640

North American Journal of Fisheries Management 25:640–645, 2005 [Management Brief] American Fisheries Society 2005

DOI: 10.1577/M04-091.1

Effect of Baiting on Hoop Net Catch Rates of

Endangered Humpback Chub

DENNIS M. STONE*

U.S. Fish and Wildlife Service, Post Office Box 338, Flagstaff, Arizona 86002-0338, USA

Abstract.—The effects of unbaited, scented (odor emitted by inaccessible hatchery feed), and baited (accessible

feed) single-throated hoop nets on the catch rates of the

federally endangered humpback chub Gila cypha ($100

mm total length) were assessed in the Little Colorado

River, Arizona, to determine how baiting affected the

catch of these fish. Of a total of 1,297 unique humpback

chub captured, 262 (20%) were caught in 179 unbaited

nets, 330 (25%) in 179 scented nets, and 705 (54%) in

178 baited nets. Humpback chub retention in unbaited

nets did not differ from a 50:50 chance event (P 5 0.075)

but probably peaked in baited nets where these fish were

preoccupied with feeding (i.e., gorging themselves),

which would explain the higher catch rates in baited

than in scented or unbaited nets (P # 0.001). Moreover,

humpback chub catch rates were not significantly higher

in scented than in unbaited nets (P 5 0.779), which

suggests that elevating both ‘‘fish attraction’’ and ‘‘fish

retention’’ are essential to substantially increase their

captures in these nets. However, scenting may still be a

viable option when used in conjunction with passive

gears possessing higher fish retention capabilities or to

target species less prone to escape. The findings of this

study should provide valuable insight to anyone wishing

to optimize catch rates by baiting or scenting passive

entrapment gear.

The humpback chub Gila cypha was federally

listed as an endangered species in 1967 (U.S. Office of the Federal Register 1967). Presently, the

largest of six remnant populations occupy the Colorado River below Glen Canyon Dam within

Grand Canyon National Park and lower Little Colorado River (LCR), Arizona (USFWS 1990; Douglas and Marsh 1996). The perpetuation of this population relies almost exclusively on LCR, which

still contains hydrological conditions, water chemistry, temperatures, and suitable habitats conducive for these fish to successfully spawn, grow,

and recruit to adulthood (Kaeding and Zimmerman

1983; Gorman and Stone 1999). Humpback chub

are primarily restricted to the LCR corridor below

the Atomizer Falls Complex, a series of travertine

dams located from 13.6 to 14 river kilometers

* Corresponding author: DennispStone@fws.gov

Received June 9, 2004; accepted October 21, 2004

Published online May 16, 2005

(rkm) upstream of the river’s mouth (Kaeding and

Zimmerman 1983; Mattes 1993).

For over a decade, hoop nets have been the primary gear used in the LCR because they inflict

less stress and cause fewer injuries and mortalities

than electroshocking (Ruppert and Muth 1997;

Snyder 2003) or entanglement gear (Hopkins and

Cech 1992), can be deployed in most LCR habitats

(Gorman and Stone 1999), and are relatively efficient at capturing all postlarval humpback chub

life stages (Stone 1999). Douglas and Marsh

(1996) primarily used hoop net capture data to

calculate monthly mark–recapture humpback chub

population estimates in the LCR during 1991–

1992.

Beginning in fall 2000, the U.S. Fish and Wildlife Service instituted a semiannual spring and fall

mark–recapture census of the LCR humpback chub

population. An idea was presented that baiting may

lure more humpback chub into nets, which could

increase the sample sizes and ultimately the precision of the population estimates. Baiting hoop

nets in other systems resulted in higher captures

of channel catfish Ictalurus punctatus, common

carp Cyprinus carpio, smallmouth buffalo Ictiobus

bubalus, bluegills Lepomis macrochirus (Mayhew

1973; Pierce et al. 1981; Gerhardt and Hubert

1989), and burbot Lota lota (Bernard et al. 1991).

