smallmouth bass produced in 2005; the numbers appeared to be even greater than those produced
during 2004. In viewing the 2005 length frequency, it appears that the size group of smallmouth
bass between 50 and 100 mm produced in 2005 were lost to the population sometime between
the winter of 2005/2006 and the summer of 2006. This size class of smallmouth bass may have
experienced high overwinter mortality and were lost prior to high spring runoff or were lost
during the 2006 spring runoff. In any event, age-0 and possibly some slower growing age-1
smallmouth bass in 2005 did not recruit to the next size classes and their numbers obviously
declined prior to the summer of 2006. The exact reason for this decline is unknown. During this
study, there was no sampling performed in the spring following the winter months or prior to the
spring runoff to assess the abundance of age-1 smallmouth bass. Therefore, it can only be
speculated as to the fate of this size class of smallmouth bass.

The rapid increase of the smallmouth bass population in the Yampa River between
2000-2004 was believed, in part, attributed to several consecutive years of drought conditions
that brought about habitat changes in the form of altered flows (i. ., reduced spring discharge in
duration and magnitude followed by lower than average post-runoff flows) and warmer water
temperatures. Warmer water and lower and earlier flow peaks could result in earlier bass
spawning, longer growing season, and increased growth rates. Increased size of age-0
smallmouth bass in the summer could lead to increased overwinter survival, which in turn, could
result in increased recruitment to the adult population (Bestgen et al. 2007). Thus, successful
smallmouth bass recruitment might be related to warmer summer and fall water temperatures.

Anderson (2004) speculated that if these conditions promoted earlier spawning or a
longer growing season, then smallmouth bass recruitment could have improved in drought years
because age-0 smallmouth bass larger than 75 mm could have had higher overwinter survival
rates than smaller young-of-the-year (from Anderson 2004: Pat Martinez, CDOW, personal
communication). Anderson (2005) demonstrated that there was strong correlation r = 0.985)
between water temperature and recruitment to age-1. In the Yampa River, smallmouth bass
recruitment to age-1 increased dramatically between 2001 and 2004 which was dominated by
lower base flows and warmer water regimes; whereas they were very rare during higher base
flows and cooler years (1998 to 2000). A similar pattern occurred in the middle Green River,
Utah, at about the same period under similar environmental conditions. Smallmouth bass began
increasing in abundance about 2001 or 2002, likely in response to warmer water temperatures
(i. ., earlier warming and increased magnitude and duration) associated with drought conditions

42


METHODS
Fish Sampling

The study utilized jon boat and raft-based electrofishing to remove smallmouth bass.
Each electrofishing craft was equipped with a Smith-Root (Model GPP 5.0) electrofishing unit.
Actual time spent electrofishing (actual circuit time) was also recorded. Main channel habitats
sampled included mostly shorelines and backwaters. Two electrofishing craft were used
concurrently to collect fish. Although smallmouth bass were the target fish for removal in this
project, all other centrarchid fishes encountered were collected. The reason for this was that the
CDOW requested that the FWS remove and preserve all centrarchid fishes collected during the
removal effort for use in the provenance (isotope signature) study. These fishes included
largemouth bass, green sunfish, bluegill, and black crappie. Samples were preserved according
to criteria provided by CDOW.

For sampling logistics, each major segment in the Upper Colorado River was further
partitioned into sub-reaches. For the Upper Colorado River between Price-Stubb Dam and
‘Westwater, Utah, eight sub-reaches were designated. There was one sub-reach in the Lower
Gunnison River (Table 1). Each sub-reach between Price-Stubb Dam and Westwater, Utah, and
the Lower Gunnison River during 2004 and 2005 was sampled at least three times with
electrofishing. Some sub-reaches where high concentrations of smallmouth bass were collected
during the first three passes were sampled a fourth time. Only one electrofishing craft was used
during the fourth pass, which was termed a “concentration pass”. This pass was dedicated to
electrofishing the higher abundance areas determined from the first three passes. All smallmouth

bass collected were lethally removed.

During 2006, the protocol was modified to include an additional initial pass to mark and
release all smallmouth bass collected in the moderate to high concentration areas of the Upper
Colorado River from the Grand Valley Irrigation Company (GVIC) Diversion Dam to the Loma
boat landing and the lower 2.3 miles of the Gunnison River. Two electrofishing rafts were used
to collect centrarchid fishes during the marking pass. All smallmouth bass collected were
marked and released. For the population estimate performed during 2006, smallmouth bass were
marked with a Fiskars® hole punch (6.4-mim diameter) in the dorsal part of the caudal fin. All
other centrarchid fishes collected were removed. Following the marking pass, four removal

passes were made using aluminum boat and raft-based electrofishing to collect centrarchid fishes


Removal of Smallmouth Bass and Four Other
Centrarchid Fishes from
the Upper Colorado and Lower Gunnison Rivers:
2004-2006

Recovery Program Project Number 126

FINAL REPORT

January 2008

Prepared for

Recovery Implementation Program
Sor Endangered Fishes in the
Upper Colorado River Basin

Bob D. Burdick
Fishery Biologist

U.S. Fish and Wildlife Service

Colorado River Fishery Project

764 Horizon Drive, Building B
Grand Junction, Colorado 81506-3946


b) Continue to collect effort data to compute a catch effort indice (total fish/hr) of
smallmouth bass and other centrarchids to compare with the earlier years (2004 and 2005)
when mark and recapture population estimates were not performed and catch effort was
the only metric available to compare annual abundance of smallmouth bass and other
centrarchids.

Continue sampling in reaches of the Upper Colorado River from the Rifle Bridge to
Beavertail Mountain in Debeque Canyon. This is necessary to 1) build upon the existing
fishery community database and monitor abundance of nonnative centrarchid fishes and
presence of other piscivorous fishes (e. g., northern pike, walleye, and yellow perch) in
these reaches which is within critical habitat for Colorado pikeminnow and razorback
sucker, and 2) particularly determine if smallmouth bass continue to proliferate in the
river reach from Rifle to Rulison. Because there are no known Colorado pikeminnow
spawning sites in these reaches, sampling can be performed earlier than those
downstream from Price-Stubb Diversion Dam.

Sample for young smallmouth bass in the spring prior to runoff to assess overwinter
mortality.

. Investigate possible escapement of smallmouth bass and other game fish (e. g., walleye,

northern pike, yellow perch) from Rifle Gap Reservoir via Rifle Creek and associated
irrigation laterals into the Upper Colorado River. Prevent future escapement of these
piscivorous fishes from this reservoir or their access to the Colorado River. This is
consistent with the second part of a management consideration identified in the Colorado
River Basin Wildlife Management Plan (CDOW 2003) which states “Evaluate the
escapement of these [fish] species from the reservoir [Rifle Gap] to determine the threat
to endangered Colorado River fishes.” Based on captures of walleye in Rifle Creek
downstream of the Rifle Gap plunge pool, CDOW biologists have recently recommended
that a screen be constructed in Rifle Creek downstream of the plunge pool of Rifle Gap
Reservoir (Lori Martin, CDOW, personal communication).

Collect and preserve early-life stages (age-0 and age-1) of smallmouth bass in ethanol to

allow for otolith extraction during removal passes. Otolith information may be useful for
understanding aspects of smallmouth bass early-life history. Otolith data could be used to

Sl


* APPENDIX A
Numbers of Centrarchids by Species
Collected with Electrofishing, 2004-2006,
by Major River Reach and Sub-reach


reserves to survive the winter period and avoid death due to starvation. The little data collected
and analyzed to date are, at best, suggestive that some environmental event or physiological
factor played a role in the demise of the age-0 smallmouth bass produced in 2005.

A high percentage (85% between Rifle and Beavertail Mountain; 90% between Price-
Stubb Dam and Westwater, Utah) of ali largemouth bass captured in both major portions of the
Upper Colorado and Lower Gunnison rivers were comprised of fish less than 150 mm total
length. From Rifle to Beavertail Mountain, of the total 314 largemouth bass collected in this 45-
mile reach, only 8% (25 fish) were greater than 254 mm in 2004, 2005, and 2006. Twelve
largemouth bass were 2 305 mm. Sixty percent of all largemouth bass were < 100 mm and 92%
were < 254 mm. Sixty-four percent (16 of 25) of all largemouth bass 2254 mm total length in
2004, 2005, and 2006 were caught at river mile (RM) 236.6, a large backwater located on the
south side of the Upper Colorado.

Between Price-Stubb Dam and Westwater, Utah, and the 2.3 miles of the Lower
Gunnison River during 2004, 2005, and 2006, a total of 2,033 largemouth bass were captured.
Of this number, only 3% (59 fish) were 2254 mm. Thirty-six largemouth bass were 2305 mm.
Sixty-two percent of all largemouth bass were < 100 mm and 92% were < 254 mm. Thirty-seven
of the 59 (63%) largemouth bass = 254 mm collected during 2004, 2005, and 2006 were caught
between Corn Lake (RM 177.4) and Redlands Parkway (RM 166.8) and between Fruita State
Park (RM 157.2) and the Loma Boat Landing (RM 152.6). Skipper’s Island backwater (RM
154.0) consistently had high densities of largemouth bass 2254 mm during 2004, 2005, and
2006. In 2006, of the eight largemouth bass 2 254 mm total length captured between Fruita State
Park and the Loma Boat Landing, seven were caught in the Skipper’s Island backwater. In 2005,
of the 14 largemouth bass caught between Fruita State Park and the Loma Landing that were =
254 mm, 13 were caught in Skipper’s Island backwater.

Unlike largemouth bass collected in main channel riverine habitats of the Grand Valley
where a vast majority (~ 90%) of the fish collected were < 150 mm, the length classes for
smallmouth bass were more proportionately represented. In 2006, 42.9 % of all smallmouth bass
collected in the Grand Valley reaches were 2255 mm, 15.1 % were 2306 mm, and 1.4 % were
2357 mm. Of the total smallmouth bass in 2006 (n=881), 57.1 % were < 255 mm and 29.6 %
were < 100 mm. The number of ‘trophy-size’ (2255 mm [10-inch]) smallmouth bass collected
increased each year since 2004, being greatest in 2006 some of which could be attributed to the

xviii


Forney, J. L. 1972. Biology and management of smallmouth bass in Oneida Lake, New York.
New York Fish and Game Journal. 19:132-154.

Haines, G. B., D. W. Beyers, and T. Modde. 1998. Estimation of winter survival, movement,
and dispersal of young Colorado pikeminnow [squawfish] in the Green River, Utah. U. S.
Fish and Wildlife Service. Final Report to the Upper Colorado River Endangered Fish
Recovery Program, Denver, CO.

Hawkins, J. A., and T. P. Nesler. 1991. Nonnative fishes in the upper Colorado River basin: an
issue paper. Colorado State University, Ft. Collins. 72 pp.

Hoar, W. S. 1983. General and comparative physiology. 3“ edition. Prentice-Hall, Englewood
Cliffs, New Jersey.

Henderson, P. A., H. A. Holmes, and R. N. Bamber. 1988. Size-selective overwintering
mortality in the sand smelt, Atherina boyeri Risso, and it role in population regulation.
Journal of Fish Biology 33:221-233.

Johnson, J. E., M. G. Pardew, and M. M. Lyttle. 1993. Predation recognition and avoidance by
larval razorback sucker and northern hog sucker. Transactions of the American Fisheries
Society 122:1139-1145.

Joseph, T. W., J. A. Sinning, R. J. Behnke, and P. B. Holden. 1977. An evaluation of the status,
life history, and habitat requirements of endangered and threatened fishes of the Upper
Colorado River Basin. Report FWS/OBS-772, U. S. Fish and Wildlife Service, Ft. Collins,
co.

Karp, C. A., and H. M Tyus. 1990. Behavior and interspecific interactions of Colorado
pikeminnow [squawfish] Ptychocheilus lucius, and five other fish species. Copeia

1990:25-34.

Langlois, T. H.. 1936. A study of smallmouth bass (Micropterus dolomieui) in rearing ponds in
Ohio. Ohio Biological Survey Bulletin 6:191—225.

57


Table 2. Total numbers of centrarchid fishes collected with raft and aluminum boat
electrofishing during removal passes 1, 2, 3, and 4 of the smallmouth bass removal
project from main channel habitats in the Upper Colorado River and Lower Gunnison
River in western Colorado and eastern Utah, July, August, and September 2004,
2005, and 2006. Note: pass 4 was a “concentration pass” which sampled sections of
river with high densities of centrarchids determined from passes 1, 2, and 3.

River
River Segment
{River Miles)
Number of Centrarchids
Colorado River Smth Lrgth Green Black
Rifle to Beavertai! Mtn Bass Bass Sunfish Crappie Bluegill
(240.7-195.7) 06 405 104 106 05 104 06 05 ‘04 06 105 04 106 105 “04
Pass | 79 230 21 211 38 65 492 606 36 0 2 0 3 10 0
Colorado River
Price-Stubb Dam-
Westwater, UT
(187.7-127.6) &
Lower Gunnison River
Redlands Dam-
Colo/Gunn River
Confluence
(3.0-0.7)
Pass 1 * 258 475 219 203 247 28 309 271 119 26 17 2 45 109 20
Pass 2° 159 119 256 326 119 23 320 236 87 18 6 4 90 53) 14
Pass 3° 225 313 504 419 168 146 568 366 321 14 8 1 116 103 62
GVIC-Loma + Lower
Gunnison River
(185.3-152.6 + 3.0-0.7)
Pass 4° 109 167 186 146 55 80 198 178 116 12 10 0 56 51 15
Year Totals 751 1366 1165. 1094 589 277 13951051 643 70 41 7 307 316 111

® Two electrofishing craft used.

* One electrofishing craft used.

15


2005

3

duly 1-20
‘Smallmouth Bass
neo

No Sampling Performed

So Nn Ro @
L

July 21-34
‘Smallmouth Bass
n=44

er eee

August 1-10
Smallmouth Bass
n=37,

a Ae eee | er

Number of Fish

August 14-20
Smalimouth Bass
n=124

August 21-34
Smallmouth Bass
n=90

75mm

oN Bo @ SON FO @ SON AM @ SON AM @ Og PD A Oo
1

September 1-20
Smallmouth Bass
n=0

No Sampling Performed

0

Figure C.2.

TUTUTTETTTTITT ETT TTT TEPID TTOTTIT ETO TTED TERT TITTTTIF ET TITIDOTT TIED PTT EIT ESATA TE TPT EET
10 20 30

50 60 70 80 90 100 110 120

Total Length (mm)

Time series length frequency for age-0 and age-1 smallmouth bass (< 115
mm total length) collected during the summer of 2005 from the Upper
Colorado (RM 187.8-127.6) and Lower Gunnison (RM 3.0-0.7) rivers.


to Corn Lake. The 2.3 miles of the Lower Gunnison River ranks fourth after 3 years which is no
surprise because it is adjacent to the two highest concentration areas in the Upper Colorado
River. However, during 2006 catch rate decreased in all river sub-reaches from 2005. Only one
reach, GVIC to Corn Lake, retained its relative concentration rating of ‘Moderately High’. The
Colorado/Gunnison River confluence to Fruita State Park sub-reach fell from a ‘Highest’ to
‘Medium’ rating. The segment from Rifle to Beavertail Mountain and the Lower Gunnison
River fell from ‘Moderately High’ to ‘Moderately Low’. In 2005, the greatest increase in
concentration was between Price-Stubb Dam to the GVIC Dam. However, in 2006 this teach fell
from a rating of ‘Highest’ to ‘Moderately Low’ (Figure 4).

A notable increase in smallmouth bass abundance was recorded between the Rifle Bridge
and Beavertail Mountain between 2004 and 2005. In 2004, 21 smallmouth bass were collected in
this reach; 20 being collected in the 10.7-mile sub-reach between Rifle and Rulison. During
2005, 230 fish were collected in the 45-mile reach, an 11-fold increase from 2004. During 2005,
187 smallmouth bass were collected between the Rifle Bridge and Rulison. One hundred seventy
two smallmouth bass (91%) were collected in a 3.8-mile reach immediately downstream from the
Rifle Bridge. And of those 172 smallmouth bass, 90% (154) were captured in a large
packwater/side channel habitat (RM 236.6) adjacent to where the Pioneer Irrigation Ditch
empties into the Colorado River. Rifle Creek, which drains Rifle Gap Reservoir, empties into
the Colorado River at RM 239.6 and the Pioneer Irrigation Ditch, which receives water from
Rifle Creek in the town of Rifle, empties into the Colorado River at RM 236.9. Thus, this main
channel backwater is in close proximity to the these two tributaries that receive water from Rifle
Gap Reservoir which eventually drain into the Colorado River. Rifle Gap Reservoir has a
smallmouth bass fishery. However, the number of smallmouth bass captured in main channel
habitats in this 45-mile reach declined 66% (79 vs. 230) in 2006 from 2005. Abundance of
smallmouth bass (all sizes) in the backwater where a majority of smallmouth bass were collected
in 2005 (154 fish) declined precipitously (73%) in 2006 (41 fish).

Largemouth bass. Largemouth bass catch/effort during each of the four passes between
Price-Stubb Dam and Westwater, Utah, and the Lower Gunnison River was: 3.38, 7.93, 10.37,
and 7.16 fish/hr, respectively, for 2006. In 2005, catch/effort during each of the four passes in
these same river reaches combined was: 4.26, 2.47, 3.36, and 2.99 fish/hr, respectively. During
2004, the same metrics were: 0.66, 0.50, 2.35, and 4.44 fish/hr, for each of the four passes
(Appendix; Tables B.4—B.6.; Appendix; Figure B.1.). In 2006, the highest catch rate for

22


Therefore, the hypothesis presented herein regarding loss of recruitment from 2005 to
2006 of early-life smallmouth bass cannot be related to environmental factors within the range
observed in this study. The little data collected and analyzed to date are, at best, suggestive at
this time that some environmental event or physiological factor played a role in the demise of the
2005 cohort of smallmouth bass. Only three years of biological data have been collected on
smallmouth bass from the Upper Colorado River and additional years of data on smallmouth bass
spawning dynamics are needed to identify the timing (i.e., hatching dates) and duration of
smailmouth bass spawning seasons and annual growth rates of early-life stages. Collection of
these data under a variety of flow and water temperature regimes may be useful to predict timing
and intensity of spawning. These data also might be used to assist managers in determining if
there is an association between year-class strength, survival, and recruitment with certain
environmental events over a wide range of different water year scenarios. And, if a consistent
association can be shown, could this be used as a management tool to reduce survival of early-
life stages of smallmouth bass and minimize recruitment to the adult population? The notion that
an environmental event played a role in the demise of the 2005 year class of smallmouth bass in
the Upper Colorado River should not be dismissed and warrants further investigation.

Water Turbidity and Smallmouth Bass Catches

Sampling crews on the Upper Colorado River noted in both 2005 and 2006 that catch
rates did not decrease when turbidity was high. In other words, higher catch rates for juvenile
and adult smallmouth bass were associated with high turbidity (usually immediately following
rainstorms). On the Upper Colorado and Lower Gunnison rivers during 2005, water conditions
were more turbid in general than 2004; the 2005 Colorado River smallmouth bass catches were
higher (about 17%) than that of 2004. These higher catch rates could simply have been a result
of higher densities of smallmouth bass during 2005. During August 2006, a 6.4-mile section of
the Lower Gunnison (2.3 miles) and Colorado River (4.1 miles) at the upper most portion of the
18-mile reach near Grand Junction were sampled twice within 4 days. Water clarity during the
first electrofishing run was clear but was turbid on the second run 4 days later. Smallmouth bass
catch rate (8.14.smallmouth bass/hr; 33 fish) was 2.39 times higher on the second run (turbid
water) than the first run (clear water: 3.42 smallmouth bass/hr; 9 fish).

There does appear to be a pattern: catch rates for smallmouth bass are higher when water
conditions are more turbid. The same pattern for smallmouth bass catches during 2006 was

47


each of the three years, catch rates generally increased (Figure 2). During 2004-2006, there
appeared to be riverine sub-reaches that consistently had higher abundance of smallmouth bass.
For smallmouth bass in 2006, the highest catch rate in main channel habitats was between Corn
Lake and the Colorado/Gunnison River confluence (8.94 fish/hr; all passes combined). The
second highest river sub-reach was from GVIC Diversion Dam to Corn Lake (6.81 fish/hr)
followed third by the sub-reach from the Colorado/Gunnison River confluence to Fruita State
Park (3.80 fish/hr). Loma boat landing to Salt Creek had the fourth highest abundance of
smallmouth bass (3.04 fish/hr). Smallmouth bass catch rate increased 5.5 fold between Rifle and
Beavertail Mountain from 1.06 fish/hr during 2004 to 5.78 fish/hr in 2005. However, during
2006 in this segment, smallmouth bass catch rate precipitously declined to 2.10 fish/hr (Figure
3). For smallmouth bass in 2005, the highest catch rate in main channel habitats was between
Corn Lake and the Colorado/Gunnison River confluence (16.36 fish/hr; all passes combined).
The second highest river sub-reach was from Price-Stubb Dam to the GVIC Diversion Dam
(11.02 fish/hr) followed third by the sub-reach from the Colorado/Gunnison River confluence to
Fruita State Park (10.43 fish/hr)(Table 3). GVIC to Com Lake had the fourth highest abundance
of smallmouth bass (8.97 fish/hr). During 2004, the highest abundance of smallmouth bass in
main channel habitats was between Corn Lake and the Colorado/Gunnison River confluence
(11.88 fish/hr; all passes combined), followed by the sub-reach between the Colorado/Gunnison
River confluence to Fruita State Park (9.47 fish/hr; all passes combined) (Table 3). The 2.3-mile
segment in the Lower Gunnison River had the third highest abundance of smallmouth bass (9.21
fish/hr; all passes combined).

Smallmouth Bass Concentration Areas. Identifying concentration areas is important
because it may allow managers to focus on riverine areas of high densities of smallmouth bass to
expedite removal and reduction to control their proliferation/invasiveness and potential negative
impacts to native fish conservation and endangered fish recovery. High to low smallmouth bass
concentration areas in riverine reaches in the Colorado and Lower Gunnison rivers were
determined using 2004, 2005, and 2006 catch/effort values (Table 3). A subjective relative

concentration rating was developed and is provided.

The river reach between Com Lake and the Colorado/Gunnison River confluence has
consistently been the highest area of concentration for smallmouth bass during the summers of
2004, 2005, and 2006. The next highest area was between the Colorado/Gunnison River
confluence and Fruita State Park. The third highest concentration area was from the GVIC Dam

18


6. Catches of smallmouth bass appear to be related to turbid and clear water conditions.
Higher catch rates for juvenile and adult smallmouth bass were associated with high
turbid water conditions (usually immediately following summer rainstorms).

RECOMMENDATIONS
The following recommendations are made:

1. Increase the number of removal passes at least two-fold (from 4 to 8 passes) in 2007 and
2008 with electrofishing in river segments that have higher concentrations of smallmouth
bass as was performed from 2004-2006. Past 2008, continue to increase the number of
removal passes to the point where the desired exploitation rate is achieved. This will
increase the number of removal passes to increase the number of smallmouth bass
captured and removed with the goal of increasing probability of capture and, therefore,
exploitation rates. This should also maximize catches of all centrarchids fishes while at
the same time minimizing harassment and negative impacts to native fishes in reaches
where centrarchid abundance is low. Concomitantly, decrease electrofishing effort in
river reaches of low smallmouth bass densities.

2. Suspend all electrofishing operations when it is determined that Colorado pikeminnow
show signs of preparing to spawn, e. g., mid- to late-June. Electrofishing will be
suspended during this period to eliminate the likelihood of harassment, interference, and
injury to spawning Colorado pikeminnow. Downstream from Price-Stubb Dam,
electrofishing should commence following cessation of spawning of Colorado
pikeminnow which should be sometime in mid- to late-July.

3. a) Perform mark-recapture population estimates of juvenile and adult (2 100 mm)
smallmouth bass at least once every three years from GVIC Dam to the Loma boat
landing in the Upper Colorado River and from the Redlands Diversion Dam to the
Colorado/Gunnison River confluence in the Lower Gunnison River to assess the size of
the smallmouth bass population and effectiveness of removal in the Grand Valley reaches

of the Upper Colorado and Lower Gunnison rivers.

50


2006

10
a -| duly 1-20
Smallmouth Bass
| n=O
4-| No Sampling Performed
2 -|
a
. July 21-31
a4 ‘Simallmiouth Bass
6 4 net.
4
2-4
18 Ll Qf Aim of f§ m@ OF
a August 1-10
‘Smallmouth Bass
s 4 n=22
4-
| | eee Cn)
40 J
a -| August 11-20

Smallmouth Bass
n=14

Number of Fish
aS

August 21-31 :
Smallmouth Bass {
nei4t H

September 1-10

a ‘Smallmouth Bass
s- n=O
1 Neo Smalimouth Bass collected between 1 & 144 mm TL
2-|
48
September 11-20 << 75mm
a Smallmouth Bass
6 n=85.
im .
2-|
0 TEETUTTATTETAD TOP TEP Dt deli TUT TAVITA POPTOGOT TOOTS TICOP FOOT TIIGPTOOPERATERVGEPOATATERIEOPEREST SECT RTATATT OPT OR ETE
o 20 30 40 50 60 70 80 30 100 110 120
Total Length (mm)
Figure C.3. Time series length frequency for age-0 and age-1 smallmouth bass (< 115

mm total length) collected during the summer of 2006 from the Upper
Colorado (RM 187.8~127.6) and Lower Gunnison (RM 3.00.7) rivers.


