9701

• UCREFRP Catalog Number: 9701
• Author: Modde, T., Z.H. Bowen and D.C. Kitcheyan.
• Title: Spatial and temporal use of a spawning site in the middle Green River by wild and hatchery-reared razorback sucker.
• USFW Year: 2005.
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

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Transactions of the American Fisheries Society 134:937-944, 2005 [Article]
© American Fisheries Society 2005
DOI: 10.1577/x04-097.1
Spatial and Temporal Use of a Spawning Site in the Middle
Green River by Wild and Hatchery-Reared Razorback Suckers
'T'IMOTHY MODDE*
U.S. Fish and Wildlife Service, 1380 South 2350 West
Vernal, Utah 84078, USA
ZACHARY H. BOWEN
U.S. Geological Survey, Fort Collins Science Center,
2150 Centre Avenue, Building C, Fort Collins, Colorado 80526, USA
DAVID C. KITCHEYAN
U.S. Fish and Wildlife Service, 3800 Commons Avenue NE,
Albuquerque, New Mexico 87109, USA
Abstract.-The population of endangered razorback suckers Xyrauchen texanus in the middle
Green River (upper Colorado River basin) has declined during the last 40 years. The apparent
cause for this decline is a lack of successful recruitment. This study used radiotelemetry to evaluate
the ability of hatchery-reared razorback suckers to locate spawning areas where wild fish congregate
during the ascending hydrographic limb of the snowmelt runoff. Hatchery-reared razorback suckers
appeared to show similar reproductive behavior to wild fish. Both wild and hatchery-reared fish
were found near the middle Green River spawning area between 1 and 25 May 2000. Hatchery
fish occupied the same areas on the spawning site as wild fish, and remained on the spawning site
during both nocturnal and diurnal hours. Males were more abundant on the spawning area than
females, but the few females captured tended to stage away from the primary spawning area. The
results from this study suggest hatchery-reared fish are capable of responding to natural cues that
prompt spawning aggregations and are successful in locating existing spawning aggregations of
wild fish. Given attention to stocking criteria, including genetic diversity and the size and time
of stocking, the challenges of recovering razorback suckers will center on those factors that led
to the population declines, particularly the survival of early life stages in off-channel habitats.
Razorback suckers Xyrauchen texanus are en-
demic to the Colorado River basin and were once
abundant in alluvial reaches of large rivers (Muell-
er and Marsh 2002). In the mid to late 20th century,
wild populations declined dramatically following
construction of main-stem impoundments, intro-
duction of nonnative fishes, and other anthropo-
genic influences on riverine environments (Best-
gen et al. 1990). Decline in abundance and distri-
bution of razorback suckers precipitated its listing
as an endangered species by the U.S. Fish and
Wildlife Service (USFWS 1991). Although suc-
cessful spawning by razorback suckers has been
observed in rivers (Muth et al. 1998; Mueller
1989) and reservoirs (Minckley et al. 1991; Hold-
en et al. 1997), recruitment has been insufficient
to maintain population levels and recover the spe-
cies (USFWS 2002).
* Corresponding author: [e-mail]
Received June 8, 2004; accepted January 7, 2005
Published online June 22, 2005
The largest extant population of wild razorback
suckers remaining in relatively free-flowing riv-
erine habitat exists in an alluvial reach of the mid-
dle Green River (Lanigan and Tyus 1989), which
includes the largest remaining floodplain complex
of the upper Colorado River basin (Irving and Bur-
dick 1995). In the spring, wild razorback suckers
in the middle Green River aggregate at one of two
spawning sites, one in the upstream reach of the
alluvial reach and the other in a canyon 42 river
kilometers (rkm) upstream of the alluvial reach
(Tyus and Karp 1990; Modde and Irving 1998).
The timing of razorback sucker spawning is related
to both temperature and discharge. As temperature
and flows increase during the ascending hydro-
graphic limb of the spring snowmelt, razorback
suckers migrate to spawning locations and typi-
cally spawn when water temperatures range be-
tween 12°C and 16°C before peak flows (Tyus and
Karp 1990). Razorback suckers spawn upstream
of most floodplain habitats in the low-gradient al-
luvial reach of the middle Green River. Spawning
just before spring flood flows allows larvae to
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