove held (3 days) versus juvenile razorback suckers 

released into the San Juan Arm of Lake Powell, Utah, May 3, 1997.

o

O)

o

Q

Average ^Low -e-High « Juvenile

Nov Apr

1995

Sept Feb April

1996

Figure 7. Comparison of the temperature regime used by one juvenile and 10 adult razorback 

suckers in Lake Mohave, Arizona-Nevada, during 1995-1996 (Mueller et al. 1998).

14
Behavioral acclimation may also be a factor. Of the 14 Lake Powell fish that remained in the 

study area for more than one month, we encountered twice as many cove held fish (64%) as 

those simply released and not held for 3 days (Figure 6). The sample size was small and might 

simply reflect normal variability, however, it appears that holding does not deter fish from 

remaining in the general area and might encourage it. The data collected from Lake Mohave 

were inadequate to draw any conclusions.

Habitat Use

Juvenile or subadult razorback suckers were found using the same broad, shallow, shoreline 

habitats as adults. They were seldom found in narrow, deep, canyon habitat. While adults are 

generally found in open areas along the shoreline (Mueller et al. 1998), juveniles are more 

secretive, being found in the back of coves or flooded washes hidden in vegetative or rocky 

cover. Fish were typically found within 10 m of shore and depths were less than 2 m.

Our findings support earlier observations in rearing ponds that young suckers were nocturnal and 

effectively concealed themselves in submergent vegetation during the daytime (Mueller and 

Marsh 1993). These shallower habitats naturally provide warmer temperatures and more food 

production; important factors in rapid growth. Surface water temperatures ranged 1 -3 degrees C 

higher in these backwaters than the main lake. This mimics earlier information we collected in 

Lake Mohave (Mueller et al. 1998,). Body temperature data collected for 10 adults and one 

juvenile suggests the two-year old fish normally inhabited a thermal regime equal to, or greater, 

than the maximum temperature range used by adults (Figure 7).

Juveniles had a strong preference for flooded backwater complexes at Castle Creek Canyon and 

Mike's Canyon. These two sites afforded fish the largest, shallow, flooded habitats in the San 

Juan Arm, next to Piute Farms when lake elevations exceed 1,120 m (3,680 ft). These areas are 

similar to areas where juvenile razorbacks have been found in the Green River at Old Charley 

Wash (Modde 1996 and 1997). Dispersal appears to be strongly influenced by habitat/cover 

availability. The rapid dispersal observed in riverine systems suggests that habitat conditions 

did not attract and hold young fish. The physical changes brought about by channelization, loss 

of backwaters and oxbows, fluctuating hydroelectric releases, and the decline of large snags and 

other woody debris, have undoubtedly effected cover availability.

External Attachment Technique

Attachment of transmitters to the dorsal keel worked well as a short-term approach and is 

possibly the only practical method of studying the movements of juvenile suckers. We observed 

no initial mortality and all 55 fish left the release sites. We feel attaching transmitters to the 

dorsal keel is less intrusive than the common dart tag which is generally inserted into the dorsal 

musculature and is less stressful than surgery for short-term, behavioral studies.

15
Following the poor results of the Lake Mohave fish, we attached transmitters to five similar sized 

razorback suckers and held them at the Bureau of Reclamation fish holding facilities at Boulder 

City, NV. The fish ranged in size from 230 to 270 mm. The fish were inspected once a week to 

determine transmitter shedding and subsequent post-healing. When the transmitter was 

eventually lost, it left a small wound which healed in 2-3 weeks. The average transmitter 

retention was 3.8 weeks (2 to >8 weeks) and all experimental fish recovered.

Transmitter retention time for the smaller (TL x = 241 mm) Lake Mohave fish was shorter (<2 

weeks) than of our tank fish or the larger Lake Powell fish (> 4 weeks). We believe there might 

be at least two reasons for this. First, we know that reservoir fish concealed themselves in 

aquatic macrophytes. We observed one study fish in Lake Mohave trailing a long strand of 

pondweed from its transmitter. Snagging undoubtedly could speed the shedding process. 

Vegetation was not a factor in the holding tank experiments nor are aquatic macrophytes 

common in Lake Powell. The second factor could be the ossification of the fishes dorsal keel. 

Younger fish have softer tissues which are less capable of supporting a transmitter. The use of a 

single, rather than multiple sutures undoubtedly is less intrusive, but may also be less permanent 

than double sutures.