Table 5. Population point estimates with 95% confidence intervals (C.L.) for smallmouth bass
for the 15- and 18-mile reaches (RM 185.3 to 152.6) of the Upper Colorado River and
2.3 miles of the Lower Gunnison River (Redlands Diversion Dam to the
Colorado/Gunnison River confluence) for the summer of 2006, and the projected
percentage of smallmouth bass removed annually by electrofishing relative to the 95%
population interval. Chapman’s (1951) modification of the Petersen-Lincoln
estimator was used to determine the abundance of smallmouth bass; probability of
capture determined from White et al. (1982). Coefficient of variation (CV = SE/N x
100) from Pollock et al. (1990). Note: bolded figures is the preferred and final
population estimate reported on.

Smalimouth Bass—All Fish (41-394 mm

Pass No. | Oniv Pass Nos. 1. 2. & 3
% of fish % of fish
Total No.of Total — removed Total No. of Total removed
Pop Est 95%C.J. FishRemoved Recaps annually* Pop Est 95% Cl. Fish Removed Recaps annually*
3,789 #2511 200 6 3.8-15.6% 8,300 £4,927 565 8 4.3-16.8%
probability of capture: 0.03 CV: 33.8% probability of capture: 0.014 CV: 30.3%

Smallmouth Bass 2100 mm

Pass No. 1 Only Pass Nos. 1.2. & 3
% of fish % of fish
Total No.of Total removed Total No.of Total removed
PopEst 95%CI Fish Removed Recaps annually PopEst 95% C.l. FishRemoved Recaps annually *
3,197 £2,100 181 6 34165% 5,247 £3,095 383 8 4.6-17.8%
probability of capture: 0.033 CV: 33.5% probability of capture: 0.021 CV: 30.1%

* Calculated from the actual number of smallmouth bass removed, point estimate, and 95% C.1.

No. of Smallmouth Bass*

All Fish Marked
Pass Type & No. (41-394 mm) 2 100mm <100 mm Recaps
Marking Pass 131 122 9 --
Removal Pass No. 1° 200 181 19 6
Removal Pass No. 2° 152 96 56 1
Removal Pass No. 3° 213 106 107 1
Total 565 383 182 8
Removal Pass No. 4° 109 53 56 0

* Includes captures and recaptures of smallmouth bass in the Upper Colorado River from river
mile 185.3-152.6 (15- and 18-mile reaches) and Lower Gunnison River from river mile 3.0--0.7.

Two electrofishing craft used.

© One electrofishing craft used; “concentration removal pass” (not used in population estimate).


APPENDIX B
Catch/effort (fish/hr) for Five Centrarchid Fishes
Collected with Electrofishing, 2004-2006,
by Major River Reach and Sub-reach


LIST OF APPENDIX TABLES AND FIGURES

Appendix

B. Figure B.1. Overall catch effort (fish/hr) by pass for

largemouth bass (29-420 mm) collected from main
channel habitats in the Upper Colorado River with
electrofishing from RM 187.7—-127.6 (Price-Stubb
Dam to the Westwater, Utah, BLM ranger station)
and in the Lower Gunnison River from RM
3.0-0.7 (Redlands Dam to the Colorado/Gunnison

River confluence), 2004, 2005, and 2006 ...................

. Figure B.2. Overall catch effort (fish/hr) by pass for
green sunfish (30-256 mm) collected from main
channel habitats in the Upper Colorado River with
electrofishing from RM 187.7—127.6 (Price-Stubb
Dam to the Westwater, Utah, BLM ranger station)
and in the Lower Gunnison River from RM
3.0-0.7 (Redlands Dam to the Colorado/Gunnison

River confluence), 2004, 2005, and 2006 .........-..-..e0ee

. Figure B.3. Overall catch effort (fish/hr) by pass for
bluegill (34-228 mm) collected from main channel
habitats in the Upper Colorado River with electrofishing
from RM 187.7-127.6 (Price-Stubb Dam to the
Westwater, Utah, BLM ranger station) and in the
Lower Gunnison River from RM 3.0-0.7 (Redlands
Dam to the Colorado/Gunnison River confluence),

2004, 2005, and 2006......... 0c cece cece eee eee e eee

. Figure B.4. Overall catch effort (fish/hr) by pass
for black crappie (68-291 mm) collected from
main channel habitats in the Upper Colorado River
with electrofishing from RM 187.7-127.6 (Price-Stubb
Dam to the Westwater, Utah, BLM ranger station)
and in the Lower Gunnison River from RM 3.0-0.7
(Redlands Dam to the Colorado/Gunnison River

confluence), 2004, 2005, and 2006 .............. se eee e eee

xi

é
:
:


TABLE OF CONTENTS (cont'd)

Size Distribution — Length Frequency ........... 00.0. cc cece ccc e eee eee nes 29
Smallmouth Bass .........

Largemouth Bass .........

Hydrology and Water Temperature . see
Hydrology 2.2.0... cece cee eect e nee ene nen een ees 40
Water Temperature 2.0.0.0... eee cece cence ences 41

Annual Abundance of Early-Life Smallmouth Bass
Related to Stream Discharge and Water Temperature
Water Turbidity and Smallmouth Bass Catches ..

Other Nonnative Fishes 2.0.0.0... cece cece cece cence cent nen eneeenee
CONCLUSIONS 000.000. 00cc cece eee ec eee eeeseeceveeveeeeneeveeneeereeenes 49
RECOMMENDATIONS «2.20.00 .0 ccc cccec cee eeteetuseetesteseueveseeeeeesenss 50
UNCERTAINTIES/UNKNOWNS 2.0.00. 0000 ccc cceueeeseseuseuseecuseeeeeeneens 52
LITERATURE CITED ..... 200.00. c0cccccceceecceeeseseusseuseteecneenseneees 53

APPENDICES

Appendix A— Numbers of Centrarchids by Species Collected with Electrofishing,
2004—2006, by Major River Reach and Sub-reach

Appendix B— Catch/effort (fish/hr) for Five Centrarchid Fishes Collected with
Electrofishing, 2004-2006, by Major River Reach and Sub-reach

Appendix C— Percentage and Number Comparison of Smallmouth Bass Collected
by Various Length Classes During the Summers of 2004-2006
& Length Frequency of Age-0 and Age-1 Smallmouth Bass collected
during 2004-2006 in the Upper Colorado and Lower Gunnison rivers

Appendix D— Water Temperature and Hydrology Recérds

Appendix E— Scientific and common names and status (native vs. nonnative) of fish
collected and mentioned in the text of this report during the smallmouth
bass removal study in the Upper Colorado and Lower Gunnison rivers,
2004-2006

List of Key Words: smallmouth bass; largemouth bass; centrarchid fishes; lethal mechanical
removal; abundance indices; length frequency; electrofishing; early-life
stage survival; recruitment; Upper Colorado River; Lower Gunnison River


largemouth bass emigrating to the main channel. Osmundson (2003) removed centrarchids twice
annually (spring and fall) from backwaters from 1999-2001 in the Upper Colorado River from
GVIC Dam to Westwater, Utah BLM ranger station. He concluded that there was no reach-wide
depletive effect from one year to the next during this 3-year removal project for largemouth bass.
Jn one backwater, he noted that there was no overall reduction during six samplings and that the
total catch in the fall of 2000 increased 5 to 15 times that of the previous three samplings.

Green sunfish, Black Crappie, and Bluegill. For black crappie, bluegill, and green
sunfish, the aggregate catch/effort steadily increased from pass 1 through pass 3 (17.27 fish/hr)
but dramatically increased to 34.23 fish/hr during pass 4 in 2006 in the sub-reaches between
Price-Stubb Dam and Westwater, Utah, and the Lower Gunnison River. During 2005, the same
aggregate metric also steadily increased with each successive pass — 6.84, 6.12, 9.55, and 13.00
fish/hr. During 2004, fish/hr catches were 3.31, 2.29, 6.17, and 7.28 for passes 1-4, respectively
(Appendix; Tables B.4.— B.6.).

The highest aggregate catch rate for black crappie, green sunfish, and bluegill during
2006 was between Fruita State Park and the Loma boat landing (38.28 fish/hr). Overall mean
catch rates (all passes combined between Price-Stubb and Westwater, Utah, plus the Lower
Gunnison River) indicate that between the summer of 2004 and summer of 2005 black crappie,
bluegill, and green sunfish aggregate catch rate increased from 4.51 to 8.07 fish/hr. Therefore,
catch rate for these three centrarchid fishes during 2005 exceeded that of the summer of 2004. In
2006, black crappie, bluegill, and green sunfish aggregate catch rate also increased to a 3-year
high of 10.94 fish/hr.

The overall mean catch/effort for each of the four passes for each of the three years was
graphed for green sunfish, black crappie, and bluegill collected between Price-Stubb Dam and
Westwater, Utah, and the Lower Gunnison River (Appendix; Figures B.2.-B.4.). For green.
sunfish and bluegill as passes proceeded through each of the 3 years, catch rates generally
increased. However, catch rate decreased during pass 4 in 2006 for green sunfish. For black
crappie, catch rates were highest during the later passes and highest during pass 4 in 2005 and
2006. In 2004, catch rate declined during passes 3 and 4. Catch/effort for each of these three
centrarchid fishes was highest in 2006.

25


Burdick, B. D. 2005(b). Removal of smallmouth bass in the Upper Colorado River between
Price-Stubb Dam near Palisade, Colorado, and Westwater, Utah. Annual Project Report to
the Upper Colorado River Endangered Fish Recovery Program. Project Number 126. U.S.
Fish and Wildlife Service, Grand Junction, Colorado.

Burdick, B. D. 2006(a). Annual operation and maintenance of the fish passage structures at the
Redlands Diversion Dam on the Gunnison River and the Government Highline Diversion
Dam on the Upper Colorado River. Annual report prepared for the Recovery Implementation
Program for the Endangered Fishes of the Upper Colorado River Basin. Recovery Program
Project Number C-4b. U. S. Fish and Wildlife Service, Colorado River Fishery Project,
Grand Junction, Colorado.

Burdick, B. D. 2006(b). Evaluation of stocked razorback sucker and Colorado pikeminnow in
the Gunnison River. Annual report prepared for the Recovery Implementation Program for
the Endangered Fishes of the Upper Colorado River Basin. Recovery Program Project
Number 121a. U. S. Fish and Wildlife Service, Colorado River Fishery Project, Grand
Junction, Colorado.

Carlson, C. A., and R. T. Muth. 1989. Lifeline of the American Southwest. Pages 220-239 in
D. P. Dodge (editor). Proceedings of the International Large Rivers Symposium. Canadian
Special Publication of Fisheries and Aquatic Sciences 106.

Chapman, A. D. 1951. Some properties of the hypergeometric distribution with applications to
zoological sample censuses, University of California Publ. Stat. 1(7):131-160.

Christie, W. J., and H. A. Regier. 1973. Temperature as a major factor influencing reproductive
success — two examples. Rapports et Proces-Verbaux des Reunions, Conseil International

pour |’Exploration de la Mer 164:208-218.

Coble, D. W. 1967. Relationships of temperature to total annual growth in adult smallmouth
bass. Journal of the Fisheries Research Board of Canada. 24:87-99.

Colorado Division of Wildlife. 2003. Colorado River Basin Aquatic Wildlife Management
Plan. Denver. 80 pp.

56


Table A.3. Numbers of centrarchid fishes collected during removal passes (P) 1, 2, 3, and 4 of
the smallmouth bass removal project from main channel habitats on the Colorado and
Lower Gunnison rivers in western Colorado and eastern Utah, July, August, and
September 2006. Note: n/s=not sampled; two electrofishing craft were used for
passes 1, 2, and 3; one electrofishing craft was used for pass 4. Note: 2004 and 2005
species totals are provided for annual comparisons.

No. of Centrarchids
Black Crappie/

River Smallmouth Largemouth Green Sunfish/
(River Miles) Bass Bass Bluegill

River Segment P-l P2 P33 P4 Pil P2 P3 P4 Pl P2 Px Pa

Colorado River

(RM 187.7-127.6)
Price-Stubb>GVICDam 10 8 12 ns 14 3 9 ws 8 1 6 Os
GVICDam>ComLake 75 48 42 44 59 75 118 52 57 26 38 23

Corn Lake »Colo/Gunn 43 49 102 34 44 100 123 35 21 30 63 29
River Confluence

Colo/Gunn R. Confl. > 78 38 S52 17 50 78 102 45 132 154 203 119
Fruita State Park

Fruita State Park > 12 7 #12 1 22 68 63 412 130 200 335 82
Loma Boat Landing

Loma Boat Landing > 23 n/s n/s nis 7 «ws ns ws 20 n/s ws nis
Salt Creek Wash

Salt Creek Wash > 8 ws ns ns 2 o/s ws nis 4 ws ws ns
Utah/Colo Stateline .
Utah/Colo Stateline > 3 n/s n/s nis 3 ws ws ns 3 ns ws ns

Westwater, Utah
BLM Ranger Station

Lower Gunnison River

(RM 3.0-0.7)
Redlands Div. Dam > 6 9 5 3 2 2 4 2 5 17 53 13
Colo/Gunn R.
Confluence
2006 Pass Totals 258 159 225 109 203 326 419 146 380 428 698 266
2006 Species Totals 751 1,094 1771
2005 Species Totals 1,366 589 1,408
2004 Species Totals 1,165 277 761

A-3


U.S. Fish & Wildlife Service

REMOVAL OF SMALLMOUTH BASS AND FOUR OTHER
CENTRARCHID FISHES
FROM THE UPPER COLORADO
AND LOWER GUNNISON RIVERS:
2004-2006

January 2008


80 Colorado-Utah Stateline USGS Gauge
0 Annual Instantaneous Peak Discharge
al
~
w
a=)
i}
a
a
3
2
=
nN
ee
0
Calendar Year
16 ~
Colorado-Utah Stateline USGS Gauge

14 Annual Mean Discharge by Calendar Year

12 /
> E
3 — : Wet

g 10 Bele
Zz | i
& *Ges E
— re FA
fs
n 6 4
g
Oo 4 :
2
1
0 ale

Calendar Year

Figure D.3.° Annual instantaneous peak discharge (upper) and annual mean discharge
(lower) by calendar year for the stateline USGS gauge near the
Colorado/Utah border (RM 133.8) for 1970-2006. Designations for “wet”
to “dry” water years adopted from McAda (2003).

D-3


TABLE OF CONTENTS

LIST OF TABLES 2.02... ener e nner enn e tenet v
LIST OF FIGURES ..... 2... cece cece cece cece een ence e tenet e nee e eee eee vi
LIST OF APPENDIX TABLES AND FIGURES ........... 000.0 c cece cece e eee nee viii
LIST OF APPENDIX TABLES AND FIGURES ........0.0 00.020 c cece cece e eee e ee ix
ACKNOWLEDGMENTS 2.0... ccc ene e eee nena XV
EXECUTIVE SUMMARY ....... 06.0. e cece cence nee c erence ence ee eeenee xvi
INTRODUCTION 2.0.2.0. een een ence ene tenn nen neee 1
Background ..... .1
Smallmouth Bass ................. 13

Upper Colorado River (Colorado) 3

Lower Gunnison River........ : 1.4

Control of Nonnative Fish by Mechanical Removal 14

Purpose and Objectives .......... 2... cece eee eens 5

Study Area 2... eee ec eee eee see e eee eeee : 6
METHODS. 2.0... ccc ee eee en eee eee nee bee eee teen eee eee ee 8
Fish Sampling ... ..8
Hydrology and Water Temperature Data . 11
Analyses 2.0... eee eee ne eee e eee e ene e eee 12
RESULTS AND DISCUSSION ...... 0... ccc c cece cece ence eter e nen eee 13
Abundance Indices +. 13
Number of Individual Fish by Species .......... 0... cece cece cece 13

Smallmouth Bass ... 2.0.06... cece cece eee eee ence eee eee 13

Largemouth Bass ... 14

Green sunfish, Black Crappie, and Bluegill....................... 16

Catch/Effort 6.0... cece cece eee eee ene eee n ee neee 16

General -.. 16

Smallmouth bass ..... 0.0... cece ccc cece eee een eee 17

Smallmouth Bass Concentration Areas .........00 2.00020 eee e eee 18

Largemouth bass 1.22

Green sunfish, Black Crappie, and Bluegill...................000. 25

Population Estimates/Projections ........... 0c cece e cece cece e nee e eens 26

Smallmouth Bass ........ 0.6. e cee ce cece cence eee eee 26

iii


25
Cameo Gauge

~ 20
”
noi
S

Hn 15
3
°
=

= 10
2

rz) 2004
5
7

2002
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Month

20
Cameo Gauge

=
On

— 2005

CFS (thousands)
S

/

2006

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Month

Figure D.4. Mean daily discharge for the Cameo USGS gauge on the Upper Colorado
River (RM 199.8) for 2002-2004 (lower water years)(upper) and 2005-2006
(higher water years)(lower).

D-4


Probability of capture (p-hat; after White et al. 1982) was also computed:
p-hat = (n, — u,)/n,
where n, = the number of smallmouth bass captured in the first removal pass
u, = the number of smallmouth bass captured in the first removal pass that
‘were not marked

Coefficient of variation (CV; Pollock et al. 1990) was also computed:

CV = SE/N-hat X 100
where SE = standard error
N-hat = estimated population size

For 2004 and 2005, population estimates for smallmouth bass (2 100 mm) were not
obtained from mark, release, and subsequent recapture of marked fish. However, an attempt was
made to linearly extrapolate a population abundance projection for 2004 and 2005 from the 2006
population estimate and catch/effort from all three years. Catch/effort data from all smallmouth
bass 100 mm collected and removed during all passes and the population estimate computed
from marked fish in 2006 of similar size collected and removed within identical river sub-reaches
during 2004 and 2005 were used to arrive at these projections. A catch/effort multiplier was
computed from the 2006 catch/effort data (e. g., the catch/effort for 2005 and 2006, respectively,
was 8.5 and 3.33; therefore the 2005 catch/effort was 2.55 times greater than 2006). The 2006
population estimate and 95% C.I. were multiplied by the multiplier to back-project what the
population size of smallmouth bass 2 100 mm may have been during 2004 and 2005. For
example for 2005: 2.55 X 3,197, = 8,152; lower C.I. = 2.55 X 1,097.96 = 2,797; upper C.1. =
2.55 X 5,297 995 = 13,507. The number of smallmouth bass/mile (2 100 mm) was then estimated
from the population estimate and population projections.

RESULTS AND DISCUSSION
Abundance Indices

Number of Individual Fish by Species

Smallmouth Bass. The number of smallmouth bass collected within each of the four

13


Table B.2. Amount of effort (electrofishing hours) expended during four passes of the
smallmouth bass removal project sampling main channel habitats on the Colorado
and Lower Gunnison rivers in western Colorado and eastern Utah, July and August
2005. Note: n/s=not sampled; two electrofishing craft were used for passes 1, 2,
and 3; one electrofishing craft was used for pass 4.

Electrofishing Effort (hr)
River
(River Miles)
River Segment Pel P2 P-3 P-4

Colorado River
(RM 187.7-127.6)

Price-Stubb»GVIC Dam 2.860 2.460 2.794 ws

GVIC Dam » Cor Lake 6.322 5.434 7.074 4.371

Cor Lake >Colo/Gunn 7.048 5.842 4.164 3.355
River Confluence

Colo/Gunn R. Confl. > 16.430 10.727 11.323 6.508
Fruita State Park

Fruita State Park > 4.154 3.133 4.647 2.103
Loma Boat Landing

Loma Boat Landing > 6.823 6.433 5.745 ws
Salt Creek Wash

Salt Creek Wash » 8.005 7.654 8.284 ws
Utah/Colo Stateline

Utah/Colo Stateline > 3.206 2.691 2.950 n/s
Westwater, Utah
BLM Ranger Station

Lower Gunnison River
(RM 3.0-0.7)

Redlands Div. Dam > 3.194 3.802 2.981 2.043
Colo/Gunn R.
Confluence

2005 Pass Totals 58.042 48.176 49.962 18.380

2005 Total 174.560



Table A.5. Summary statistics of centrarchids collected during reconnaissance sampling in main
channel habitats of the Upper Colorado River from Rifle, Colorado, to Beavertail
Mountain in Debeque Canyon, July12—15; 21, 2005.

Reach: Rifle Bridge-Rulison Bridge
River Mile: 240,7-230.0; River Mile Length: 10.7
‘Number of Electrofishing Crafis: 3
Effort (Ir): 12.368

Smallmouth Largemouth
Bass Bass.

Green
Sunfish

Bluegill

Black
Crappie

No. No.
of Total Length(mm) of Total Length (mm)
Fish Min Max Mean Fish Min Max Mean

187) 410 435 199 13, <100 446 © 339

No.
of Total Length (mm)

353 81 165) 117

No.
of Total Length (mm)
Min Max Mean

10 101 174 152

of Total Length (mm)

2 106 120 113

Reach; Rulison Bridge-Parachute Bridge
River Mile: 229,9-223.0; River Mile Length: 6
Number of Electrofishing Crafts: 2
Effort (hr): 5.410

Smallmouth Largemouth
Bass Bass

Green
Sunfish

Bluegill

Black
Crappie

No. No.
of Total Length(mm) of Total Length (mm)
Fish Min Max Mean Fish Min Max Mean

No.
of — Total Length (mm)
Fish Min_ Max Mean

No.
of Total Length (mm)
Fish Min Max Mean

No,
of Total Length (mm)
Fish Min Max Mean

0 -- eee O = eee 32 <100 130 ~115 0 -- -+ ss O == ee
Reach: Parachute Bridge-Debeque I-70 Bridge
River Mile: 223.0-209,7; River Mile Length: 13.3
Number of Electrofishing Crafts: 2
Effort (hr): 12,092
Smallmouth Largemouth Green Black
Bass Bass Sunfish Bluegill Crappie
No. No. No. No. No.

of Total Length(mm) of /—_Total Length (mm)
Fish Min Max Mean Fish Min Max Mean

of Total Length (mm)
Fish Min Max Mean

of Total Length (mm)
Fish Min Max Mean

of Total Length (mm)
Fish Min) Max Mean

3170 437° «204-245 373142176 <100 175122 0 -- -- = O we eee
Reach: Debeque I-70 Bridge-Beavertail Mountain (Debeque Canyon)
River Mile: 209.7~195.7; River Mile Length: 14.0
Number of Electrofishing Crafts: 2
Effort (hr): 9.929
Smallmouth Largemouth Green Black
Bass Bass Sunfish Bluegill Crappie
No. No. No. No.

of Total Length (mm) of — Total Length (mm)
Fish Min Max Mean Fish Min Max Mean

of — Total Length (mm)
Fish Min_ Max Mean

45 7 151 115

No.
of Total Length (mm)
Fish Min Max Mean

QO -- -- -

of — Total Length (mm)
Fish Min Max Mean

A-5S


ACKNOWLEDGMENTS

The author wishes to thank the following individuals from various federal and state
agencies who participated in the sampling, handling, and the processing of centrarchid, percid,
and esocid fishes collected afield during this project. From the U. S. Fish and Wildlife Service:
Tony Bonacquista, Jamie Carrillo, Matt Carroll, Travis Francis, Tara Hicks, Chris Hinds, Chris
Lyons, Chuck McAda, Pat Nelson, Doug Osmundson, Logan Poisson, Mike Shideler, Andrew
Scott, Rick Smaniotto, John Soenen, John Stegmeier, and Kirstie Yeager; from the National Park
Service: Melissa Trammell; from the U. S. Forest Service: Chris Hirsch and from the Colorado
Division of Wildlife: Brian Gray. Patricia Solberg and Cory Williams from the U. S. Geological
Survey office in Grand Junction retrieved and provided hydrology and water temperature records.

The draft report was reviewed and comments provided by Patrick Martinez, Colorado
Division of Wildlife; Kevin Bestgen, Larval Fish Laboratory, Colorado State University; Dave
Speas, U. S. Bureau of Reclamation; and Craig Walker, Utah Division of Wildlife Resources.
Emily Buchanan proofread the final report and Laurie Bjornestad produced the cover page.

xv


Largemouth Bass

While largemouth bass were not the focus of this study, total length was recorded for all
largemouth bass collected and removed during this study because there was interest in the
location and distribution of ‘trophy size’ (2254 mm total length) largemouth bass in main
channel river habitats. Furthermore, if enough trophy-size largemouth bass could be located,
there was consideration for re locating these sizes of fish alive to other Colorado waters to
provide additional sport fishing opportunities. Length-frequency distribution of all sizes of
largemouth bass collected with electrofishing during 2004, 2005, and 2006 between Price-Stubb
Dam and Westwater, Utah, and the Lower Gunnison River (Figure 10) and for the 45-mile reach
between Rifle and Beavertail Mountain were plotted (Figure 11).