However, a major concern was that the distended

intestines of humpback chub satiated with bait

would be more susceptible to perforations upon

abdominal insertions of passive integrated transponder (PIT) tags (Biomark, Inc.) than those of

unfed individuals (M. Childs, Arizona Game and

Fish Department, unpublished data). Therefore, it

was suggested that we should rely solely on the

scent from inaccessible bait to chum fish into nets.

Jester (1977) found that perforated cans of dog

food attracted channel catfish into gill nets, and

Stott (1970) reported that adding copper sulfate to

trap nets increased the catch of redfin perch (also

known as the Eurasian perch) Perca fluviatilis and

roach Rutilus rutilus 11-fold. The objective of this

study was to assess humpback chub catch rates

among unbaited, scented, and baited nets to pro-
MANAGEMENT BRIEF 6

FIGURE 1.—Map and sampling design for the baiting

experiment conducted in the Little Colorado River, Arizona. The river corridor below the Atomizer Falls Complex (13.6 rkm) was separated into nine (;1.5 rkm)

stream sections. All nets deployed within each stream

section were unbaited (U), scented (S), or baited (B) for

the first haul, and then redeployed using different treatments for the second and third hauls. Stream sections

sampled concurrently (1st, 2nd, 3rd) and corresponding

treatments (e.g., U, S, B) for successive hauls are given.

vide guidance for future management activities in

the LCR and elsewhere.

Methods

Hoop net treatments.—The miniature hoop nets

used in this study were 50 cm in diameter, 100 cm

long, had a single 10-cm throat, and were covered

with 6-mm dark-green, nylon mesh netting. The

three treatments included unbaited, scented, and

baited hoop nets. Baited and scented nets were

treated similarly whereby a single nylon mesh bag

(30 3 30 cm, 6-mm mesh) containing approximately 160 g of bait (AquaMax Grower 600 for

Carnivorous Species, Purina Mills Inc., Brentwood, Missouri) and one common white sock were

hung near the cod end of each net. The bait inside

of mesh bags was made inaccessible to fishes in

scented nets by enclosing it within the socks and

accessible to fishes in baited nets by placing it

loose outside of the socks.

Sampling design.—The lower 13.6 rkm of the

LCR was separated into nine (;1.5 rkm) stream

sections (Figure 1). Three survey crews stationed

at Boulder (1.9 rkm upriver from mouth), Coyote

(5.0 rkm), and Salt (10.4 rkm) sampling areas were

each responsible for first sampling an upper, f

lowed by middle, and then lower stream secti

within their designated areas. Each stream secti

was sampled with 20 nets that contained one sp

cific net treatment (i.e., either unbaited, scent

or baited) for the first ;24-h haul, then resamp

by redeploying nets to new locations and applyi

a different treatment for a second and third ha

Net treatments varied daily among the three stre

sections being sampled, which resulted in the d

ployment of 60 net sets of each treatment per h

(180 over three hauls). This sampling strategy w

implemented to reduce potential biases associa

with unbalanced treatments, catch rate differenc

among disparate habitats, and diminished ca

rates over time.

This study was primarily designed to comp

the net treatment effects on catch rates of uniq

(first captures only) humpback chub measuri

100 mm or greater in total length (TL). Becau

this trip was also the recapture event for the f

humpback chub population estimate, the typi

procedure of marking fishes with PIT tags w

replaced by clipping the right pelvic fin of ea

fish greater than or equal to 100 mm TL. Fin cl

ping allowed for analytical comparisons sol

among unique individuals, still allowed for the 

tio of marked to unmarked fish for the stock 

sessment, and alleviated concerns over PIT ta

ging well-fed fish. The study was conducted O

tober 21–30, 2002, under base flow dischar

(mean 5 6.3 m3/s near LCR mouth; Cooley 197

Water temperature (8C) and nephelometric turb

ity unit (NTU) measurements (Hach Model 210

Turbidimeter, Loveland, Colorado) were obtain

daily between 1300 and 1700 hours.