Unfortunately, mortality is common with surgical procedures. Survival of adults reported by 

other researchers has also been highly variable (0-100%) with most studies achieving a 50-70% 

survival rate (Marsh and Minckley 1989, Creef and Clarkson 1993, Ryden and Pfeiffer 1995, 

Karp and Mueller 1996, Burdick and Bonar 1997, Holden et al. 1997, Ryden 1997b). While 

external attachment may be inappropriate for long-term studies, it does provide an alternative 

for short-term studies. The dorsal keel found on the razorback sucker and some other native 

Colorado River fish provides a unique attachment spot. This approach is non-lethal, less 

intrusive than abdominal surgery and allows a mechanism for transmitter shedding for all ages of 

fish.

Management and Research Implications

Augmentation and Recovery Efforts

Reservoir habitat will continue to play a role in augmentation and recovery of native Colorado 

River fishes. There is growing evidence that razorback suckers migrate between flowing and 

non-flowing habitats (Karp and Mueller 1996, Ryden 1997a, Mueller and Wydoski 1995, and 

unpublished data). High use of shallow, flooded backwaters by juvenile razorback suckers in 

both Mohave and Powell lends credence to the importance of these habitats during their early life 

stage. This dependency is somewhat disturbing since these habitats are also havens for known 

predators. In stable habitats, such as Lake Mohave, territorial predators like largemouth bass and 

channel catfish are not subjected to high fluctuation in reservoir elevation, which influences 

habitat availability. However, in larger reservoirs as lakes Powell and Mead, annual water 

elevation can fluctuate as much as 20 m which can cause inflow habitats to migrate as much as

16
15 km in only a few weeks. Changes this rapid undoubtedly influence the distribution and 

reproductive cycles of non-native predators, and might be manipulated to regulate predator 

densities.

If successful, present programs to augment spawning cohorts in either the San Juan, Green, or 

Colorado rivers will result in larval sucker transport into Lake Powell. With the general absence 

of nursery habitat in the lower 100 km reach of these rivers, natural recruitment associated with 

these portions of the river might be largely dependent upon nursery habitat found either further 

upstream, or downstream, in Lake Powell. Manipulation of reservoir elevations may provide the 

greatest chance for these, and other, young natives to survive. The concept certainly deserves 

more evaluation.

RECOMMENDATIONS

The behavioral acclimation test suggests that holding fish on site for 3 days may influence their 

dispersal rate. We recommend further testing be conducted to confirm this in both reservoir and 

riverine habitats.

We recommend that external attachment techniques be considered by other researchers when 

studying the short-term movements and behavior of the razorback sucker and other similarly 

keeled, Colorado River fishes. This approach is less intrusive than surgery, non-lethal, and 

possibly best suited for juveniles or wild fish.

Juveniles have a strong fidelity toward shoreline habitats which are also used by known predators 

such as largemouth bass and channel catfish (Harlan and Speaker 1951, Tyus 1997). This habitat 

attraction may help explain the virtual absence of young razorback suckers. We recommend that 

further research be directed at developing and evaluating methods of reducing or eliminating 

predation. Current efforts to augment existing population by stocking larger razorback suckers 

does not address the problems of early life stage survival. We also need to better understand 

non-native predator effectiveness, and explore methods that might reduce or minimize predator 

densities found in habitats used by early life stages of razorback sucker.

Until more information is available, we suggest that larger (>30-cm) fish be stocked and that 

stocking be delayed until winter when predators are dormant (Marsh and Brooks 1989). 

Predation concerns stemming from assessed survival rates has resulted in a recommended 

stocking size of 40-cm for augmenting San Juan River stocks (Ryden 1997a). We support this 

approach.

17
ACKNOWLEDGMENTS

We wish to express our sincere appreciation to Dean Foster, Richard Brunette, Christine Miller, 

and numerous others who collected the field data. Ed Wick, Tom Burke, Kent Turner, Bill Pelle, 

and Norm Henderson provided additional equipment, logistical support, secure funding, and field 

assistance. Tim Modde, Chuck Minckley, Bob Burdick and Rick Bradford reviewed and 

provided comments on the report. We thank the states of Arizona, Nevada, Utah, and USFWS, 

and NFS for the issuance of necessary permits. The study was funded by the USGS and NFS.

