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Western North American Naturalist 60(2), 02000,, pp. 180-187
<br />DISTRIBUTION, MOVEMENTS, AND HABITAT USE OF RAZORBACK
<br />SUCKER (XYRAUCHEN TEXANUS) IN A LOWER COLORADO RIVER
<br />RESERVOIR, ARIZONA-NEVADA
<br />Gordon Muellerl, Paul C. Marsh2, Glen Knowles3, and Ty WolterS4
<br />ABSTBACr-Distribution, movements, and habitat use of 10 wild adult razorback suckers (Xyrauchen texanus) were
<br />examined in Lake Mohave, Arizona-Nevada, from November 1994 through July 1997. Movement rates (0.00-17.35 km
<br />(1-1) and ranges (T= 39 km) were similar to those for riverine populations. All study fish returned to spawning sites used
<br />in previous years, but they also visited other spawning areas. Spawning females were significantly (P = 0.031) more
<br />active than males (480 vs. 87 in d-1) and moved substantial distances between spawning sites during peak reproduction
<br />(1-28 February). Fish became most active (m it-], km month-1) after spawning and moved to areas known to support
<br />higher algal production. Fish were typically within 50 m (P < 0.001) of shore and at average depths between 3.1 and
<br />16.8 m (range 0.2 to >30.0 m). Adults were detected throughout the available thermal gradient (12'-30°C), but during
<br />summer typically had body temperatures between 18' and 22°C. Vertical movements within the water column showed
<br />no correlation with depth or time of day, but seasonal shifts suggest fish may regulate body temperature by seeking spe-
<br />cific temperatures during reservoir stratification.
<br />Key words: Xyrauchen texanus, razorback sticker, reservoir, spawning, habitat, movements, telemetry.
<br />Xyrauchen texanus, the razorback sucker, is
<br />the largest catostomid in North America and is
<br />endemic to the Colorado River basin. Histori-
<br />cally common, this riverine species now is
<br />reduced to relic and fragmented populations;
<br />3 of 4 known populations (>I 00 fish) are in
<br />reservoirs (Minckley et al. 1991, Modde et al.
<br />1996, Holden et al. 1997), the largest located
<br />in Lake Mohave, Arizona-Nevada. It was listed
<br />by the U.S. Fish and Wildlife Service as an
<br />endangered species in 1991 (USFWS 1991),
<br />Telemetric research has focused primarily
<br />on rivers where adults have been found to use
<br />backwater and other lentic type habitats (Tyus
<br />1987, Marsh and Minckley 1989, Modde and
<br />Wick 1997). However, riverine monitoring has
<br />been hampered by problems associated with
<br />working in large, remote systems, a scarcity of
<br />wild fish, and a short (2-3 wk) spawning sea-
<br />son that occurs on the ascending limb of spring
<br />runoff (Tyus 1987, Minckley et al. 1991). Pub-
<br />lished reports specific to lentic environments
<br />are limited to McAda and Wydoski's (1980)
<br />description of X. texanus use of a gravel pit
<br />adjacent to the Colorado River in Colorado
<br />and Medel-Ulmer's (1983) abstract describing
<br />'United States Geological Survey; Box 25007, D-8220, Denver, CO 80225.
<br />'Department of Biology, Arizona State University, Tempe, Az 85287-1501_
<br />3U,uted States Fish and Wildlife. Service, Carlsbad, CA.
<br />'Bureau of Becbmatwn, Boulder City NV 89006.
<br />X. texanus movement in Senator Wash Reser-
<br />voir in California. While information is scarce,
<br />backwater and floodplain habitat is viewed as
<br />critical for species restoration (Valdez and
<br />Wick 1981, Wydoski and Wick 1998). The fol-
<br />lowing report presents telemetry data describ-
<br />ing X. texanits distribution, movements, and
<br />habitat use in a Colorado River mainstem
<br />reservoir and provides new information on
<br />spawner movements and female use of multi-
<br />ple spawning sites.
<br />STUDY AREA
<br />Lake Mohave is a mainstem Colorado
<br />River reservoir created with the construction
<br />and closure of Davis Dam located 5 km
<br />upstream of Laughlin, Nevada. The reservoir
<br />borders both Arizona and Nevada and extends
<br />100 km upstream to the tailrace of Hoover
<br />Dam. When full (surface elevation 197 m/msl)
<br />the reservoir has a surface area of 11,655 ha.
<br />The reservoir inundates Black Canyon, located
<br />immediately downstream of Hoover Dam, and
<br />Pyramid Canyon where Davis Dam was con-
<br />structed. Between these canyons the reservoir
<br />broadens, forming Cottonwood Basin, which
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