Analyses.—Three-way analysis of varian

(ANOVA) was used to model the potential infl

ences of net treatment, haul number, and sampli

area (fixed factors) on unique humpback ch

catch–set. Catch rates were not standardized 

effort because effort remained largely consist

throughout the study (mean 6 SD 5 23 6 2.2 

for 536 net sets). Although assumptions for a pa

metric test were violated, ANOVA was sufficien

robust under these large and nearly equal sam

sizes (Ott 1993; Zar 1996). A second three-w

ANOVA was used to examine for potential infl

ences of net treatment, haul number, and sampli

area on humpback chub mean TL. In additi

Pearson’s correlation tests were used to exam

for linear correlations between humpback chub 

and net treatment (ordered as follows: 1 5 u

baited, 2 5 scented, 3 5 baited), haul number, a
642 STONE

FIGURE 2.—Numbers and proportions of unique

humpback chub greater than or equal to 100 mm TL

captured in unbaited, scented, and baited hoop nets deployed for three separate 24-h hauls in the Little Colorado River, Arizona. Captures resulted from 59 unbaited nets, 59 scented nets, and 58 baited net sets during

the first haul, and 60 net sets of each treatment for both

the second and third hauls (536 total net sets).

sampling area (ordered in an upriver direction as

follows: 1 5 Boulder area, 2 5 Coyote area, 3 5

Salt area).

The capacity of hoop nets to retain humpback

chub overnight (i.e., fish retention) was examined

October 24–28, 2003. Eighty-one PIT-tagged

humpback chub (mean 6 SD 5 199 6 38 mm TL;

range 5 102–342 mm TL) were returned to 30

unbaited nets. Twelve nets each held one individual, and the other 18 nets contained from two to

six fish. These nets were redeployed in the same

areas until the following day when remaining and

newly captured humpback chub greater than or

equal to 100 mm TL were tallied. A binomial test

was conducted to examine whether the retained

versus escaped proportions of previously returned

fish significantly differed from a 50:50 chance

event. A two-sample, pooled-variance t-test was

used to examine for TL differences between individuals that remained and those that exited the

nets; pooling variances was justified by Levene’s

homogeneity of variances test results (F 5 0.122;

df 5 1, 79; P 5 0.728).

A laboratory experiment was conducted December 13–16, 2002, to ensure that odors were dispersing from the bait-filled socks used for the

scented net treatment. An unused white sock was

filled with 160 g of bait and placed in a clean,

covered container with 1,500 mL of tap water. The

mean of three NTU samples were calculated initially and on three other occasions over the next

68 h. The remaining bait was dried and reweighed

at the end of the experiment.

Statistical tests that resulted in P-values less

than 0.05 were considered significant. All statistical tests were conducted using SPSS for Windows, Release 9, 1998 (SPSS, Inc., Chicago, Illinois).

Results

The LCR maintained relatively warm temperatures (mean 6 SE 5 18.4 6 0.448C) and high water

clarities (4.8 6 0.45 NTU) throughout the baiting

study. Prior to the first haul, one unbaited, one

scented, and two baited nets had collapsed and

were therefore omitted from the data set. This resulted in sample sizes of 59 unbaited, 59 scented,

and 58 baited net sets for the first haul, and 60 net

sets of each treatment for the second and third

hauls. Humpback chub constituted 68.8% of the

overall catch, of which 1,297 were unique individuals (mean 6 SD 5 181 6 69.5 mm TL; range

5 100–467 mm TL), 264 were fin-clipped recaptures (100–389 mm TL), and 79 were age 0 (50–

99 mm TL). Other native species (21% of total

catch) included 304 speckled dace Rhinichthys osculus, 145 flannelmouth suckers Catostomus latipinnis, and 51 bluehead suckers C. discobolus.