A high percentage (85% between Rifle and Beavertail Mountain; 90% between Price-
Stubb Dam and Westwater, Utah) of all largemouth bass captured in both major portions of the
Upper Colorado and Lower Gunnison rivers were comprised of fish less than 150 mm total
length. From Rifle to Beavertail Mountain, of the total 314 largemouth bass collected in this 45-
mile reach, only 8% (25 fish) were greater than 254 mm in 2004, 2005, and 2006. Twelve
largemouth bass were 2 305 mm. Sixty percent of all largemouth bass were < 100 mm and 92%
were < 254mm. Sixty-four percent (16 of 25) of all largemouth bass 2254 mm total length in
2004, 2005, and 2006 were caught at RM 236.6, a large backwater located on the south side of
the Upper Colorado.

Between Price-Stubb Dam and Westwater, Utah, and the 2.3 miles of the Lower
Gunnison River during 2004, 2005, and 2006, a total of 2,033 largemouth bass were captured.
Of this number, only 3% (59 fish) were 2254 mm. Thirty-six largemouth bass were 2305 mm.
Sixty-two percent of all largemouth bass were < 100 mm and 92% were < 254mm. Thirty-seven
of the 59 (63%) largemouth bass 2 254 mm collected during 2004, 2005, and 2006 were caught
between Corn Lake (RM 177.4) and Redlands Parkway (RM 166.8) and between Fruita State
Park (RM 157.2) and the Loma Boat Landing (RM 152.6). Skipper’s Island backwater (RM
154.0) consistently had high densities of largemouth bass 2254 mm during 2005 and 2006. In
2006, of the eight largemouth bass 2 254 mm total length captured between Fruita State Park and
the Loma Boat Landing, seven (mean = 367 mm, 299-420 mm) were caught in the Skipper’s
Island backwater. In 2005, of the 14 largemouth bass caught between Fruita State Park and the
Loma Landing that were 2 254 mm, 13 (mean = 343 mm, 259-340 mm) were caught in this

37


Colorado River (RM 187.7-127.6)
Lower Gunnison River (RM 3.0-0.7)
2004, 2005, 2006

5
all bluegill
(34-228 mm)
4-
=
s
a
6 3
=
€
= 2
2
aS
1S)
1 om
0

Pass Number

Figure B.3. Overall catch effort (fish/hr) by pass for bluegill (34-228 mm) collected
from main channel habitats in the Upper Colorado River with electrofishing
from RM 187.7—127.6 (Price-Stubb Dam to the Westwater, Utah, BLM
ranger station) and in the Lower Gunnison River from RM 3.0-0.7
(Redlands Dam to the Colorado/Gunnison River confluence), 2004, 2005,
and 2006. Note: The number of fish collected by pass is in parentheses.


Lentsch, L. D., R. Muth, P. D. Thompson, T. A. Crowl, and B. G. Hoskins. 1996. Options for
selectively controlling non-indigenous fish in the Upper Colorado River Basin. Final Report.
Publication 96-14, Utah Department of Natural Resources, Division of Wildlife Resources,
Salt Lake City.

Lucas, J. A., and D. J. Orth. 1995. Factors affecting nesting success of smallmouth bass in a
regulated stream. Transactions of the American Fisheries Society 124:726-735.

MacLeod, J. C. 1967. Factors affecting year class strength of smallmouth bass in Ontario
waters. Ontario Ministry of Natural Resources manuscript report. Toronto, Canada.

Maddux, H. R., L. A. Fitzpatrick, and W. R. Noonan. 1993. Colorado River endangered fishes
and critical habitat: Biological Support Document. U.S. Fish and Wildlife Service, Salt Lake
City, UT. 225 pp.

McAda, C. W. 2003. Flow recommendations to benefit endangered fishes in the Colorado and
Gunnison rivers. Final Report prepared for the Recovery Implementation Program for
Endangered Fishes in the Upper Colorado River Basin. Recovery Program Project Number
54. U. S. Fish and Wildlife Service, Colorado River Fishery Project, Grand Junction, CO.

Minckley, W. L. 1982. Trophic interrelations among introduced fishes in the lower Colorado
River, Southwestern United States. California Fish and Game 68(2):78-89.

Minckley, W. L., and J. E. Deacon. 1991. Battle against extinction: native fish management in
the American West. University of Arizona Press, Tucson, AZ. 517 pp.

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 303-358 in W.L. Minckley and J.E. Deacon
eds. Battle against extinction. University of Arizona Press, Tucson.

Oliver, J. D., G. F. Holeton, and K. E. Chua. 1979. Overwinter mortality of fingerling

smallmouth bass in relation to size, relative energy stores, and environmental temperature.
Transactions of the American Fisheries Society 108:130-136.

58


Table 3. Concentration areas for smallmouth bass in the Upper Colorado and Lower Gunnison
rivers during the summer of 2004, 2005, and 2006 using catch effort indices.

2004 2005 2006
Concentration Concentration Concentration
Catch/Effort* Rating" Catch/Effort * Rating * Catch/Effort* Rating *
River
River Segment
Upper Colorado River
Rifle-Beavertail Min 1.06 Lowest 5.78 Moderately 2.10 Moderately
High Low
Price Stubb Dam-GVIC 4,07 Medium 11.02 Highest 2.89 Moderately
Dam Low
GVIC Dam-Corn Lake 7.05 Moderately 8.97 Moderately 6.81 Moderately
High High High
Corn Lake-Colo/Gunn 11.88 Highest 16.36 Highest 8.94 Moderately
River confluence High
Colo/Gunn River 947 Highest 10.43 Highest 3.80 Medium
confluence-
Fruita State Park
Fruita State Park- 5.35 Moderately 3.78 Medium 215 Moderately
Loma Boat Landing High Low
Loma Boat Landing- 3.19 Medium 6.21 Moderately 3.04 Medium
Salt Creek High
Salt Creek-Utah/Colo 1,92 Lowest 1.60 Lowest 1,05 Lowest
Stateline
Utah/Colo Stateline- 0.47 Lowest 1,02 Lowest 0.94 Lowest
Westwater, UT,
Ranger Station
Station
Lower Gunnison River 921 Highest 144 Moderately 2.68 Moderately
Redlands Dam- High Low
Colo/Gunn River
confluence

* All passes combined. Catch effort was defined as the total catch per unit of effort and was reported as fish/hr.

* Key
Catch/Effort Value Relative Concentration Rating,
12.00-9.00 Highest
8.99-5.00 Moderately High
4.99-3.00 Medium
2,99-2.00 Moderately Low
< 2,00 Lowest

19


Figure 5.

No. of Smallmouth Bass (x 1000)

Figure 6.

let
mNw
bo

Catch/Effort (fish/hr)
a
Ce NWAUATIMOS

14
12
10

oN RO Dw

CATCH/EFFORT (fish/hr)

All Passes Combined Within Years
Smth Bass > 99 mm

8.41

n

1

2004 2005 2006

Year

Comparison of overall catch/effort (fish/hr) for smallmouth bass (2100 mm)
with electrofishing from the 15- and 18-mile reaches of Upper Colorado
River (RM 185.3.8-152.6) and the Lower Gunnison River (RM 3.0-0.7)
during 2004, 2005, and 2006. Note: all passes combined within years. See
Table 6.

POPULATION ESTIMATE (2006)
POPULATON PROJECTION (2004 & 2005)

—T 13,401 JT 13,507 Single Marking +
First Removal Pass

4 8,088 8,152
p-hat: 0.033
7 CV: 33.5%
—— 3.297
—— 3775 1 3,97 3997

—_—— 1,097

T T T
2004 2005 2006

Year
Population point estimate (2006) and projections (2004, 2005) with 95%
confidence intervals for smallmouth bass (2 100 mm) for the 15- and 18-

mile reaches of the Upper Colorado River (RM 185.3—152.6) and the Lower
Gunnison River (RM 3.0-0.7). See Table 6.

31


collected in the Grand Valley reaches were 2255 mm, 15.1 % were 2306 mm, and 1.4 % were
2357 mm. Of the total smallmouth bass in 2006 (n=881), 57.1 % were < 255 mm and 29.6 %
were < 100mm. The number of ‘trophy-size’ (2255 mm [10-inch]) smallmouth bass collected
has increased each year since 2004, being greatest in 2006 some of which could be attributed to
the increased removal pass in 2006. The number of smallmouth bass 2306 mm (232; 10.7%),
2357 mm (41; 1.9%), and 2406 mm (4; 0.2%) was greatest in 2006.

For the Silt to Beavertail Mountain reaches, the number of smallmouth bass collected
from the removal passes by the same seven length categories was also tallied for 2004, 2005, and
2006 (Appendix; Table C.3.). Because the number of removal passes have been increased
steadily from 2004 (n=1) to two removal passes each in 2005 and 2006, comparison of numbers
collected among years is more difficult. However, there is one apparent similarity with the
downstream Grand Valley reaches: the number of ‘trophy-size’ smallmouth bass relative to the
total number collected were well represented in collections in these upper reaches. For example,
a 3-year relative average of smallmouth bass 2255 mm was 40.1 % (132 of 329 total smallmouth
bass) and smallmouth bass 2306 mm was 19.8 % (65 of 329 fish). About 5% (n=17) were
2357 mm.

‘There is one dissimilarity between these upper reaches and the Grand Valley reaches. In
the upper reaches, the number of smallmouth bass < 255 mm collected during 2004-2006 was
less than that of the Grand Valley reaches. For example, the three-year relative average of
smallmouth bass < 255 mm in the upper reaches was 50.2 % (165 of 329 total smallmouth bass)
compared to 68.1 % (2,430 of 3,567 total smallmouth bass) in the Grand Valley reaches.

In the Rifle to Beavertail Mountain reach, apparent was the lack or even absence of
smallmouth bass between 100 and 200 mm in 2006, similar to that observed in the Grand Valley
reaches of the Colorado River (Figure 8). Also, it was apparent from collections, that in some
river segments (15-mile reach [GVIC Diversion Dam to the Colorado/Gunnison River
confluence], 18-mile reach [Colorado/Gunnison River confluence to the Loma boat landing], and
Rifle to Beavertail Mountain), smallmouth bass reproduced during 2004, 2005, and 2006. It
cannot be proven if these fish were produced in the river, or in off-channel habitats (e. g., ponds
or irrigation returns that connect to the main river) and later migrated to the river.

36


7)

6) & Gunnison River (RM 3.0-0-

Smallmouth Bass Electrofishing Captures-July & August 2004

Colorado River (RM 187.6-127.-

ast oh 5 ge
< Osh <
3 6br-OPr Oo| ¢ 6hr-orP 8 be e
Hy Geer O34) é 6Eh-0Eb 93
6tr-0zh no 6eh-Ozh go] s
4 GLP OIP 49) GUPOIP Be] o
3 60}-00F Ss|2& 60h-00F o SE
2 668-068 DEI ELE 66E-06E OS| 3 Ee
& 68E-08E Pe) ees 68E-08E o%| ges
I GLE-OLE ul FES f} 6LE-OLE vy | SES
& G9E-O9E O| & 4 is} GOE-O9E eel ao"
a OSE-OSE es} ag & 6SE-OSE Wo! gor
5 fa] GhE-OFE Saha [E]. Ghe-one a2) aay
8 fe] see-oee at) oy Es] Gee-0ce Oe) weg
3 Ey OCE-OTE Del tee GzE-OTE ac| ede
i fas] OLE-DIE 2o0;/Teé GIE-O1E 6| ae
© [sq]. 60€-00€ o@| REE 6DE-00€ sal] FFF
fa}. 667-062 OE => 2
Gq 687-082 ke 3
GLT-OLE 25 25
oro 5 a5 2 of
6S7-0ST et 4 Q 0
6hC-OVT
scence BP OS ae
Coa a) a 26
eicoie ER! wom
ero: = ER = OF
2G a N
gar £ of
oh o PS
& 68 Be &e@
5h iN
Oo Oo 0
ar 5 v
us bs
gt ge
a. =.
ag uy
ce 02
Fag oe
5 a
: ° ao
. ic oo 3
z 6E-0E Es fs/ $s
4 6C-07 = HI 5 6 S
6-01 ae os,
oL £0 6°
go0 20
eeseeseeoeo eoesce 3 o
aAaaeetes SRSRSEIRS EPTRSeesR?
7)
Ysiq Jo taquinyy Ysiy Jo saquinyy Ysiq Jo saquinyy

and 2006, with electrofishing in the
127.6) and the Lower Gunnison River

8

Total Length (mm)
Total length frequency for all smallmouth bass (26-414 mm) collected

Upper Colorado River (RM 187

(RM 3.0-0.7).

during the summer of 2004, 2005

Figure 7.


White, G. C., D. R. Anderson, K. P. Burnham, and D: L. Otis. 1982. Capture-recapture and
removal methods for sampling closed populations. Los Alamos National Laboratory, Los
Alamos, New Mexico. LA-8787-NERP. 235 pp.

Wiltzius, W. J. 1978. Some factors historically affecting the distribution and abundance of
fishes in the Gunnison River. Colorado Division of Wildlife, Ft. Collins, CO. 215 pp.

Winemiller, K. O., an D. H. Taylor. 1982. Smallmouth bass nesting behavior and nest site
selection in a small Ohio stream. Ohio Journal of Science 82:266-273.

61


Table B.1. Amount of effort (electrofishing hours) expended during four passes of the
smallmouth bass removal project sampling main channel habitats on the Colorado
and Lower Gunnison rivers in western Colorado and eastern Utah, July and August
2004. Note: n/s=not sampled; two electrofishing craft were used for passes 1, 2,
and 3; one electrofishing craft was used for pass 4.

Electrofishing Effort (hr)
River
(River Miles)
River Segment P-L P-2 P33 P-4

Colorado River
(RM 187.7-127.6)

Price-Stubb>GVIC Dam 2.275 2.438 2.656 n/s

GVIC Dam > Com Lake 5.432 4.943 8.273 2.920

Corn Lake »Colo/Gunn. 4.701 5.581 8.696 3.750
River Confluence

Colo/Gunn R. Confl. » 9.248 11.572 16.328 7.633
Fruita State Park

Fruita State Park > 2.902 3.172 4.496 1.949
Loma Boat Landing

Loma Boat Landing > 7.372 5.564 7.733 o/s
Salt Creek Wash

Salt Creek Wash > 6.029 6.988 7.295 ns
Utah/Colo Stateline

Utah/Colo Stateline > 1.244 2.434 2.664 n/s
Westwater, Utah
BLM Ranger Station

Lower Gunnison River

(RM 3.0-0.7)

Redlands Div. Dam 3,363 3.196 4.070 1.748
Colo/Gunn R.
Confluence

2004 Pass Totals 42.566 45.888 62.211 18.00



Between Rifle and Beavertail Mountain, green sunfish catch/effort increased from 13.1
fish/br to 15.2 fish/hr from 2005 to 2006. Numbers of bluegill and black crappie were few and
therefore were insignificant in this 45-mile reach during all three years (see ‘Numbers of
Individual Fish Species’ section above for numbers of these species).

Population Estimates/Projections

Smallmouth Bass. A total of 131 smallmouth bass ranging from 66 to 394 mm total
length were marked and released alive between the GVIC Diversion Dam and the Loma boat
landing and 2.3 miles of the Lower Gunnison River (Table 4), Eight smallmouth bass (202-372
mm) were later recaptured in subsequent passes. Six of these fish were recaptured in pass 1, one
each in passes 2 and 3; no fish were recaptured in pass 4. All eight of the marked smallmouth
bass were recaptured within the original marking reaches. Two smallmouth bass were recaptured
jn the 15-mile reach, five in the 18-mile reach, and one in the Lower Gunnison River.

The population estimate generated was for the 15- and 18-mile reaches of the Colorado
River and 2.3 miles of the Lower Gunnison River downstream from Redlands Diversion Dam
(total=35.3 miles). Four different estimates were calculated: 1a) all smallmouth bass sizes
(41-394 mm), using smallmouth bass recaptured from pass 1 only, 1b) all smallmouth bass sizes
(41-394 mm), using smallmouth bass recaptured from passes 1, 2, and 3; 2a) only smallmouth
bass >100 mm, using smallmouth bass recaptured from pass 1 only, and 2b) only smallmouth
bass > 100 mm, using smallmouth bass recaptured from passes 1, 2, and 3 (Table 5). Since
smallmouth bass < 100 mm, which mostly represented young-of-the-year fish, were not available
to sampling during the marking pass, the abundance estimate which did not include fish < 100 is
probably the better population estimate for the smallmouth bass population. Using recaptured
smallmouth bass from pass 1 only and smallmouth bass 2 100 mm, the population point estimate
(95% C.I. in parenthesis) was 3,197 (1,097-5,297). This was the preferred and final population
estimate reported on in this study. The probability of capture (p-hat) was computed as 0.033; the
CV: 33.5%. This translated to 31.1 to 150.1 fish/mile (mean=91). Using recaptured smallmouth
bass from passes 1, 2, and 3 and smallmouth bass 2100 mm, the population point estimate was
elevated to 5,247 (2,152-8,342). The probability of capture (p-hat) was computed as 0.021; the
CV: 30.1%. The CV can be used as a measure of estimate precision and Pollock et al. (1990)
suggests a good ‘rule of thumb’ is to achieve a CV of 20% or less. This level of precision was
never met in any of the four abundance estimates computed for smallmouth bass during 2006.

26


Table E.1. Scientific and common names and status (native vs. nonnative) of fish collected and
mentioned in the text of this report during the smallmouth bass removal study in the
Upper Colorado and Lower Gunnison rivers, 2004-2006.

Family Common Name Status
Scientific Name
Clupeidae
Dorosoma cepedianum gizzard shad nonnative
Cyprinidae
G. robusta roundtail chub native
Gila cypha humpback chub native
G. elegans bonytail native
Ptychocheilus luicius Colorado squawfish native
Catostomidae
Catostomus discobolus bluehead sucker native
C. latipinnis flannelmouth sucker native
Xyrauchen texanus razorback sucker native
Ictaluridae
Ameiurus melas black bullhead nonnative
Ictalurus punctatus channel catfish nonnative
Esocidae
Esox lucius northern pike nonnative
Centrarchidae
Lepomis cyanellus green sunfish nonnative
Lepomis macrochirus bluegill nonnative
Micropterus dolomieu smallmouth bass nonnative
Micropterus salmoides largemouth bass nonnative
Pomoxis nigromaculatus black crappie nonnative
Percidae
Perca flavescens yellow perch nonnative
Sander vitreus walleye nonnative



This study was funded by the Recovery Implementation Program for Endangered Fish
Species in the Upper Colorado River Basin. The Recovery Program is a joint effort of the U. S.
Fish and Wildlife Service, U. S. Bureau of Reclamation, Western Area Power Administration,
states of Colorado, Utah, and Wyoming, Upper Basin water users, environmental organizations,
the Colorado River Energy Distributors Association, and the National Park Service.

DISCLAIMER

The opinions and interpretation of the data expressed in this report are those of the author
and do not necessarily reflect the views of the Fish and Wildlife Service or the Recovery
Program.

Mention of trade names, commercial products, or firms and businesses does not
constitute endorsement or recommendation for use by the author, the Fish and Wildlife Service,
U.S. Department of Interior, or members of the Recovery Implementation Program.

Throughout this report, a combination of English and metric measurements are used
according to their predominant usage for specific data categories and what are meaningful to
many readers. English equivalents are used to identify distances within and along river drainages
(river miles). Metric units are most commonly used for biological work associated with
endangered and nonnative fishes and they were retained for this report.

Suggested citation:

Burdick, B. D. 2008. Removal of smallmouth bass and four other centrarchid fishes from

the Upper Colorado and Lower Gunnison Rivers: 2004-2006. Final Report prepared for the
Upper Colorado River Endangered Fish Recovery Program. Recovery Program Project Number
126. U.S. Fish and Wildlife Service, Colorado River Fishery Project, Grand Junction, Colorado.
61 pp + appendices.


Table D.1. Discharge characteristics (instantaneous peak discharge, lowest and highest mean
daily flow, and 90% exceedence) and degree days (214 ° C) for five calendar years
(2002-2006) at the Cameo USGS gauge (RM 199.8) on the Upper Colorado River.
N/A=data not available; P=preliminary.

Cameo 2002 2003 2004 2005
Lowest Daily 925 871 1,040 1,240 1,360
Mean (cfs)
Highest Daily 4,020 20,300 7,010 16,800 16,400
Mean (cfs)
Instantaneous Peak 4,260 21,000 7,450 17,200 17,700
Discharge (cfs) &
Date 6/01 6/2 6/8 5/24 5/23
90% Exceedence 1,160 1,090 1,250 1,390” N/A
(cfs)
Total Degree Days 749.9 600.9 538.8 443.7 558.8
214°C
Total Degree Days 718.7 597.5 527.3 443.6 558.8
214°C
(6/1-10/31)
No. of Days Water 139 124 129 113 99
Temp Equalled or
Exceeded 14°C
Max Mean Daily 23.6 24.4 23.4 22.1 24.1
Water Temp (C)

800
Cameo

o GOO =P ~~~ Farabate Waiertemp) 7 T

3 EqualledExceeed 14 C

a 2002: 5/1

g 400

s

oa

8

3 200

o- ue
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Month

Figure D.1. Cumulative degree days (z 14 ° C) on the Upper Colorado River at the
Cameo USGS gauge for 2002-2006.

D-1


CONCLUSIONS

. Smallmouth bass abundance was the lowest in three years at the end of the 2006 sampling
season in main channel riverine habitats. However, it is premature to determine if this
downward trend in smallmouth bass abundance will continue.

. River reaches that had the highest concentration for smallmouth bass after three years in
descending order on the Upper Colorado and Lower Gunnison rivers were, a) Corn Lake
to the Colorado/Gunnison River confluence, b) Colorado/Gunnison River confluence to
Fruita State Park, c) GVIC Dam to Corn Lake, and d) Redlands Dam to the
Colorado/Gunnison River confluence in the Lower Gunnison River.

. Despite smallmouth bass abundance decreasing significantly during 2006, the direct
opposite was apparent for largemouth bass. In main channel riverine habitats in the
Grand Valley sub-reaches, there was a significant increase for largemouth bass during
2006 from the previous two years: a 101% increase in catch/effort from 2005 and a 312%
increase in catch/effort from 2004. Between Rifle and Beavertail Mountain largemouth
bass catch rate increased in 2006 (5.62 fish/hr) from 2005 (0.95 fish/hr) and 2004 (3.29
fish/hr). Despite both species being lethally removed, largemouth bass numbers have
continued to increase in main channel habitats.

. Green sunfish and black crappie abundance increased in main channel habitats in the
Grand Valley sub-reaches of the Upper Colorado and Lower Gunnison rivers.

. The smallmouth bass year class produced in the summer of 2005 appeared not to recruit
to 2006. The loss of this year class cannot be directly attributed to environmental factors
within the range observed in this study. Some of the environmental factors could be
colder summer water temperatures that occur during higher discharge water years which
result in a later spawning period, later larval hatch, and a shorter-growing season. As a
result of these environmental factors, the biological and physiological implication could
have been that small and medium-size age-0 smallmouth bass were unable to accumulate
adequate lipid reserves to survive until the following spring, and death may have been
due to exhaustion of energy reserves.

49


increase in average size is most probably due in part to the lack of or absence of smallmouth bass
catches between 100 and 180 mm in the Grand Valley reaches of the Colorado River during
2006. In viewing the 2005 length frequency, it appears that the size group of smallmouth bass
between 50 and 100 mm was lost to the population sometime between the winter of 2005/2006
and summer sampling during 2006, or simply were not captured in 2006. There did not appear to
be a lack of young-of-the-year smallmouth bass produced in 2005; the numbers appeared to be
even greater than those produced during 2004. In any event, size classes of smallmouth bass
represented by young-of-the-year and slowing growing age-1 smallmouth bass in 2005 did not
recruit to the next size classes as their numbers obviously declined during the summer of 2006.
The exact reason for this is unknown. It can be speculated that this size group of smallmouth
bass may have been lost prior to high spring runoff and had experienced high overwinter
mortality or were lost during the 2006 spring runoff (see later section on ‘Annual Abundance of
Early-Life Smallmouth Bass Related to Stream Discharge and Water Temperature’).