LITERATURE CITED:

Brooks, I.E. 1985. Annual reintroduction and monitoring report for the razorback sucker

Xyrauchen texanus in the Gila River basin, Arizona, 1985. USFWS, Albuquerque, New 

Mexico.

Burdick, B.D., and R.B. Bonar. 1997. Experimental stocking of adult razorback sucker in the 

upper Colorado and Gunnison Rivers. Recovery Program Project Number 50, FWS, 

CRFP, Grand Junction, Colorado.

Chart, T.E., and E.P. Bergersen. 1992. Impacts of mainstream impoundment on the distribution 

and movements of the resident flannelmouth sucker (Catostomideae: Catostomus 

latipinnis) population in the White River, Colorado. The Southwestern Naturalist 37

Creef, E.D. and R.W. Clarkson. 1993. Razorback Sucker (Xyrauchen texanus) and Colorado 

Squawfish (Ptychocheilus lucius) Monitoring , Verde and Salt Rivers, Arizona, 1991- 

1993. Arizona Game and Fish Department, Phoenix, Arizona.

Gutermuth, F.B., L.D. Lentsch, K.R. Bestgen. 1994. Collection of Age-0 razorback suckers 

(Xyrauchen texanus} in the lower Green River, Utah. The Southwestern Naturalist 

39:389-391.

Harlan, J.R. and E.B. Speaker. 1951. Iowa Fish and Fishing. Iowa State Conservation 

Commission, Des Moines, Iowa 365 pp.

Holden, P.B., P.O. Abate and J.B. Ruppert. 1997. Razorback sucker studies on Lake Mead, 

Nevada. 1 996- 1 997 Annual Report, PR-578- 1 . Submitted to Southern Nevada Water 

Authority, Las Vegas, Nevada by Bio/West, Inc. Logan, Utah.

Johnson, J.E. 1985. Reintroducing the natives: razorback sucker. Proceedings of the Desert 

Fishes Council, 13:73-79.

18
Karp, C., and G. Mueller. 1996. Annual Report of Razorback Sucker Telemetry Study in the 

lower San Juan River, Utah, 1996. Bureau of Reclamation, Denver Technical Services 

Center, D-8220, Denver, Colorado.

Knowles, G.W., P.C. Marsh, G. Mueller, and T. Wolters. 1996. Sonic telemetry of razorback

sucker in Lake Mohave, Arizona-Nevada. Oral presentation to the Desert Fishes Council

McAda, C.W., and R.S. Wydoski. 1980. The razorback sucker, Xyrauchen texanus, in the upper 

Colorado River basin, 1974-76. USFWS Technical Paper 99, 1-15.

Marsh, P.C. 1997. Razorback Sucker Monitoring in Lake Mohave, Arizona and Nevada, for the 

Period 01 November 1995 to 31 October 1996. Submitted to USBR, work order #1425- 

97-PG-30-06390, Boulder City, NV.

Marsh, P.C., and J.E. Brooks. 1989. Predation by ictalurid catfishes as a deterrent to 

re-establishment of introduced razorback suckers. The Southwestern Naturalist 

34:188-195.

Marsh, P.C. and W.L. Minckley. 1989. Radiotelemetry of razorback sucker in the Gila River, 

eastern Arizona. Proceeding of the 21st Annual Desert Fishes Council Meeting, 

Albuquerque, New Mexico, Pages 163-171.

Marsh, P.C., G.W. Knowles, G. Mueller. 1996. Bonytail (Gila elegans) telemetry in Lake 

Mohave, Arizona and Nevada. Abstract, presented at Desert Fishes Council Meeting, 

Mexico.

Matthews, K.R., T.P. Quinn, and B.S. Miller. 1990. Use of ultrasonic transmitters to track 

demersal rockfish movements on shallow rocky reefs. American Fisheries Society 

Symposium 7:375-379.

Minckley, W.L. 1983. Status of the razorback sucker, Xyrauchen texanus (Abbott), in the lower 

Colorado River basin. The Southwestern Naturalist 28, 165-187.

Minckley, W.L., P.C. Marsh, J.E. Brooks, J.E. Johnson and B.L. Jensen. 1991. Management 

toward recovery of the razorback sucker. Pages 303-357 in Minckley and Deacon, eds., 

Battle Against Extinction: Native Fish Management in the American West. The 

University of Arizona Press, Tucson.

Modde, T. 1996. Juvenile razorback sucker in a managed wetland adjacent to the Green River. 