Nonindigenous fishes (10.2% of total catch) included 142 fathead minnow Pimephales promelas,

72 common carp, 21 black bullheads Ameiurus melas, seven rainbow trout Oncorhynchus mykiss, and

one plains killifish Fundulus zebrinus.

The 1,297 unique humpback chub were disproportionately captured among nets possessing disparate treatments and deployed during different

hauls (Figure 2). Total captures for each net treatment declined with each ensuing haul; the capture

proportions among net treatments were most disparate during the first haul followed by the second

haul, but very similar during the third haul. Overall, 262 fish (20%) were caught in 179 unbaited

nets, 330 (25%) in 179 scented nets, and 705 (54%)

in 178 baited nets.

The three-way ANOVA indicated that unique

humpback chub catch–set was not affected by sampling area (F 5 0.147; df 5 2, 509; P 5 0.863)

or by its interactions with net treatment (F 5

1.601; df 5 4, 509; P 5 0.173) or haul number (F

5 1.162; df 5 4, 509; P 5 0.327); therefore, sampling area was omitted from the model. The re-
MANAGEMENT BRIEF 6

FIGURE 3.—Mean catch–set 6 2 SE of unique humpback chub greater than or equal to 100 mm TL from

unbaited, scented, and baited hoop nets deployed for

three separate 24-h hauls in the Little Colorado River,

Arizona. The number of net sets (N) for each treatment

of each haul is given.

sulting two-way model indicated that net treatment

(F 5 11.711; df 5 2, 527; P # 0.001), haul number

(F 5 17.165; df 5 2, 527; P # 0.001), and their

interaction (F 5 5.279; df 5 4, 527; P # 0.001)

were all related to humpback chub catch–set.

Catch rates incrementally decreased from the first

to third haul in a manner that direction of response

was the same for all treatments; however, the magnitude of decrease was greatest for the baited treatment, intermediate for scented nets, and lowest for

unbaited nets (Figure 3). Because the interaction

was orderly, inferences made on the F-tests of the

main effects were considered reliable (Ott 1993),

and a posteriori Tukey’s honestly significant difference tests were conducted on the main effects

(Zar 1996).

Tukey’s tests indicated that humpback chub

catch rates were higher in baited nets than in either

scented or unbaited nets (both P # 0.001), but were

similar between scented and unbaited nets (P 5

0.779). Overall, catch rates were higher during the

first haul than either the second or third hauls (both

P # 0.001), but did not differ between the last two

hauls (P 5 0.127). Therefore, catch rates from

baited nets were only higher than those from scented and unbaited nets during the first two hauls, but

were similar among treatments by the third haul

(Figures 2, 3). The significant haul effect indicated

that a relatively large portion of the population

was being captured, which was expedited more by

baited than by scented or unbaited nets.

Humpback chub mean TL differed primarily

among the sampling areas from which they were

captured. The three-way ANOVA model indica

that humpback chub mean TL was related to sa

pling area (F 5 31.629; df 5 2, 1,270; P # 0.00

and its interactions with net treatment (F 5 2.63

df 5 4, 1,270; P 5 0.033), haul number (F 

3.443; df 5 4, 1,270; P 5 0.008), and net tre

ment–haul number (F 5 3.193; df 5 8, 1,270

# 0.001), but revealed no effect of net treatm

(F 5 1.338; df 5 2, 1,270; P 5 0.263), haul nu

ber (F 5 0.517; df 5 2, 1,270; P 5 0.596), 

their interaction (F 5 2.189; df 5 4, 1,270; P 

0.068). Moreover, an increase of humpback ch

TL was correlated with captures at consecutiv

upriver sampling areas (r 5 0.304; df 5 1,29

P # 0.001), which was also evident by the hum

back chub mean TL (6SD) of fish captured at 

Boulder (156 6 49.4 mm; N 5 444), Coyote (1

6 72.2 mm; N 5 409), and Salt (207 6 74.6 m

N 5 444) sampling areas. In contrast, humpba

chub TL showed no linear relationship to eith

the net treatment (r 5 0.049; df 5 1,295; P 

0.078) or the haul number (r 520.033; df 5 1,29

P 5 0.230).