It is also apparent that the number of smallmouth bass within all size groups in 2006
declined from 2004 and 2005. Overall, 3-year catches of smallmouth bass in all sub-reaches
were the lowest in 2006. With no certainty can this decline be directly attributed to mechanical
removal. However, if the decline was related to an environmental event (e. g., high stream
discharges, lower water temperatures), it would be desirable to be able to identify and attempt to
mimic that event and utilize that condition to our advantage to continue to reduce smallmouth
bass populations. All groups of smallmouth bass (young-of-the-year, juveniles, and adults) were
represented in the collections in the summer of 2004, 2005, and 2006. In 2004, smallmouth bass
ranged from young (~ 50 mm) to adult (414 mm) fish. During 2005, smallmouth bass ranged
from young (26 mm) to adult (437 mm) fish. During 2006, smallmouth bass ranged from young
(42 mm) to adult (394 mm) fish. ‘

In addition to the length frequency histograms, the number of smallmouth bass
collected for marking and removal passes by seven length categories was tallied for 2004, 2005,
and 2006, for the Grand Valley river reaches. The percentage of the smallmouth bass collected
was also computed to directly compare numbers collected among the three years because an
additional pass (marking) was added in 2006. Unlike largemouth bass collected in main channel
riverine habitats of the Grand Valley where a vast majority (~ 90%) of the fish collected were
< 150 mm, the length classes for smallmouth bass were more proportionately represented
(Appendix; Tables C.1. and C.2.). For example, in 2006, 42.9 % of all smallmouth bass

35


Table C.3. Number of smallmouth bass by seven different length categories collected with
electrofishing from marking and removal (REM-) passes from main channel riverine
habitats from the Upper Colorado River (RM 248.0-195.7) during the summers of

20042006.

Reach: Silt to Smallmouth Bass

Beavertail Mtn Length Category-- mm {inches}
Year < 100 100-199 | 200-254 | 255-305 | 306-356 | 357-406 > 406

Pass Type/No. <4} | {4-8} | {8-10} | {10-12} | (12-143 | {14-16} | 16}
2006

REM-1 2 0 5 10 18 5 0

REM-2 34 2 0 1 1 1 0
2005

REM-1 10 28 26 34 18 3 3

REM-2 48 26 6 13 10 2 2
2004

REM-1 3 4 3 9 1 0 1

C-3


Table 1. Designated river segments and sub-reaches for the centrarchid removal project in the
Upper Colorado River from Rifle to Beavertail Mountain, Price-Stubb Diversion Dam
to Westwater, Utah, and the Lower Gunnison River from the Redlands Diversion
Dam to the Colorado/Gunnison River confluence, 2004-2006.

River
River Segment Length of
Sub-Reach River Miles Segment/Sub-Reach

Colorado River

Rifle to Beavertail Mountain 240.4-195.7 44.7
Rifle Bridge-Rulison 240.4-230.0 10.4
Rulison—Parachute Bridge 230.0-223.0 7.0
Parachute Bridge—Debeque I-70 Bridge 223.0-209.7 13.3
Debeque I-70 Bridge~Beavertail Mountain 209.7~-195.7 14.0
Sub-Reach Total --- 44.7

Price-Stubb Diversion Dam— 187.7-127.6 60.1

Westwater, Utah
Price-Stubb Dam—GVIC Dam 187.7-185.3 2.4
GVIC Dam-—Corn Lake 185.3-177.4 19
Corn Lake-Colo/Gunn River Confluence 177.4-171.0 6.4
Colo/Gunn River Confl Fruita State Park 171.0-157.2 13.8
Fruita State Park—Loma Boat Landing 157.2-152.6 4.6
Loma Boat Landing-Salt Creek Wash 152.6-144.0 8.6
Salt Creek Wash—Utah/Colo State Line 144.0-131.9 12.1
Utah/Colo State Line-Westwater, Utah 131.9-127.6 4.3
Sub-Reach Total --- 60.1

Lower Gunnison River

Redlands Diversion Dam—Colo/Gunn 3.0- 0.7 2.3
River Confluence
Sub-Reach Total --- 2.3



an impediment to the recovery of endangered fish species.” The goal for nonnative fish control
or management in the Upper Colorado River Basin is to reduce the adverse impacts of nonnative
fishes on the endangered fishes which will hopefully increase the distribution and abundance of
the endangered fishes and contribute to their recovery. It is not likely that nonnative fishes that
have become established in the Upper Colorado River Basin can be eliminated. However,
preventive measures (e. g., reservoir escapement, illicit translocation and release) and active
control programs could be implemented to reduce the abundance of nonnative fishes in riverine
and adjacent floodplain habitats. Consequently, reducing the abundance of some problematic,
nonnative fishes would reduce the potential for predation and competition on both listed and
unlisted native fishes.

Management to promote recovery of listed fish species may have to include long-term or
periodic suppression of some problematic nonnatives, such as mechanical removal, that
minimizes impacts to remaining native fishes. If removal can be sufficient to cause a population
collapse, numbers may decline to a density level in which recruitment is not effective and
populations remain small until they can expand to a level when they are again abundant. Even if
control measures are effective in removing smallmouth bass, an unfortunate event such as an
influx of fish from an off-river source as much as ten years apart can negate the gains of multiple
years of removal. Mechanical removal is the most common method being used to control
nonnative fish in the upper basin. The prevailing gear being used to accomplish this objective is,
by far, electrofishing.

Purpose and Objectives

The purpose of this study was to remove as many smallmouth bass of all sizes in main
channel riverine habitats in a 105-mile portion of the Upper Colorado River between Rifle and
Beavertail Mountain and between Price-Stubb Dam and Westwater boat landing in eastern Utah
and a 2.3-mile reach of the Lower Gunnison River. The goal was to reduce the abundance of
smallmouth bass as quickly as possible in this reach which would ultimately benefit native listed
fishes, and possibly contribute to their recovery. In 2006, objective number 2 was added to
obtain an abundance estimate for smallmouth bass in concentration areas of the Upper Colorado
River from Price Stubb Dam to Westwater, Utah. The study objectives were to:

1. remove all sizes of smallmouth bass collected by boat and raft-based electrofishing,


APPENDIX D
Water Temperature and Hydrology Records


be highly variable and is not the most reliable metric for population analyses or comparing trends
in population abundance densities among years. It is more likely that unexplained variations in
capture probability or “catchability” (not catch per unit of effort per se) preclude the use of catch
per unit of effort as an abundance estimate. During 2004 and 2005, since the initial study
objective was to lethally remove as many smallmouth bass and other centrarchids as quickly as
possible, fish were not marked and released and, therefore, a population estimate was not
possible. For those years, effort was recorded (Appendix; Tables B.1. and B.2.) and catch/effort
was calculated and used to monitor increases and declines in centrarchid populations. To
determine if densities of smallmouth bass and largemouth bass were being depleted as a result of
the removal effort, we calculated and interpreted catch effort indices (e. g., fish/hr) over time (i.
@., by pass) in each river sub-reach (Appendix; Tables B.4.-B.6.). Because population estimates
for smallmouth bass were not available for 2004 and 2005, effort was still recorded during 2006
(Appendix; Table B.3.) and catch/effort was computed (Appendix; Table B.6.) for use as a trend
to compare annual abundance of smallmouth bass and other centrarchids during 2004, 2005, and
2006.

Electrofishing effort in 2004 (168.665 hours) was similar to 2005 (174.560 hours)
between Price-Stubb Dam and the Westwater, Utah, ranger station and the Lower Gunnison
River (Appendix; Table B.1—B.2). In 2006, electrofishing effort in these reaches was 161.906
hours (Appendix; Tables B.3.). Between Rifle and Beavertai] Mountain, the effort expended in
2004 was 19.750 hours compared to 39.799 hours during 2005 and 37.512 hours during 2006
(Appendix; Tables A.4.—A.6.).

Smallmouth bass. A decline in abundance of smallmouth bass was detected in 2006 from
the previous two years using catch effort indices (fish/hr) in main channel habitats of the Upper
Colorado River in western Colorado and eastern Utah and the Lower Gunnison River. From
Price-Stubb Dam to the Westwater ranger station, overal] mean catch effort (Appendix; Table
B.6.) for smallmouth bass during passes 1—4 was: 4.30, 3.87, 5.57, and 5.34 fish/hr, respectively,
for 2006. For 2005, overall mean catch effort (Appendix; Table B.5.) during passes 14 was:
8.18, 8.53, 6.26, and 9.09 fish/hr, respectively. For 2004, overall mean catch effort (Appendix;
Table B.4.) during passes 14 was 5.14, 5.58, 8.11 and 10.33 fish/hr, respectively. In the Grand
Valley reaches, overall mean catch effort for smallmouth bass declined in 2006 (4.64 fish/hr)
from 2005 (7.83 fish/hr) and 2004 (6.91 fish/hr). Smallmouth bass overall mean catch/effort by
each of the four passes for each of the three years was graphed. As passes proceeded through

17


Water Temperature

: Degree days (2 14 °C) at both Cameo (443.7) and stateline (692.0) were lowest in 2005
and greatest during 2002 (749.7 at Cameo; 1,023.4 at stateline)(Appendix; Tables D.1. and D.2.;
Figures D.1. and D.2.). The first date that the water temperature equalled or exceeded 14° C
varied each year. At Cameo, the earliest 14 ° C was reached was April 27 during 2004. During
2005, which was the highest flow year during the study, the first date that water temperature
reached 14 ° C occurred the latest of any of the years: June 15 (Appendix; Figure D.1 .). At
stateline, the earliest water temperature 14 ° C was observed was in 2004 (March 23). Similar to
Cameo, in 2005, 14° C was first attained the latest of any of the five years analyzed: May 20
(Appendix; D.2.). The total number of days the water temperature equalled or exceeded 14 °C
was highest in 2002 at Cameo (139). At stateline, the highest number of days this occurred was
in both 2002 and 2004 (169 days). For 2004 and 2006, at Cameo, an anomalous and
unexplainable situation was obvious. At Cameo, the mean annual discharge for the entire year
from April 1 to October 1 (considered the growing season for warm water fish) during 2004, was
considerably less (~ 40 %) than the same period for 2006. However, both degree days and the
number of days water temperature equalled or exceeded 14 ° C were greater during 2006 than
2004. Just the opposite occurred at stateline. At stateline, the number of degree days and days
the water temperature equalled or exceeded 14 ° C was what one would expect: 2004 had a
greater number of degree days (870.2) and days equalling or exceeding 14 ° C (169) than 2006
(749.4 and 132 days).

The five water years between 2002 and 2006 were ranked warmest to coolest using total
degree days (1 April to 1 October) at the Utah—Colorado stateline gauge. This descending order
by calendar water year was: 2002, 2003, 2004, 2006, and 2005 (Appendix; Table D. 2.).

Annual Abundance of Early-Life Smallmouth Bass
Related to Stream Discharge and Water Temperature

Smallmouth bass between 100 and 180 mm were noticeably less abundant in the catches
during the summer of 2006 than 2004 and 2005 in the Grand Valley sub-reaches of the Colorado
River (Figure 7). In the Rifle to Beavertail Mountain segment, apparent was the lack or even
absence of smallmouth bass between 100 and 200 mm, similar to that observed in the Grand
Valley sub-reaches of the Colorado River. There did not appear to be a lack of young

4l


APPENDIX E
Scientific and Common Names of Fishes
Mentioned in the Smallmouth Bass Removal Study
2004-2006


Osmundson, D. B., and L. R. Kaeding. 1989. Studies of Colorado pikeminnow [squawfish] and
razorback sucker use of the "15-Mile Reach" of the upper Colorado River as part of
conservation measures for the Green Mountain and Ruedi reservoir water sales. Final
Report. Colorado River Fishery Project, U. S. Fish and Wildlife Service, Grand Junction,
CO. 85 pp.

Osmundson, D. B. 2003. Removal of non-native centrarchids from upper Colorado River
backwaters, 1999-21: summary of results. Final report prepared for the Recovery
Implementation Program for Endangered Fishes in the Upper Colorado River Basin.
Recovery Program Project Number 89. U. S. Fish and Wildlife Service, Colorado River
Fishery Project, Grand Junction, CO. 35 pp.

Papoulias, D. and W. L. Minckley. 1990. Food limited survival of larval razorback sucker,
Xyrauchen texanus, in the laboratory. Environmental Biology of Fishes 29: 73-78.

Peterson, J. T., and T. J. Kwak. 1999. Modeling the effects of land use and climate change on
riverine smallmouth bass. Ecological Applications 9:1391—1404.

Pollock, K. H., J. D. Nichols, C. Brownie, and J. E. Hines. 1990. Statistical inference for
capture-recapture experiments. Wildlife Monographs 107.

Pitlick, J., and R. Cress. 2000. Longitudinal trends in channel characteristics of the Colorado
River and implications for food-web dynamics. Final Report prepared for the Recovery
Implementation Program for the Endangered Fishes of the Upper Colorado River Basin.
Recovery Program Project Number 48-C. University of Colorado, Boulder. 45 pp +
appendices.

Quarterone, F. 1993. Historical accounts of Upper Colorado River basin endangered fish.
Colorado Division of Wildlife, Denver, 66 pages.

Ricker, W. E. 1975, Computation and interpretation of biological statistics of fish populations.
Dept. of Environment, Fisheries and Marine Service, Ottawa, Canada, 382 pp.

59


Hydrology and Water Temperature Data

Discharge and water temperature records for the Upper Colorado River were retrieved
from the U.S. Geological Survey (USGS) stream gauging stations at Cameo (no. 09095500) and
stateline (09163500) near the Colorado/Utah border for 2002-2006. Only discharge records
from the Palisade USGS gauge (no. 09106150) were retrieved for 2002-2006. Various
hydrology and water temperature parameters were used to characterize different flow years (e. g.,
wet, moderate, and dry) prior to and during the study period. The discharge parameters included
highest and lowest daily mean flow, peak instantaneous flow and date it occurred, and 90 %
exceedence. Total and cumulative annual degree days (214 ° C) were generated for the Cameo
and stateline stations for 2002-2006. Additional water temperature parameters included
maximum daily water temperature, the number of days the water temperature equalled or
exceeded 14° C, and the total degree days (214 ° C) between June 1 and October 31 of each of
the years examined. The years 2004-2006 coincided with biological data collected during the
smallmouth bass removal project. Even though smallmouth bass data were not collected during
2002 and 2003 in the same manner as this study, these years were considered drought years and
were used to compare discharge and water temperature parameters between 2004-2006.

For this study, a degree day was defined as one degree of temperature (° C) above the
developmental zero for a period of one day (Berven et al. 1979). In terms of smallmouth bass
growth, developmental zero would be the mean daily water temperature that equalled or
exceeded 14 ° C because this was the temperature at which smallmouth bass growth was
believed to be initiated (Shuler et al. 1980). For example, a mean daily water temperature of 14.6
°C on May 1 of a particular year would be calculated as 0.6 (14.6 minus 14.0 = 0.6) degree day.
Likewise, a mean daily water temperature of 21.2 ° C on a particular day would calculated as a
7.2, (21.2 minus 14.0 = 7.2) degree day. Negative degree days (e. g., those days when the mean
daily water temperatures were less than 14 ° C) were not used and were not subtracted from the
days when the mean daily water temperature exceeded 14° C. The mean daily water temperature

for days when no readings were made or were unavailable were estimated by interpolation.

The total number of degree days for a calendar year was the summation for each of the
days when the mean daily water temperature exceeded 14°C, The cumulative degree days were
the increasing or successive accumulation of additive degree days when the mean daily water


Colorado River (RM 187.7-127.6)
Lower Gunnison River (RM 3.0-0.7)

p 2004, 2005, 2006

all lgmth bass
(29-420 mm)

(419)

_
o
1

io)
1

(146)
— 2006

(80)

Catch/Effort (fish/hr)
a

4 2004
wes) 2005

2 -|

0 T t T t

Pass Number

Figure B.1. Overall catch effort (fish/hr) by pass for largemouth bass (29-420 mm)
collected from main channel habitats in the Upper Colorado River with
electrofishing from RM 187.7-127.6 (Price-Stubb Dam to the Westwater,
Utah, BLM ranger station) and in the Lower Gunnison River from RM
3.0-0.7 (Redlands Dam to the Colorado/Gunnison River confluence),
2004, 2005, and 2006. Note: The number of fish collected by pass is in
parentheses.

B-7


LIST OF APPENDIX TABLES AND FIGURES

Appendix

c.

Table C.1. Number of smallmouth bass by seven
different length classes collected with electrofishing
from marking and removal (REM-) passes from main
channel riverine habitats from the Grand Valley river
reaches of the Upper Colorado (RM 187.8-127.6)
and the Lower Gunnison (RM 3.0-0.7) rivers

during the summers of 2004-2006 ..........0.... 0222 e eee eee

. Table C.2. Percentage and number (in parenthesis)

comparison of smallmouth bass by six different

length classes collected with electrofishing from
marking and removal (REM-) passes from main channel
riverine habitats from the Grand Valley river reaches

of the Upper Colorado (RM 187.8-127.6) and the Lower
Gunnison (RM 3.0-0.7) rivers during the summers of

2004-2006 . 0... eee cece cence eben een eens

. Table C.3. Number of smallmouth bass by seven

different length classes collected with electrofishing
from marking and removal (REM-) passes from main
channel riverine habitats from the Upper Colorado
River (RM 248.0-195.7) during the summers of

2004-2006 2... eect eee eee e ene e eens

Figure C.1. Time series length frequency for age-0
and age-1 smallmouth bass (< 115 mm total length)
collected during the summer of 2004 from the Upper
Colorado (RM 187.8-127.6) and Lower Gunnison

(RM 3.0-0.7) rivers... ce cece eee eee

Figure C.2. Time series length frequency for age-0
and age-1 smallmouth bass (< 115 mm total length)
collected during the summer of 2005 from the Upper
Colorado (RM 187.8-127.6) and Lower Gunnison

(RM 3.0-0.7) rivers . 06... eee cece cece cece eee eee

xii

E
po
Ia


Ruppert, J. B., R. T. Muth, and T. P. Nesler. 1993. Predation on fish larvae by adult red shiner,
Yampa and Green rivers, Colorado. The Southwestern Naturalist 38:397-399.

Shuter, B. J., J. A. MacLean, F. E. J. Fry, and H. A. Regier. 1980. Stochastic simulation of
temperature effects on first-year survival of smallmouth bass. Transactions of the American
Fisheries Society 109:1-34.

Shuter, B. J., P. E.,Ihssen, D. L. Wales, and E. J. Snucins. 1989. The effects of temperature, pH
and water hardness on starvation of young-of-the-year smallmouth bass, Micropterus
dolomieui Lacepede. J. Fish Biol. (1989) 35, 765-780.

Thompson, J. M., E. P. Bergersen, C. A. Carlson, and L. R. Kaeding. 1991. Role of size,
condition, and lipid content in the overwinter survival of age-0 Colorado pikeminnow
[squawfish]. Transactions of the American Fisheries Society 120:346-353.

Tyus, H. M, B. D. Burdick, R. A. Valdez, C. M. Haynes, T. A. Lytle, and C. R. Berry. 1982.
Fishes of the Upper Colorado River Basin: distribution, abundance, and status. Pages 12-70,
in WH. Miller, H.M. Tyus, and C.A. Carlson (eds). Fishes of the Upper Colorado River
System: Present and Future. Fishes of the Upper Colorado River Basin: distribution,
abundance, and status. American Fisheries Society, Bethesda, MD.

Tyus, H. M. and J. F. Saunders, II]. 1996. Nonnative fishes in natural ecosystems and a strategic
plan for control of nonnatives in the Upper Colorado River Basin. Draft Report. Center for
Limnology, University of Colorado, Boulder, Colorado. For the Recovery Implementation
Program for Endangered fish Species in the Upper Colorado River Basin. Cooperative
Agreement No. 14~48-0006-923, U.S. Fish and Wildlife Service, Denver, Colorado.

Valdez, R. A., P. G. Mangan, R. P. Smith, and B. Nilson. 1982. Upper Colorado River
investigations. Pages 101-279 in W. H. Miller et al., editors. Colorado River Fishery
Project., Final Report; Part Two, Field Studies. U. S. Fish and Wildlife Service and Bureau
of Reclamation. Salt Lake City, UT.

Valdez, R. A., and R. T. Muth. 2005. Ecology and conservation of native fishes in the Upper
Colorado River Basin. American Fisheries Society Symposium 45:157-204.

60


Table A.4. Summary statistics of centrarchids and percids collected during reconnaissance
sampling in main channel habitats of the Upper Colorado River from Rifle,
Colorado, to Beavertail Mountain in Debeque Canyon, August 23-26, 2004.

Reach: Rifle Bridge—Rulison Bridge
River Mile: 240.7-230.0; River Mile Length: 10.7
Number of Electrofishing Crafts: 2
Effort (hr): 10.26

Smallmouth Largemouth Green
Bass Bass Sunfish

Walleye

No. No. No.
of  TotalLength(mm) of TotalLength(mm) oof Total Length (mm)

No.
of Total Length (mm)
Fish Min Max Mean

Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean

20 63 412 235 42 38 184 82 8 <100 112 ~100 1 -- -- 610
Reach: Rulison Bridge~Parachute Bridge

River Mile: 229.9-223.0; River Mile Length: 6

Number of Electrofishing Crafts: 2

Effort (hr): 2.17

Smallmouth Largemouth Green
Bass Bass Sunfish Walleye

No. No. No. No.

of TotalLength(mm) of  TotalLength(mm) of : Total Length (mm)
Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean

of Total Length (mm)
Fish Min Max Mean

0 ee ose -- 4 66 420 225 3. <100 <100 <100

Reach: Parachute Bridge—-Debeque I-70 Bridge
River Mile: 223.0-209.7; River Mile Length: 13.3
Number of Electrofishing Crafts: 2
Effort (hr): 4.38

Smallmouth Largemouth Green
Bass Bass Sunfish

Walleye

No. No. No.
of TotalLength(mm) of  TotalLength(mm) oof Total Length (mm)
Fish Min Max Mean Fish Min Max Mean Fish Min_ Max Mean

No.
of Total Length (mm)
Fish Min Max Mean

loo--  -- 53 8 43 93 63 19 <100 135 ~104 QO -- -- --
Reach: Debeque I-70 Bridge-Beavertail Mountain (Debeque Canyon)

River Mile: 209.7-195.7; River Mile Length: 14.0

Number of Electrofishing Craft: 1

Effort (hr): 2.94

Smallmouth Largemouth Green
Bass Bass Sunfish Walleye

No. No. No. No.

of TotalLength(mm) of  TotalLength(mm) of — Total Length (mm)
Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean

of Total Length (mm)
Fish Min Max Mean

0 we ee -- i 85 189) «113 6 90 117 99

0 -- -- =



LIST OF FIGURES

Figure

10. Total length frequency for all largemouth bass

11.

(29-544 mm) collected during the summer of
2004, 2005, and 2006, with electrofishing in
the Upper Colorado River (RM 187.8-127.6)

and the Lower Gunnison River (RM 3.0-0.7) ............-04-

Total length frequency comparison of all largemouth
bass (38-430 mm) collected with electrofishing
between Rifle and Beavertail Mountain in

Debeque Canyon (RM 240.4~195.7) in the Upper
Colorado River, late August 2004, mid-July 2005,

and mid-July and mid-September 2006 ................--05.

LIST OF APPENDIX TABLES AND FIGURES

Appendix

A. Table A.1. Numbers of centrarchid fishes collected during

pass (P) 1, 2, 3, and 4 of the smallmouth bass removal
project from main channel habitats on the Colorado and
Lower Gunnison rivers in western Colorado and eastern

Utah, July and August 2004.00... 2.2... 2 eee eee eee eee

. Table A.2. Numbers of centrarchid fishes collected during

pass (P) 1, 2, 3, and 4 of the smallmouth bass removal
project from main channel habitats on the Colorado and
Lower Gunnison rivers in western Colorado and eastern

Utah, July and August 2005 ........ 0... cee cece eee eee eee

. Table A.3. Numbers of centrarchid fishes collected during

removal passes (P) 1, 2, 3, and 4 of the smallmouth bass
removal project from main channel habitats on the
Colorado and Lower Gunnison rivers in western Colorado

and eastern Utah, July, August, and September 2006 ...........

viii

B
is
cD

38

39

&
5
Io


30
Stateline Gauge

25
+— 2003
20
15

10

CFS (thousands)

2004
004

3 a
0 2002.

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Month

35
Stateline Gauge

30

<— 2005

CFS (thousands)

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Month

Figure D.6. Mean daily discharge for the stateline USGS gauge on the Upper Colorado
River (RM 133.8) for 2002-2004 (lower water years)(upper) and 2005-2006

(higher water years)(lower).

D-6


Table A.2. Numbers of centrarchid fishes collected during pass (P) 1, 2, 3, and 4 of the
smallmouth bass removal project from main channel habitats on the Colorado and
Lower Gunnison rivers in western Colorado and eastern Utah, July and August 2005.
Note: n/s=not sampled; two electrofishing craft were used for passes 1, 2, and 3; one
electrofishing craft was used for pass 4. Note: 2004 species totals are provided for
annual comparisons.