Great Basin Naturalist 56:375-376.

19
Modde, T. 1997. Fish use of Old Charley Wash: an assessment of floodplain wetland

importance to razorback sucker management and recovery. Final report submitted to the 

Recovery Implementation Program for the Recovery of Endangered Fishes in the Upper 

Colorado River Basin. USFWS, Denver CO. 63pp.

Modde, T., K.P. Burnham, and E.J. Wick. 1996. Population status of the razorback sucker in 

the middle Green River. Conservation Biology 10(1): 110-119.

Modde, T., and D.B. Irving. 1998. Use of multiple spawning sites and seasonal movements of 

razorback sucker in the Green River, Utah. North American Journal of Fisheries 

Management 18 impress.

Mueller, G. 1995. A program for maintaining the razorback sucker in Lake Mohave. American 

Fisheries Society Symposium 15:127-135.

Mueller, G. 1997. Restoration of the Razorback Sucker in the Colorado River, Southwestern 

United States. Pages II26-II33 in Proceedings of the World River Conference, Gifu, 

Japan.

Mueller, G, .and P.C. Marsh. 1993. Assessment of the effectiveness of the barrier net and

summary of the Scuba studies; February 1992 to June 1993. BOR Summary Report to 

the NFWG, Boulder City, NV 5pp

Mueller, G., and P.C. Marsh. 1995. Bonytail and razorback sucker in the Colorado River basin. 

Pages 324-326 in Laroe, Farris, Puckett, Doran, and Mac, eds. Our Living Resources: a 

report to the nation on the distribution, abundance, and health of U.S. plants, animals, and 

ecosystems. USDOI, NBS, Washington DC. 530 pp.

Mueller, G., and R. Wydoski. 1995. Fish survey of San Juan River inflow area of Lake Powell, 

March 13-28, 1995. National Biological Service, Denver, Colorado.

Mueller, G., P.C. Marsh, and G. Knowles. 1998. Distribution, migratory behavior, and habitat 

use of razorback sucker (Xyrauchen texanus) in Lake Mohave, Arizona-Nevada. 

U.S.G.S., Biological Resources Division, Open Files Report 98-252, Denver, Colorado 

80225.

Mueller, G., and E.J. Wick. 1997. Testing of golf course ponds at Page, Arizona for suitability 

as grow-out facility for razorback sucker using surplus fish from Ouray National Fish 

Hatchery. USGS, Technical Service Center, Denver, Colorado.

Ryden, D.W. (Draft) 1997a. Five-year augmentation plan for razorback sucker in the San Juan 

River. USFWS, Colorado River Fishery Project, Grand Junction, Colorado.

20
Ryden, D.W. 1997b. Memo (4/2/97) to Michelle Thieme. Fish and Wildlife Service, 

Colorado River Fishery Project, Grand Junction, Colorado 81506.

Ryden, D.W., and F.K. Pfeifer. 1995. Monitoring of experimentally stocked razorback sucker in 

the San Juan River. USFWS, Colorado River Fishery Project, Grand Junction, Colorado.

Stasko, A.B., and D.G. Pincock. 1977. Review of underwater biotelemetry, with emphasis on 

ultrasonic techniques. Journal of the Fisheries Research Board of Canada 34 (9): 1261- 

1285.

Stickney, R.R. 1983. Care and handling of live fish. Pages 84-94 in L.A. Nielsen and D.L. 

Johnson, Editors. Fisheries techniques. American Fisheries Society, Bethesda, 

Maryland.

Tyus, H.M., and C.A. Karp. 1989. Habitat use and streamflow needs of rare and endangered 

fishes, Yampa River, Colorado. U.S. Fish and Wildlife Service, Biological Report 

89(14). 27pp.

Tyus, H.M. 1987. Distribution, reproduction, and habitat use of razorback sucker in the Green 

River, Utah, 1979-1986. Transactions of the American Fisheries Society 116:111-116.

Tyus, H.M. 1997. Razorback Sucker (Xyrauchen texanus), Draft Recovery Plan. USFWS, 

Region 6, Denver, CO.

Ulmer, L. 1987. Management plan for the razorback sucker in California. Proceedings of the 

Desert Fishes Council 17:185 (abstract).

U.S.D.O.I. 1996a. Memorandum of Agreement among: DOI, FWS,NPS, UDONR, and 

UDWR. Glen Canyon National Recreation Area, Page, Arizona.