The LCR during the October 2003 fish retenti

experiment was 198C and slightly turbid (50–

NTU). Of the 81 humpback chub (102–342 m

TL) initially returned to the 30 nets, 49 were s

present (60% retained) and 32 left (40% escape

by the following day; the retained versus escap

ratio did not significantly differ from a 50

chance event (binomial test: P 5 0.075). Retenti

of humpback chub was highly variable among ne

For example, 7 of 12 nets that harbored only o

initially returned fish retained that individu

Moreover, none of six initially returned humpba

chub escaped from one net, while four of six 

dividuals escaped from another. Total lengths d

not differ (t 5 0.397; df 5 79; P 5 0.693) betwe

individuals still present (mean 6 SD 5 198 6 

mm TL) and ones that exited the nets (201 6 

mm TL). Overall, 60 new humpback chub grea

than or equal to 100 mm TL were captured in the

experimental nets.

Results from the laboratory tests indicated t

scent was escaping from the bait-filled socks. T

mean NTU (6SE) were 0.85 6 0.07, 41.5 6 3

416 6 7.8, and 972 6 7.4 at the beginning of 

experiment, 4 h later, 21 h later, and 68 h la

respectively. By the second day the odor had p

meated throughout the room. At the end of 

experiment the remaining dried bait weighed 1

g, indicating that 42 g had dissolved in the wat
644 STONE

Discussion

My finding that baited nets captured significantly more unique humpback chub ($100 mm

TL) than unbaited nets was anticipated. Whereas

hoop nets are deployed with their mouths facing

downstream to the current, fishes must voluntarily

choose to enter these passive entrapment devices

(Stott 1970) and accessible food provides a good

incentive. Baiting entrapment gears has been a

common practice among commercial fishermen for

over 50 years (Starrett and Barnickol 1955) and is

essential for capturing certain species (e.g., burbot;

Bernard et al. 1991). However, the significantly

lower humpback chub catch rates in scented than

baited nets, and similar captures between scented

and unbaited nets was unexpected. Scent has also

been shown to increase fish captures in entrapment

gears (Stott 1970) and, as my laboratory study

indicated, the odor from bait must have been dispersing from scented nets in the LCR. Presumably,

humpback chub (particularly adults) rely heavily

on their olfactory senses to procure food, especially at night when they are most active (Stone

1999) and vision is impaired (Hara 1993). Apparently, however, more is required to substantially

increase humpback chub captures in these nets

than merely relying on scent to elevate fish attraction to these devices.

The higher humpback chub catch rates from

baited nets was likely related to fish retention. The

fish retention experiment indicated that there was

a 50:50 chance of humpback chub escaping these

unbaited, single-throated hoop nets overnight;

however, it is unknown whether those ‘‘retained’’

individuals were unable to find the mouth opening

to escape, could have escaped but chose to remain,

or escaped then returned (Patriarche 1968). In addition, as some individuals were escaping, others

were entering these nets. However, humpback

chub were clearly feeding in baited nets whereby

many individuals became so gorged that they

would immediately defecate upon handling. Moreover, the feeding process would have been prolonged because they had to extract food material

through a 6-mm-mesh bait bag. Therefore, those

humpback chub feeding in baited nets were likely

remaining longer than those occupying unbaited

or scented nets, which would result in an overall

increase of fish retention and higher catch rates.