No. of Centrarchids
Black Crappie/

River Smallmouth Largemouth Green Sunfish/
(River Miles) Bass Bass Bluegill
River Segment P-l P2 P3 P4 Pl P2 P3 P4 Pl P2 PB

Colorado River
(RM 187.7-127.6)

Price-Stubb> GVICDam 20 60.11 ms 10 1 4 ns 48 10 27 ws
GVIC Dam*>ComLake 60 46 64 38 4 12 52 18 39 50 105 74

Corn Lake +Colo/Gunn 89 74 70 46 33 35 54 6 57 58 60 33
River Confluence

Colo/Gunn R. Confl. > 183 158 53 75 132 25 .23 24 154 50 38 77
Fruita State Park

Fruita State Park > 6 2 41 4 56 39 19 1 62 44 201 8
Loma Boat Landing

Loma Boat Landing > 79 #19 27 n/s 5 2 6 ws 22 5 18 ns
Salt Creek Wash

Salt Creek Wash 17 9 13 ns 2 0 5 ws 9 3° 9 ols
Utah/Colo Stateline
Utah/Colo Stateline » 6 1 2 os 565 2 os 2 2 2 ns
Westwater, Utah
BLM Ranger Station
Lower Gunnison River
(RM 3.0-0.7)
Redlands Div. Dam > 15 42 32 4 0 0 3 6 4 73 17 47
Colo/Gunn R.
Confluence
2005 Pass Totals 475 411 313 167 247 119 168 55 397 295 477 239
2005 Species Totals 1,366 589 1,408
2004 Species Totals 1,165 277 761



Table D.2. Discharge characteristics (instantaneous peak discharge, lowest and highest mean
daily flow, and 90% exceedence) and degree days (214 ° C) for five calendar years
(2002-2006) at the stateline USGS gauge (RM 133.8) on the Upper Colorado River.
N/A=data not available; P=preliminary.

Stateline 2002 2003 2004 2005 2006
Lowest Daily 1,280 1,350 1,370 2,500 2,650
Mean (cfs)

Highest Daily 4,470 24,500 9,230 30,300 20,900
Mean (cfs)
Instantaneous Peak 5,520 26,100 9,450 31,000 21,700
Discharge (cfs) &
Date 9/12 6/3 5/12 5/25 5/24
90% Exceedence 1,570 1,840 2,110 2,990" N/A
(cfs)
Total Degree Days 1,023.4 898.7 870.2 692.0 749.4
214°C
Total Degree Days 923.4 868.8 803.4 690.2 733.9
214°
(6/1-10/31)
No. of Days Water 169 158 169 123 132
Temp Equalled or
Exceeded 14°C
Max Mean Daily 25.6 26.2 25.8 24.7 25.1
Water Temp (C)

1200

Stateline
1000

800

600

400

Degree Days (> 13.9 C)

200

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Month

Figure D.2. Cumulative degree days (214 ° C) for the Upper Colorado River at the
stateline USGS gauge for 2002-2006.

D-2


Table B.5. Catch effort (fish/hr) for five centrarchid fishes (young-of-the-year) collected during
: pass (P) 1, 2, 3, and 4 of the smallmouth bass removal project from main channel
habitats on the Colorado and Lower Gunnison rivers in western Colorado and
eastern Utah, July and August 2005. Note: n/s=not sampled; two electrofishing
craft were used for passes 1, 2, and 3; one electrofishing craft was used for pass 4.
Note: 2004 catch/effort by species is provided for annual comparisons.

Catch/Effort (fish/hr}

Black Crappie/
River Smallmouth Largemouth Green Sunfish/
(River Miles) Bass Bass Bluegill
River Segment Pl P-2 P33 P-4 P-l P2 P3 P4 Pl P2 P33 Pa

Colorado River
(RM 187.7-127.6)

Price-Stubb > GVIC Dam 6.99 24.39 3.94 ns 3.50 0.41 143 m/s 16.78 4.07 9.66 nis
GVIC Dam> Com Lake 9.49 8.47 9.05 8.69 0.63 2.21 7.35 4.12 6.17 9.20 14.84 16.93

Corn Lake »Colo/Gunn 12.63 12.67 16.81 13.71 4.68 5.99 12.97 1.79 8.09 9.93 14.41 9.84
River Confluence

Colo/Gunn R. Confl.> 11.20 14.73 4.68 11.52 8.03 2.33 2.03 3.69 9.37 4.46 3.36 11.83
Fruita State Park

Fruita State Park » 1.44 0.64 882 1.90 13.48 12.45 4.09 0.48 14.93 14.04 43.25 3.80
Loma Boat Landing

Loma Boat Landing > 11.58 2.95 4.70 ws 0.73 0.31 1.04 m/s 3.22 0.78 3.13 ws
Salt Creek Wash

Salt Creek Wash > 212 1.18 1.57 ws 0.25 0.00 0.60 ms 1.12 039 1.09 ws
Utah/Colo Stateline

Utah/Colo Stateline > 1.87 0.37 0.68 o/s 1.56 1.86 0.68 n/s 0.62 0.74 0.68 m/s
Westwater, Utah
BLM Ranger Station

Lower Gunnison River

(RM 3.0-0.7)

Redlands Div. Dam > 4.70 11.05 10.73 1.96 0.00 0.00 1.01 2.94 1.25 19.20 5.70 23.01
Colo/Gunn R.
Confluence

Mean of 2005 Passes 8.18 8.53 6.26 9.09 4.26 247 3.36 2.99 684 6.12 9.55 13.00
Mean of 2005 Species 7.83 3.37 8.07

Mean of 2004 Species 6.91 1.64 4.51

B-S


(Bestgen et al. 2006(a)). In both river systems, drought conditions provided habitat alterations
that were positive for and favored smallmouth bass. Conversely, both Anderson (2004) and
Bestgen et al. (2007) hypothesized that higher and cooler flows or releases of cold water from
upstream reservoirs could impact survival and recruitment of early-life stages of smallmouth bass
by reducing the suitability of the Yampa River for this species and may serve as a riverwide
mechanism to reduce their abundance.

However, Anderson (2004) commented that he was uncertain if a return to more normal
hydrologic conditions in the Yampa River would restore or increase native fish populations to
their historic levels in the presence of smallmouth bass that had become so well established.

The literature supports the notion that cooler, higher flows, flow fluctuations, or turbidity
events may limit growth and reproductive success for smallmouth bass (Winemiller and Taylor
1982; Lucas and Orth 1995; Peterson and Kwak 1999) and possibly recruitment. In many natural
populations, growth of both young and adult smallmouth bass is influenced by temperature
(Langlois 1936; Brown 1960; Coble 1967; MacLeod 1967; Forney 1972). In many northern
smallmouth bass populations, cohort size upon recruitment to the adult stock is strongly
correlated with average water temperatures during the first growing season (Christie and Regier
1973). Most organisms have a sensitive life stage which make them vulnerable to intrinsic and
extrinsic factors that affect survival and recruitment. Identifying an “Achilles Heel” would be
critical if managers are to be successful in effectively and economically controlling a problematic
nuisance fish species. Two aspects of smallmouth bass early life history have been identified as
potential “Achilles Heels” and both can impact the survival of young size classes of smallmouth
bass. First, disturbing nesting adults, and secondly, displacing fry. Both stream discharge and
water temperature manipulations can disrupt spawning and nesting thus reducing survival. High
stream discharge with concomitant lower warmer water temperatures can displace young-of the-
year fish from sheltered habitats and further reduce survival. Higher stream discharges and
multiple peaks associated with spring and early-summer runoff usually delay water temperatures
from warming resulting in fish spawning and larvae hatching later, a shorter growing season,
and, ultimately, reduced growth for smallmouth bass. It is believed, at least in the Upper
Colorado River, smallmouth bass larger than 75 mm at the end of the growing season tend to
have much better overwinter survival than smaller fish.

43


n=64 largemouth bass

Largemouth Bass Electrofishing Captures-August 2004
Colorado River (RM 240.4-195.7)

s

3

—

R
enenene
gaan

yst[ Jo 1aquinyy

Total Length (mm)
Largemouth Bass Electrofishing Captures-July 2005

4
i

3£u

fee

By

a

a} Ee

y| eEE

t

o| =

BI Bee ree
3]

es

g

5

2

i

o

al

iM

8

9

ty)

wn

g

s
ewoneonm
aeana

ys Jo saquinyy

Total Length (mm)
Largemouth Bass Electrofishing Captures-July & Sept. 2006

211 largemouth bass

mean=106 mm
range: 43-430 mm

ey

Ss:

Tt

1S

=

=

Colorado River (RM 240.4-195.7)

a

om.

ae

ae

oe

ate

Total Length (mm)

Total length frequency comparison of all largemouth bass (38-430 mm)

collected with electrofishing between Rifle and Beavertail Mountain in

Ysty Jo 19quinyy

Figure 11.

Debeque Canyon (RM 240.4-195.7) in the Upper Colorado River, late

August 2004, mid-July 2005, and mid-July and mid-September 2006.

39


INTRODUCTION
Background

Significant anthropogenic changes to the physical riverine habitat have undoubtedly
played an important role in the decline and endangered status of Colorado pikeminnow, '
humpback chub, bonytail, and razorback sucker, but changes in the biological environment may
also have been equally significant. Physical changes in the riverine habitat have been
accompanied by the introduction, establishment, and proliferation of nonnative fishes, and.
concomitant declines in native fishes in the Upper Colorado River basin. The role of nonnative
fishes is often identified, in association with habitat changes, as a major obstacle to conservation
of native fish communities.

At least 67 nonnative fishes have been introduced actively or passively into the Colorado
River system during the last 100 years (Minckley 1982; Tyus et al. 1982; Carlson and Muth
1989; Minckley and Deacon 1991; Maddux et al. 1993). By 1980, more than 50 nonnative fishes
had been actively introduced into rivers and reservoirs of the Colorado River basin (Minckley
1982; Tyus et al. 1982; Carlson and Muth 1989). Many of the wild populations of the ‘big river’
native fishes now occupy less of their historic habitat. For example, the endangered Colorado
pikeminnow are presently found only in the upper basin in about 25% of historic range basin-
wide (Valdez and Muth 2005). The humpback chub occupies about 68% of its historic habitat in
the upper basin, the razorback sucker now exists naturally in only a few locations, and bonytail is
virtually extinct (Valdez and Muth 2005). Other more abundant, non-endangered native species
also occupy less of their historic habitat in the upper Colorado River basin (flannelmouth sucker:
50%; bluehead sucker: 45%; roundtail chub: 55%)(Bezzerides and Bestgen 2002). While native
fishes have declined in their historic habitat, introduced fishes have become more widespread
and abundant. Former studies have also documented a decline in the abundance of native fish

species as nonnative species increased in abundance (Joseph et al. 1977; Behnke 1980;

Osmundson and Kaeding 1989; Quarterone 1993).

| Scientific and common names with status (native vs. nonnative) of all fishes mentioned in this report are given in

Appendix E; Table E.1. Only common names for these fishes are used in the text.


Table 6. Smallmouth bass population projections for 2004 and 2005 extrapolated from the 2006
catch/effort and population estimate. The river segments included the 15- and 18-mile
reaches of the Upper Colorado River (GVIC Dam to the Loma boat landing) and the 2.3
miles of the Lower Gunnison River (Redlands Dam to the Colorado/Gunnison River
confluence). Note: the number of river miles is 35.3.

Abundance Estimators

Year No. of Smth Bass ‘Smth Bass > 100 mm’

2 100 mm Catch/Effort Catch/Effort Population Estimate

Removed * Effort (hrs) —_(fish/hr) Multiplier or Projection

from 2006" w/95% CI. Fish/Mile

2006 443 132.968 3.33 aii 1,097-3,197— 5,297° 31.1— 90.6-150.1
2005 974 114.655 8.50 2.55X 2,797-8,152-13,507% 79.2-230.9-382.6
2004 959 113.973 8.41 2.53X 2,775-8,088-13,401° 78.6-229.1-379.6

® Four removal passes used to compute catch/effort.
> Multiplier used to project population estimate.

© One mark and release pass plus one removal pass used to compute population estimate for 2006.

4 Population projection.

2006 (Figure 9). This analyses was performed to determine if there had been any change
(increase or decrease) in the length structure of the smallmouth bass captured over the four
passes among 2004, 2005, and 2006. During 2006, overall mean total length increased in four
river segments: Westwater, Utah, to the Loma boat landing, Loma boat landing to the
Colorado/Gunnison River confluence, Lower Gunnison River, and Beavertail Mountain to Rifle
(Figure 9). In three of these four river segments there was a statistically significant increase
(«=.05) in the mean total length of smallmouth bass captured between 2006 and 2005. In only
one segment did the overall mean total length decline: Colorado/Gunnison River confluence to
Price-Stubb Dam; but the size decline was not statistically significant («=.05)(Figure 9). This

30


300

250

200

150

Total Length (mm)

100

50

Figure 9.

Smallmouth Bass Length Comparison by River Reach

Colorado & Lower Gunnison Rivers
2004 vs. 2005 vs. 2006

i ‘04
06 s 06
06
04 ? "04 i
} 106 t |
‘04 ; "05
| tt ost "05
‘05
05
number of fish:
108 34 491 227 453 467 114 23 21. «+79
173 406 514 93 230
Mean Total Length with 95% Confidence Limits
All Passes Combined Within Each River Reach
Westwater Ranger Loma Boat Colo/Gunn Lower Rifle
Station-Loma Boat Landing- River Gunnison Bridge-
Landing Colo/Gunn _Confluence- River Beavertail
River Price Stubb Mountain
Confluence Dam
River Reach

Comparison between the mean total length and 95% confidence interval for
smallmouth bass collected with electrofishing from five major river
segments on the Colorado and Gunnison rivers during the summer of 2004,
2005, and 2006. The mean is the middle horizontal line; the 95%

confidence intervals are represented by the error bars (7 1).

34


Table A.1. Numbers of centrarchid fishes collected during pass (P) 1, 2, 3, and 4 of the
smallmouth bass removal project from main channel habitats on the Colorado and
Lower Gunnison rivers in western Colorado and eastern Utah, July and August 2004.
Note: n/s=not sampled; two electrofishing craft were used for passes 1, 2, and 3; one
electrofishing craft was used for pass 4.

No. of Centrarchids

Black Crappie/
River Smallmouth Largemouth Green Sunfish/
(River Miles) Bass Bass Bluegill
River Segment Pl P-2 P-3 P4 Pl P2 P3 P4 Pl P2 P3 Po

Colorado River
* (RM 187.7-127.6)

Price-Stubb > GVICDam 9 16 5 ws 0
GVIC Dam>ComLake 33 26 69 24 0

Corn Lake »Colo/Gunn 64 52 100 54 3
River Confluence

Colo/Gunn R. Confl. > 45 82 206 91 15 18 65 35 21 46 152 38
Fruita State Park

Fruita State Park > 10 19 32 6 5 2 6 12 30 7 52 28
Loma Boat Landing

Loma Boat Landing > 23 13 «30 ws 5 0 19 ns 10
Salt Creek Wash

Salt Creek Wash > 6 19 14 ns 0 0 3. n/s 0 5 3 ws
Utah/Colo Stateline

Utah/Colo Stateline > 1 1 1 o/s 0 0 0 ns 1 0 0 ns
Westwater, Utah
BLM Ranger Station

o
°

n/s 1 #18 9 nis
13 57 13. 47) «23
35 (16 16 4 101 31

wo
an
)

w
a

ws

Lower Gunnison River
(RM 3.0-0.7)

Redlands Div. Dam > . 28 #28 #47 «411 0 0 1 4 6 7 5 1
Colo/Gunn R.
Confluence

2004 Pass Totals 219 256 504 186 28 «23 146 «#80 141 105 384 131
2004 Species Totals 1,165 277 761



EXECUTIVE SUMMARY

The purpose of this study was to remove as many smallmouth bass of all sizes in main
channel riverine habitats in a 105-mile reach of the Upper Colorado River between Rifle and
Beavertail Mountain and between Price-Stubb Dam and Westwater boat landing in eastern Utah
and a 2.3- mile reach of the Lower Gunnison River. The goal was to reduce the abundance of
smallmouth bass as quickly as possible in these river reaches which would ultimately benefit
native fishes, and possibly contribute to their recovery. Specific objectives were to:

1. remove all smallmouth bass collected with boat and raft-based electrofishing, and
2. obtain an abundance estimate for smallmouth bass (> 100 mm) during 2006 by mark and
recapture methods for the Upper Colorado River between Price Stubb Dam and Fruita
State Park and 2.3 miles of the Lower Gunnison River between Redlands Diversion Dam
and the Colorado/Gunnison River confluence.
The two objectives were achieved during the 3-year study which was initiated in 2004.
Additionally, while smallmouth bass were the target fish species of concern, four other
centrarchid fishes were also collected and removed from main channel habitats during this study
to fulfill objectives associated with other fish research projects in Colorado.

Smallmouth bass abundance was greatest during the summer of 2005 and lowest during
2006. Total number of fish collected with boat and raft-based electrofishing by species during
the 2006 smallmouth bass removal from Price Stubb Dam to the Westwater, Utah, Ranger
Station and the Lower Gunnison River was, smallmouth bass: 751; largemouth bass: 1,094; black
crappie: 70; green sunfish: 1,395; bluegill: 307. Numbers of smallmouth bass collected in 2006
declined by 45% from 2005 and 36% from 2004 in the Grand Valley river reaches and declined
66% from Rifle to Beavertail Mountain from 2005 to 2006. The four highest concentration river
sub-reaches for smallmouth bass after three years in descending order in the Upper Colorado and
Lower Gunnison rivers were, a) Corn Lake to the Colorado/Gunnison River confluence, b)
Colorado/Gunnison River confluence to Fruita State Park, c) Grand Valley Irrigation Company
Dam to Corn Lake, and d) Redlands Dam to the Colorado/Gunnison River confluence in the
Lower Gunnison River.

xvi


7

0-0.

0) & Gunnison River (RM 3.

hh Bass Electrofishing Captures-—July & August 2004

n=279 largemouth bass

mean=106 mm
range: 40-404 mm

2004

Colorado River (RM 187.6-132.

Largemout!

150

2 o
S 7
=

Ysa Jo 1aqUNN

Total Length (mm)
Largemouth Bass Electrofishing Captures-July & August 2005

Colorado River (RM _187.6-132.

.0) & Gunnison River (RM 3.0-0.7)

589 largemouth bass

mean=93 mm

range: 29-544 mm

2005

es &
sta Jo 1aquinn,

Total Length (mm)

August, & Sept. 2006
ison River (RM 3.0-0.7)

July,

Largemouth Bass Electrofishing Captures:

Colorado River (RM 187.6-132.0) & Gunni

170 largemouth bass

4,

mean=106 mm

range: 41-420 mm

n

2
nm

150
100

Ysta Jo z9qunN,

Total Length (mm)

Total length frequency for all largemouth bass (29-544 mm) collected

during the summer of

Figure 10.

River

2004, 2005, and 2006, with electrofishing in the

Upper Colorado River (RM 187.8-127.6) and the Lower Gunnison

(RM 3.0-0.7).

38


LIST OF TABLES
Table

1. Designated river segments and sub-reaches for the
centrarchid removal project in the Upper Colorado
River from Rifle to Beavertail Mountain, Price-Stubb
Diversion Dam to Westwater, Utah, and the Lower
Gunnison River from the Redlands Diversion Dam

to the Colorado/Gunnison River confluence, 2004-2006 .......

2. Total numbers of centrarchid fishes collected with raft and
aluminum boat electrofishing during removal passes
1, 2, 3, and 4 of the smallmouth bass removal project
from main channel habitats in the Upper Colorado
River and Lower Gunnison River in western Colorado
and eastern Utah, July, August, and September 2004,

2005, and 2006 ........ 2... cece ccc eee eee eee

3. Concentration areas for smallmouth bass in the Upper
Colorado and Lower Gunnison rivers during the summer

of 2004, 2005, and 2006 using catch effort indices ............

4, Number and size of smallmouth bass and other
centrarchids captured during the marking pass during
July 2006 in main channel habitats on the Colorado

and Lower Gunnison rivers in western Colorado..............

5. Population point estimates with 95% confidence intervals
(C.L) for smallmouth bass for the 15- and 18-mile reaches
(RM 185.3 to 152.6) of the Upper Colorado River
and 2,3 miles of the Lower Gunnison River (Redlands
Diversion Dam to the Colorado/Gunnison River
confluence) for the summer of 2006, and the projected
percentage of smallmouth bass removed annually by

electrofishing relative to the 95% population interval ..........


Burdick, B.D. 2001. Five-year evaluation of fish passage at the Redlands Diversion Dam on the
Gunnison River near Grand Junction, Colorado: 1996-2000. Recovery Program Project
Number CAP-4b. Final Report prepared for the Recovery Implementation Program for
Endangered Fishes in the Upper Colorado River Basin. U. S. Fish and Wildlife Service,
Colorado River Fishery Project, Grand Junction, CO. 57 pp. + appendices.

Burdick, B. D. 2003(a). Development of a channel catfish removal and control program in the
Upper Colorado River of western Colorado. Annual Project Report to the Upper Colorado
River Endangered Fish Recovery Program. Project Number 126. U. S. Fish and Wildlife
Service, Grand Junction, Colorado.

Burdick, B. D. 2003(b). Annual operation and maintenance of the fish passage structure at the
Redlands Diversion Dam on the Gunnison River. Annual Project Report to the Upper
Colorado River Endangered Fish Recovery Program. Project Number C-4b. U. S. Fish and
Wildlife Service, Grand Junction, Colorado.

Burdick, B. D. 2003(c). Monitoring and evaluating various sizes of domestic-reared razorback
sucker stocked in the Upper Colorado and Gunnison rivers: 1995-2001. Final report prepared
for the Recovery Implementation Program for Endangered Fishes in the Upper Colorado
River Basin. Recovery Program Project Number 50. U. S. Fish and Wildlife Service,
Colorado River Fishery Project, Grand Junction, CO. 54 pp + appendices.

Burdick, B. D. 2004(a). Evaluation of the effectiveness of the fish passage structure at the
Redlands Dam. Annual report prepared for the Recovery Implementation Program for the
Endangered Fishes of the Upper Colorado River Basin. Recovery Program Project Number
C-4b. U.S. Fish and Wildlife Service, Colorado River Fishery Project, Grand Junction,
Colorado.

Burdick, B. D. 2005(a). Annual operation and maintenance of the fish passage structures at the
Redlands Diversion Dam on the Gunnison River and the Government Highline Diversion
Dam on the Upper Colorado River. Annual report prepared for the Recovery Implementation
Program for the Endangered Fishes of the Upper Colorado River Basin. Recovery Program
Project Number C-4b. U. S. Fish and Wildlife Service, Colorado River Fishery Project,

Grand Junction, Colorado.

55


from 25 July to 19 September 2006. Two electrofishing craft were used in every river segment
during passes 1, 2, and 3. One electrofishing craft was used in pass 4. The number of removal
passes for areas of low densities of smallmouth bass as determined from 2004 and 2005 capture
data was reduced during 2006. These river segments included the canyon-bound reaches of Ruby
and Horsethief canyons to Westwater, Utah (RM 152.6-127.6). The reduced effort in these
reaches was re-directed to increase the number of removal passes in river segments where
smallmouth bass had proliferated over the past two years. Therefore, only one pass was
performed from the Loma boat landing to Westwater, Utah, during 2006. Some river segments
were not electrofished during pass 4 (e. g., Loma boat landing to the Westwater ranger station
and Price-Stubb Dam to GVIC Dam). Captures of smallmouth bass marked during the earlier
marking pass were recorded for determining an abundance estimate.

For the Rifle to Beavertail segment the sampling protocol varied from that of downstream
reaches. This segment was further partitioned into four sub-reaches for sampling logistics (Table
1). During 2004 two electrofishing craft were used and only one pass was made in the 45-mile
segment. During 2005 and 2006, two passes were made. All sub-reaches were sampled during
the first pass with two electrofishing craft. During pass 2, only one electrofishing craft was used,
but not all sub-reaches were sampled. For pass 2, only the 10.4-mile section from Rifle to
Rulison was sampled during 2005 and only a portion (RM 240.4-235.5) of this sub-reach was
sampled during 2006. The reason for targeting the Rifle to Rulison sub-reach was that during
pass 1 in 2004 and 2005, the highest densities of smallmouth bass were recorded there.

For 2004, 2005, and 2006 the number of individuals was recorded for all centrarchid
fishes by species. All smallmouth bass and largemouth bass were measured (total length [TL] +
2mm). For all other centrarchids total length was recorded for those specimens that were _
greater than 100 mm. Capture date and corresponding location (within the nearest river mile) for
each centrarchid fish collected were recorded along with actual time electrofished (seconds;
converted to hrs fished).

All juvenile and adult endangered fish collected were checked for a PIT tag, weighed,
measured, tagged ifno tag was detected, and immediately returned to the river. Both 400 khz
and 134 khz PIT tags were checked for in endangered fish. The newer 134 khz tag was inserted.
in endangered fish if they had the older 400 khz tag or were untagged.

10


b) The level of electrofishing effort (e. g., the number of removal passes per year; the
annual periodicity or frequency removal passes need to be performed) necessary to affect
population self-sustainability which ultimately could provide a measurable, lasting
reduction in centrarchid population abundance.

LITERATURE CITED

Anderson, R. M. 1997. An evaluation of fish community structure and habitat potential for
Colorado squawfish and razorback sucker in the unoccupied reach (Palisade to Rifle) of the
Colorado River, 1993-1995. Final Report, Colorado Division of Wildlife, Ft. Collins.

Anderson, R. M. 2004. Riverine fish-flow investigations: Quantification of impacts of the 2002
drought on native fish population in the Yampa and Colorado rivers. Colorado Division of
Wildlife. Federal Aid Project F-288-R-7. Job Prog. Report. Fort Collins, CO. 96 pp.