U.S.D.O.I. 1996b. Glen Canyon National Recreation Area, Utah/Arizona, Fish Management 

Plan. Glen Canyon National Recreation Area, Page, Arizona.

U.S.F.W.S. 1992. A Plan to Evaluate Stocking to Augment or Restore Razorback Sucker in the 

Upper Colorado River. Recovery Program for the Endangered Fishes of the Upper 

Colorado. Fish and Wildlife Service, Denver, Colorado.

U.S.F.W.S. 1994. Coordinated Hatchery Facility Plan: Need for captive-reared endangered fish 

and propagation facilities. Recovery Implementation Program for Endangered Fish 

Species in the Upper Colorado River Basin. Fish and Wildlife Service, Region 6, 

Denver, Colorado.

21
Wedemeyer, G.A., B.A. Barton and DJ. McLeay. 1990. Stress and Acclimation. Pages 451-491 

in C.B. Schreck and P.B. Moyle, editors. Methods for Fish Biology. American Fisheries 

Society, Bethesda, Maryland.

Winter, J.D., V.B. Kuechle, D.B. Siniff, and J.R. Tester. 1978. Equipment and methods for 

radio tracking freshwater fish. University of Minnesota, Agricultural Experimental 

Station, Miscellaneous Report 152-1978.

22
APPENDIX A Specific Fish Data 

Razorback Suckers released at Castle Creek Canyon, Lake Powell, Utah on May 3,1997.

Transmitter 

Code

3-3-7

3-3-5

3-3-6

3-3-8

3-3-9

2-2-5

2-2-6

2-2-7

2-2-8

2-2-9

2-3-9

2-3-8

2-3-6

4-3-5

4-3-6

4-3-7

4-3-8

4-3-9

3-4-5

3-4-6

4-4-6

4-4-7

4-4-5

4-4-8

4-4-9

3-4-7

3-4-8

3-4-9

2-3-7/2-3-5

Length Weight 

<TL mm} (Grt

370

351

360

384

362

335

365

368

348

340

350

375

370

342

355

352

390

342

330

344

365

350

358

358

352

351

358

362

Malfunctioned

610

680

760

925

745

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

665

695

660

Held or 

Released

Held

Held

Held

Held

Held

Released

Released

Released

Released

Released

Held

Held

Held

Held

Held

Released

Released

Released

Released

Released

Held

Held

Held

Held

Held

Released

Released

Released

* Electric scale malfunctioned 

x = 357 mm, range 330-390 mm.

23
Razorback Suckers released In Lake Mohave, Arizona-Nevada on May 20,1997.

Trans. 

Code

2-3-7

2-3-5

2-3-8

2-3-6

2-3-9

4-4-5

4-4-9

4-4-6

4-4-7

4-4-8

4-3-7

4-3-8

4-3-5

4-3-9

4-3-6

2-2-6

2-2-5

2-2-9

2-2-7

2-2-8

3-3-5

3-3-9

3-3-7

3-3-8

3-3-6

3-4-8

3-4-5

Length 

<TL mm)

236

238

285

228

222

282

220

290

276

234

276

218

256

245

262

254

245

225

235

233

222

224

235

210

216

220

221

Weight 

(g)

152

156

264

134

126

230

112

294

254

140

240

116

172

168

198

190

160

126

138

122

110

122

128

94

114

114

112

PIT Tag

#

41272B2729

41276E217E

41270E2C77

41272C4E49

41270A2D58

4127143D76

41270D4216

4127184933

412766023D

41272B6BOC

4127025E1C

41272F5436

4128066579

4127690336

41272A3660

41280B7DOE

4127107248

41277B7F65

4127741771

4127306C49

4127681665

41270F1B13

4127150905

41271F1D51

41277A6E2C

41271E5D3C

41277A287B

Site Location * 

(Held/Release)

1 fU\ i {ri)

1 (H.)

1 (H)

1 (H)

1 (H)

1 (R)

1 (R)

1 (R)

1 (R)

1 (R)

2(H)

2(H)

2(H)

2(H)

2(H)

2(R)

2(R)

2(R)

2(R)

2(R)

3(R)

3(R)

3(R)

3(R)

3(R)

3(R)

3(R)

* 1 = Owl Cove (RK 45), 2 = Tequila Cove (RK 34), 3 = Mesa Cove (RK 24) 

x = 241 mm, range 210-290 mm.

24