Baiting hoop nets could improve mark–recapture

stock assessments of humpback chub in the LCR

and elsewhere. The findings that baited nets captured over twice as many unique humpback chub

as either scented or unbaited nets in the first two

hauls, and expedited a significant catch rate decline between the first and later hauls, suggest that

baiting could be used to either improve the precision of ensuing mark–recapture stock estimates

without increasing sampling effort or to allow for

less sampling effort to achieve the same precision

as that from unbaited or scented nets. The 262

unique humpback chub caught in unbaited nets,

330 in scented nets, and 705 in baited nets constituted 5, 7, and 15%, respectively, of the estimated 4,807 individuals ($100 mm TL) existing

in the population (Van Haverbeke 2003). It was

also encouraging that unique humpback chub did

not exhibit size-related capture differences among

disparate treatments nor did they differentially escape nets, as either of these suggest that the assumption of equal capture probability was being

violated and, therefore, the accuracy of population

estimates may be biased (Pine et al. 2003).

Scenting hoop nets or any other passive entrapment gear may still be a viable option under different circumstances. Interspecific fishes possess

different propensities to enter and remain in nets

(Patriarche 1968; Stott 1970) and differential attractions and repulsions to assorted baits (Mayhew

1973; Jester 1977). Thus, scenting may still increase captures of those fishes less prone to escapement if they are attracted by the emitted odors.

Conversely, scenting for fishes that are prone to

escapement may necessitate using passive entrapment gears that possess higher fish retention capabilities (e.g., multithroated devices).

Management Implications

The findings of this study should provide valuable insight to anyone wishing to optimize catch

rates by baiting or scenting passive entrapment

gear. Studies that use passive devices possessing

low fish retention capabilities, such as singlethroated hoop nets, may need to use accessible bait

unless the target species have a low propensity to

escape. The deleterious ramifications of abdominally PIT tagging well-fed fish may be avoided by

holding fish, intramuscular PIT tagging, fin clipping, using external tags, or possibly using scent

rather than bait in conjunction with other passive

devices possessing higher fish retention capabilities. Either method, if successful, will bias relative

abundance comparisons with historical data collected from unbaited gear and may attract undesirable piscivorous fishes into nets with the target

species. Conversely, both methods may improve

fishery management activities, such as population
MANAGEMENT BRIEF 6

estimates, presence–absence surveys, translocations, and removals before stream renovations.

Acknowledgments

I thank D. Wesley, R. Van Haverbeke, P. Sponholtz, C. Nelson, E. Kohagen, C. Giuaque, A. Martinez, L. Johnstone, A. Pate, and M. Melnychuk

for field assistance; B. Burch and C. Walters for

statistical support; M. Santee for helicopter transport; T. Gushue for creating the LCR map; and

three anonymous reviewers for remarks that greatly improved this manuscript. Permits to conduct

this research and handle endangered fish were provided by the Arizona Game and Fish Department,

Navaho Fish and Wildlife Department, U.S. National Park Service, and U.S. Fish and Wildlife

Service (USFWS; Federal Endangered Species

Permit TE676811–8). Funding was provided by

the U.S. Geological Survey’s Grand Canyon Monitoring and Research Center (Interagency Agreement 01–3022-R1009). The views expressed in

this article are mine and do not necessarily reflect

those of the USFWS or other federal agencies.

Reference to trade names does not imply endorsement by the U.S. Government.

References

Bernard, D. R., G. A. Pearse, and R. H. Conrad. 1991.

Hoop traps as a means to capture burbot. North

American Journal of Fisheries Management 11:91–

104.

Cooley, M. E. 1976. Spring flow from pre-Pennsylvanian

rocks in the southwestern part of the Navajo Indian

Reservation, Arizona. U.S. Geological Survey Professional Paper 521-F.

Douglas, M. E., and P. C. Marsh. 1996. Population estimates/population movements of Gila cypha, an endangered cyprinid fish in the Grand Canyon region

of Arizona. Copeia 1996:15–28.

Gerhardt, D. R., and W. A. Hubert. 1989. Effect of

cheese bait on seasonal catches of channel catfish

in hoop nets. North American Journal of Fisheries

Management 9:377–379.