Anderson, R. M. 2005. Riverine fish-flow investigations: Quantification of impacts of the 2002
drought on native fish population in the Yampa and Colorado rivers. Colorado Division of
Wildlife. Federal Aid Project F-288-R-8. Job Prog. Report. Fort Collins, CO. 105 pp.

Anderson, R. M. 2006. Riverine fish-flow investigations: Quantification of habitat availability
and instream flows on the Gunnison River and impacts of long term drought on native fish
populations in the Dolores River. Colorado Division of Wildlife. Federal Aid Project F-288-
R-9. Job Prog. Report. Fort Collins, CO. 85 pp.

Anderson, R. O., and S. J. Gutreuter. 1985. Length, weight, and associated structural indices.
Pages 283 — 300 in L. A. Nielsen and D. L. Johnson (editors). Fisheries Techniques.
American Fisheries Society, Bethesda, Maryland.

Behnke, R. J. 1980. The impacts of habitat alterations on the endangered and threatened fishes

of the Upper Colorado River Basin. Bulletin 503A. Cooperative Extension Service,
Colorado State University, Ft. Collins. 34 pp.

53


Upper Colorado River in relation to the type of water year is unknown at this time. Length
frequencies can provide some insight for annual comparisons of the magnitude of larval
smallmouth bass produced and growth progression of their first year of life. However, length
frequencies alone cannot pinpoint annual spawning time and hatching date(s) of larval fish.
Consequently, it cannot be determined if smallmouth bass spawned later in 2005 than 2004 or
2006. Additionally, it is acknowledged that length frequency cannot distinguish overlap in age
classes, only ageing fish can provide that information. In the case of the length frequency for
smallmouth bass collected from the Upper Colorado River, length frequency of early-life fish is
probably represented by young-of-the-year and late spawned or slower growing age-1 fish from
the previous year.

It was believed that time series of length frequencies partitioned by 10-day periods from
July 1 through September 20 for young-of-the-year and slowing growing age-1 smallmouth bass
collected in the summer of 2004, 2005, and 2006, would be useful in comparing growth and size
of these fish at the end of the growing season. Comparing the length frequency for the 11-day
period between August 21-31 during 2005, 67% of smallmouth bass were 2 75 mm whereas for
the same period in 2006, only 36% of the smallmouth bass were 2 75 mm (Appendix; Figures
C.2. and C.3.). In 2004, 100% of the smallmouth bass were > 75 mm by this same time period,
but this comprised only four fish (Appendix; Figure C.1.). Age-0 smallmouth bass produced in
2004, a low water year, appeared to have good overwinter survival and, therefore, recruited to the
next size classes as they were collected in the summer of 2005 (Figure 7). So, according to the
length frequency graph, it appears that about two-thirds of smallmouth bass produced during
2005 attained the 75 mm length target, the length CDOW fish researcher Pat Martinez believed
was necessary to survive overwinter. This still does not account for the almost complete loss of
smallmouth bass that did not recruit to the 100 to 180 size classes in 2006. If the 2005 cohort did
overwinter sticcessfully, it is possible some of the remaining cohort were displaced downstream
outside the reaches sampled by the 2006 spring runoff discharge or simply did not survive spring
runoff, thus the reason for their disappearance in the 2006 summer sampling. Sampling in the
spring for young fish immediately prior to runoff might clarify this. Since about 86% of the
smallmouth bass collected in 2006 attained a size of 75 mm or greater (Appendix; Figure C.3.)
by mid-September, it can be expected that the 2006 cohort should have overwintered. However,
the ultimate fate of the 2006 cohort and slower growing age-1 fish and whether they successfully
survived and recruited to the next size classes by the summer of 2007 would not be certain until
the 2007 field sampling was completed.

46


Smallmouth Bass

Upper Colorado River (Colorado)

Prior to 2003, in the Upper Colorado River between Price-Stubb Dam (river mile [RM]
188.3) and the head of Westwater Canyon, (RM 125), abundance and distribution information
was scarce for smallmouth bass. Until 2003, smallmouth bass were only reported as incidental,
rare captures in the Upper Colorado River from Price Stubb Dam (RM 188.3) to the
Colorado/Green River confluence. However, Burdick (2003(a)) documented the capture of 318
smallmouth bass in main channel riverine habitats in a 39-mile reach of the Upper Colorado
River from the Gunnison/Colorado River confluence to the Utah/Colorado stateline during a 4-
month sampling period between late-June and late-October 2003. Catch rates (fish/hr and
fish/mile) steadily increased throughout this 4-month period (1.31 to 4.04 fish/hr; 0.53 to 2.54
fish/mile). The source(s) of these smallmouth bass were unknown.

The rapid increase in the numbers of smallmouth bass in the Upper Colorado River
prompted biologists and managers to become concerned that smallmouth bass abundance could
increase quickly, and further impact recovery of native endangered fishes (Burdick 2003(a)).
Some speculate that the rapid proliferation of smallmouth bass in the Upper Colorado River was
the result of a combination of factors. There is speculation that while a small number of
smallmouth bass may have been present in the system, an influx of fish from an off-river source
created a critical mass of spawners that was followed by optimal spawning conditions (i. e., low-
flow years and warmer water temperatures) which were associated with drought years in the late-
1990s and early-2000s. The possibility of an influx of smallmouth bass from an accidental
release of water from Rifle Gap Reservoir, an off-main channel reservoir, could have provided
the critical mass of spawning adults that resulted in the large increase in numbers occurring
around 2001-2003. Unauthorized translocation and illicit stocking by non-state or non-federal
agencies cannot be ruled out as a contributing factor.

Price-Stubb Dam on the Upper Colorado River upstream from Palisade, Colorado,
presently acts as an effective upstream movement barrier for all fishes. Fish passage at Price-
Stubb Dam will be completed during the winter of 2008 and will undoubtedly allow further
upstream movement past this barrier. A fish passage constructed and completed in August 2004
at the Government Highline Diversion Dam (RM 193.7) 5.4 miles upstream will allow for


Colorado River (RM 187.7-127.6)
Lower Gunnison River (RM 3.0-0.7)
2004, 2005, 2006

12

all smth bass
(26-414 mm)

10,

Catch/Effort (fish/hr)
Nn

(219)

at 2006

4-
(258) (159)

2 |
0 i} i 1 1

1 2 3 4

Pass Number

Figure 2. Overall catch effort (fish/hr) by pass for smallmouth bass (26-414 mm)
collected from main channel habitats in the Upper Colorado River with
electrofishing from RM 187.7-127.6 (Price-Stubb Dam to the Westwater,
Utah, BLM ranger station) and in the Lower Gunnison River from RM
3.0-0.7 (Redlands Dam to the Colorado/Gunnison River confluence),
2004, 2005, and 2006. Note: The number of fish collected by pass is in
parentheses.

20


backwater. In 2004, no largemouth bass 2254 mm were caught in the Skipper’s Island
backwater.

Hydrology and Water Temperature

Hydrology

In the Upper Colorado River several years of high flow between 1995 and 1999 were
followed by five consecutive years of low flows between 2000 and 2004, 2002 being the lowest
(Appendix; Figure D.3.). The annual mean stream discharge in 2005 was the highest since 1999
and mean annual stream discharge in 2006 was slightly less than 2005. The 2005 calendar year
was marked by two distinct discharge peaks, the first in mid-May (Cameo: 17,200 cfs on May
24; stateline: 31,000 cfs on May 25) and the second in mid-June (Cameo: 13,200 cfs on June 24;
stateline: 17,700 cfs on June 24)(Appendix; Figures D.4. and D.6.). Two peaks also occurred
during 2006, but of less magnitude than those of 2005, the first occurring at almost the same
period as that in 2005. The second peak in 2006 occurred on June 6 (12,600 cfs) at Cameo
which was 18 days earlier than 2005; at stateline the second peak occurred on June 10 (14,900
cfs) which was 14 days earlier than 2005. The duration of both peaks in 2006 was shorter than
that observed in 2005. A single peak was observed at both Cameo (21,000 cfs on June 2) and
stateline (26,100 cfs on June 3) during 2003 (Appendix; Figures D.4. and D.5.). There was
virtually no peak observed in either 2002 or 2004. At the Palisade USGS gauge located at the
head end of the 15-mile reach, as expected, the same stream flow pattern mimicked that of the
upstream gauge at Cameo and downstream gauge at stateline (Appendix; Figure D.5.).

The seven water years (calendar) between 2000 and 2006 were ranked from highest to
lowest using annual mean stream discharge at the Utah—Colorado stateline gauge. This
descending order by calendar water year was: 2005, 2006, 2000, 2001, 2003, 2004, and 2002
(Appendix; Figure D.3.). Using the hydrologic categories (wet, average and moderately wet,
average and moderately dry, and dry) developed by McAda (2003) at stateline, 2002 was
considered a dry or drought year, and the remaining five years fell into the average and
moderately dry category (Appendix; Figure D.3.).

40


and .

2. obtain an abundance estimate for smallmouth bass (2 100 mm) during 2006 by mark
and recapture methods for the Upper Colorado River between Price Stubb Dam and
Fruita State Park and 2.3 miles of the Lower Gunnison River between Redlands
Diversion Dam and the Colorado/Gunnison River confluence.

Study Area

The study was conducted in both Mesa and Garfield counties in western Colorado and
Grand County in eastern Utah. The study area included 105 miles of the Upper Colorado River
from Rifle (RM 240.4) downstream to Beavertail boat landing (RM 195.7) and Price-Stubb Dam
(RM 187.6) to the Westwater, Utah, BLM ranger station (RM 127.6). On the Gunnison River,
2.3 miles were sampled between Redlands Diversion Dam (RM 3.0) and confluence with the
Colorado River (Figure 1). For logistical considerations, the Upper Colorado River portion was
divided into four different reaches or segments based on hydro-geomorphic features. These
included, 1) a 3-mile section between Price-Stubb and Grand Valley Irrigation dams and the 15-
mile section that extended from Palisade to the Gunnison/Colorado River confluence (RMs
185.5-171), 2) the 18-mile reach that extended from the confluence of the Gunnison and
Colorado rivers to thé Loma boat landing (RMs 171.0-152.6), 3) the 25-mile long reach in Ruby
and Horsethief canyons (RMs 152.6-127.6) which extended from the Loma boat landing to
Westwater, Utah, and 4) a 45-mile reach between the Rifle Bridge and Beavertail Mountain. The
Rifle to Beavertail reach was outside the original defined removal area. However, there were
unsubstantiated reports that anglers had encountered smallmouth bass in these upstream reaches,
and it was determined that “reconnaissance” investigations were warranted to confirm or refute
these claims.

The 15- and 18-mile reaches flow through a wide alluvial section of the lower Grand
Valley and the Ruby and Horsethief canyon sub-reach is considered a quasi-alluvial sub-reach.
The upper extent (~ 36 miles) of the Rifle to Beavertail reach flows through an alluvial valley;
the lower extent (~ 9 miles) flows through a canyon-bound area. The physical characteristics of
individual river reaches were previously described for the Upper Colorado River from Rifle to
‘Westwater by Valdez et al. (1982) and Pitlick and Cress (2000), and by Burdick (1995) for the
Lower Gunnison River. All of these river reaches are within critical and occupied habitat for
Colorado pikeminnow and razorback sucker.


Table B.3. Amount of effort (electrofishing hours) expended during four removal passes of the
smallmouth bass removal project sampling main channel habitats on the Colorado
and Lower Gunnison rivers in western Colorado and eastern Utah, July, August, and
September 2006. Note: n/s=not sampled; two electrofishing craft were used for
passes 1, 2, and 3; one electrofishing craft was used for pass 4.

Electrofishing Effort (hr’

River
(River Miles)

River Segment Pel P2 B3 P-4

Colorado River
(RM 187.7-127.6)

Price-Stubb>GVIC Dam 3.739 3.792 2.861 w/s

GVIC Dam > Corn Lake 9.439 8.021 8.540 4.106

Corn Lake »Colo/Gunn 6.455 7.178 7.574 4,289
River Confluence

Colo/Gunn R. Confl. > 14.242 13.633 13.088 7.104
Fruita State Park

Fruita State Park > 5.018 6.360 5.771 2.367
Loma Boat Landing

Loma Boat Landing > 7.557 n/s m/s n/s
Salt Creek Wash

Salt Creek Wash » 7.607 n/s n/s ws
Utah/Colo Stateline

Utah/Colo Stateline > 3.202 n/s n/s ws
Westwater, Utah
BLM Ranger Station

Lower Gunnison River
(RM 3.0-0.7)

Redlands Div. Dam > 2.573 2.108 2.574 1.328
Colo/Gunn R.
Confluence

2006 Pass Totals 60.012 41.092 40.408 20.394

2006 Total 161.906

2005 Total 174.560

2004 Total 168.665

B-3


Table 4. Number and size of smallmouth bass and other centrarchids captured during the
marking pass during July 2006 in main channel habitats on the Colorado and Lower

Gunnison rivers in western Colorado. Note: n/s = not sampled.

Marking Pass
Number of Fish
River Black Crappie/
(River Miles) Smth Total Lrgth Green Sunfish/
River Segment Bass Length (mm) Bass Bluegill
Colorado River
(RM 187,7-127.6)
Price-Stubb>GVIC Dam ns as ws
GVIC Dam > Com Lake 15 151-353 33 14
Corn Lake »Colo/Gunn Al 88-394 29 16
River Confluence
Colo/Gunn R. Confl. > 45 104-298 15 65
Fruita State Park
Fruita State Park > 25 66 -328 9 35
Loma Boat Landing
Loma Boat Landing > n/s ws m/s
Salt Creek Wash
Salt Creek Wash > n/s ms n/s
Utah/Colo Stateline
Utah/Colo Stateline > n/s n/s ws
Westwater, Utah
BLM Ranger Station
Lower Gunnison River
(RM 3.0-0.7)
Redlands Div. Dam > 5 168-314 0 29
Colo/Gunn R.
Confluence
Totals 131 86 159

27


Table A.6. | Summary statistics of centrarchids collected during reconnaissance sampling in main
channel habitats of the Upper Colorado River from Rifle, Colorado, to Beavertail
Mountain in Debeque Canyon, July 5-7; 10; 12; September 19, 2006.

Reach: Rifle Bridge-Rulison Bridge
River Mile: 240.4-230.0; River Mile Length: 10.4
Number of Electrofishing Crafts: 3
Effort (hr): 12.567

Smallmouth Largemouth Green Black
Bass Bass Sunfish Bluegill Crappie

No. No. No. No. lo.
of TotalLength(mm) of Total Length(mm) of —TotalLength(mm) of Total Length(mm) of Total Length (mm)
Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean

72 58 «384 195 115 33. 114 430 201 27:«158 9 3) 112: «176 «140 0 choose --

Reach: Rulison Bridge-Parachute Bridge
River Mile: 229.9-223.0; River Mile Length: 6
Number of Electrofishing Crafts: 2
Effort (hr): 5.563

Smallmouth Largemouth Green Black
Bass Bass Sunfish Bluegill Crappie
No, No. No, No.
of Total Length (mm) of Total Length (mm) of Total Length(mm) of Total Length (mm) of Total Length (mm)
Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean’ Fish Min Max Mean Fish Min Max Mean

ne aS od O =e wee

Reach: Parachute Bridge-Debeque I-70 Bridge
River Mile: 223.0-209.7; River Mile Length: 13.3
‘Number of Electrofishing Crafts: 2
Effort (hr): 8.100

Smallmouth Largemouth Green Black
Bass Bass Sunfish Bluegill Crappie
No. ‘No. No, lo. No.
of Total Length (mm) of Total Length (mm) of Total Length(mm) of Total Length (mm) of Total Length (mm)
Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean Fish Min, Max Mean

5 270 357 308 38 45 329 128 97 42 172 4 O -- se oo To -- == 170

Reach: Debeque |-70 Bridge-Beavertail Mountain (Debeque Canyon)
River Mile: 209.7~195.7; River Mile Length: 14.0
Number of Electrofishing Crafis: 2
Effort (hr): 11.282

Smallmouth Largemouth Green Black
Bass Bass Sunfish Bluegill Crappie

No. No. No. No. No.

of Total Length(mm) of Total Length(mm) of ~— ‘Total Length(mm) of | Total Length(mm) — of

Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean Fish Min Max Mean i

1 ttt 82 58 43 «(161 4 177, 41131 77 To -+ -- <100 0 -- - --

A-6


he reported that lipid content of hatchery-reared age-0 Colorado pikeminnow increased as total
length increased. Age-0 Colorado pikeminnow in all size classes and feeding regimes depleted
their lipid reserves over time, but only the starved small and medium size fish died. Large age-0
Colorado pikeminnow had higher initial lipid contents and, therefore, had sufficient energy
reserves to survive the winter, regardless of feeding regime. To survive through their first winter,
fish must either accumulate a certain critical amount of lipid prior to winter or feed during winter
to partially offset the drain on lipid reserves typical of this period.

Bestgen et al. (2006(b)) believed that even though relatively small and slow-growing
Colorado pikeminnow could survive to autumn, small bodied juveniles may have relatively low
overwinter survival. Haines et al. (1998) found that small (mode, 28 mm TL) wild Colorado
pikeminnow had only 6 % overwinter survival in the Green River, Utah, during a high-flow
winter period, whereas in a different year when Colorado pikeminnow were larger (> 38 mm)
overwinter survival was higher (56 to 65 %) despite winter flows being lower. Other researchers
have similarly found that mortality of age-0 fish during winter is attributed to exhaustion of
stored energy reserves (Oliver et al. 1979; Henderson et al. 1988). Year-class strength in
northern populations of smallmouth bass is strongly influenced by winter starvation of young-of-
the-year fish (Shuter et al. 1989). In laboratory experiments, at 7° Cand below, age-0
smallmouth bass ceased to feed (Shuter et al. 1980). In Lake Opeongo, Canada, the smallest
young-of-the-year fish began to die and thereafter, the mean size of dying fish increased steadily.
Length distributions from field sampling of this Canadian lake implied a relatively higher rate of
mortality among the smaller young-of-the year smallmouth bass during their first winter which
was consistent with laboratory findings (Shuter et al. 1980). Oliver et al. (1979) reported that
large age-0 smallmouth bass survive their first winter better than smaller ones. The probability
that an age-0 smallmouth bass will survive the winter starvation period is a function of both its
size at the start of the hibernation and the duration of the hibernation period (Shuter et al. 1980).

Age-0 smallmouth bass produced in 2005 had a shorter growing season because the total
number of degree days in 2004 (870.2) was greater than 2005 (692.0) at stateline. Possibly, a
significant number of these fish produced during 2005 did not attain the size necessary for
surviving overwinter during 2005/2006. The suspected reason for the reduced growing season
was that 2005 was a higher water year, the highest since 1999, marked by a dual peak during
spring runoff in which water temperatures warmed later in the summer than during the previous
five lower water years. Information on when smallmouth bass spawn and larvae hatch in the

45


Table A.7. | Number and catch effort (fish/mile) for smallmouth bass collected from main
channel habitats with electrofishing in the Upper Colorado River from RM
187.7-127.6 (Price-Stubb Dam to Westwater Ranger Station, Utah), and the
Lower Gunnison River from RM 3.0-0.7 (Redlands Diversion Dam to the
Colorado/Gunnison River confluence) during July, August, and September 2006.
Note: see Appendix; Tables B.4-B.6. for the total electrofishing effort (hrs)
sampled for each river segment; n/s=not sampled. Two electrofishing craft were
used for removal passes 1, 2, and 3; one electrofishing craft was used for removal
pass 4. Values for 2005 are italicized; values for 2004 and underlined for annual

comparisons.
Smallmouth Bass
No. of Fish Fish/Mile
Pl P2 P3 Po Pl P-2 P33 Pe
Colorado River
Price-Stubb Dam- 128 105 156 *78 3.8 3.1 47 5.5
Colo/Gunn Confl. 169 = 180 145 "84 5.1 5.4 4.3 59
Segment Length: 16.7 miles 106 94 174 278 32 2.8 55 5.5
Miles Sampled: 33.4 .
Colo/Gunn Confl- 90 4S 64°28 2.5 1.2 1.7 L5
Loma Boat Landing 189 160 94°79 51 43 12 43
Segment Length: 18.4miles 55 101 238 °97 15 28 65 53
Miles Sampled: 36.8
Loma Boat Landing- 23 n/s ws n/s 14 ows os ns
Salt Creek Wash 79 19 27 ls 47 11 16 ws
Segment Length: 8.4 miles 23, 1B 300s ns 14 08 18 ws
Miles Sampled: 16.8
Salt Creek Wash- 8 n/s ws  n/s 0.3 ns n/s_ o/s
Utah/Colo Stateline 17 9 13 nhs 0.7 04 O05 nls
Segment Length: 12.3 miles 6 19 144 ps 02 O08 06 ms
Miles Sampled: 24.6
Utah/Colo Stateline- 3 n/s ws v/s 03 os ns ns
Westwater Ranger 6 1 2 nls 0.7 0.1 0.2 . nls
Station, Utah 1 1 1 ns Ol O01 O81 ns
Segment Length: 4.3 miles
Miles Sampled: 8.6
Lower Gunnison River

Redlands Div. Dam- 6 9 5 °3 13 2.0 11 0.7
Colo/Gunn Confl. 15 42 32 °4 330° 91 6.7 17
Segment Length: 2.3 miles 28 28 47 S11 61 61 102 48

Miles Sampled: 4.6 *

*Price-Stubb Dam to GVIC Diversion Dam river segment was not sampled during pass 4. Only
14.3 miles were sampled:185.3—171.0.

° One electrofishing craft was used; miles sampled=18.4 for Pass 4.

© One electrofishing craft was used; miles sampled=2.3 for Pass 4.

A-7


major river segments for each of the three years by pass number is provided in Table 2. This
included all smallmouth bass sizes (26-437 mm total length) collected within main channel
habitats. Between Price-Stubb Dam and Westwater, Utah, the number of smallmouth bass for
2004, 2005, and 2006, was 1,165, 1,366, and 751 fish, respectively. The actual total number of
smallmouth bass removed was highest during 2005 from all reaches combined. The total number
of smallmouth bass collected during 2006 declined 45% from 2005 and 36% from 2004.

Between Rifle and Beavertail Mountain, the actual total number of smallmouth bass
collected during 2004, 2005, and 2006 was 21, 230, and 79 fish, respectively. The highest total
number of smallmouth bass was removed during 2005 for all reaches combined. The actual total
number of smallmouth bass removed declined 66% from 2005 to 2006. The total number of
smallmouth bass (includes young-of-the-year, juvenile, and adult) collected for each pass for
each of the eight sub-reaches in the Upper Colorado River between Price-Stubb Dam and
Westwater, Utah, plus the Lower Gunnison River is provided in Appendix; Tables A.1—-A.3.
The actual total number of smallmouth bass collected for each of the four sub-reaches between
Rifle and Beavertail is provided in Appendix; Tables A.4.-A.6.

The actual total number of smallmouth bass (young-of-the-year, juvenile, and adult; 26 —
414 mm total length) collected and removed/river mile for each of the three years for each of the
four passes for five river segments on the Upper Colorado River and one segment on the Lower
Gunnison River is provided in Appendix; Table A.7. These fish/mile estimates are not to be
confused with the fish/mile estimates projected from population estimates (see Table 6).

Largemouth Bass. The actual total number of largemouth bass collected within each of
the four major river segments for each of the three years by pass number is provided in Table 2.
This included all largemouth bass sizes (young-of-the-year, juvenile, and adult; 29-544 mm total
length) collected within main channel habitats. Between Price-Stubb Dam and Westwater, Utah,
the actual total number of largemouth bass removed for 2004, 2005, and 2006 was 277, 589, and
1,094 fish, respectively. The total number of largemouth bass removed was greatest during 2006.
Actual total number of largemouth bass that were removed steadily increased throughout the 3-
year removal period. The total number of all largemouth bass removed increased 113% from
2004 to 2005 and 86% from 2005 to 2006. Between Rifle and Beavertail Mountain, the total
number of largemouth bass collected and removed in 2004, 2005, and 2006 was 65, 38, and 211
fish, respectively. Largemouth bass (all length sizes [38-446 mm total length]) increased

14


LIST OF APPENDIX TABLES AND FIGURES

Appendix

B.

Table B.2. Amount of effort (electrofishing hours)
expended during four passes of the smallmouth
bass removal project sampling main channel
habitats on the Colorado and Lower Gunnison
rivers in western Colorado and eastern Utah,

July and August 2005 00... 0... eee eeee eee eee eee

. Table B.3. Amount of effort (electrofishing hours)

expended during four removal passes of the smallmouth
bass removal project sampling main channel habitats

on the Colorado and Lower Gunnison rivers in western
Colorado and eastern Utah, July, August, and September

2006 rece een n eet ete e een eee

. Table B.4. Catch effort (fish/hour) of centrarchid fishes

collected during pass (P) 1, 2, 3, and 4 of the smallmouth
bass removal project from main channel habitats on the
Colorado and Lower Gunnison rivers in western Colorado

and eastern Utah, July and August 2004 ...................000.

