7304

• UCREFRP Catalog Number: 7304
• Author: Tyus, H. M.
• Title: Distribution, Reproduction, and Habitat Use of the Razorback Sucker in the Green River, Utah, 1979-1986
• USFW Year: 1987
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

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RAZORBACK SUCKER BIOLOGY IN UTAH

113

TABLE I.-Catches of adult razorback suckers, Colorado squawfish, and flannelmouth suckers per hour of elec-
trofishing in the Green River, 1979-1986. Standardized sampling: March-October 1979-1981; spring sampling:
April and May 1984-1986. Numbers in parentheses are total fish caught.

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Standardized sampling Spring sampling
Section Colorado Flannelmouth Colorado Flannelmouth
length Razorback squawfish sucker Razorback squawfish sucker
Section" (km) sucker (5) (278) (1,776) sucker (57) (175) (1,839)
A 114 0 0.28 1.2 0.05 0.89 7.08
B 59 0.04 0.34 7.6 0.04 0.35 14.79
C 38 0 0.05 10.2 0 0.48 14.51
D 86 0 0.12 6.8 0 0.19 11.59
E 59 0.03 0.23 3.9 0 1.24 2.93
F 112 0.04 0.44 3.9 0.40 0.69 5.02
Mean 0.02 0.24 5.62 0.22 0.68 7.14
" See Figure I for locations of sections.

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cantly longer and heavier than males (Student's t;
P < 0.01 for both variables). A length-frequency
histogram was unimodal and thus was not useful
in separating potential age-groups. It was assumed
that all fish were adults.
Numbers of razorback suckers (five) caught dur-
ing standardized sampling were low relative to
those of other species captured, e.g., to 1,776 adult
flannelmouth suckers Catostomous latipinnis, the
most abundant species collected (Table 1). Thus,
the ratio of razorback to flannelmouth suckers
taken in all types of gear was 1:355 (0.28%). In
comparison, the same ratio calculated from the
spring electrofishing catch, when razorback suck-
ers were highly vulnerable during spawning, was
1:32 (3%). Two hundred seventy-eight Colorado
squawfish were caught by all gear types during
standardized sampling and 175 were caught by
spring electro fishing (Table 1). The scarcity of ra-
zorback suckers is demonstrated by their total
catch and spring electro fishing catch, which
equaled only 1.8% and 33% of the catches of the
officially endangered Colorado squawfish, respec-
tively.
The razorback suckers collected in the Green
River were smaller than those from the lower Col-
orado River basin. The latter appeared to be old
fish; males and females were as long as 640 mm
and 740 mm TL, respectively (Minckley 1983).
Scales were not taken in this study, because scale
readings have not proven to be reliable for aging
razorback suckers (McAda and Wydoski 1980;
McCarthy 1986). My inspection of vertebrae from
one 505-mm-long Green River specimen revealed
12 distinct annular rings, suggesting the fish was
more than 12 years old; also, another 560-mm
specimen collected in this study and aged by oto-
lith readings at the University of Michigan was

estimated to be 19 years old (D. L. Schultz, written
communication). This indicates that the average
age of Green River fish may be less than the ages
of 24 to 44 years reported by McCarthy (1986) for
Lake Mohave fish.
Thirty-nine adult razorback suckers were recap-
tured 1-8 years after tagging. A comparison of
totallengths between capture and recapture indi-
cated a slow but significant growth (greater than
0.0; Student's t, P < 0.01) of only 2.2 mm/year.
Minckley (1983) and McCarthy (1986) observed
similar growth rates for adult razorback suckers
in lower Colorado River reservoirs.

Reproduction
Razorback suckers were most readily captured
in the upper Green River (E-G in Figure 1) during
spring, and 101 in breeding condition were cap-
tured from May 3 to June 15 in 1981, 1984, and
1986. The years 1984 and 1986 were apparently
years of heavy spawning activity, because the ra-
tiosof ripe fish to the total collected those years
were 55% and 58.7%, respectively (N= 163). The
years 1983 and 1985 may represent years oflow
spawning activity, since few fish (N = 16) were
collected with comparable sampling effort on the
shallow spawning grounds, and no ripe fish were
found.
Ripe fish were captured in three reaches: Island
and Echo parks of the Green River (G in Figure
1) in DNM, including the lower 1 km of the Yam-
pa River; the Jensen area of the Green River from
Ashley Creek to Split Mountain (section F); and
the Ouray area of the Green River (section F),
including the lower few kilometers of the Du-
chesne River. Two fish with breeding tubercles
. were also captured in Labyrinth Canyon. The Jen-
sen area produced more ripe razorback suckers