Gorman, O. T., and D. M. Stone. 1999. Ecology of

spawning humpback chub, Gila cypha, in the Little

Colorado River near Grand Canyon, Arizona. Environmental Biology of Fishes 55:115–133.

Hara, T. J. 1993. Role of olfaction in fish behaviour.

Pages 171–199 in T. J. Pitcher, editor. Behavior of

teleost fishes, 2nd edition. Chapman and Hall, London.

Hopkins, T. E., and J. J. Cech, Jr. 1992. Physiological

effects of capturing striped bass in gill nets and fyke

traps. Transactions of the American Fisheries Society 121:819–822.

Jester, D. B. 1977. Effects of color, mesh size, fishing

in seasonal concentrations, and baiting on catch

rates of fishes in gill nets. Transactions of the Am

ican Fisheries Society 106:43–56.

Kaeding, L. R., and M. A. Zimmerman. 1983. Life h

tory and ecology of the humpback chub in the Li

Colorado and Colorado rivers of the Grand Cany

Transactions of the American Fisheries Society 1

577–594.

Mattes, W. P. 1993. An evaluation of habitat conditi

and species composition above, in, and below 

Atomizer Falls Complex of the Little Colorado R

er. Master’s thesis. University of Arizona, Tucs

Mayhew, J. 1973. Variations in the catch success 

channel catfish and carp in baited hoop nets. P

ceedings of the Iowa Academy of Science 80(

136–139.

Ott, R. L. 1993. An introduction to statistical meth

and data analysis, 4th edition. Duxbury Press, B

mont, California.

Patriarche, M. H. 1968. Rate of escape of fish from t

nets. Transactions of the American Fisheries Soci

97:59–61.

Pierce, R. B., D. W. Coble, and S. Corley. 1981. F

catches in baited and unbaited hoop nets in the up

Mississippi River. North American Journal of Fi

eries Management 1:204–206.

Pine, W. E., K. H. Pollock, J. E. Hightower, T. J. Kw

and J. A. Rice. 2003. A review of tagging meth

for estimating fish population size and compone

of mortality. Fisheries 28(10):10–23.

Ruppert, J. B., and R. M. Muth. 1997. Effects of el

trofishing fields on captive juveniles of two end

gered cyprinids. North American Journal of Fi

eries Management 17:314–320.

Snyder, D. E. 2003. Electrofishing and its harmful effe

on fish. Information and Technology Report USG

BRD/ITR-2003-0002: U.S. Government Printing 

fice, Denver. Available: http://www.fort.usgs.g

products/Publications/21226/21226.asp. (June 200

Starrett, W. C., and P. G. Barnickol. 1955. Efficien

and selectivity of commercial fishing devices u

on the Mississippi River. Illinois Natural Hist

Survey Bulletin 26(4):321–366.

Stone, D. M. 1999. Ecology of humpback chub (G

cypha) in the Little Colorado River, near Grand C

yon, Arizona. Master’s thesis. Northern Arizo

University, Flagstaff.

Stott, B. 1970. Some factors affecting the catching po

er of unbaited fish traps. Journal of Fish Biology 

15–22.

USFWS (U. S. Fish and Wildlife Service). 19

Humpback chub recovery plan. USFWS, Denv

Available: http://ifw2es.fws.gov/Documents/r2

humpbackchub.pdf. (June 2004)

U.S. Office of the Federal Register. 1967. Federal R

ister 32:48(11 March 1967):4001.

Van Haverbeke, D. R. 2003. Stock assessment and fi

eries monitoring activities in the Little Colora

River within Grand Canyon during 2002. Final 

port of U.S. Fish and Wildlife Service to U.S. G

logical Survey, Grand Canyon Monitoring and R

search Center, Flagstaff, Arizona.

Zar, J. H. 1996. Biostatisical analysis, 3rd edition. Prenti

Hall, Inc., Upper Saddle River, New Jersey.