. Table B.5. Catch effort (fish/hour) of centrarchid fishes

collected during pass (P) 1, 2, 3, and 4 of the smallmouth
bass removal project from main channel habitats on the
Colorado and Lower Gunnison rivers in western

Colorado and eastern Utah, July and August 2005 ...............

Table B.6. Catch effort (fish/hour) of centrarchid fishes
collected during removal passes (P) 1, 2, 3, and 4 of the
smallmouth bass removal project from main channel
habitats on the Colorado and Lower Gunnison rivers
in western Colorado and eastern Utah, July, August,

September 2006 0.00.0... eee eee eee eee neers


A population estimate serves as a baseline for any future abundance estimation
comparisons. Periodic population estimates are necessary to assess the size of nonnative fish
populations and the effectiveness of removal. One other useful tool from this exercise is that one
can calculate the percentage of fish removed annually or exploitation rate (i. ¢., how efficient are
we at mechanical removal) from the total population estimated using the actual number of fish
removed, the point estimate, and 95% C.I.s. For example, 181 smallmouth bass 2100 mm were
actually removed during pass 1. We then removed as few as 3.4% (181/5,297: upper limit of the
95% C.D or as many as 16.5% (181/1,097: lower limit of the 95% C.L) of the estimated
population. The percentage removed using the point estimate would simply be 5.7% (1 81/3,197)
(Table 5). The 2006 population estimate was used to project population abundance for
smallmouth bass (> 100 mm) in 2004 and 2005 in the same river sub-reaches (Table 6). Overall
catch effort for 2006 was 3.33. The 2005 catch/effort was 2.55 times greater than 2006; the 2004
catch/effort was 2.53 times greater than 2006 (Figure 5). The abundance estimate with 95% C.I.
projected for 2004 and 2005 was 8,088 + 5,313 and 8,152 + 5,355 individuals 2100 mm,
respectively (Figure 6). The number of fish/mile was estimated at 78.6 to 379.6 and 79.2 to
382.6 for 2004 and 2005, respectively (Table 6).

Size Distribution — Length Frequency
Smallmouth Bass

Changes in size (i. e., length) have been used to detect changes in age composition of a
fish population over time. Length-frequency distributions provide an important description of
population structure (Anderson and Gutreuter 1985). In this instance, we are looking for an
index that could reliably be used to detect changes in the overall size [age] structure of
smallmouth bass in designated river segments over time. Size structure changes over time then
could be used to evaluate whether mechanical removal is reducing the numbers of a particular
size [length] group, and therefore, if this technique could be recommended as an effective
management tool for removal or to detect failure of year classes.

Length-frequency distribution of all sizes of smallmouth bass collected with
electrofishing during 2004, 2005, and 2006 between Price-Stubb Dam and Westwater, Utah, and
the Lower Gunnison River was plotted (Figure 7) and for the 45-mile reach between Rifle and
Beavertail Mountain (Figure 8). The mean total length and 95% C.I. were calculated for
smallmouth bass for all passes combined for five different river segments for 2004, 2005, and

29


LIST OF APPENDIX TABLES AND FIGURES

Appendix

A. Table A.4. Summary statistics of centrarchids and percids

collected during reconnaissance sampling in main
channel habitats of the Upper Colorado River from
Rifle, Colorado, to Beavertail Mountain in Debeque

Canyon, August 23-26, 2004.0... 0... eee eee eee eee

. Table A.5.Summary statistics of centrarchids collected
during reconnaissance sampling in main channel habitats
of the Upper Colorado River from Rifle, Colorado, to
Beavertail Mountain in Debeque Canyon, July12-15;

21,2005 6... cc cece eee cence cence eee

. Table A.6. Summary statistics of centrarchids collected
during reconnaissance sampling in main channel habitats
of the Upper Colorado River from Rifle, Colorado, to
Beavertail Mountain in Debeque Canyon, July 5-7;

10; 12; September 19, 2006 ........... cece cece eee eee

. Table A.7. Number and catch effort (fish/mile) for
smallmouth bass collected from main channel habitats
with electrofishing in the Upper Colorado River from
RM 187.7-127.6 (Price-Stubb Dam to Westwater
Ranger Station, Utah), and the Lower Gunnison River
from RM 3.0-0.7 (Redlands Diversion Dam
to the Colorado/Gunnison River confluence) during

July, August, and September 2006 ................0. 00sec eee

. Table B.1. Amount of effort (electrofishing hours)
expended during four passes of the smallmouth
bass removal project sampling main channel
habitats on the Colorado and Lower Gunnison
tivers in western Colorado and eastern Utah, July

and August 2004.0... 0... cece cece cece cece eee eee

ix

A
fy
io


“son[BA Tenjou JOF € O1qRL, 99 “9007 PUP “SOOT

007 JO JouKuNs a4) SULINP SIOAL UOSTUUND JaMOT pue Ope10[O, Jedd] ay Jo SayoRar-qns/sayoued JOAL JUSIOZFIP
OL Ur poroayqoo (tut J ¢f-97) sseq YINOWTT[UUS []e JO Svore LOHPAUSOUOO pUe wos}1eduL0D (myqysy) Hoyeppyea = “p ond Ty

yoeey-qns/yoray Jeary

900cmmTM = S002

ul JEp-92 :SSBg YINOLUI[EWUS
y00c sea, UIUWM paulquiog sessed |IV

Baily UoTje1jUaI00Z

T
oO w
(uujysy) womaruoye9

wo
=

i=)
N

9
i]


Many of the nonnative fishes introduced into the Colorado River basin are suspected of
adversely affecting the native mainstem fishes in some fashion. Warmwater gamefish are
thought to have the greatest adverse effect on endangered native fishes. Centrarchids (e. g.,
largemouth bass, green sunfish, bluegill, black crappie, and smallmouth bass), ictalurids (e. g.,
channel catfish and black bullhead), and esocids (northern pike) are frequently listed as
contributors to the decline of native fishes. An increasing body of evidence characterizes the
negative interactions of nonnative fishes with the endangered big river fishes (Hawkins and
Nesler 1991; Minckley et al. 1991; Maddux et al. 1993; Lentsch et al. 1996). Some of this
evidence is indirect, including inferences from field data or results from laboratory studies of
predation by nonnatives on natives. Laboratory studies have documented agonistic behavior,
resource sharing, and vulnerability to predation (Papoulias and Minckley 1990; Karp and Tyus
1990; Ruppert et al. 1993; Johnson et al. 1993). Direct evidence of predation includes native
fishes obtained from stomach contents of nonnative fishes and by visual observation of
predation. Other means by which nonnative fishes may adversely affect native fishes are by
competition for food, which limits the success of razorback sucker (Papoulias and Minckley
1990). The extent of predation pressure by some nonnative fishes on populations of native fishes
is not exactly known.

Smallmouth bass have the potential to prey on or compete with different life stages of the
four native endangered fishes as well as the unlisted native fishes. During the 1990s the Yampa
River experienced a dramatic increase in northern pike and then smallmouth bass in critical
habitat. Predation by these species wreaked havoc on the native fish community. Anderson
(2004; 2005) documented significant declines of native fish densities in parts of the river
between 1998 and 2004 coincident with an increase in smallmouth bass abundance. The rapid
increase of the smallmouth bass population in the Yampa River between 2000-2004 was
believed, in part, attributed to a response to warmer water temperatures associated with several
years of consecutive drought conditions.

Tyus and Saunders (1996) went on to conclude that smallmouth bass along with channel
catfish and northern pike were the main threat to juvenile Colorado pikeminnow and razorback
sucker. Participants of the smallmouth bass summit held in Grand Junction in November 2005
ranked smallmouth bass as the number one predatory threat in the Upper Colorado River basin to
native fishes.


Despite both bass species being lethally removed, largemouth bass numbers continued to
increase in main channel habitats and were highest in 2006. Largemouth bass numbers in 2006
increased 86% from 2005 and 295% from 2004 in the Grand Valley sub-reaches. From Rifle to
Beavertail Mountain, largemouth bass numbers in 2006 increased 455% from 2005 and 225%
from 2004.

Green sunfish and black crappie abundance increased in main channel habitats in the
Grand Valley sub-reaches of the Upper Colorado and Lower Gunnison rivers from 2004 to 2006.
Green sunfish numbers in 2006 increased 33% in the Grand Valley sub-reaches over 2005 but
declined 19% between Rifle and Beavertail Mountain; black crappie numbers increased 11% in
the Grand Valley reaches. In 2006, bluegill! numbers declined in both the Grand Valley sub-
reaches (3%) and Rifle to Beavertail Mountain sub-reaches (70%) from 2005.

A decline was detected in abundance of smallmouth bass in 2006 from the previous two
years using catch effort indices (fish/hr and fish/mile) in main channel habitats of the Colorado
River in western Colorado and eastern Utah and the Lower Gunnison River. Catch/effort
mimicked the same pattern as actual numbers of fish collected. In the Grand Valley sub-reaches,
mean total catch effort for smallmouth bass declined in 2006 (4.64 fish/hr) from 2005 (7.83
fish/hr) and 2004 (6.91 fish/hr). However, largemouth bass catch rate was the highest in 2006
(6.76 fish/hr) compared to 3.37 fish/hr in 2005 and 1.64 fish/hr in 2004. Green sunfish/black
crappie/bluegill aggregate catch rate was the highest during 2006 (10.94 fish/hr) compared to
8.07 fish/hr (2005) and 4.51 fish/hr (2004). Between Rifle and Beavertail Mountain, smallmouth
bass catch rate in 2006 (2.10 fish/hr) declined from 2005 (5.78 fish/hr); largemouth bass catch
rate increased in 2006 (5.62 fish/hr) from 2005 (0.95 fish/hr) and 2004 (3.29 fish/hr).

A statistically significant increase («=.05) in mean total length of smallmouth bass was
detected in 3 of 5 river segments in 2006 which may be due in part to the lack or absence of fish
between 100 and 180 mm in the Grand Valley and between 100 and 200 mm in the Rifle to
Beavertail Mountain reach. The hypothesis that the reduced survival and loss of recruitment of
the 2005 cohort of smallmouth bass could not be related to mechanical removal or to
environmental factors within the range observed in this study. There is still insufficient evidence
to support the notion that overwinter survival of a cohort of young-of-the-year smallmouth bass
may be size dependent. In other words, have fish attained a size large enough (e. g., 75 mm) by
the fall of that year or have they had a long enough growing season to accumulate adequate lipid

xvii


LIST OF TABLES

Table

6.

Fi

1.

N

Smallmouth bass population projections for 2004 and
2005 extrapolated from the 2006 catch/effort and
population estimate. The river segments included the
15- and 18-mile reaches of the Upper Colorado River
(GVIC Dam to the Loma Boat Landing) and the 2.3
miles of the Lower Gunnison River (Redlands Dam

to the Colorado/Gunnison River confluence) ...............

LIST OF FIGURES
re

General area for the centrarchid removal study
performed during 2004-2006 in the Upper Colorado
River of western Colorado and eastern Utah and the
Lower Gunnison River in western Colorado with

major landmark descriptors ....... 60... cece e eee e eee eee

Overall catch effort (fish/hr) by pass for smallmouth
bass (26-414 mm) collected from main channel
habitats in the Upper Colorado River with
electrofishing from RM 187.7-127.6 (Price-Stubb
Dam to the Westwater, Utah, BLM

ranger station) and in the Lower Gunnison River
from RM 3.0-0.7 (Redlands Dam to the
Colorado/Gunnison River confluence), 2004, 2005,

and 2006 2.0... eee eee cece cece eee teen nee eee

Comparison of catch/effort (fish/hr) for smallmouth
bass (41-437 mm) collected with electrofishing from
the Upper Colorado River between Rifle and
Beavertail Mountain (RM 240.4-195.7) during 2004,

2005, and 2006... 6... cece eee e ec ce eee ence eee

B
iS
1D


25
Palisade Gauge
a
mol
i<j
o
an
Ss
°
=
=
n
rs
o
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Month
20
Palisade Gauge
@ 15
ao}
=
o
$
°} 10
<=
=
wo
pre
oO 5
0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Month

Figure D.5. Mean daily discharge for the Palisade USGS gauge on the Upper Colorado
River (RM 184.5) for 2002-2004 (lower water years)(upper) and 2005-2006
(higher water years)(lower).

D-5


back calculate hatching dates to identify the timing and duration of smallmouth bass
spawning. This biological information could be useful to determine if environmental
factors, e. g., hydrologic conditions such as higher flows in non-drought periods and
accompanying cooler water temperatures might disrupt or delay spawning resulting in
slower growth of early-life stages of smallmouth bass reducing survival and recruitment
success. Managers might be able to take advantage of such events to periodically reduce
smallmouth bass populations in some reaches of the Upper Colorado River.

. Increase catches of centrarchid fishes by targeting specific in-river features that provide
habitat for centrarchid fishes. These include but are not limited to beaver lodges, tree
stumps and logs, rock piles, and concrete rip-rap. Sampling these features with
electrofishing may increase catches of centrarchid fishes. Also, sample on days when
turbidity is high to increase catches of smallmouth bass.

UNCERTAINTIES/UNKNOWNS

. Growth rate of early-life stages (age-0 and age-1) of smallmouth bass in the Upper
Colorado River.

. Spawning dynamics for smallmouth bass in the Upper Colorado River, i. e., hatching
times/dates and duration of spawning over a variety of flow (e. g., wet, moderate, dry)
and water temperature regimes.

. The reason(s) (e. g., an environmental event or physiological factor) why age-0
smallmouth bass produced in 2005 did not survive and recruit to the summer of 2006.

.. The empirical (not theoretical) number of passes required to achieve the desired
probability of capture (p-hat) and target exploitation rate or percent of smallmouth bass
removed.

. a) Electrofishing being a cost-effective, long-term mechanical removal method for

collecting, removing, and reducing the abundance of nuisance and problematic nonnative
fishes.

52


eel

Stateline
(RM 132)
Westwater Ranger
Station (RM 128)

Rulison Rifle
COLORADO (RM 240) (RM 240.4)
Parachute ©

Salt
Wash Fruita : Debeque
State Canyon,
Park Grand Government Highline Dam
(RM 157.2) Gran (RM 193.7)

Junction Price-Stubb Dam (RM 188.3)

‘Grand Valley Diversion Dam
‘Corn Lake (RM 185.3)
(RM 177.4)

(RM 152.6)
COLORADO/

GUNNISON RIVER.
‘Confluence RM 171
Redlands Dam

MAP . LOCATION

cs
t

>

a

oS,
S
>
=
(e}
al
3
“i
co)
Tice me omens

at aetetr eter tetany

20 . 40 60

20 °

Scole

of Miles

Figure 1. General area for the centrarchid removal study performed during 2004-2006
in the Upper Colorado River of western Colorado and eastern Utah and the
Lower Gunnison River in western Colorado with major landmark descriptors.

Refer to Table 1.


LIST OF APPENDIX TABLES AND FIGURES

Appendix

Cc.

Figure C.3. Time series length frequency for age-0
and age-1 smallmouth bass (< 115 mm total length)
collected during the summer of 2006 from the Upper
Colorado (RM 187.8-127.6) and Lower Gunnison

(RM 3.0-0.7) rivers... 0. eee eee eet e eee

. Table D.1. Discharge characteristics (instantaneous

peak discharge, lowest and highest mean daily flow,
and 90% exceedence) and degree days (214 ° C) for
five calendar years (2002-2006) at the Cameo
USGS gauge (RM 199.8) on the Upper Colorado

REVEL. ee cee een eee n eee ae

. Table D.2. Discharge characteristics (instantaneous

peak discharge, lowest and highest mean daily flow,
and 90% exceedence) and degree days (214 ° C) for
five calendar years (2002-2006) at the stateline
USGS gauge (RM 133.8) on the Upper Colorado

RIVEE eee ete eet teen eee neta

. Figure D.1. Cumulative degree days (214 ° C)
at the Cameo USGS gauge for 2002-2006 ..............0..00088

. Figure D.2. Cumulative degree days (214 ° C)
at the stateline USGS gauge for 2002-2006 .................-04-

. Figure D.3. Annual instantaneous peak discharge

(upper) and annual mean discharge (lower) by
calendar year for the stateline USGS gauge near the

Colorado/Utah border for 1970-2006 .......... 00. e cece ee eee

. Figure D.4. Mean daily discharge for the Cameo

USGS gauge on the Upper Colorado River (river mile 199.8)
for 2002-2004 (lower water years)(upper) and 2005-2006

(higher water years)(lower) 0.0.0... 0... e cece cece erence eee

xiii


temperature exceeded 14° C. This statistic was generated primarily for graphic presentation of
the onset of the annual thermal regime of the river and the progressive accumulation of degree
days in a particular growing season which could be compared among years. For each day that the
mean daily water temperature exceeded 14 ° C, this was considered 1 degree day and was
irrespective how great the mean daily water temperature exceeded the 14° C value. Degree days
were a means to characterize and describe the annual thermal water conditions in a particular
river reach.

Analyses

While smallmouth bass were the focus of this removal study, data were collected and
reported on four other centrarchid fishes that were also removed. Total numbers and catch per
unit of effort for smallmouth bass and largemouth bass, and green sunfish, black crappie, and
bluegill in the aggregate were determined for each sub-reach per sampling pass for 2004, 2005,
and 2006. Catch per unit of effort was computed as total catch per effort and reported as fish/hr.
For smallmouth bass only, another catch effort index, fish/mile, was computed. This index was
computed from the actual number of fish collected and removed during 2004, 2005, and 2006,
for five major riverine segments on the Upper Colorado River and one segment for the Lower
Gunnison River for each of the four passes. Changes in the mean individual size (total length + 2
mm) of smallmouth bass among the 3 years were also compared.

Chapman’s (1951) modification of the Petersen-Lincoln estimator was used to determine
abundance of smallmouth bass. This estimator was believed to be the most appropriate because
it would reduce bias due to the small number of recaptured smallmouth bass.

N-hat = ((n, + 1)(n, + 1)/(m, + 1))-1

where N-hat = estimated population size
n, = the number of smallmouth bass marked in the marking pass
n= the number of smallmouth bass captured in the first removal pass
m, = the number of marked smallmouth bass recaptured
The upper and lower 95% confidence limits (C.1.) were computed by:

Nehat + 1.96 * (ar +1)(n2 + (1 —m2){n2-m2)//(m2+ 1)? (m2 +2)

12


APPENDIX C
Percentage and Number Comparison of Smallmouth Bass
by Various Length Classes Collected During the Summers of 2004-2006
&
Length Frequency of Age-0 and Age-1 Smallmouth Bass
collected during 2004-2006
in the Upper Colorado and Lower Gunnison rivers


Table B.4. Catch effort (fish/hr) for five centrarchid fishes (young-of-the year, juvenile, adult)
collected during pass (P) 1, 2, 3, and 4 of the smallmouth bass removal project from
main channel habitats on the Colorado and Lower Gunnison rivers in western
Colorado and eastern Utah, July and August 2004. Note: n/s=not sampled; two
electrofishing craft were used for passes 1, 2, and 3; one electrofishing craft was
used for pass 4.

Catch/Effort (fish/hr}
Black Crappie/

River Smallmouth Largemouth. Green Sunfish/
(River Miles) Bass Bass Bluegill
River Segment Pl P2 P3 P4 Pl P2 P3 P4 Pl P2 Pd

Colorado River
(RM 187.7-127.6)

Price-Stubb > GVIC Dam 3.96 6.56 1.88 ws 0.00 0.00 0.00 m/s 044 7.38 3.39 nls
GVIC Dam > Corn Lake: 6.08 5.26 8.34 8.22 0.00 0.00 2.05 4.45 10.49 2.63 5.68 7.88

Corn Lake »Colo/Gunn 13.61 9.32 11.50 14.40 0.64 0.54 4.02 4.27 3.40 0.72 11.61 8.27
River Confluence

Colo/Gunn R. Confl. + 4.87 7.09 12.62 11.92 1.62 156 3.98 4.59 2.27 3.98 9.31 4.98
Fruita State Park

Fruita State Park » 3.45 5.99 7.12 3.08 1.72 0.63 1.33 6.16 10.34 2.21 11.57 14.37
Loma Boat Landing

Loma Boat Landing » 3.12 2.34 3.88 o/s 0.68 0.00 246 n/s 1.36 0.90 194 ws
Salt Creek Wash

Salt Creek Wash > 1.00
Utah/Colo Stateline

Utah/Colo Stateline > 0.80 0.41 0.38 ms 0.00 0.00 0.00 n/s 0.80 0.00 0,00 ms
Westwater, Utah
BLM Ranger Station

i)
S
i)

1.92 n/s 0.00 0.00 0.82 ms 0.00 0.72 0.82 n/s

Lower Gunnison River

(RM 3.0-0.7)

Redlands Div. Dam > 8.33: 8.76 11.55 6.29 0.00 0.00 0.25 699 1.78 2.19 1.22 6.29
Colo/Gunn R.
Confluence

Mean of 2004 Passes 5.14 $.58 8.11 10.33 0.66 0.50 2.35 444 3.31 2.29 6.17 7.28
Mean of 2004 Species 6.91 1.64 4.51

B-4


LIST OF APPENDIX TABLES AND FIGURES

Appendix

D. Figure D.5. Mean daily discharge for the Palisade
USGS gauge on the Upper Colorado River (river mile 184.5)
for 2002-2004 (lower water years)(upper) and 2005-2006
(higher water years)(lower) ......... 000s cece e cece eee eee eee

D. Figure D.6. Mean daily discharge for the stateline
* USGS gauge on the Upper Colorado River (river mile 133.8)
for 2002-2004 (lower water years)(upper) and 2005-2006
(higher water years)(loWer) ... 6.6... eee eee eee eee teen eens

E. Table E.1. Scientific and common names and status
(native vs. nonnative) of fish collected and mentioned
in the text of this report during the smallmouth bass
removal study in the Upper Colorado and Lower
Gunnison rivers, 2004-2006 0.2... . cc cece cece ee ence eee eee eee

xiv


Colorado River (RM 187.7-127.6)
Lower Gunnison River (RM 3.0-0.7)

1 2004, 2005, 2006
all black crappie
(68-291 mm)
0.8-
2
<=
am
& 0.6] 9)-2006
5
€
= 0.4 —— 2005
oe
B
é)
0.2-
(es) 2004
0. ® @ )
| T T T !
1 2 3 4

Pass Number

Figure B.4. Overall catch effort (fish/hr) by pass for black crappie (68-291 mm)
collected from main channel habitats in the Upper Colorado River with
electrofishing from RM 187.7-127.6 (Price-Stubb Dam to the Westwater,
Utah, BLM ranger station) and in the Lower Gunnison River from RM
3.0-0.7 (Redlands Dam to the Colorado/Gunnison River confluence), 2004,
2005, and 2006. Note: The number of fish collected by pass is in
parentheses.

B-10


2004

a
2 -| duly 1-10
‘Smallmouth Bass
s -| ned
4-|
. nhl
a
July 14-20
a ‘Smallmouth Bass
6 - n=6
a -|
2-|
I i io i i i
8
a July 21-34
‘Smallmouth Bass
64 n=13
4-]
2 -
im! [sane
-
o , - August 1-10
L ‘Smallmoouth Bass
Ss 4 n=55
3 | Aug 5
a 4 |
|
2 1
8
August 11-20
a ‘Smallmoouth Bass
6 -| neat
4 .
i” mt Md kh Ul |
oO
10
a - August 21-31
‘Smallmouth Bass
6 n=4
a-l
2 -|
0 Ak At
10
a - Spetamber 1-20
‘Smallmouth Bass
6-4 n=0
a- No Sampling Performed
2-|
QUOTA TTT T TPT TTP TTT ETE TT ETE ET PET TTT TTT TTTTTI TP TTTITTTETTI TTT TSP
ti) 10 20 30 40 50 60 70 80 90 100 410 120
Total Length (mm)
Figure C.1. Time series length frequency for age-0 and age-1 smallmouth bass (< 115

mm total length) collected during the summer of 2004 from the Upper
Colorado (RM 187.8-127.6) and Lower Gunnison (RM 3.0-0.7) rivers.


noticed for other river sub-reaches in the Upper Colorado River. At first, this may seem
perplexing since one might assume that catch rates may be lower when turbidity is high.
Researchers performing smallmouth bass removal in the Green River sub-basin noted that their
highest catch rates were associated with high turbid water conditions in both 2005 (e-mail
transmittal, Mark H. Fuller, FWS, Vernal, Utah, 8/26/2005), 2006, and 2007 (e-mail transmittal,
M. Fuller, 9/19/2007). Fuller attributed the substantial catch of adult smallmouth bass during
early-September 2007 to late season storm events that resulted in large flushes of debris and silt
into the river between Echo Park and Split Mountain in the Green River, Utah. He further
speculated that increased turbidity stressed and increased the catchability of larger smallmouth
bass at shoreline habitat. Possibly smallmouth bass are more vulnerable to capture when turbid
water conditions exist and less capable of avoiding electroshock and capture because they move
to shallower shoreline habitats where most of the electrofishing sampling is performed. Every
attempt should be made to sample on days when turbidity is high to increase catches of
smallmouth bass.

Other Nonnative Fishes

Despite only a relatively few other nonnative fishes, both game and non-game, being
collected during this removal study, the occurrence of some of these fishes deserves mentioning
since only a few years ago catches of smallmouth bass were rare and abundance densities were
almost non-existent in Grand Valley sub-reaches of the Upper Colorado River. Adult walleye
(483-610 mm) were collected in the Rifle to Rulison sub-reach during 2004 (1 fish), 2005 (1),
and 2006 (6). Smallmouth bass, walleye, northern pike, and yellow perch occur in Rifle Gap
Reservoir which has a spillway that drains into Rifle Creek. Rifle Creek is hydrologically
connected to Upper Colorado River south of the town of Rifle. Therefore, the likely source of
the walleye found in the river was from Rifle Gap Reservoir. One adult northern pike (589 mm)
was collected in 2005 in the 18-mile reach and one young (~ 65 mm) yellow perch was collected
in the 15-mile reach in 2006. Twelve adult gizzard shad (338-462 mm) were collected during
2006. Eleven of these fish were collected in the 15- and 18-mile reaches of the Upper Colorado
River and one in the plunge pool of the Redlands Diversion Dam in the Lower Gunnison River.
This is believed to be the first sightings of gizzard shad in the Grand Valley area of the Upper
Colorado River. Gizzard shad occur in Lake Powell which the Colorado River drains into.

48


Berven, K. A., D. E. Gill, and S. J. Smith-Gill. 1979. Countergradient selection in the green
frog, Rana clamitans. Evolution 33: 609 — 623.

Bestgen, K. R., K. A. Zelasko, and R. I. Compton. 2006(a). Response of the Green River fish
community to changes in flow and temperature regimes from Flaming Gorge Dam since 1996
based on sampling conducted from 2002 to 2004. Final report to the Upper Colorado River

Recovery Implementation Program. Project no. 115.

Bestgen, K. R., D. W. Beyers, J. A. Rice, and G. B. Haines. 2006(b). Factors affecting
recruitment of young Colorado pikeminnow: synthesis of predation experiments, field
studies, and individual-based modeling. Transactions of the American Fisheries Society
135:1722-1742.

Bestgen, K. A. Zelasko, and C. T. Wilcox. 2007. Non-native fish removal in the Green River,
Lodore and Whirlpool canyons, 2002~2006, and fish community response to altered flow and
temperature regimes, and non-native fish expansion. Recovery Program Project Number 115.
Final Report prepared for the Recovery Implementation Program for the Endangered Fishes
of the Upper Colorado River Basin. Colorado State University Larval Fish Lab, Contribution
149, Ft. Collins.

Bezzerides, N., and K. Bestgen. 2002. Status review of roundtail chub, Gila robusta,
flannelmouth sucker, Catostomus latipinnis, and bluehead sucker, Catostomus discobolus in
the Colorado River basin. Colorado State University Larval Fish Lab, Contribution 118, Ft.
Collins.

Brown, E.H. 1960. Little Miami River headwater stream investigations. Ohio Department of
Natural Resources, Division of Wildlife, Columbus, Ohio, USA.

Burdick, B.D. 1995. Ichthyofaunal studies of the Gunnison River, Colorado, 1992-1 994. Final

Report. Recovery Implementation Program for the Endangered Fishes of the Upper Colorado
River Basin. U.S. Fish and Wildlife, Denver, Colorado. 60 pp. plus appendices.

54


increased removal pass in 2006. The number of smallmouth bass 2306 mm (232; 10.7%), 2357
mm (41; 1.9%), and 2406 mm (4; 0.2%) was greatest in 2006.

The Silt to Beavertail Mountain reaches shared a similarity with the downstream Grand
Valley reaches: the number of ‘trophy-size’ smallmouth bass relative to the total number
collected were well represented in collections in these upper reaches. The 3-year relative average
of smallmouth bass 2255 mm was 40.1 % (132 of 329 total smallmouth bass) and smallmouth
bass 2306 mm was 19.8 % (65 of 329 fish). About 5 % (n=17) were 2357 mm.

Also, it was apparent from collections, that in some river segments (15-mile reach [Grand
Valley Irrigation Company Diversion Dam to the Colorado/Gunnison River confluence], 18-mile
reach [Colorado/Gunnison River confluence to the Loma boat landing], and Rifle to Beavertail
Mountain), smallmouth bass reproduced in 2004, 2005, and 2006.

The abundance for smallmouth bass (2100 mm) in the 18- and 15- mile reaches plus the
2.3 miles of the Lower Gunnison River for 2006 was estimated to be 3,197 + 2,100 (95% C.L.)
individuals or about 91 smallmouth bass per mile using a single mark and first removal pass.

Catches of smallmouth bass appear related to turbid and clear water conditions. Higher
catch rates for juvenile and adult smallmouth bass were associated with higher turbidity (usually
immediately following summer rainstorms).

Recommendations include, 1) increasing the number of removal passes in 2007 and 2008
at least two-fold (from 4 to 8 passes) with the goal of increasing probability of capture and
smallmouth bass exploitation rates; 2) suspending all electrofishing operations during the
Colorado pikeminnow spawning period to eliminate the likelihood of harassment, interference,
and injury to spawning Colorado pikeminnow; 3) performing mark-recapture population
estimates at least once every three years to assess the size of the smallmouth bass population and
effectiveness of removal in the Grand Valley reaches of the Upper Colorado and Lower
Gunnison rivers; 4) continuing to sample reaches of the Upper Colorado River from the Rifle
Bridge to Beavertail Mountain in Debeque Canyon; 5) sampling for young smallmouth bass in
the spring prior to runoff to assess overwinter mortality; 6) preventing future escapement of
piscivorous fishes (smallmouth bass, walleye, northern pike, and yellow perch) from Rifle Gap
Reservoir or their access to the Colorado River; 7) collecting and preserving early-life stages

xix


Table C.1. Number of smallmouth bass by seven different length categories collected with
electrofishing from marking and removal (REM-) passes from main channel riverine
habitats from the Grand Valley river reaches of the Upper Colorado (RM
187.8—127.6) and the Lower Gunnison (RM 3.00.7) rivers during the summers of

2004-2006.

Reach: Grand Valley

Smallmouth Bass

Length Categories-- mm {inches}

Year
Pass Type/No.

< 100
{<4}

100-199
{4-8}

200-254
{8-10}

255-305
{10-12}

306-356
{12-14}

357-406
{14-16}

2006

> 406
{> 16}

Marking 10 26 39 33 21 4 0
REM-1 23 25 61 77 41 6 0
REM-2 49 8 25 29 12 1 0
REM-3 100 9 22 43 17 0 0

9 0

REM-4 79 18 63 30 1
2005

REM-1 30 152 182 69 35 5 0
REM-2 40 94 165 73 31 8 0
REM-3 99 79 80 38 14 3 0
REM-4 84 20 35 15 8 5 0
2004 .
REM-1 0 91 76 34 15 1 1
REM-2 15 119 76 29 17 1 0
REM-3 44 309 74 53 23 2 0
REM-4 33 99 21 23 6 3 i)



selective removal of undesirable nonnative fishes. Four smallmouth bass were collected in the
fish trap of the Government Highline fish passage during 2005 (Burdick 2005(b)) and one during
2006 (Burdick 2006(a)). Smallmouth bass are located in Rifle Gap Reservoir and adult
smallmouth bass have been reported in the Colorado River between Rifle and Price-Stubb Dam
(Anderson 1997; this study).

Lower Gunnison River

The Redlands Diversion Dam constructed in 1918 serves as an effective barrier to
smallmouth bass and all other fish attempting to move further upstream in the Gunnison River.
A fishway with fish trap was constructed and completed at this site in 1996 has provided a means
to allow native fish to pass upstream into historic habitat, and allow for selective removal of
undesirable nonnative fishes. In the fish trap of the Redlands Dam fish passageway in the Lower
Gunnison River, the number of smallmouth bass have recently increased (19 fish in 2002 and
2003)(Burdick 2003(b)) over previous years of monitoring (1996-2001: 1 fish)(Burdick 2001).
Nine smallmouth bass were collected in the fish trap at Redlands during 2004 (Burdick 2004(a))
and 21 during 2005 (Burdick 2005(a)). No smallmouth bass were collected in 2006 (Burdick
2006(a)) or 2007. About 1,800 fingerling smallmouth bass were stocked by the Colorado
Division of Wildlife (CDOW) in 1973 in the Gunnison River near Delta (Wiltzius 1978)
upstream from Redlands Diversion Dam. None of these stocked smallmouth bass have been
subsequently captured upstream from the diversion dam (Wiltzius 1978, Valdez et al. 1982;
Burdick 1995; Burdick 2003(c); Anderson 2006; Burdick 2006(b)).

Control of Nonnative Fish by Mechanical Removal

Currently, the core of the nonnative fish control strategy in the upper Colorado River
basin is mechanical removal. Mechanical removal strives to reduce numbers of problematic fish
species, affects long-term viability by suppressing sustainable numbers of fish, and effectively
increases native fish populations to promote recovery of endangered fishes. Control of
smallmouth bass and other nonnative fish species is a primary emphasis, along with habitat
restoration, propagation and stocking, and instream flow management within the Recovery
Program for the four endangered fish species. In the strategic plan for the control of nonnative
fishes in the Upper Colorado River Basin (Tyus and Saunders 1996), “control” was defined as
“reducing the numbers of one of more nonnative species to levels below which they are no longer


60
50
40
30
20
10

Number of Fish

60
50
40
30
20
10

Number of Fish

60
50
40
30
20
10

Number of Fish

Figure 8.

Upper Colorado River
Rifle Bridge-Beavertail Mountain (Debeque Canyon)

2004 Pass No. 1

n=21
mean=226 mm
std dev.=97.9

_———————

S
ES SF SP
ss s

Total Length (mm)

Pass No.1 & 2
n=230

mean=196 mm
std dev.=106.8

s Ny
Ss - Sf a oe Ri 2 ea ©

s ££ £ Ss
Total Length (mm)

2006 Pass No.1 &2

n=79
mean=200 mm
std dev.=120.1

S) 5 J S <) S
ea a as s Ca 7 ©
SP LS KF Ss
Total Length (mm)

Total length frequency comparison of all smallmouth bass (41-437 mm)
collected with electrofishing between Rifle and Beavertail Mountain in
Debeque Canyon (RM 240.4-195.7) in the Upper Colorado River, late
August 2004, mid-July 2005, and mid-July and mid-September 2006.

33


Colorado River (RM 187.7-127.6)
Lower Gunnison River (RM 3.0-0.7)

2004, 2005, 2006
15~| all green sunfish
(30-256 mm) (568)
2006
i”
< (198)
= 10-
& —— 2005
: (178)
=
= “ig 2004
o
g
8 5
(87)
0 T 1 i 1
1 2 3 4

Pass Number

Figure B.2. Overall catch effort (fish/hr) by pass for green sunfish (30-256 mm)
collected from main channel habitats in the Upper Colorado River with
electrofishing from RM 187.7-127.6 (Price-Stubb Dam to the Westwater,
Utah, BLM ranger station) and in the Lower Gunnison River from RM
3.0-0.7 (Redlands Dam to the Colorado/Gunnison River confluence), 2004,
2005, and 2006. Note: The number of fish collected by pass is in
parentheses.


225% from 2004 to 2006. The total number of largemouth bass (includes young-of-the-year,
juvenile, and adult) collected for each pass for each of the eight sub-reaches in the Upper
Colorado River between Price-Stubb Dam and Westwater, Utah, plus the Lower Gunnison River
is provided in Appendix; Tables A.1—A.3. The total number of largemouth bass collected for
each of the four sub-reaches between Rifle and Beavertail is provided in Appendix; Tables A.4.
-A.S.

Green sunfish, Black Crappie, and Bluegill. The total number of each of these three
species for all length sizes collected within each of the four major river segments for each of the
three years by pass number is provided in Table 2. Between Price-Stubb Dam and Westwater,
Utah, the number of green sunfish increased each year. The total number of green sunfish
collected in 2004, 2005, and 2006 was 643, 1,051, and 1,395 fish, respectively. This translated
into a 61% increase from 2004 to 2005 and a 33% increase from 2005 to 2006. Between Rifle
and Beavertail Mountain, the total number of green sunfish numbers was 36, 606, and 492 in
2004, 2005, and 2006, respectively.

Black crappie comprised the fewest number of fish captured and removed of the five
centrarchid fishes encountered during this 3-year removal program. Between Price-Stubb Dam
and Westwater, Utah, the total number of black crappie collected increased from 7 fish in 2004 to
41 in 2005 (486% increase) to 70 in 2006 (71% increase). Only two black crappie were collected
in the 3 years between Rifle and Beavertail Mountain. Bluegill, traditionally considered a lentic
species, were encountered in high numbers in main channel riverine habitats. Between Price-
Stubb and Westwater, the total number removed in 2004, 2005, and 2006 was 111, 316, and 307,
respectively. Between Rifle and Beavertail Mountain, 10 were removed in 2005 and only 3 in
2006. The aggregate number of green sunfish, black crappie, and bluegill collected and removed
in each of the eight sub-reaches between Price-Stubb Dam and Westwater, Utah, plus the Lower
Gunnison River is provided in Appendix; Tables A.1— A.3. The number of each of these three
species collected within each of the four sub-reaches from Rifle to Beavertail is provided in
Appendix; Tables A.4.~A.6.

Catch/Effort

General, Catch rate or catch/effort is often used as an index of population size if it is
consistently proportional to absolute abundance (Ricker 1975). Unfortunately, catch/effort can

16


(age-0 and age-1) of smallmouth bass annually during lethal removal passes to determine timing
and duration of spawning and early-life stage growth rates; and 8) increasing catches of
centrarchid fishes by targeting in-river features that provide habitat for centrarchid fishes and
sampling on days when turbidity is high.


An attempt is made here to explain why the cohort of smallmouth bass produced in the
summer of 2005 did not recruit to 2006 and determine if this might be associated with discharge,
water temperature expressed as degree days, the first date water temperature equalled or
exceeded 14 ° C, and length of the growing season during the first year of life for smallmouth
bass. If there is an association between higher stream discharge with lower water temperatures
that routinely occur during higher discharge years and reduced survivability and recruitment of
young size classes of smallmouth bass, this would be an important step in identifying an
“Achilles heel” for controlling this species. A series of length frequency histograms in 10-day
increments were generated from smallmouth bass collected from the Upper Colorado River from
Price-Stubb Dam to Westwater, Utah, and Lower Gunnison River for each of these 3 years
(Appendix; Figure C.1.—C.3.). These included smallmouth bass < 115 mm. The basis for this
cutoff was that the mean annulus for age-1 smallmouth bass was 111 mm which was determined
from ageing otoliths from smallmouth bass collected from the Upper Colorado River during
2004 and 2005 (Pat Martinez, CDOW, personal communication).

The hypothesis presented here is: overwinter survival of a cohort of young-of-the-year
smallmouth bass may be dependent upon whether fish grow to a large enough size by the fall of
that year. In years of large, prolonged runoff that delays the seasonal warming of the Upper
Colorado River, late spawning by smallmouth bass may leave age-0 fish with only 2 to 3 months
to grow and accumulate fat (lipid) reserves before the onset of winter. However, length, alone,
cannot foretell if fish can accumulate adequate lipid reserves for overwintering. A shorter
growing season may allow for growth in length, but may not be enough time for age-0 fish to
accumulate adequate lipid reserves. Furthermore, a shorter growing season could lead to a longer
winter season in which lipid reserves must be drawn upon longer to ensure survival into the next
growing season. The physiological implication is that small and medium-size age-0 smallmouth
bass may be unable to accumulate adequate lipid reserves to survive until following spring; death
may be due to exhaustion of energy reserves.

Hoar (1983) stated than an organism must maintain a “constant element” of fat in order to
survive. Thompson et al. (1991) found that overwinter survival depends on fish size in his
laboratory results with age-0 Colorado pikeminnow. Whether an age-0 Colorado pikeminnow
survived the winter was a function of fish length and feeding regime (i. e., fed vs. starved). He
found that both fed and starved Colorado pikeminnow that were relatively small (mean, 30 or 36
mm TL) had lower survival than larger fish (44 mm) over simulated winter conditions. Further,

44


Cover page images courtesy of New York State Department of Environmental
Conservation (smallmouth bass) and Duane Raver, USFWS (largemouth bass, bluegill,
green sunfish, and black crappie)

Colorado River Fishery Project
764 Horizon Drive, Bldg B
Grand Junction, CO 81506
970/245-9319
bob_burdick@fws.gov

U.S. Fish & Wildlife Service
http://www.fws.gov

January 2008

—_—


LIST OF FIGURES
re

. Catch/effort (fish/hr) comparison and concentration
areas for all smallmouth bass (26-437 mm) collected
in 10 different river reaches/sub-reaches of the Upper
Colorado and Lower Gunnison rivers during the

summer of 2004, 2005, and 2006 ..............00 cece eee eee

. Comparison of overall catch/effort (fish/hr) for
smallmouth bass (>100 mm) with electrofishing
from the 15- and 18-mile reaches of Upper
Colorado River (RM 185.3.8-152.6) and the
Lower Gunnison River (RM 3.0-0.7) during 2004,

2005, and 2006 ..... 6... eee e eee e eee en eee ee

. Population point estimate (2006) and projections

(2004, 2005) with 95% confidence intervals for
smallmouth bass (= 100 mm) for the 15- and'18-mile
reaches of the Upper Colorado River (RM 185.3—152.6)

and the Lower Gunnison River (RM 3.0-0.7) ..............-

. Total length frequency for all smallmouth bass
(26-414 mm) collected during the summer of 2004,
2005, and 2006, with electrofishing in the Upper
Colorado River (RM 187.8-127.6) and the Lower

Gunnison River (RM 3.0-0.7)... 2.0... ee cece eee eee nee

. Total length frequency comparison of all smallmouth
bass (41-437 mm) collected with electrofishing
between Rifle and Beavertail Mountain in Debeque
Canyon (RM 240.4-195.7) in the Upper Colorado
River, late August 2004, mid-July 2005, and mid-July

and mid-September 2006... 22.0.0... 00. e cece eee eee eee

. Comparison between the mean total length and
95% confidence interval for smallmouth bass
collected with electrofishing from five major
river segments on the Colorado and Gunnison

tivers during the summer of 2004, 2005, and 2006 ...........

é
Is
io

23

31

31


Table B.6. Catch effort (fish/hr) for five centrarchid fishes (young-of-the-year) collected during
removal passes (P) 1, 2, 3, and 4 of the smallmouth bass removal project from main
channel habitats on the Colorado and Lower Gunnison rivers in western Colorado
and eastern Utah, July, August, September 2006. Note: n/s=not sampled; two
electrofishing craft were used for passes 1, 2, and 3; one electrofishing craft was
used for pass 4. Note: 2004 and 2005 catch/effort by species is provided for annual

comparisons.
Catch/Effort (fish/hr}
Black Crappie/
River Smallmouth Largemouth Green Sunfish/ ~
(River Miles) Bass . Bass Bluegill
River Segment Pl P-2 P-3 P4 Pl P2 P3 P4 Pl P2 PR Pd

Colorado River
(RM 187.7-127.6)

Price-Stubb » GVIC Dam 2.67 2.11 4.19 w/s 3.74 0.79 3.15 ws 2.14 0.26 210 ns
GVIC Dam» CornLake 7.95 5.98 4.92 9.35 0.53 9.35 13.8211.05 6.04 3.24 445 4.89

Corn Lake »Colo/Gunn 6.66 6.83 13.47 7.93 4.66 13.93 16.24 8.16 3.25 4.18 8.32 4.29
River Confluence

Colo/Gunn R. Confl. > 5.48 2.79 3.81 2.21 7.75 5.72 7.79 5.84 9.27 11.30 15.51 15.45
Fruita State Park

Fruita State Park > 0.20 1.10 2.08 4.65 4.38 10.69 10.92 5.07 25.91 31.44 58.05 34.64
Loma Boat Landing

Loma Boat Landing > 3.04 ws ns ns 093 ws ns ms 265 ws ns nis
Salt Creek Wash

Salt Creek Wash > 1.05 ws ns ws 0.26 ns ws ns 053 ws ws nis
Utah/Colo Stateline

Utah/Colo Stateline > 0.94 ns os ns 0.94 ns ws ws 0.94 ns ns ns
Westwater, Utah
BLM Ranger Station

Lower Gunnison River : r

(RM 3.0-0.7)

Redlands Div. Dam > 2.18 4.27 194 2.26 0.73 0.95 1.55 1.51 1.82 8.06 20.59 9.79
Colo/Gunn R.
Confluence

Mean of 2006 Passes 4.30 3.87 5.57 5.34 3.38 7.87 10.37 7.16 6.33 10.42 17.27 13.04

Mean of 2006 Species 4.64 6.76 10.94
Mean of 2005 Species 7.83 3.37 8.07
Mean of 2004 Species 6.91 1.64 4.51



Smallmouth Bass Catch/Effort (fish/hr)
Upper Colorado River-RM 240.4-195.7
2004, 2005, 2006

All Passes Combined within Years

6, 5.78

Catch/Effort (fish/hr)
mn

4+
34
2.11
24
1.06
_
0 ' y
2004 2005 2006

Year

Figure 3. Comparison of catch/effort (fish/hr) for smallmouth bass (41-437 mm)
collected with electrofishing from the Upper Colorado River between
Rifle and Beavertail Mountain (RM 240.4-195.7) during 2004, 2005, and
2006.

21


Table C.2. Percentage and number (in parenthesis) comparison of smallmouth bass by six
different length categories collected with electrofishing from marking and removal
(REM-) passes from main channel riverine habitats from the Grand Valley river
reaches of the Upper Colorado (RM 187.8—-127.6) and the Lower Gunnison (RM
3.0-0.7) rivers during the summers of 2004-2006. Number of total passes per year in
brackets [ ]. See Table C.1. for number of smallmouth bass collected by pass by

length category.
Smallmouth Bass Length Categories
Year <100mm | <255mm | 2 255mm | 2 306mm | 2357mm | >406mm
{<4%} {<10"} {2 10 “} {2 12“) {2 14“} {14 “}
2006 29.6% 57.1% 42.9% 15.1% 14% aia
(261) (503) (378) (133) (12) (0)
2005 18.5% 71.7% 83.5% 8% 1.5% ---
. [4] (253) (1,060) (304) (109) (21) (0)
2004 TTM% 65.6% 34.4% 5.2% 0.6% < 0.01%
[4] (92) (867) (455) (69) (8) QQ)

C-2


jargemouth bass in main channel habitats was between Corn Lake and the Colorado/Gunnison
River confluence-(11.84 fish/hr; all passes combined) followed by the river reach between GVIC
Dam and Corn Lake (9.90 fish/hr), and the segment between Fruita State Park and the Loma boat
landing (8.45 fish/br (Appendix; Table B.6.)). In 2005, the highest catch rate for largemouth bass
in main channel habitats was between Fruita State Park and the Loma boat landing (8.19 fish/hr;
all passes combined) followed by the river reach between Corn Lake and the Colorado/Gunnison
River confluence (6.27 fish/hr), and the segment between the Colorado/Gunnison River
confluence to Fruita State Park (4.53 fish/hr)(Appendix; Table B.5.). The highest abundance of
largemouth bass was collected between the Colorado/Gunnison River confluence and Fruita State
Park during 2004 (2.97 fish/hr)(Appendix; Table B.4.). Between Rifle and Beavertail Mountain
largemouth bass catch rate increased in 2006 (5.62 fish/hr) from 2005 (0.95 fish/hr) and 2004
(3.29 fish/hr).

While smallmouth abundance decreased significantly during 2006, the direct opposite
was apparent for largemouth bass. Therefore, in main channel habitats of the Colorado River in
western Colorado and eastern Utah and the Lower Gunnison River in western Colorado during
the summer of 2006, there was a significant increase in largemouth bass abundance (101% in
catch/effort) from 2005. The 2006 largemouth bass abundance was also greater (312% in
catch/effort) than 2004. Despite both bass species being lethally removed, largemouth bass
numbers continued to increase in main channel habitats. The increase in largemouth bass during
this 3-year removal period may have been attributed to young fish being produced and reared in
off-main channel habitats, e. g., backwaters that were isolated or semi-isolated from the main
channel during base flow (due to below-average flow conditions or dammed by beavers). During
several consecutive low-water years associated with drought conditions in the early 2000s in the
Upper Colorado River, many backwaters did not connect to the main channel in spring as in
previous years and became year-round, isolated ponded backwaters. These habitats were more
lacustrine-like and may have provided better habitat for centrarchids than more typical
backwaters open to the main channel and generally devoid of vegetation. Hydrologic connection
to the main channel occurred during spring runoff when they either became flow-through side
channels or were either inundated at the mouth. Thus, largemouth bass could have infiltrated
into main channel river habitats when higher spring flows returned (e. g.. 2005). Irrigation waste
water or overflow water from off-channel ponds that are unscreened that return to the river also
are another means by which largemouth bass can immigrate to the main channel. These various
lacustrine habitats could have and still may be providing a perpetual source of small (< 150 mm)

24